Microbial communities are often sensitive to changes in N availability, yet the direction of microbial responses to N is difficult to predict. Are N effects on microbial growth and function linked to plant diversity and community composition shifts under N fertilization?  Do these changes in function influence ecosystem processes? Our meta-analysis will address these questions by testing the following hypotheses:

1.   Diversity in litter chemistry should support the production of a more diverse suite of extracellular enzymes by soil microbes. The diversity of extracellular enzymes in soils should decline with decreasing plant diversity under N fertilization.

2.  N fertilization increases plant production and the availability of C for microbial consumption.  Thus, if C resource availability is a driver of microbial growth, microbial biomass should respond to N fertilization by initially increasing with plant production, reaching an optimum biomass as plant production increases, and then declining as plant production continues to increase (hump-shaped curve).

3.  Reduced N limitation and increased C availability should lead to higher production of C-targeting versus N-targeting microbial enzymes.

Data needs: 
Extracellular enzyme activities and microbial biomass date from N fertilization experiments in each of 10 LTER sites.  Enzymes of interest include beta-glucosidase, phenol oxidase, peroxidase, laccase, proteases.  N and C mineralization data from these sites, including gross and net min fluxes.