Soil biochemical responses to nitrogen addition in a secondary evergreen broad-leaved forest ecosystem

In order to investigate the effects of N deposition on soil biochemistry in secondary forests, one N addition experiment was conducted in a secondary evergreen broad-leaved forest in the western edge of Sichuan Basin, with the highest level of background N deposition (about 95 kg N ha(−1) yr(−1)) in China. Three N treatment levels (+0, +50, +150 kg N ha(−1) yr(−1)) were monthly added to soil surface in this forest beginning in April 2013. Soil biochemistry and root biomass of the 0–10 cm soil horizon were measured from May 2014 to April 2015. Soil respiration was measured for two years (September 2013 to August 2015). It was showed that N additions were correlated to significantly lower soil pH, microbial biomass C (MBC) concentration, MBC/microbial biomass N (MBN) ratio, root biomass, and soil respiration rate, and significantly higher concentrations of ammonium (NH(4) (+)) and nitrate (NO(3) (−)). These results indicate that N additions had a significant effect on the size of soil microbial community. In addition, soil C storage may potentially increase due to the dropped soil C release under N addition.