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Partnering with the best gasket supplier for your application can help you minimise downtimes, reduce expenses, improve daily operations, and so on.
Gaskets are mechanical seals intended to fill the space between two or more mating surfaces. Once they are installed, they can prevent fluids, gases, or debris from entering or escaping the surfaces. Some industries that take advantage of these mechanical seals are automotive, aerospace, chemical processing, energy, food and beverage, marine, medical, and oil and gas.
If your business is part of one of these industries, you already know how relevant gaskets are to your main application. Without using quality gaskets, your parts and components may fail or get contaminated due to leaks. Safety and environmental hazards may likewise develop, harming the environment and the people on your worksite. Your property may also violate regulations and standards due to the lack of quality gaskets.
To make sure you only maximise quality gaskets, you must work with the best supplier for your application. Here are some tips on how to find and pick one.
Know Your Gasket Requirements
Before looking for a gasket supplier, you must know your gasket needs first. It means that you must understand the specifications required for your application, which include the size, shape, material, temperature, and pressure requirements. Knowing these things helps you narrow down your search to suppliers who can give you gaskets that meet your specific needs.
Look for Experience and Expertise
The next tip you must do when looking for a gasket supplier is to look for a company with enough experience and expertise in the industry. Gasket suppliers who have been in business for a long time can often provide high-quality products and services. Hence, you must go for one that has been in the industry for numerous years. You must also pick one who has experience working with your specific industry or application to avoid any issues.
Consider Product Quality
The quality of the gasket you will be using on your application can have a significant impact on the longevity and performance of your equipment. Therefore, you must select a gasket supplier that utilises high-quality materials in making gaskets. They should also have strict quality control processes to avoid faulty gaskets in the long run.
Check Relevant Certifications
Choosing a gasket supplier who is certified and compliant with industry standards can help you receive high-quality products that meet regulatory requirements. Suppliers who are certified to quality management standards for gaskets can help you obtain gaskets that can match your needs without expecting any issues. When looking for a gasket supplier, you must consider those who are compliant with ASME B16.21, AS/NZS 4020, ISO 3601, AS 1935, and AS 1210.
Assess Customer Service and Support
Another tip you can do when choosing a gasket supplier for your application is to assess their customer service and support. You must choose one that provides excellent customer service and support so they can respond to your needs and provide technical support when necessary. They must also offer value-added services like custom gasket design and manufacturing, inventory management, and delivery services. Selecting the right gasket supplier ensures that your equipment operates smoothly and reliably. By considering these factors and doing your research, you can find and pick the best gasket supplier for your needs. You can contact us at Gasketech if you want access to quality gaskets.
Various types of gaskets are utilised by industries to ensure they can seal their surfaces effectively. One of these types is the ring gasket.
Ring gaskets are sealing components that can prevent leaks. They can also seal fluid or gas flow in industrial systems. They are circular and integrated with a round cross-section, which is designed to fit between two flat surfaces like flanges or valve bodies. To date, many materials can be maximised in making these gaskets. But one particular material that many industries opt for when selecting ring gaskets is polytetrafluoroethylene or PTFE.
PTFE ring gaskets are widely known for being versatile as they can be used in many industries for various applications. These gaskets are made from a synthetic fluoropolymer, which has excellent chemical and high-temperature resistance. They also have low friction and non-stick properties. Some industries that use them are as follows.
1. Automotive Industry
The automotive industry uses PTFE ring gaskets in sealing engines, transmissions, and fuel systems. The industry takes advantage of these ring gaskets since they can withstand high temperatures and pressures and are resistant to chemicals and corrosives, which are common elements found in most automotive components.
2. Chemical Industry
PTFE ring gaskets are also commonly used in the chemical industry due to their excellent chemical resistance. They are used in applications where the material being processed is abrasive or corrosive. They can also be utilised in processes where high pressures or temperatures are present. One great use of PTFE ring gaskets in the chemical industry is the production of chemicals like acids, alkalis, and solvents.
3. Pharmaceutical Industry
The pharmaceutical industry also takes advantage of PTFE ring gaskets as they are safe, inert, and have excellent chemical resistance. These gaskets can be used in manufacturing drugs and medical devices since they can ensure that the products will not be contaminated.
4. Aerospace Industry
The aerospace industry needs materials that can withstand extreme temperatures and pressures. Aerospace applications like engines, fuel systems, and hydraulic systems can benefit from PTFE ring gaskets due to their high performance and reliability.
5. Food Industry
The food industry requires materials that are safe for human consumption. Fortunately, PTFE ring gaskets can be safe, making them useful in food processing equipment. These gaskets are non-toxic, non-reactive, and have a non-stick surface, which makes them safe.
6. Oil and Gas Industry
The oil and gas industry uses PTFE ring gaskets in pipelines, valves, and pumps. PTFE ring gaskets are useful in this industry because they can withstand high temperatures and pressures, and can resist chemicals and corrosives.
7. Electrical Industry
PTFE ring gaskets are used in the electrical industry because they are excellent insulators and can withstand high voltages. These gaskets can be installed in electrical connectors, switches, and other applications that need a high degree of insulation.
8. Water Treatment Industry
PTFE ring gaskets are also maximised in the water treatment industry because they can withstand the effects of chemicals, high temperatures, and pressures. They are used in pumps, valves, and other equipment that is intended to process and treat water.
9. Mining Industry
The mining industry, ultimately, requires materials that can withstand harsh environments and corrosive substances. PTFE ring gaskets are used in mining applications like pumps and valves as they can resist chemicals and withstand high temperatures and pressures. PTFE ring gaskets are highly versatile and can be used in a wide range of industries for a variety of applications.

domain: chemistry


text:
JAHILIYYAH RHETORIC AS A DIVINE LEGITIMACY FOR VIOLENCE: A STUDY OF THE INFLUENCE OF SAYYID QUTB AND THE CONTEMPORARY ISLAMIST ORTHODOXY ON AL-QAEDA, THE TALIBAN, AND THE ISLAMIC STATE
Keywords:Islamism, religious violence, Islamist orthodoxy, Jihad, Muslim extremism, Jahiliyyah
The Islamic conception of Jahiliyyah brings together the three most debated Muslim militant organizations of our times, namely Al-Qaeda, the Islamic State, and the Taliban in terms of their justification for violence. It is discussed here that despite significant differences in their political agendas, social and cultural motives as well as religious denominational affiliations, the three organizations are hegemonic in their resort to the notion of Jahiliyyah while opposing the non-Shari’ah based political rule. They converge on the idea that there is an imperative to install a system based on Shari’ah and that any actors opposed to this can be treated as enemies, deviants, and infidels, hence, worthy of violent aggression. It is demonstrated here that this particular connotation of Jahiliyyah was essentially espoused in the works of Sayyid Qutb, one of the most influential twentieth century proponents of Islamism and global Jihad. Although developed primarily to denounce Western imperialists in a postcolonial context, one may see Jahiliyyah as a contemporary Islamic rhetoric for providing the three organizations in question, valid pretexts to wage armed insurgencies against whoever they view as hostile political forces. This overall narrative, as this study indicates, relates to the broader contemporary Islamist discourse on the legitimacy of political violence in the name of religion.
Alvarez-Ossorio Ignacio, The Sectarian Dynamics of the Syrian Conflict, The Review of Faith & International Affairs, Vol. 17, No. 2, 2019. https://doi.org/10.1080/15570274.2019.1608644
Bloom Mia, Dying to Kill. The Allure of Suicide Terror, New York, Columbia University Press, 2003.
Borthakur Anchita and Angana Kotokey, Ethnicity or religion? The genesis of the Taliban movement in Afghanistan, Asian Affairs, Vol. 51, No. 4, 2020. https://doi.org/10.1080/03068374.2020.1832772
Bowering Gerhard, Islamic Political Thought: An Introduction, Princeton University Press, 2015.
Calvert John, Sayyid Qutb and the origins of radical Islamism, Oxford University Press, 2009.
Esposito John, The Oxford Dictionary of Islam, Oxford University Press, 2004.
Garner Godfrey and Maeghin Alarid-Hughes, Origins of Terrorism: The Rise of the World’s Most Formidable Terrorist Groups, London: CRC Press, 2021.
Giustozzi Antonio, The Taliban at War: 2001-2021, Oxford University Press, 2019, p. 70.
Ingram Haroro J., Craig Whiteside, and Charlie Winter, The ISIS Reader: Milestone Texts of the Islamic State Movement, Oxford University Press, 2020
Johnson Thomas H. and Ludwig W. Adamec, Historical Dictionary of Afghanistan, 5th edition, Rowman & Littlefield, 2021
Kafadar Cemal, Between two worlds: The construction of the Ottoman state, University of California Press, 1995.
Kamal Pasha Mustapha, Political theology and sovereignty: Sayyid Qutb in our times, Journal of International Relations and Development, Vol. 22, No. 2, 2019. https://doi.org/10.1057/s41268-018-0151-3
Liebl Vern, Pushtuns, tribalism, leadership, Islam and Taliban: a short view: report from the field, Small Wars & Insurgencies, Vol. 18, No. 3, 2007. https://doi.org/10.1080/09592310701674481
Lowry Heath W., The nature of the early Ottoman state, Binghampton, Suny Press, 2003.
Matesan Emy, The Violence Pendulum: Tactical Change in Islamist Groups in Egypt and Indonesia, Oxford University Press, 2020.
Middle East Conflicts from Ancient Egypt to the 21st Century: An Encyclopedia and Document Collection, Spencer Tucker (ed.), New York, ABC-CLIO, 2019.
Musallam Adnan A., The Posthumous Impact of Sayyid Qutb (1906–1966) on Ayman Al-Zawahiri and Global Jihadists of Al-Qa'eda, Journal of South Asian and Middle Eastern Studies, Vol. 43, No. 2, 2020. https://doi.org/10.1353/jsa.2020.0002
Qutb Sayyid, Milestones, AB al-Mehri (ed.), Birmingham, Maktabah booksellers and publishers, 2006.
Quṭb Sayyid, Social justice in Islam, Oneonta NY, Islamic Publications International, 2000.
Rashid Samory, The Islamist Challenge and Africa, London, Lexington Books, 2018.
Robinson Glenn E, Global Jihad: A Brief History, Stanford University Press, 2020.
Shepard William E., Sayyid Qutb's doctrine of jāhiliyya, International Journal of Middle East Studies, Vol. 35, No. 4, 2003. https://doi.org/10.1017.S0020743803000229
Skovgaard-Petersen Jakob, Heirs of Abu Bakr: On the Ideology and Conception of History in al-Qaeda and Islamic State, Connections, Vol. 16, No. 1, 2017. https://doi.org/10.11610/Connections.16.1.02
Stark Rodney, Religion, Deviance, and Social Control, London, Routledge, 1997.
Steed Brian, ISIS: An Introduction and Guide to the Islamic State, New York, ABC-CLIO, 2016.
The Cambridge History of Terrorism, Richard English (ed.), Cambridge University Press, 2021.
Van Linschoten Alex Strick and Felix Kuehn, An Enemy We Created: The myth of the Taliban-al Qaeda merger in Afghanistan, Oxford University Press, 2012.
Williams Brian Glyn, Counter Jihad: America's Military Experience in Afghanistan, Iraq, and Syria, University of Pennsylvania Press, 2016.
Zollner Barbara, The Muslim Brotherhood: Hasan Al-Hudaybi and Ideology, New York, Routledge, 2009.
“Global Terrorism Database 1970 – 2020”, available at: https://www.start.umd.edu/gtd (accessed October 4, 2022).
“National Consortium for the Study of Terrorism and Responses to Terrorism”, 2022.

domain: library


text:
As we begin the New Year, there are three priority areas that are critical to monitor and keep abreast of: The Affordable Care Act; the Defense of Marriage Act; and IRS activity. While these are areas of interest that many businesses are already familiar with, 2014 is expected to be a year in which significant changes take effect. Regardless of the amount of preparation that has already taken place, clients will need your help to ensure the changes they’re making are implemented properly and with as little risk as possible.
Following are the three issues Entrepreneurs and their accountants need to stay up-to-date on for 2014:
• The Affordable Care Act: Numerous provisions related to health care reform continue to affect small business owners and their employees. Beginning this year, most individuals will be required to carry insurance for themselves and their dependents or potentially pay a tax. While small business owners aren’t required to offer insurance to their employees, those that already chose to will need to comply with reforms that take effect this year. Although the reporting and enforcement of the Employer Shared Responsibility provision was delayed until 2015, employers should determine their applicable large employer status and ensure that appropriate tracking of employee hours begins in 2014. A significant clarification regarding Flexible Spending Accounts (FSAs) for 2014 is that employers offering a health FSA must also offer group health insurance coverage.
Also changing this year is the small business tax credit for employers that offer health insurance coverage. To qualify for the tax credit, coverage must be purchased through the Small Business Health Options Program (SHOP) marketplace or be certified for SHOP-eligible coverage in states that have federally facilitated SHOP marketplaces.
• The Defense of Marriage Act (DOMA): The Supreme Court’s ruling in 2013, which expands the federal definition of marriage to include same-gender spouses, has a significant effect on federal laws including payroll taxes and health insurance, and employment laws such as the Family Medical Leave Act (FMLA). Affected employees are now eligible to pay for same-gender spousal benefits such as health insurance premiums and FSA/Section 125 participation on a pretax basis for federal taxes. Individuals whose legal spousal status was changed by the ruling also have the option to claim refunds and/or request adjustments due to overpayment of FICA taxes, and employers may be entitled to a refund of federal unemployment tax on wages paid to legally married same-gender spouses. Regarding state taxes and withholding on the state level, this will vary depending on whether a state recognizes same-sex marriages and chooses to follow federal rules.
• IRS Priorities: The United States Supreme Court will begin hearing arguments this month to determine if severance pay should be taxable or exempt from FICA tax. If the Court rules against the IRS, the agency will need to process retroactive refund claims submitted by employers and employees. These claims could reach a total in the billions, and cause the IRS to lose a major source of future revenue. The IRS has also announced its intent to more closely examine the taxation of tips and service charges in 2014. This will be important to industries where tipping is customary such as the hospitality and restaurant industries.
It is important to stay abreast with how these items progress for effective tax planning. Keep in touch regularly with your CPA to make sure he/she keeps you informed!

domain: law


text:
ISLAMABAD/LAHORE: Adviser to Prime Minister on Accountability Shahzad Akbar on Sunday claimed that the government has made recoveries worth Rs210 billion from Punjab over the course of the past two-and-a-half years.
He claimed that of the amount, Rs24 billion worth of recoveries were made from 36 PML-N members, from whom 8,085 acres of land was taken back. "This is the reality behind the hue and cry being raised by the PML-N," he said, as he addressed a press conference in Islamabad.
Shahzad Akbar said the party was accusing the government of exacting political revenge simply to save their own skins. He spoke of the land razed by the Lahore Development Authority (LDA) where the Khokhar brothers had established Khokhar Palace. "They had grabbed land belonging to the government worth Rs1.5 billion," he said.
The adviser said that besides the recovery from the Khokhars, land worth Rs92.5 million was also taken back from Khurram Dastagir, "which has been turned into a public park". Shahzad Akbar said what remains now is for the government to collect "penal rent" worth Rs5 billion.
Discussing further recoveries, he said that land worth Rs7 billion was taken back from Chaudhry Tanveer and 2,400 kanals worth Rs2.5 billion from Daniyal Aziz. Moreover, he said 8 kanals 2 marlas of government land was recovered from Javed Latif; land worth Rs2 billion was taken back from Abid Sher Ali; and 70 acres of land worth millions was also recovered from Maiza Hameed's husband.
Among other leaders he named are Mudasar Qayum Nahra and Mir Badshah Qaisrani. Shahzad Akbar said that a common man cannot "occupy government lands" and that these are "powerful people".
He said these recoveries "were not an easy task" but the Punjab government's performance over the past two-and-a-half years has been "excellent". The premier's adviser said all the land taken back was either forest land or agricultural and will be put to use for the welfare of the people. He said work is underway to raze an "illegal plaza" in Sialkot, adding that Khawaja Asif "has also occupied a housing society".
An operation on Sunday was launched in the housing society owned by Khawaja Asif to retrieve occupied land. The authorities concerned said the operation was launched to recover the land reserved for graveyard and parking but occupied by the Kent View Housing Society. The management of the society illegally built a four-storey building on the site, necessitating action from the government. The district administration and municipal corporation officials in the presence of policemen demolished the structures.
Shahzad Akbar, recalling the PML-N's rule, said that former prime minister Nawaz Sharif "promoted Changa Manga politics" and "politics of money" at the time. He said this is why the Supreme Court of Pakistan had used the word "mafia" in its judgment when Nawaz was disqualified.
The premier's adviser said that if one were to ask Nawaz what his ideology is, "he won't be able to answer". Meanwhile, Special Assistant to Punjab Chief Minister on Information Dr Firdous Ashiq Awan said the operation by the Punjab government against a housing society in Sialkot over making building on the land meant for parking and graveyard is a main step towards clutching the land mafia. She said the land mafia will raise hue and cry as and when the government will step action against them.
Meanwhile, the PML-N leaders warned the bureaucracy to abstain from following “illegal” orders of the government otherwise they will have to face a similar fate in future. The PML-N leaders also slammed the government over the report of Transparency International (TI) and stated that the report has blackened the faces of incompetent rulers. They said the PML-N would move the court against revengeful actions of the government.
These views were expressed by PML-N leaders Khawaja Saad Rafique, former NA speaker Ayaz Sadiq and Attaullah Tarar during a joint press conference in Lahore. Saad Rafique said the NAB had not recovered anything. He said the government put names of PML-N workers and leaders in the list of land grabbers but still were unable to break a single man of the party.
Saad Rafique said that in the new Pakistan bread had been taken away from the people. “Opposition will not end chasing the rulers,” he said, adding that they were dreaming about PDM day and night.
To a question, he said he had seen four martial laws in this country but the worst martial law was imposed in the country during the current regime. “You are malicious and creating chaos in the country by using state institutions,” he stated.
Targeting the bureaucracy, Khawaja Saad said that the same civil servants, who worked in Punjab and the Federation, became cowards and were working on the agenda of the rulers without raising objections to the illegal orders.
Sardar Ayaz Sadiq said that it was the first time that the government had stopped the standing committee of the National Assembly from working and today the nation had come to know the reality that the government was making every effort to stop the standing committee to discuss the case of Broadsheet.
He said when Saqib Nisar decided the case of Banigala, he forgot that Imran Khan's house had an anonymous permit. He said ruler should also be made answerable about the expenses of millions of rupees spent on his Zaman Park’s residence.
“Sometimes they put drugs on someone and sometimes they demolish someone's house, but no one is looking into the thefts being made by the government,” he said. Attaullah Tarar alleged that Shahzad Akbar's brother tried to occupy the land in Rawalpindi and four officers were transferred for the illegal occupation of this land.
“Shahzad Akbar is using government vehicles and resources to occupy the land. Shahzad Akbar should also be held accountable,” he alleged, and said that it had been a year since the government was unable to justify Shahzad Akbar’s actions.
Tarar said that some pictures of Shahzad Akbar were leaked, in which he was taking out some documents from a vehicle in London. “We will not spare Shahzad Akbar,” he said, adding that billions of rupees of the nation have been spent on blind revenge. He also warned the chief secretary and IG Punjab to not become a part of the revenge actions of the rulers.
RAWALPINDI: Minister for Interior Sheikh Rashid Ahmed on Wednesday said that the next general elections would be held...
ISLAMABAD: Minister of State for Information and Broadcasting Farrukh Habib on Wednesday said the required steps were...
ISLAMABAD: Federal Minister for Information and Broadcasting Chaudhry Fawad Hussain Wednesday hailed rally of Pakistan...
Pakistan and Russian officials discuss defence, counter-terrorism and cyber security cooperation
ISLAMABAD: Prime Minister Imran Khan emphasised that timelines specified for completion of China-Pakistan Economic...
LHC observes that desperate times call for desperate measures and health emergency must be imposed in the entire...

domain: sociology


text:
Somali discrimination/intimidation, illegal campaigning and registration problems highlight our post-11 a.m. update:
One of the interesting stories out of today might be how Somali voters are treated.
Minnesota Independent’s Molly Priesmeyer says GOP vote-challengers arrived at Cedar-Riverside’s Brian Coyle Center claiming they’d been told a translator was telling people who to vote for. Witnesses tell Priesmeyer the only translator doing that was pitching for Norm Coleman. Later, Coleman staffer Mahamoud Wardere, who refused to reveal his identity originally., came in and also “translated for Coleman.”
[Note to mainstream media: if true, this is a big one given the translators’ day jobs.]
The Strib’s Whistleblower offers an infuriating-then-reassuring tale of an “elderly white woman” election judge who insisted a Somali woman had to speak English to cast her ballot. The crowd, and other election judges, got that ruling overturned. Note: this is a reader report.
MPR’s Bob Collins puts it bluntly: “Same-day registration is saving voter rights in Minnesota.”
Writes Collins, “Occasionally, there are claims in Minnesota that same-day voter registration could lead to voter fraud. Today, it appears to be preventing fairly widespread voter disenfranchisement.”
He says a “handful” of people who have voted before are told they’re not registered. No biggie; someone can vouch for them, or they can use a driver’s license.
OurVoteLive currently has 68 Minnesota problem reports.
The pro-DFL Minnesota Campaign Report says West St. Paul City Council candidate Mark Mohr has campaigned inside polling places, perhaps by representing himself as a poll-watcher. That’s uncool. MCR says the report is confirmed, but doesn’t say how.
Minnesota Democrats Exposed says Third District Congressional candidate Ashwin Madia was illicitly campaigning near polling places. Minnesota Campaign Report says both DFLer Madia and Republican Erik Paulsen were asked to leave a polling place. Both reports are unconfirmed by independent media.
Twitterer mdean_tps claims over 500 calls have been made to the Election Protection Hotline today.
For context, both dailies agree that overall, things are good.
Strib: “Voting moves briskly with few problems.” Interesting notes from the ‘burbs and exurbs: Credit River Township saw a third of its registered voters move through in three hours (the polling day is 13 hours long), while half the registered voters in Columbia Heights had cast ballots by noon.
The PiPress quotes Secretary of State officials saying, “Across the state things are going well,” noting only “small glitches” that shouldn’t stop turnout from topping an 80 percent turnout goal. Also, “officials have printed extra ballots — as many as twice the expected turnout in some cases — to make sure they don’t run short.”
St. Cloud lines are moving fine on an “extremely busy” day, the St. Cloud Times reports. A few balky voting machines have gummed up the works in isolated spots.
Fox9 offers a very short list of busy polling places, including evening-turnout hotspots.

domain: news


text:
Famdra is wholly a South African company involved in design, manufacture and maintenance of INDUSTRIAL WEIGHING EQUIPMENT.
Products & Services
Brand name Products
Loadtech is the leading manufacturer and supplier of load cells in Southern Africa.
A Full range of Pressure, Temperature, Flow and Level Instrumentation. Brands offered include, Dresser, Siemens, Ashcroft
EngNet Ltd. EngNet®
EngNet Design Group

domain: design


text:
Exuding femininity, romance and fresh-faced Southern California lifestyle, the Joie Spring/Summer 2014 Campaign uses gorgeous top models Josephine Skriver and Caroline Brasch Nielsen to headline the lookbook.
The Joie Spring/Summer 2014 Campaign is shot with romantic backdrops by fashion photographer Glen Luchford, capturing the models looking very dreamy and carefree as they twirl around in the label’s designs featuring airy shapes, floral prints and long-sleeved shirts.
These summer-craving pieces will undoubtedly have the contemporary, savvy and understated chic designs that Joie is known for. The new collection will feature pieces that are perfect for a casual coffee with the girls, a sophisticated business lunch with clients or a romantic date.
Inspired by vintage finds, while keeping things modern all the same time, the Joie Spring/Summer 2014 collection is bound to be a winner.


text:
Welcome to the purchase artwork page! If you are interested in purchasing a work of art or a print, please fill out the form below. If you have any questions or requests, please add them in the comments box below. You will receive a email response after your form is submitted.
Final prices may have an additional charge due to shipping and packaging fees. Payments can be made in several ways, and it is up to the customer on how they pay.

domain: artistic


text:
- A-Z Publications
- Southern African Forestry Journal
- Previous Issues
- Volume 2005, Issue 204, 2005
Southern African Forestry Journal - Volume 2005, Issue 204, 2005
Volume 2005, Issue 204, 2005
Author Mary ScholesSource: Southern African Forestry Journal 2005, pp 1 –2 (2005)More Less
Extracted from text ... Southern African Forestry Journal - No. 204, July 2005 1 Guest Editorial Scientific excellence: A decent legacy Citations still remain the key tool for analyses of scientific impact. South Africa produces only 0.5% of the global publications (1997-2001), trailing way behind Brazil, Taiwan, and Greece (King, 2004). Sustainable economic development in competitive global markets requires a direct engagement in the generation of knowledge. Constructive engagement between the North and the South and between partners in the South requires recognition of scientific capacity and delivery. As King points out, citation statistics can also mask a great deal. We want to improve ..
Prescribed under-canopy burning in Pinus patula plantations of the Mpumalanga highveld : the effects of fire on tree growth : scientific paperSource: Southern African Forestry Journal 2005, pp 3 –13 (2005)More Less
The effect of controlled undercanopy burning on tree growth has been studied under 16-year-old Pinus patula trees in Mpumalanga. Three fire intensity treatments and a control "no-burn" treatment, were applied to 1 ha plots. Average fuel depth was 42cm with a mean fuel load of 14.3 tons/ha. Fuel load was reduced by 15%, 30% and 60% in the three intensity burns. Fire intensity parameters were calculated using the BEHAVE fire behaviour prediction and fuel modeling system. Fireline intensity was predicted to be 134, 277 and 761kW/m for low, medium and high intensity experimental burns, respectively. Bark scorch height was found to be significantly greater in the plots under the high intensity burn treatment than in the low and medium intensity treatments. Most trees experienced scorch damage to between 0 and 40% of the crown volume. There was a significant negative effect on tree growth after a period of 36 months in the high intensity burn treatment. A low level (3 dead trees in sample of 360) of mortality occurred. This study showed clearly that undercanopy burning, at a low intensity, could significantly reduce fuel loads without resulting in decreased tree growth. It is recommended that this approach should be explored at an operational scale.
Root volume and raising period affect field performance of Pinus patula cuttings in South Africa : scientific paperSource: Southern African Forestry Journal 2005, pp 15 –21 (2005)More Less
The propagation of pines through cuttings has become a commercial means of rapidly multiplying improved genetic material for operational use in forestry companies. Cuttings of pines are produced entirely in containers in South Africa. Containers, however, can negatively affect plant growth and postplanting field performance if plants are allowed to grow beyond the constraints of the root cavity. The aim of this study was to determine the effects of tray type and plant age on the field performance of Pinus patula rooted cuttings. Field assessments indicate that the combination of greater root mass at planting and increased media volumes improved field growth with the most significant response observed in stem diameter. Factors responsible for producing greater root dry mass at planting were increased media volume and a longer raising period in the nursery. Seven years after planting, cuttings with the largest root mass at planting (0.560 g) were 27% larger in individual tree volume than trees produced from cuttings having the smallest root mass at planting (0.159 g). Field survival was exceptionally good and did not differ among nursery treatments.
Production speed effects on log-making error rates and value recovery for a mechanized processing operation in radiata pine in New Zealand : management paperSource: Southern African Forestry Journal 2005, pp 23 –35 (2005)More Less
Mechanized processing operations are complex "man-machine" systems. The impacts of changes to work practices are, therefore, dependent on the effects the changes have on both the machine and the man. A mechanized processor, delimbing and cutting tree length stems into logs on a landing, was studied in two Pinus radiata plantation forest stands in New Zealand in early 2004 to determine the effect that production speed had on operator decision making and on the machine measurement accuracy and precision. The processor operator was experienced and had a reputation for high value recovery performance. The operator was asked on four occasions to process stems at different production speeds; slow, normal, fast and very fast. Over 150 stems were processed into 849 logs during the four trials. Value recovery, log-making error rates and productivity were assessed during each of the trials. It was found that production speeds ranging from 430 to 610 m3 per day had no impact on gross value recovery, the types of logs cut, or log-making error rates. It was also found that, while length measurement accuracy was not affected by production speed, length measurement precision decreased with higher speeds. Diameter measurement accuracy and precision were both affected by production speed, but there was no obvious trend. Net value recovery increased at higher production speeds as a result of lower production costs.
Application of a 'stem number guide curve' for sustainable harvest control in the dry woodland savanna of northern Namibia : research noteSource: Southern African Forestry Journal 2005, pp 37 –44 (2005)More Less
The savanna woodlands of north-eastern Namibia are a significant source of essential resources for the rural population. Thus far, however, there is little or no growth data available to predict future timber supplies and current yield regulation is limited to the issuing of harvesting permits based on the assessment of available tree sizes, rather than a tree population as a whole. This paper presents the negative exponential function for the development of a guide curve. The curve defines an optimum stand structure based on desired timber yields for specific tree sizes, the intrinsic mortality rates of individual species and the total desirable stocking of a stand. The application of the approach is assessed using the size class distributions of two prominent tree species of the Kanovlei area in north-eastern Namibia. While the function models the development of the populations of the species well, timber and non-timber trees will need to be modelled separately. In the coming years it will be an important priority to establish a system of sample plots to obtain growth data that may support or augment the system.

domain: literature


text:
NRG Dog Treat Smokehouse Salmon Jerky 100g
NRG True North Treats Smokehouse Salmon Jerky slowly dehydrated into the best treat your dog has ever tasted.
Wild Caught Salmon fillet, sweet potato, cider vinegar, herbs, and spices.
No GMO ingredients.
Crude Protein 72%
Crude Fat 8%
MORE NUTRITION, MORE QUALITY, MORE VALUE
100% edible, table grade ingredients, from North American Farmers
- Fresh fruits and vegetables 100% of the time
No 'off shore' or Asian ingredients
- No Genetically Modified Organisms
Free-range meats and wild-caught salmon
- Organically Balanced™
- No Hormones or Antibiotics
- Made with Non-GMO Ingredients
- 100% fresh fruits & vegetables- Human Grade
- Dried with low temp renewable energy

domain: pet


text:
1. When Kim Kardashian was held up at gunpoint and robbed in October last year, it was clear the horrific ordeal would have some kind of lasting impact on her future.
2. And in an unprecedented move, Kim removed herself from the public eye and abstained from social media for three months as she recovered from the incident.
5. The video, posted to her website, shows intimate family moments, including Saint learning to walk.
6. And heartfelt hugs with Kanye.
7. Kim then took to her favourite social media platform, Instagram, to execute part two of her comeback. She shared this photo of the Wests alongside the caption: “Family.”
8. Deciding to make her return with a home video and a simple family portrait sent a powerful message to the media and public: She and Kanye are united.
Kimye have been dogged by persistent nasty rumours about their marriage recently, with constant reports suggesting a divorce is imminent.
However, rather than commenting on the rumours about her marriage, Kim let the visible happiness in the video and the unity in the photo do all the talking. The video was even set to a soundtrack of Jeremih’s “Paradise” – as if to directly counter the rumours of there being “trouble in paradise” for Kimye.
9. Silencing the speculation in this way is something the Kardashians often do in order to control their own narratives.
In fact, Kim did the same thing this time last year when Kanye had an almighty Twitter spat with Wiz Khalifa and Amber Rose. While the media was rife with suggestions that Amber, Kim, and Kanye all hated each other, Kim stepped in.
10. Two days after the spat, she and Amber posed for a selfie together and simultaneously shared it to their accounts, with Kim captioning it “Tea anyone?” and Amber posting the “sips tea” emojis.
The selfie completely changed the conversation from one of negativity to one of excitement and intrigue, and also shifted the focus off Kanye.
But, more importantly, the use of a selfie and the chosen captions implied that the drama was being fabricated by the press. It gave the impression that neither the press nor the public knew what was going on behind the scenes – and in turn allowed Kim to take back control of the narrative.
11. Kim’s return to social media has had the exact same effect in shutting down divorce rumours. And it effectively proves that despite three months away from the public eye, Kim is still an incredibly savvy media operator.
It was also interesting that the photo Kim chose to return to the limelight with displayed none of the things that have come to define her social media presence: no selfie, no emojis, nothing overly ~sexy~ or posed.
In fact, her face was turned away from the camera, and that’s also the case for each subsequent photo she’s posted since. Sharing a family photo with a simple caption, referring to the three people most important to her, is a clear signifier that they are her priority now.
That’s unsurprising, given the confirmation that Kim begged for her life during the robbery because she “has babies,” and the fact she flew straight to them afterwards. She also remained at Kanye’s side during his week in hospital at the end of the year, and reports have suggested Kim has decided to alter her lifestyle since the robbery, focusing less on ~celebrity~ and more on family.
It’s unlikely Kim will withdraw from the public eye completely – but perhaps 2017 will see her scale back her public appearances in favour of more time at home.
12. The idea that her priorities have shifted was confirmed by Khloé Kardashian this week.
Writing on her app, Khloé revealed:
I think with everything that has happened with Kim’s life this year, she really had to redefine her priorities. Time does heal and I think she’s in a much better place now. So, I just want her to focus on her family and her own happiness this year.
14. There’s also been a literal change in how Kim is presenting herself, given that her new photos have a distinctly ’90s Polaroid aesthetic.
The images have a blurry quality and an incredibly personal feel. It’ll be interesting to see whether this is something Kim continues, if the images are symbolic of a less flashy lifestyle.
15. Kim returning to social media this week is also interesting, as her first public appearance since the robbery is scheduled for next week on 13 January.
The appearance is at a makeup masterclass she’s hosting with her makeup artist, Mario Dedivanovic, in Dubai. The appearance was originally scheduled for 14 October – 10 days after the robbery – but was cancelled. Kim coming back to social media a week before the appearance was presumably planned so as to ease her back into the public eye.
17. However, it’s clear that if anything, Kim’s absence has simply heightened the public’s interest in her. The family portrait Kim returned with has now amassed over 4 million likes, making it the most-liked photo any Kardashian/Jenner has ever shared.
18. One thing is very clear: THE. QUEEN. IS. BACK.
Cortesía de: BuzzFeedFollow @DifusionLibre1

domain: celebrity


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The world is becoming more and more urban, posing new and difficult challenges for urban water management. Today, around 55% of the world’s 4.2 billion people live in cities. This trend is expected to continue; by 2050, the urban population will double and almost 7 out of 10 people will live in urban centers. In this sense, on World Cities Day, we at Almar Water Solutions want to highlight the role that the cities of the future, Smart Cities, play in water management.
The water sector is getting ‘smart’ to provide innovative services and solve problems with automation, data collection and analysis. Almar Water Solutions, through its subsidiary Datakorum, is committed to digital solutions and IoT products and services to manage its water treatment plants.


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Over the past 30 years, Karen Rago, RN, has interacted with thousands of transplant patients and has watched organ transplantation evolve from a risky, often short-term solution into a procedure that can offer decades of greatly improved health.
But despite the huge role transplants have played in her professional life, they stayed far removed from her personal life — until recently.
“For so long, the thought that one of my family members would need a transplant never crossed my mind,” said Rago, executive director of UCSF service lines and the UCSF Heart and Vascular Center.
All of that changed a few years ago when her younger sister Kay Roberts, a longtime smoker, began having severe lung problems after a bout with pneumonia. Roberts was soon cycling in and out of the hospital and had to leave her job as a pre-school teacher in Atlanta.
“Eventually, her lung function was down to about 25 percent,” Rago said. “It was so hard to watch that happen to her. I tried to talk to her about being considered for a lung transplant, but I didn’t want to push too hard.”
After quitting smoking and discussing her options further with Kerry Kumar, RN, a transplant nurse-coordinator at UCSF, Roberts agreed to be evaluated for a lung transplant at Atlanta’s Emory Transplant Center. She was found to be a suitable candidate and after a mere eight days on the transplant list, she underwent a successful double lung transplant.
It has been two years since the surgery, and Roberts is now back to work and back to taking part in an annual “girls’ getaway” trip with Rago, their other sister Barbara and their mother.
“Her immune system will always be somewhat compromised, but she’s doing really well,” Rago said.
The experience has reaffirmed Rago’s support for organ donation, and she has encouraged all of her extended family members and their spouses to sign up as donors, she said.
Campaign Sets Ambitious Goal
Rago is also a driving force behind an online effort to enlist the entire UCSF community as organ donors. Today, (Sept. 14), the student group Coalition of Organ Donation Exponents (CODE), is launching a 10-week “eCampaign” to direct students, faculty and staff to the website of Donate Life California, a nonprofit organ and tissue donor registry. The campaign will run through Friday, Nov. 20.
There are currently 20,000 patients awaiting transplants in California, including 775 in San Francisco, according to Donate Life California. Every day, 18 patients die waiting for new organs.
A similar effort by CODE in April yielded 117 signups from UCSF — a higher number than all of the other regional organizations participating in the campaign, according to CODE’s leader, second-year medical student Patricia Zheng.
Zheng said she has received tremendous support for CODE’s efforts from Rago, as well as other members of the UCSF faculty and staff.
“I’ve also been amazed by the amount of dedication shown by UCSF transplant patients and their families, many of whom have been willing to share their stories to help increase awareness,” she said.
New Organ, New Life
Two of those individuals, Carmen Hartono and Sharon Fong, have teamed up as outspoken advocates for the cause since the mid-1990s, when a stranger-than-fiction scenario caused their lives to be forever intertwined.
The pair’s tale—which Hartono is turning into a book—began on May 8, 1993, when Hartono’s 13-year-old son Nick fell off his bicycle while out riding with a friend near his Oakland home. A driver failed to see him lying in the road and hit him, killing him almost instantly, Hartono said.
Later, while waiting at the hospital for her husband John to arrive from an overseas trip, doctors approached Hartono about the possibility of donating Nick’s organs — something she had never really considered before that moment, she said.
“I talked to my husband about it, and to our priest, and I realized it could be a form of resurrection,” she said. “Organ donation provided a way for us to bring new life from his death; it keeps part of Nick living in others.”
Three days later, Nick’s organs were transplanted into three anonymous recipients. One of them, UCSF patient and Oakland resident Sharon Fong, had been on the list for a liver transplant for seven months after suffering for more than two decades from chronic autoimmune hepatitis, a disease in which her immune system attacked her liver and caused inflammation.
Fong said she was “shocked” to receive the call from John Roberts, MD, chief of transplant surgery at UCSF Medical Center, telling her an organ was available. After recovering from the successful surgery, Fong wrote a letter of thanks and asked the medical center staff to pass it along to the donor’s family, whose name she didn’t know.
“I received a letter back, telling me about my 13-year-old donor — a boy with a passion for music — as well as a cassette tape of songs he had composed,” Fong recalled recently.
For two years, that was the end of it. Then, in 1995, Fong’s 19-year-old daughter Stephanie died and she found herself at a meeting for bereaved parents, listening to a couple named Hartono talk about their late son, a music-lover who had died in 1993.
“Something about it just rang a bell and I started putting the pieces together,” Fong said. “But I didn’t say anything because I was trying to figure out the appropriate time to go up to them and tell them, ‘Hey, guess what?’”
The following spring, at a California Transplant Donor Network (CTDN) event in San Francisco honoring donor families, Fong saw the Hartonos from across the room and felt the timing was finally right. She approached them and, to their immense surprise, introduced herself as the grateful recipient of Nick’s liver.
The Hartonos and Fong have been a strong presence in each other’s lives ever since, attending birthday parties and weddings and speaking out publicly in support of organ donation. And every year, they gather to honor August 2, which coincidentally is the date of both Nick’s birthday and Stephanie’s death.
“There has been so much joy amidst the sorrow, and this experience has made my life incredibly full,” Carmen Hartono said in a recent phone interview. “I am sure Nick and Stephanie have become the best of friends in heaven, watching over their families here on earth.”
Fong, a retired pharmacist, said her transplant at UCSF changed her focus and her priorities in life, and she appreciates each day her new liver has made possible.
“I am grateful to a young boy: my donor, my hero,” she said. “His legacy lives on through me, and I have a responsibility to live life to its fullest, to cherish my second chance at living.”
Long History of Transplant Success
UCSF Medical Center is home to the country’s third-largest solid organ transplant program, and has earned national recognition for its success in converting potential donors into actual donors.
In 2008, UCSF celebrated its 45th year of transplantation, with more than 10,000 successful operations under its belt. Also that year, the UCSF Heart and Lung Transplant Program performed its 500th procedure. The program’s patient survival rates exceeded the national average in 2008, according to data from the Scientific Registry of Transplant Recipients.
In addition, the University continues to work aggressively to expand its living donor transplant program, which consists of kidney and liver transplants. The medical center is currently the second-largest center for living-donor kidney transplants in the country.
In addition to the eCampaign, on Monday, Nov. 9, CODE will present a free screening of the award-winning documentary, “D tour,” which follows musician Pat Spurgeon as he searches for a living kidney donor while touring with his band — a search that ends with a successful transplant surgery at UCSF.
Earlier that day, at another CODE event, organ donation liaison Jill Noonan, RN, will talk to UCSF students about how donors are identified and cared for after they are declared brain dead. Noonan works for CTDN, an independent organ procurement organization that UCSF helped establish in 1987.
To find out more about the CODE events or eCampaign, email [email protected].
Photo courtesy of Karen Rago
With Thousands in Need of Transplants, UCSF Intensifies Efforts to Promote Organ Donation
UCSF Today, April 3, 2009

domain: medical


text:
Understanding how water-use regulation relates to biomass accumulation is imperative for improving crop production in water-limited environments. Here, we examine how the vulnerability of xylem to water stress-induced cavitation and the coordination between water transport capacity and assimilation (A) influences diurnal water-use efficiency (WUE) and dry-matter production in Lolium perenne L. – a commercial forage grass. Plants were exposed to a range of water stresses, causing up to 90% leaf death, by withholding water and then rewatering to observe the recovery process. Leaf hydraulic conductance (Kleaf) declined to 50% of maximum at a leaf water potential (ψleaf) of −1 MPa, whereas complete stomatal closure occurred well after this point, at −2.35 MPa, providing no protection against hydraulic dysfunction. Instantaneous A remained maximal until >70% of hydraulic conductivity had been lost. Post-stress rewatering showed that 95% loss of Kleaf could be incurred before the recovery of gas exchange exceeded 1 d, with a rapid transition to leaf death after this point. Plants exposed to sustained soil water deficits through restricted nightly watering regimes did not suffer cumulative losses in Kleaf; instead, ψleaf and gas exchange recovered diurnally. The effect was improved WUE during the day and optimal ψleaf during the night for the maintenance of growth.
A fundamental limitation to the ability of plants to survive and grow under water-limited conditions is the capacity of the water transport system to maintain a hydraulic connection between leaves and the soil. As the soil dries, xylem vessels come under increasing physical tension, which when great enough, causes the water column to break and become air-filled, resulting in cavitation and loss of hydraulic conductivity (Tyree & Sperry 1989). Reduced hydraulic conductivity has the potential to impact plant growth rate (Mencuccini 2003; Tyree 2003; Poorter et al. 2010; Russo et al. 2010) because of the close relationship between water transport efficiency and photosynthetic capacity (Hubbard et al. 2001; Brodribb, Feild & Jordan 2007). Furthermore, drought-induced xylem failure can lead to plant death without efficient control of leaf hydration, or the ability to repair dysfunction in the hydraulic system (Sperry 2000; Sperry et al. 2002). Despite the risks to productivity and survival, it is acknowledged that some plants operate close to the minimum leaf water potential at which incipient loss in hydraulic conductivity occurs (Tyree & Sperry 1988). Therefore, water stress-induced hydraulic dysfunction presents a problem not only for long-term survival during severe drought events, but also for daily productivity during short-term fluctuations in soil water availability.
Closure of stomata to regulate the decline in leaf water potential (ψleaf) under water stress is an important mechanism in slowing the loss of hydraulic conductivity. Stomatal closure generally pre-empts significant loss of hydraulic conductivity, and the gap between the ψleaf at 95% stomatal closure and the ψleaf at 50% loss of hydraulic conductivity provides an indication of the hydraulic safety margin (Brodribb & Holbrook 2004; Sack & Holbrook 2006). In species with a wide safety margin, the risk of reaching leaf water potentials low enough to induce xylem failure is minimal because stomata close before hydraulic conductivity substantially declines. However, in other species with a narrow or even negative safety margin, stomata tend to exhibit a threshold response to ψleaf which triggers after the point of incipient loss in hydraulic conductivity (Brodribb et al. 2003).
The importance of stomatal response to desiccation as an indicator of water-stress resilience requires an understanding of the timing and mechanisms associated with hydraulic dysfunction (Zwieniecki & Holbrook 2009). For example, a rapidly reversible decline in hydraulic conductivity has been associated with turgor loss of bundle sheath cells (Brodribb & Holbrook 2006; Kim & Steudle 2007) and xylem collapse (Cochard et al. 2004; Brodribb & Holbrook 2005; Blackman, Brodribb & Jordan 2010), whereas slow recovery of hydraulic conductivity is more likely to be where cavitation of xylem has occurred, requiring positive pressure for embolism repair. In conifers displaying resistant xylem and conservative stomatal regulation (i.e. operate with a large safety margin), the transition from recoverable to non-recoverable water stress has been shown to be rapid once 50% hydraulic loss has been transgressed (Brodribb & Cochard 2009). Comparatively in woody angiosperms displaying a narrow safety margin (Brodribb & Holbrook 2004), it has been recently demonstrated that near-complete loss of leaf hydraulic conductivity can be incurred before plant death ensues (Blackman, Brodribb & Jordan 2009).
The relationship between xylem dysfunction and plant recovery rate still remains to be specifically quantified; however, in the case of cavitation-induced hydraulic dysfunction, it is likely to relate to both physical constraints on the generation of root pressure under soil-saturated conditions and limitations on the rate at which replacement xylem can be grown (Brodribb et al. 2010). In herbaceous plants, root pressure is readily observed alongside observations of diurnal cavitation and refilling of xylem. In both rice (Stiller, Lafitte & Sperry 2003) and sugarcane (Neufeld et al. 1992), for example, over 60% of hydraulic conductivity may be lost during peak transpiration under well-watered conditions but can be restored overnight by root pressure. Diurnal declines and recovery of hydraulic conductivity have also been demonstrated in the petioles (Bucci et al. 2003) and leaves (Brodribb et al. 2003; Johnson et al. 2009) of some woody species. It is, however, unlikely that once cavitation is widespread throughout the plant, woody plants would be able to generate enough root pressure to traverse the long distances required (Fisher et al. 1997).
The comparative analysis of hydraulic efficiency and vulnerability in crop plants remains scant. Furthermore, it has only been in recent years that the direct use of hydraulic traits in breeding efforts for improved water use and production has been considered (Cochard et al. 2008; Sinclair, Zwieniecki & Holbrook 2008). This is in part due to the mixed interpretations of what may be regulating stomatal closure – namely the situation where ψleaf and hydraulic conductivity appear to remain stable, but stomata close due to increases in the hormone abscisic acid (ABA) in the transpirational stream (Comstock 2002). However, from the work undertaken on woody plants, the application of hydraulic information to crop plants seems paramount to the characterization of absolute drought tolerance and water use under soil water deficit conditions (Sperry, Stiller & Hacke 2003; Monclus et al. 2005; Fichot et al. 2009). Knowing why stomata regulate with certain safety margins and the consequences of hydraulic failure will be important questions when it comes to designing irrigation practices with limited water resources and for selecting plant attributes for production in arid environments.
In this study, we investigate how hydraulic conductivity, xylem vulnerability and patterns of diurnal gas exchange influence production and water-use efficiency (WUE) in a commercial pasture grass. From a theoretical perspective, a temperate forage grass was selected specifically to contrast the extensive work on woody plants. Two watering methodologies were employed in order to answer two related sets of questions. The first method involved withholding water from pots to five levels of increasing drought stress followed by rewatering to field capacity to: (1) analyse the relations between hydraulic dysfunction and water-loss regulation, and therefore production potential with declining leaf water potential; (2) quantify the hydraulic safety margin and how this relates to xylem vulnerability; and (3) identify the point at which plants suffer irreversible desiccation damage. Using a different cohort of plants, the second method examined whether plants were able to recover from daily losses in hydraulic conductance when maintained at five narrow soil water levels using a nightly watering regime. The interaction between acclimation, dynamic recovery of hydraulic conductance and gas exchange were examined in the context of growth rate over a ryegrass regrowth cycle.
MATERIALS AND METHODS
Growing conditions and establishment
The experiment was conducted in a controlled glasshouse environment (14 h days at 20/10C day/night), with unfiltered natural light supplemented with sodium vapour lamps to ensure a minimum of 300–500 µmol quanta m−2 s−1 at the leaf surface throughout the day period. Relative humidity was maintained between 30 and 50% by a dehumidifier coupled to a humidity probe. Seeds of Lolium perenne L., cv. ‘Impact’ were germinated in seedling trays in a combination of potting mix and pea gravel, before being transplanted to 3.7 L pots, packed to an average density of 1.04 g cm3−1 with sandy-loam soil. To transplant, the roots were cut to 3 cm and washed to remove any remaining potting mix, and the leaf material above a standing height of 5 cm was cut. Seedlings with 7–10 tillers were selected to ensure that plants were of a similar size and maturity. Triple superphosphate and potassium phosphate fertilizers at rates of 200 kg P/ha, 45 kg K/ha and 184 kg S/ha were mixed into the sandy-loam soil before sieving and potting occurred to ensure that soil fertility would not limit plant growth during the experiment. Subsequent soil testing showed that at the commencement of treatments, the soil nutrient status was 80.3 mg kg−1 P (Olsen extraction), 272 mg kg−1 K (Colwell extraction) and 42 mg kg−1 S [KCl extraction, with a pH of 6.3 (H2O)]. During the establishment phase, on the completion of the third leaf expanding (one ‘regrowth’ period), plants were cut to 5 cm and urea was applied at a rate of 46 kg N ha−1. Soil water content during the establishment phase was maintained at field capacity, determined to be 43.5% (volumetric) using the Haynes apparatus.
Experimental watering strategies
Two watering strategies were employed, each using a different cohort of plants – (1) dry-down with rewatering from different drought intensities to investigate recoverability and limitations of plant hydraulics on leaf gas exchange; and (2) sustained watering levels by pot weight maintenance to examine daily water use and growth.
Dry-down with recovery
Plants were arranged in a completely randomized design, with three plants maintained at field capacity throughout the duration of the experiment to act as controls, and the remaining 15 plants (three plants per treatment) allowed to dry-down by withholding water to different drought intensities determined according to visual signs of leaf necrosis once a pre-dawn leaf water potential (ψPD) of 1.5 MPa (turgor loss point of non-drought adapted plants) had been reached. Leaf damage was calculated as the percentage length of leaf that was dead, totalled across all leaves per tiller and expressed as an average of five tillers. The resulting five plant stress levels at which plants were rewatered to field capacity were 10, 20, 40, 80 and 90% tiller death.
Corresponding minimum leaf water potentials (ψleaf) and soil relative water contents (RWC%) were also defined at each of the five treatment levels. ψleaf was measured on excised leaves, placed immediately in a humidified bag, using a Scholander pressure bomb (Model 615, PMS Instrument Company, Albany, OR, USA). Soil RWC% was calculated for each individual plant according to the weight of the soil at the time of rewatering (initial weight) and the weight of the soil after being dried at 105C for 24 h (final weight), according to the equation:
Once leaves had reached approximately −3 MPa, the live portion of the leaf was quite minimal and easily damaged during measurement, which is a common problem in ryegrass (Thomas 1987, 1991; Clark, Newton & Barker 1999). As a result, minimum ψleaf of the two driest treatments were estimated according to the relationship between leaf RWC % and 1/ψleaf where leaf turgid weight was calculated from the relationship of leaf dry weight to turgid weight (data not shown).
At the target tiller damage plants were rewatered to field capacity by placing the pot in a shallow tray and left to draw water from the bottom of the pot until field capacity had been attained. During the subsequent recovery phase, pots were weighed every second day and watered from the top to maintain field capacity. During dry-down and recovery, plants were not cut at the usual completion of three leaves fully expanded in order for there to be enough leaf material to perform the measurements. As a result of ryegrass only maintaining 3–4 live leaves, leaf turnover was relatively high, particularly in the controls.
Sustained drought levels
To assess the impact of water stress on WUE and growth potential, three plants per five soil water deficit levels were maintained according to pre-defined pot weights to achieve a range of ψMD and corresponding gas exchange capacities. The average pot weight targets included soil volumetric water contents (VWC %) of 28, 21, 19, 16.5 and 15%, which corresponded to average daily watering applications of 119, 78, 64, 44 and 27 mL day−1. Foil was placed on top of the soil surface and around the base of the tillers, and the pot double-bagged so that water loss could be attributed to transpiration. After 6 pm each night, pots were individually weighed and watered back up to target weight. Water was applied down a 2.5 cm wide plastic pipe that was inserted 2 cm into the soil. This method was used to avoid preferential flow down the side of the pots as well as to ensure that water uptake was only via the roots and not through direct contact with the leaf or tiller bases. The plastic pipe was capped to prevent water loss via soil evaporation. There were three plants in each treatment, arranged in a randomized design. To ensure time for plant adjustment, plants were pre-treated at their prospective target weights for one regrowth before being cut and the measurement period beginning.
Leaf vulnerability (Kleaf)
The response of leaf hydraulic conductivity (Kleaf) to ψleaf was assessed according to the method of Brodribb & Holbrook (2003) where Kleaf is calculated from the kinetics of ψleaf relaxation in leaves rehydrated through the tiller base. Five plants at various initial hydration states were used to construct the curve. Individual tillers were removed roots intact, and allowed to further dry on the lab bench at 25 °C for different periods, before being placed in a sealed plastic bag for approximately 1 h to minimize variation in water potential between leaves. Initial ψleaf was then determined by measuring leaves subtending the youngest fully expanded leaf (YFEL), or where equilibrium ψleaf between leaves could not be obtained in severely desiccated tillers; half of the YFEL was sampled prior to rehydration. The tiller base was then cut under water, taking care not to wet the leaf itself, and allowed to rehydrate between 30 s and 4 min depending on the initial ψleaf. The remaining leaf was then cut at the leaf sheath junction and immediately placed in a humidified bag for measurement of final ψleaf. Kleaf was calculated from the ratio of initial to final ψleaf and the leaf capacitance, and corrected for the viscosity of water at 20 °C.
where ψo = initial water potential (MPa), ψf = final water potential (MPa), t = duration of rehydration and Cleaf = leaf capacitance (mmol m−2 MPa−1).
The relationship between ψleaf and Kleaf was plotted and a sigmoidal regression of the form Kleaf = α / [1 + e(β-γϕleaf)] was fitted to the data to describe the leaf vulnerability. To assess the degree of xylem protection against cavitation afforded by stomatal closure, the hydraulic safety margin between stomatal closure and the depression in Kleaf was calculated. This was defined as the difference between the ψleaf at 50% loss of hydraulic conductivity determined from the vulnerability curve, and the ψleaf where stomatal conductance first reached a minimum and did not appear to substantially decline further with ψleaf, determined during the withholding of water from pots. This definition was preferred to a set stomatal closure point of 95%, due to epidermal conductance potentially being a large portion of conductance measured at the tail-end of the observed stomatal range.
For determination of leaf turgor loss, osmotic adjustment (OA) and leaf capacitance, pressure–volume (PV) curves were constructed for each treatment replicate using three leaves (Tyree & Hammel 1972). Leaves were cut at the leaf-sheath intersection before being bagged and recut at the distal end under water to leave only a small amount of leaf area in direct contact with water. Leaves were sampled at dusk and allowed to rehydrate overnight before PV determination. Leaf weight and water potential were measured periodically during slow desiccation of sample leaves in the laboratory. The turgor loss point was located at the inflection point of the 1/ψleaf versus RWC curve. Using this value in the relationship of ψleaf versus RWC, leaf capacitance was determined by fitting linear regressions either side of the inflection point. The capacitance slopes pre- and post-turgor loss were averaged across the treatments to take into account the use of both well-watered and droughted plants used in the construction of the vulnerability curve. Construction of the vulnerability curve requires leaf capacitance in the calculation of Kleaf, be expressed in absolute terms and normalized by leaf area (Brodribb & Holbrook 2003). This was determined by multiplying the capacitance calculated from the PV curve by the ratios of (leaf dry weight:leaf area) and (saturated mass of water:leaf dry weight), which were averaged across all plants:
where DW is leaf dry weight (g), LA is leaf area (m2), WW is mass of leaf water at 100% RWC (g) and M is molar mass of water (18 g).
Limitations of Kplant on leaf gas exchange
Gas exchange parameters including assimilation (A), stomatal conductance (gs) and transpiration (E) were measured using a portable gas analyser (Li-6400; Licor, Lincoln, NE, USA), with a light intensity of 1000 µmol quanta m−1 s−1 at a target air temperature of 20 °C and vapour pressure deficit (VPD) of 1.5 KPa. Three YFELs were sampled intact, per pot, and the results corrected for leaf area. Measurements were made between 1100 and 1400 h, including ψleaf, which was taken directly after gas analysis. For the determination of ψleaf, two leaves off each plant were removed and placed in a humidified bag for immediate measurement. Kplant was calculated as:
where ψPD = pre-dawn leaf water potential, ψMD = midday leaf water potential and E = transpiration according to leaf gas exchange measurements.
Gas exchange and ψleaf measurements were made almost daily in plants subjected to the one drought cycle, but were restricted to five times during the growth of plants under sustained soil water deficit conditions to limit the amount of leaf material removed during ψleaf measurements so that dry-matter (DM) production could be estimated.
Recovery from water stress was assessed according to the number of days taken for plants to return to 50% of the pre-drought maximum rate of Kplant and A following rewatering (t1/2). The inverse of half-time (t1/2−1) was plotted as a function of the treatment ψleaf minimum (Brodribb & Cochard 2009), where t1/2−1 decreases as the time taken to recover increases – zero indicating plant death. This was compared with the proportion of leaf dieback associated with the treatment levels to provide a measure of the net loss in A capacity compared with the individual leaf potential.
Diurnal patterns in leaf extension, water use and WUE
Leaf extension was monitored over a 6 d period at the emergence of the third leaf on two tagged tillers per plant under the sustained soil water deficit conditions. The length of the elongating leaf was measured from the ligule to the tip with a ruler at 8 am (beginning of light hours) and at 6 pm (when plants were watered), and the rate of extension (cm h−1) during the night (6 pm–8 am) expressed as a percentage of daily growth.
The day before plants were cut for DM yield determination, a diurnal series of whole-plant water loss was performed by weighing pots every hour between 600 and 2100 h, to an accuracy of ±0.01 g (Mettler-Toledo PG5002-S). Plant E was calculated by the loss of weight of each plant between measurements divided by the total leaf area. Leaf area was determined for each plant by taking a mixed subsample of leaves after being cut, and the relationship between DM and leaf area used to calculate leaf area of the whole plant.
Leaf tissue (above 5 cm) was harvested from plants and leaf DM yield/plant determined after drying samples for at least 24 h at 60 °C in a forced draught oven. WUE was calculated according to leaf DM per plant (g)/cumulated water applied (mL). Instantaneous WUE (A/gs) calculated from gas exchange information and averaged across the experimental period per treatment was used as a comparative measure.
Nonlinear and linear regressions were analysed using PROC NLMIXED procedures from the SAS statistical package, version 9.1 (SAS Institute Inc., Cary, NC, USA) and graphed using Sigmaplot (SPSS Inc., Chicago, IL, USA). A log likelihood ratio chi-square test was used to compare nested models, for the purpose of selecting the most parsimonious model. The P-value for model selection was derived from the difference in the −2 log likelihood statistics between two models, assuming chi-square distribution with degrees of freedom given by the difference in the number of parameters between models. Where there was no significant difference, the reduced model was selected. Akaike's information criterion (AIC) (Akaike 1974) and biological reasonableness was used to distinguish between non-nested models.
To determine whether plants under sustained soil moisture conditions had adjusted their water-use patterns, the progression of gs with ψleaf was compared with progressively droughted plants. A sigmoid model that fitted each dataset independently by solving for two curves with the form was compared to the single parameterization of the model applied to the combined dataset using a chi-square test as described earlier. If non-significant, the simpler model was retained. For visualizing the main differences in the shapes of the two response curves, gs data was condensed by pooling across −0.2 MPa increments and standard error bars calculated. The coefficient of determination (R2) was used to indicate the level of variance explained by the model and was expressed as where SSerror = residual sum of squares and SStotal = total sum of squares. Treatment effects of the five different sustained watering levels on DM production were analysed using analysis of variance (anova) of a complete randomized block design using Genstat version 9.1 (Lawes Agricultural Trust, Rothamsted Experimental Station, UK). Unless otherwise stated, a significance level of 5% was used throughout.
Leaf hydraulic vulnerability and relationship to stomatal closure
Hydraulic conductivity of excised leaves decreased in response to declining ψleaf. Below a threshold ψleaf of −1 MPa, Kleaf fell sharply over a narrow range of leaf water potentials before reaching a minimum at −2.35 MPa (Fig. 1). Stomatal closure in droughted plants followed a similar trajectory (Fig. 2) indicating a close link between liquid and vapour conductance across the entire range of functional leaf water potentials. A negative safety margin of 1.35 MPa was observed, indicating that stomata closed after 50% loss of Kleaf. In plants subjected to sustained soil moisture deficits, OA occurred in the leaves, with the turgor loss point increasing as a function of the average ψMD (Fig. 2). Consequently, stomatal closure of plants under sustained water deficits followed a shallower sigmoid curve despite having a similar gs minimum as non-acclimated plants (Fig. 2).
Relationship between plant hydraulic conductivity and assimilation rate
Assimilation rate and plant hydraulic conductivity, estimated from gas exchange and leaf water potentials, were sampled during the dry-down and recovery (after rewatering) of plants spanning a leaf water potential range of −0.2 to −2.4 MPa. Although A and Kplant were strongly correlated, the relationship was non-linear of the form , with A initially insensitive to declining Kplant, then dropping in parallel only once Kplant fell below 5 mmol m−2 s−1 MPa−1 (Fig. 3).
Drought-induced leaf dieback and gas exchange recovery
In plants subjected to water stress, there was a clear threshold of ψPD after which leaves began to become visibly damaged progressively from the leaf tip. This threshold for leaf damage occurred at a ψPD of −1.5 which coincided with ∼80% loss of functionality of both hydraulic conductivity and stomatal opening (Fig. 4). Within a soil water content range of 12.6–9.8%, the amount of leaf dieback increased exponentially from 10 to 90% of the total length of leaves. Although the transition from non-damaged to highly damaged occurred over a very small change in both the water status of the leaves and soil (Fig. 4), this represented an extended period of time, around 18 d, due to the fact that stomata were closed and evaporation from the soil by this stage was minimal.
Upon rewatering, recovery of the remaining live portion of leaves was rapid, requiring only half a day to regain 50% of gas exchange capacity in leaves which had lost leaf turgor, and up to 2 d in plants dehydrated to −3.1 MPa. Although in the latter case we observed hydraulic recovery in the living portions of these plants, leaf loss by this stage was already as great as 60% (Fig. 4 inset). The gradient between hydraulically recoverable and non-recoverable (in terms of existing leaf material) paralleled the steep progression of leaf dieback. Accordingly, 100% leaf damage was predicted to occur at −4 MPa from the fitted curve of leaf dieback, and unrecoverable A and Kplant at a similar average ψleaf of −3.6 MPa based on where t1/2−1 falls to zero (Fig. 4). Overall net recovery of leaf biomass was limited to a greater degree by leaf dieback and therefore the time to grow new leaves, than gas exchange and plant hydraulic conductivity. Complete plant death, i.e. the point where new leaves were unable to be initiated, was not reached in this experiment.
Diurnal water use and DM production
Nightly applications of water ranging from 27 to 119 mLs resulted in average ψMD of −0.5, −0.8, −0.9, −1.1 and −1.9 MPa for each of the soil water content targets of 28, 21, 19, 16.5 and 15%, respectively. This was in contrast to ψPD which was similar across all watering levels at an average value of 0.15 MPa (Fig. 5), despite the large range of water applied to the different treatments (27 to 119 mL day−1). The diurnal course of transpiration showed strong variation between treatments, with drier treatments producing depressed maximum E (Fig. 6). When compared to the well-watered controls, the average diurnal E rates declined by 21, 30, 53 and 71% for each of the soil water content targets of 21, 19, 16.5 and 15%, respectively.
Plants maintained at drier soil water targets were found to change leaf elongation patterns such that a greater proportion of daily growth occurred during the night compared with plants maintained at higher soil water contents (Fig. 7). Cumulatively, the restrictions to gas exchange imposed by the soil moisture deficits were insufficient to significantly (P ≤ 0.05) affect DM production; the largest yield penalty being 30% as observed in the driest treatment (Fig. 8). Furthermore, WUE increased by twofold in the most droughted treatment according to instantaneous gas exchange measures, and threefold based on DM production and total water applied (Fig. 9).
One of the constraints in plant water-stress research has been the lack of a cohesive framework by which to assess how genetic manipulations relate to functional changes in plant water use and survival, along with a quantifiable scale by which to compare levels of plant water stress and hence relative drought tolerance. Due to the fundamental link between water transport capacity and gas phase conductance, plant hydraulics provide a useful framework by which to evaluate the capacity of plants to lose water and the ultimate limitations to carbon gain. Using a hydraulics approach in this study, we identified that ryegrass has the capacity to transport a lot more water than required to maintain maximal A rates. Furthermore, water use could be reduced without permanent hydraulic damage, i.e. leaves remained responsive to water inputs for the majority of the leaf functional water potential range. With knowledge of the hydraulic limits of ryegrass, it was demonstrated that manipulations in diurnal soil water availability can achieve major increases in WUE without affecting biomass production. The implications of the results and the application of the hydraulics framework are discussed with relevance to both natural and agricultural systems.
Water-spending hydraulic strategy
Perennial ryegrass was found to be extremely vulnerable to hydraulic dysfunction under soil water deficit, with 50% loss in hydraulic conductivity occurring at −1 MPa and 95% loss of function at −2.2 MPa (Fig. 1). While it cannot be deduced using the pressure relaxation technique whether cavitation was the cause of declining hydraulic function with leaf water potential, Brodribb & Holbrook (2006) suggest that low levels of conductance, particularly 95% loss of functionality, are most likely the result of embolism formation.
Closure of stomata during drying followed a similar trajectory to the loss in hydraulic conductivity, but importantly, it was found that stomatal closure did not occur until after the loss of 50% Kleaf (Fig. 2). Although a similar degree of sensitivity of xylem to water stress-induced hydraulic dysfunction has been reported for both herbaceous (Neufeld et al. 1992; Maize, Cochard 2002; Rice, Stiller et al. 2003) and woody plants (Vogt 2001; Brodribb & Holbrook 2004; Hukin et al. 2005), most angiosperms tend to produce parallel declines in Kleaf and gs resulting in safety margins close to zero. Ryegrass is unusual in this context, producing a significantly negative safety margin of 1.35 MPa.
This risky stomatal behaviour depicts the extreme scenario of the water-spending strategy described by Jones & Sutherland (1991). Based on hydraulic models of maximum permissible water extraction (Sperry et al. 2002), the stomatal response of ryegrass indicates that this species operates at the extraction capacity of the xylem, therefore maximizing the utilization of xylem investment. This is in contrast to plants with higher resistance to xylem cavitation which tend to produce a concomitant increase in the hydraulic safety margin (Meinzer et al. 2009). In these plants, not only does the relative sensitivity of stomata increase such that plants utilize xylem investment less efficiently, but the costs associated with construction of resistant xylem are also much greater. As such, these intrinsically drought tolerant plants tend to be limited in distribution to arid environments as they are unable to compete in mesic or shaded environments where growth rate and carbon economy are at a premium (Givnish 1988).
The water extraction capacity of ryegrass plants was enhanced through OA in the leaves, with acclimated plants observing higher rates of gs under water stress (ψMD range 1.3–1.7 MPa) compared with plants exposed to only the one drought cycle (Fig. 2). It is interesting to note, however, that OA shifted the leaf turgor loss point beyond the point of 95% loss of Kleaf in three of the driest treatments (Fig. 2 inset). This would appear maladaptive, unless there was a coordinated shift in the vulnerability curve (Awad et al. 2010). The fact that stomatal closure occurred at a similar ψleaf between adapted and non-adapted plants suggests that hydraulic acclimation did not occur. This may help to explain the inconsistent benefits reported of OA in increasing crop yield under water-deficit conditions (Serraj & Sinclair 2002). A large research effort with rice, for example, has failed to produce evidence of a benefit of OA on crop yield (Jongdee, Fukai & Cooper 2002). Considering that rice (which displays similar physiology to ryegrass) already incurs losses of Kleaf during normal diurnal cycles in plants under well-watered conditions (Stiller et al. 2003), there seems little benefit, in terms of gas exchange at least, in further increasing the osmotic concentration in the leaf and stomata beyond the transport capacity of the leaves. In some situations, therefore, reduced OA and a resultant protection from hydraulic failure may be more beneficial where water supply is transient.
Recovery and hydraulic limits
Ryegrass plants rewatered after exposure to water stress conformed to a hydraulic-stomatal limitation model (Brodribb & Cochard 2009), whereby gas exchange was strongly mediated by the recovery of leaf hydraulic conductance (Fig. 3). However, due to the saturating relationship between A and Kplant, the recovery of A to 50% of the pre-drought maximum (t1/2) was more rapid than for Kplant (Fig. 4). While the mechanism of hydraulic repair was not investigated in this study, the fact that ryegrass operates so close to its hydraulic limits suggests an inherent ability to repair dysfunctional xylem on a daily basis. One possible explanation for this ability to rapidly repair xylem after water stress is that dysfunction is caused by cavitation, and repair is achieved by the generation of root pressure to refill emboli at night.
Root pressure is readily observed in the herbaceous crops including grasses (Tyree et al. 1986; Neufeld et al. 1992; Cochard, Ewers & Tyree 1994; Hughes & Brimblecombe 1994; McCully, Huang & Ling 1998; Tang & Boyer 2008), and may have similarly provided for a rapid recovery of ryegrass. This is supported by the observation that ψPD remained close to zero in all plants (Fig. 5). For root pressure to have been active, however, the majority of the root system would have to be hydraulically disconnected from the soil. Otherwise, the majority of the water applied to the soil surface would have been predicted to have redistributed throughout the pot under the passive process of equilibration of water tension in the soil–plant-atmosphere–continuum (Richards & Caldwell 1987), resulting in a much lower ψPD than observed.
Alternatively, cavitation may not be responsible for loss of hydraulic function and instead turgor loss or cell collapse may be driving diurnal declines in hydraulic conductance, both of which do not require positive pressure to refill emboli in order to restore hydraulic conductivity (Brodribb & Holbrook 2005; Blackman et al. 2010). This is quite probable as plants sustained at even at the most severe soil water deficit still maintained ψMD above the TLP. Furthermore, beyond a ψPD of −2.5 MPa, there was a steep transition to leaf death, suggesting that the transition between a readily reversible process and non-recoverable hydraulic dysfunction is very close to the functional limits of the leaves. To a degree, this transition was buffered by leaf dieback which increased exponentially with declining ψPD (Fig. 4). Leaf dieback or plant segmentation theory suggests that the sacrificial death of more disposable plant regions would help improve the hydraulic conductance and water status to remaining foliage, acting as a last resort mechanism to avoid whole-plant mortality and aid long-term survival by protecting vital plant parts such as stems and nodal regions (Cochard, Ridolfi & Dreyer 1996; Davis et al. 2002; Vilagrosa et al. 2003; Lo Gullo et al. 2004). For ryegrass, this is a reasonable proposition because regrowing three live leaves (maximum number that can be supported per tiller) under temperate summer conditions would require only ∼21 d. This compares to woody species described in Brodribb & Cochard (2009) which in some cases required over 100 d to replace leaves damaged during drought.
Understanding the critical nature of hydraulic dysfunction for maximizing water productivity
Daily water use was determined by the nightly watering volume, resulting in a decline in maximum E with decreasing soil moisture availability, which was sustained over a longer period of the day (Fig. 6). There was an expectation that water would be used preferentially during the morning in the drier treatments when ψleaf was optimal, with steady declines subsequently during the day. This was not observed which suggests hysteresis in the ψleaf versus gs relationship during drought. The plant hormone ABA has been mooted as a candidate for such transpirational control (Lovisolo, Hartung & Schubert 2002), and in a recent study by Lovisolo et al. (2008), ABA was suggested to help promote the gradual hydraulic repair of xylem by limiting the rate of stomatal reopening. The water supply limitations during the daylight hours were further evidenced by a linear increase in the proportion of leaf elongation growth conducted during the night with decreasing soil VWC % (Fig. 7). The summation of responses to restrictions in water uptake was therefore a water stress-induced increase in WUE during the daylight hours, with optimal leaf water status overnight when plants were watered, ensuring carbon fixed could be utilized in growth.
The fact that DM accumulation was minimally affected by exposure to ψleaf capable of reducing gs and Kleaf in three of the five treatments (Fig. 8) is a significant finding, as to date, the majority of plant hydraulic enquiry has been based on the idea that prevention of hydraulic dysfunction is the a priori position, and any hydraulic conductivity loss incurred is likely to have deleterious effects on gas exchange and long-term survivability from drought (e.g. Tyree et al. 2003). Such conclusions have been drawn from the extensive research conducted on woody plants where loss of hydraulic conductivity is slow to recover (Blackman et al. 2009; Brodribb & Cochard 2009). The assumption that hydraulic dysfunction needs to be prevented is challenged here by the fact that, firstly, recovery was rapid (Fig. 4), and, secondly, A in ryegrass remained maximal until >70% of Kleaf had been lost (Fig. 3). Saturation of the A versus Kleaf relationship across species has been alluded to (Brodribb & Holbrook 2006, 2007; Brodribb et al. 2007) but few studies have shown this in an individual species (Stiller et al. 2003). Hydraulic redundancy provides a greater buffering capacity of ψleaf and hence gas exchange to VPD (Maherali & DeLucia 2000, 2001; Brodribb et al. 2005), and from this perspective may be considered the equivalent of the stomatal safety margin displayed in drought-tolerant plants. However, saturating A versus Kleaf does incur the loss of more water for a similar carbon gain. In the context of this study, increases in VPD may therefore have resulted in larger differences in DM production obtained under the restricted watering regimes.
In agricultural production systems and natural systems alike, predicting both maximal production under optimal soil moisture conditions and production risks under water-limited conditions are important to both the design of irrigation strategies and the distribution of species across soil moisture gradients. The plant hydraulics approach utilized in this work reflects the basic need to conserve the hydraulic connection between soil and plant in order to maintain gas exchange and prevent desiccation. Ryegrass was identified here as being intrinsically drought-sensitive with xylem highly susceptible to water stress-induced hydraulic dysfunction, along with stomatal behaviour characteristic of a water-spending hydraulic strategy. In this regard, stomata maximized short-term carbon gain by allowing hydraulic conductivity to decline. However, unlike previous observations in woody species, hydraulic dysfunction was neither detrimental to A up to a point, nor restrictive to the recovery of hydraulic conductivity on rewatering. By exploiting these two characteristics, diurnal soil water availability could be manipulated in order to achieve increases in WUE without affecting biomass production. Further characterization of crop plants in terms of their hydraulic traits is recommended if our understanding and prediction of plant water use is to improve, and will be imperative to the achievement of yield maximization in water-limited cropping systems.
The authors would like to gratefully acknowledge the statistical advice provided by Ross Corkrey and glasshouse maintenance by Ian Cummings. This research has been funded by an Australian Research Fellowship (TJB), a Discovery Grant from the Australian Research Council and Dairy Australia Research and Development Scholarship (MHP). Ms Holloway-Phillip's stipend was provided by an Australian Postgraduate Award and additional funds by the Tasmanian ICT Centre, CSIRO.