鼎湖山森林土壤渗透水酸度和无机氮含量对模拟氮沉降增加的早期响应

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

在林地分别喷加0、50、100 和150 kg N hm-2 a-1,研究鼎湖山马尾松林、马尾松针阔混交林和季风常绿阔叶林中土壤20 cm深渗透水酸度和无机氮含量在开始9个月的变化。结果表明,3种森林对照样方土壤渗透水pH值为3.82-4.24,外加氮处理使其平均降低了0.08-0.18。3个森林对照样方土壤渗透水无机氮平均含量分别为6.14、6.66和11.64 mg L-1,铵态氮占15.0%、11.9%和3.0%。外加氮处理使3种森林土壤渗透水铵态氮和硝态氮含量均有不同程度的提高,这表明外加氮处理不但增加了无机氮从森林土壤流失的潜力,而且使土壤进一步酸化。

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 Medium N treatments were established for mixed and pine forests. pH values in soil solution in the control plots of the 3 forests ranged from 3.82 to 4.24, but pH values decreased by 0.08-0.18 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 treatment and by 68.4%, 93.2%, and 188.8% in medium N treatment for pine forest, mixed forest, and mature forest, respectively. As in high N treatment it increased by 1254.7% for mature forest. The increases of NO3--N concentrations were by 56.4%-88.5% in low N treatment, by 65.6%-132.2% in medium N treatment, and by 85.5% in high N treatment. The results showed that additional N deposition increased the potential of inorganic N leaching losses and enhanced soil acidity.