Warmer climates don't necessarily mean more fertile soils

Brian Wallheimer in Phys.org: Warmer climates won't necessarily speed the return of nitrogen to soils as scientists once thought, according to a Purdue University study.  Increased temperatures from climate change have been expected to speed decomposition of plant materials and the return of nitrogen to soils, making the soil more fertile for plants.

But Jeff Dukes, an associate professor of forestry and natural resources at Purdue, found that the microbes responsible for returning nitrogen to soils react differently to a range of climate scenarios. "More nitrogen being available is not something we can count on in all ecosystems," said Dukes, whose findings were published in the journal Global Change Biology.

The findings suggest that while warming has been expected to accelerate nitrogen cycling, it may actually have little to no effect on the process in some ecosystems. This means that climate models that assume increased soil fertility in warmer conditions may overestimate the amount of plant productivity in those ecosystems.

Dukes runs the Boston-Area Climate Experiment, which measures ecosystem responses to climate change. His research group uses heaters, plastic roofs and sprinklers to change the climate over small plots of land and then tests plant and soil responses to increases in temperature and increases or decreases in precipitation.

In this experiment, Dukes tested 36 plots under 12 different climate scenarios - four levels of warming and three different levels of precipitation - over two years. Although Dukes and his team expected to find that warming would speed the return of nitrogen to the soil, they instead found that warming and changes in precipitation rarely influenced this rate. Instead, warming and drought caused the processes involved in nitrogen cycling to become less sensitive to temperature. "It seems that some ecosystems are less responsive than we expected," Dukes said. "It may be that as you warm up, the soil microbes in those ecosystems adjust and the rate of nitrogen cycling winds up being the same."...