Effects of nitrogen deposition on soil enzymatic activity and soil microbial community in a Mediterranean holm oak forest

Ongoing increases in global levels of nitrogen (N) deposition are predicted to continue, causing important shifts in the structure and function of ecosystems worldwide. Soil microbes and enzymes are key components of biogeochemical cycles and ecosystem functioning, so understanding their response to N deposition is crucial. We studied the effects of N addition on the activities of five extracellular enzymes and microbial biomass and composition in a mesic Mediterranean holm oak forest characterized by moderate soil N-and P-limitation. Addition of N increased photosynthetic potential of higher plants, activities of P-and C-, but not N-related enzymes, and biomass of total microbes, bacteria and fungi, and decreased ratios of fungi:bacteria. Overall, N deposition increased general biological activity of the mesic Mediterranean forest, enhanced ecosystem invest-ment in P mobilization and affected soil microbial community structure.