Dinghushan Forest Ecosystem Research Station, South China Botanical Garden, the Chinese Academy of Sciences, Zhaoqing 526070, China 2. Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
Impacts of simulated atmospheric nitrogen (N) deposition on soil fauna biomass were studied in a 16 month period from May 2003 to August 2004. Plots were built in pine forest (PF), pine and broad-leaf mixed forest (MF) and monsoon evergreen broad-leaf forest (MEBF) in Dinghushan of subtropical China. Dissolved NH4NO3 equivalent to the control (No addition), low ［50 kg/(hm2·a)］, and medium ［100 kg/(hm2·a)］ was sprayed during the testing period. The biomass of soil fauna group was decided by an experimental standard based on research performed a long time in this area. When the data was averaged throughout the period and across the forests, there were no significant effects of N treatment on soil fauna biomass. However, effects could be observed in the interactions between N and forest type, and the interactions between N and sampling date. There were obviously positive effects of N treatment on soil fauna biomass in PF, but negative effects under abundant N deposition in MEBF. After one year the distribution of soil fauna biomass in different forests was changed significantly, with MEBF>MF>PF before the treatments and PF>MEBF>MF after the treatments. Low N treatment was positive to soil fauna biomass to a certain extent, which increased soil fauna biomass by 44.33% in MEBF, 9.19% in MF and 60.66% in PF; but soil fauna biomass declined generally under the medium treatment, 32.55% in MEBF and 2.81% in MF. The results indicated that there might be a threshold in the effects of N deposition on soil fauna biomass.