Jul 21, 2014 01:34 PM EDT By J Baulkman, UniversityHerald Reporter

The size and age of plants may have more of an impact on their productivity than temperature and precipitation, according to a recent study.

Researchers from the University of Arizona found that climate has a relatively minor direct effect on net primary productivity, or the amount of biomass that plants produce by harvesting sunlight, water and carbon dioxide.

"Essentially, warm and wet environments are thought to allow plant metabolism to run fast, while cold and drier environments slow down metabolism and hence lower biomass production in ecosystems," researcher Brian Enquist said in a statement. "This assumption makes sense, as we know from countless experiments that temperature and water control how fast plants can grow. However, when applied to the scale of entire ecosystems, this assumption appears to not be correct."

For the study, the research team developed a new mathematical theory that assesses the relative importance of several hypothesized drivers of net primary productivity. That theory was then evaluated using a massive new dataset assembled from more than 1,000 different forest locations across the world.

They found that plant size and plant age control most of the variation in plant productivity, not temperature and precipitation as traditionally thought.

"This general relationship shows that climate doesn't influence productivity by changing the metabolic reaction rates underlying plant growth, but instead by determining how large plants can get and how long they can live for," Sean Michaletz, lead author of the study and a postdoctoral researcher at the UA Department of Ecology and Evolutionary Biology, said. "This means that plants in warm, wet environments can grow more because their larger size and longer growing season enable them to capture more resources, not because climate increases the speed of their metabolism."

Researchers warned that the finding does not, however, mean that climate is unimportant for plant productivity.

"Climate is still an important factor, but our understanding of how it influences ecosystem functioning has now changed," Michaletz said.

The team's new findings suggest that mathematical models used for predicting the effects of global climate change can be improved by accounting for the effects of plant size and plant age on net primary productivity.

"Understanding exactly how climate controls net primary production is important for understanding the plant-atmosphere feedbacks that control climate change," said Michaletz.

The findings were recently published in the journal Nature. 

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