Acidity and Inorganic Nitrogen Concentrations in Soil Solution in Short-term Response to N Addition in Subtropical Forests

Abstract:

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.