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World’s forests at risk of injury from drought, CSUB biology professors find

Picture of Jacobsen and PrattFor most of their research careers, two biology professors at California State University, Bakersfield have been studying drought tolerance and the response of plants to water stress. Now, research findings by Drs. Anna Jacobsen and Brandon Pratt have been published in the international journal Nature as part of a study that looks at the vulnerability of the water transport system in trees during times of drought.

Published Nov. 29, 2012, the study finds that most forests have a very slim safety margin in terms of ability to cope with drought, regardless of their rainfall environment - a signal of likely consequences of climate change for forests.

The study is a meta-analysis of data collected by 24 academic scientists from 81 locations around the world. Drs. Jacobsen and Pratt provided about 10 percent of the data from their research in South Africa and California over the past 10 years.

"Through the international collaboration, we found that most woody forest species operate very close to their hydraulic limits, meaning all forests are equally vulnerable to drought," Dr. Jacobsen said. "This explains, in part, why recent drought-induced forest decline has occurred in both arid regions and also in wet forests not normally considered at drought risk. Thus, forest systems, regardless of their current climate, do not appear to be well buffered against future change."

Increasing temperatures and declining rainfall resulting from climate change are predicted to cause droughts of increasing intensity and duration in many regions of the world, which will impact negatively on plants. Plants undergoing drought stress experience reduced pressure in the xylem (the tissue that transports water from the soil to the leaves). If the pressure drops below a threshold, owing to reduced moisture in the soil, bubbles may form and block water transport. The study shows that 70 percent of 266 forest species worldwide operate at very narrow safety margins to drought injury.

For the multi-author study, Dr. Jacobsen supplied some of the data she collected in South Africa in 2004 while conducting research funded by a Fulbright Fellowship and National Science Foundation Grant. For the California data, Drs. Jacobsen and Pratt - who are married to each other - collected samples from wooded areas around the state. In a biology lab at CSUB, they cut the samples underwater and used a tubing system to measure how much water the xylem tissue in the stem could transport. They then spun the samples in a custom-built centrifuge to induce water stress and measure the drought response. CSUB students at both the graduate and undergraduate level assist the biology professors with their research.

"For all people involved in science, we want to understand the world and how it works," Jacobsen said. "It's nice to zoom out to the bigger picture, look at this pattern globally, and see that what my students are learning here at CSUB is information that applies to plant species from around the world."

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