The effects of simulated N deposition on acidity and inorganic N concentrations in soil solution collected at 20 cm soil depth under pine forest， needle broadleaved mixed forest， and mature monsoon evergreen broadleaved forest in subtropical China were studied．Additional N(NH4NO3 solution)treatments were established for mature forest：Low N(50 kg N hm-2 a-1)，Medium N(100 kg N hm-2 a-1 )and High N(150 kg N hm-2 a-1), and Low N and M edium N treatm ents were established for mixed an d pine forests．PH values in soil solution in the control plots ofthe 3 forests ranged from 3.82 to 4.24，but pH values decreased bV 0.08—0.1 8 in plots treated by spraying additional nitrogen under the forests for 5 months． NH4+-N concentrations in soil solution increased averagely by 74.0％ ，355.6％ and 57.9％ in low N treatm ent and by 68.4％ ，93.2％ ，and l88.8％ in medium N treatment for pine forest，mixed forest，and mature forest，respectively．As in high N treatm ent it increased by 1254．7％ for mature forest．The increases of N03--N concentrations were by 56.4％-88.5％ in low N treatment by 65.6％-l32.2％ in medium N treatment，and by 85.5％ in high N treatment．The results showed that additional N deposition increased the potential of inorgan ic N leaching losses and enhanced soil acidity.
