The cycling of organic nitrogen (N) in soil links soil organic matter decomposition to ecosystem productivity.  Amino acids are a key pool of organic N in the soil, whose cycling is sensitive to alterations in microbial demand for carbon and N.  Further, the amino acids released from the breakdown of protein by proteolytic enzymes are an important source of N that supports terrestrial productivity.  The objective of this study was to measure changes in amino acid cycling in response to experimental alterations of precipitation and temperature in eleven global change experiments during the 2009 growing season.  The study sites ranged from arctic tundra to xeric grasslands.  The treatments experimentally increased temperature, increased or decreased precipitation, or some combination of both factors.  

Results/Conclusions

The response of amino acid cycling to temperature and precipitation manipulations tended to be site specific, but the responses could be placed into a common framework.  Changes in soil moisture drove a large response in amino acid cycling.  Precipitation augmentation in xeric sites increased both amino acid pool sizes and production whereas in mesic sites additional precipitation had little effect.  Warming manipulations that increased water stress led to a decline in amino acid cycling rates.  The largest response in amino acid cycling was seen in those experiments investigating the interaction between temperature and precipitation.  Experiments that created warmer and wetter soils increased amino acid production and turnover whereas experiments that resulted in warmer and drier soils decreased amino acid cycling rates.  These results provide evidence for both a positive and negative feedback of global change on the rate of amino acid cycling in soils that can alter the availability of soil nitrogen to sustain ecosystem production.