When push comes to shove, all ecosystems have the same maximum rain-use efficiency, a measure of total plant growth per unit of precipitation.

The finding indicates there's an upper limit to ecosystems' productivity, said Travis E. Huxman, a plant physiological ecologist at the University of Arizona in Tucson. He and a team of researchers calculated the upper limit, which they call RUEmax (maximum rain-use efficiency).

Life depends on the productivity of plants, Huxman pointed out, adding, "RUEmax defines the limits of that production."

However, the research indicates that under drought conditions, high-productivity systems like grasslands and forests grow even less than expected. Most of the climate-change scenarios for the next century predict an increase in extreme events, including more droughts.

Huxman said, "We originally expected drought to impact grasslands to some degree, but this finding says that if we get extreme variability, there will be even less plant growth than we originally thought."

Huxman, first author of the research report, led the research team along with Melinda D. Smith of Yale University. The team's article, "Convergence across biomes to a common rain-use efficiency," will be published in the June 10 issue of the journal Nature. A complete list of authors and their affiliations is at the end of this article.

The work sheds light on what Huxman called "one of the oldest ecological questions on the face of the planet: how does water affect how an ecosystem works?"

Although it seems a simple question, it turns out to be a toughie, he said. "My wife can answer it for her garden, but you can't take the information that my wife knows for her garden and apply it to many different biomes a
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Contact: Travis Huxman
huxman@email.arizona.edu
520-621-8220
520-271-6637 (cell)
University of Arizona
9-Jun-2004