June 7, 2004

Plants adapt to drought by becoming more water efficient, Nature study shows

Changes occur from desert to tropical forest

By Jennifer McNulty

Plants in wet tropical forests adapt to changes in precipitation and become as efficient in their water use during droughts as plants in arid deserts, according to a study to be published in the June 10 issue of Nature.

While scientists have known for a long time that desert plants are efficient with water use, they were surprised to find that plants in grasslands and forest ecosystems demonstrate the same ability to acclimate.

The study also suggests that there is a point beyond which plants may not be able to acclimate to precipitation changes.

“Understanding the ability of plants to adapt to precipitation changes has important implications for agriculture, forestry, and grazing,” said study coauthor Michael Loik, an assistant professor of environmental studies at UCSC. “If global climate change causes precipitation levels to drop below historic levels, some plants will be unable to grow, which could result in dramatic changes in the species composition of ecosystems.”

Precipitation patterns are expected to change as part of other global climate changes, but researchers predict effects that vary from an 80 percent reduction in precipitation to an increase of more than 100 percent. The next step in understanding the ecosystem effects of precipitation is for researchers to conduct a broad study in which they manipulate precipitation levels--both increasing and decreasing amounts--in multiple locations, said Loik.

Loik founded PrecipNet, an international consortium of researchers focusing on the precipitation and ecosystem aspects of climate change, and was a catalyst behind the Nature study. The lead authors of the Nature study are Travis E. Huxman of the University of Arizona, Tucson, and Melinda D. Smith of UC Santa Barbara and Yale University; the complete list of authors can be found below.

Loik secured funding to bring together the team of researchers who conceived of the study and conducted the research.

During a series of workshops held at the National Center for Ecological Analysis and Synthesis at UC Santa Barbara, the researchers analyzed precipitation and growth data collected at 14 long-term research sites in nine regions throughout North and South America. The sites represent a range of ecosystems, from the arid Mojave Desert to Panama’s wet tropical forest and the vast, cold, treeless landscape of Patagonia in Argentina. Each site had at least six years of growth and precipitation data.

In addition to finding that all ecosystems were equally productive in drought conditions, researchers found that low-precipitation regions were much more sensitive to changes in precipitation than they’d expected. “It appears that there may be a certain threshhold of precipitation change that plants may be able to tolerate, at least in the decreasing direction,” said Loik.

Researchers at 40 sites around the globe are engaged in long-term monitoring of precipitation and plant interactions, said Loik. Understanding the interaction of climate and precipitation changes on ecosystems will help land-use managers and water-resource specialists make informed policy decisions about irrigation for agriculture and the productivity of forests and grazing land, added Loik. “It comes down to our ability to produce food, fiber, and fuel,” he said.

In addition to Loik, Huxman, and Smith, coauthors of the Nature paper are:
Philip A. Fay of the Natural Resources Research Institute, Duluth, Minn.; Alan K. Knapp of Colorado State University in Fort Collins; M. Rebecca Shaw of the Carnegie Institution of Washington in Stanford, Calif.; Stanley D. Smith of the University of Nevada, Las Vegas; David T. Tissue and John C. Zak of Texas Tech University in Lubbock; Jake F. Weltzin of the University of Tennessee in Knoxville; William T. Pockman of the University of New Mexico in Albuquerque; Osvaldo E. Sala of the University of Buenos Aires in Argentina; Brent M. Haddad of UCSC; John Harte of UC Berkeley; George W. Koch of Northern Arizona University in Flagstaff; Susan Schwinning of Biosphere 2 Center, Columbia University, Oracle, Ariz.; Eric E. Small of the University of Colorado at Boulder; and David G. Williams of the University of Wyoming in Laramie.

The research was funded by the National Science Foundation, the U.S. Department of Agriculture, the U.S. Department of Energy, and the National Park Service.

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