Effects of nitrogen deposition on soil microbial biomass, microbial functional diversity and enzyme activities in fir plantations of subtropical China

The effects of simulated nitrogen (N) deposition on soil microbial biomass, microbial functional diversity and enzyme activities involved in C cycling (sucrase, beta-glucosidase, cellulose, amylase, polyphenol oxidase and peroxidase) were studied in southeast Chinese fir plantation (Cunninghamialanceolata (Lamb.)). All soil parameters measured decreased with increasing soil depth. The results indicated that low N (N1) deposition could accelerate soil microbial biomass and functional diversity, but moderate or high N deposition (N2, N3) restrain them. Nitrogen additions promoted soil sucrase, beta-glucosidase and cellulase activities, while inhibited soil amylase, polyphenol oxidase and peroxidase activities to some extent, suggesting that decomposition of labile and recalcitrant organic matter were promoted and restricted by extra N deposition, respectively. Changes in microbial community biomass and function under extra N deposition indicated soil ecosystems experienced functional shifts under the current or future condition of human-accelerated N supply.