Response of soil microbial carbon and nitrogen pools to increasing atmospheric nitrogen deposition in forest surface soil

Soil microbial carbon(C) and nitrogen(N) pools play importance roles in C and N cycle of forest soil ecosystem. In order to investigate the effects of increasing N deposition to soil microbial C and N pools in forest surface soil, we carried out a field-based observation experiment in a temperature broad-leaved mixed forest during growth season(from May to October), and N deposition was implemented in forms of NH4Cl and KNO3 with dose as 40 kg·hm-1·y-1. The results indicated that the concentrations of soil dissolved organic C and soil inorganic N were not affected by N deposition in forest surface soil; N deposition in forms of NH4Cl induced significant decrease in soil pH value, i.e. the soil pH value decreased by 0.2 units, and resulted in significant decrease by 18% and 32% in soil microbial biomass C and N pools respectively, as contrast to Control. In current study condition, N deposition in forms of KNO3 did not affect the soil microbial biomass C and N pools. The correlation coefficient of soil C and N pools with those of soil microorganism under different forms of N deposition showed that the relationship between soil active C pools and soil microbial biomass C and N pools were increased by N deposition in form of KNO3, but not in those of NH4Cl form. Moreover, the possible mechanism which N deposition affect the forest soil C and N pools was discussed, our study emphasized that it is important to pay attention to the different effects of N forms in research of atmospheric N deposition.