Effects of N deposition on soil fauna:a summary for one year

Impacts of simulated atmospheric nitrogen (N) deposition on soil fauna were studied during 14 months from July 2003 to August 2004.Dissolved NH₄NO₃ at the following rates:control(0), low (50 kg/(hm²·a)), medium (100 kg/(hm²·a)), high (150 kg/(hm²·a)) and double high (300 kg/(hm²·a)), and it was sprayed during the period.Plots were built in seedling stands (SD), pine forests (PF), mixed pine and broadleaved forests (MF) and monsoon evergreen broadleaved forests (MEBF) in subtropical China.It suggested that soil fauna' responses were correlated significantly with the type of ecosystem.N levels influenced soil fauna significantly in SD, which indicated the existence of a threshold about the effects of N deposition.The data, averaged over the entire period and all forests, did not show any significant effects of N levels on soil fauna.But it could be discovered in the interactions between N and forest type and interactions between N and sampling date.Accumulated effects from N deposition were found.Under continuous and high N deposition, soil fauna became concentrated into the deeper soil, which also indicated the negative effects of N.The threshold and accumulation effects of N deposition could also be predicted by an intermediate disturbance hypothesis (IDH).Finally a preliminary discussion was presented on the mechanisms of the effects of N deposition on soil fauna.The responses of soil fauna to N deposition might indirectly be shown in inorganic soil changes in the environment, and the effects of N levels, ecosystem types and time accumulation might reflect the reaction of "N saturation" status of the ecosystem to atmospheric N deposition.