城市化对湿地松人工林氮素供应的影响

以位于南昌市城乡梯度(城区、郊区和乡村)的湿地松人工林为研究对象,采用离子交换树脂袋法,估测城乡梯度森林土壤有效氮的季节动态,分析城市化对土壤供氮能力的影响.结果表明:湿地松人工林土壤有效氮的供应存在明显的季节波动,其中秋、冬季铵态氮高于春、夏季,而春、夏季硝态氮、矿质氮和相对硝化速率高于秋、冬季(P＜0.05);有效氮供应的季节动态与湿地松的生长节律(即需氮过程)基本吻合.城乡梯度不同位置森林土壤有效氮及其各组分与相对硝化速率的差异明显,城区均显著高于乡村(P＜0.05);城市化会加快森林土壤的矿化和硝化过程,增强土壤的供氮能力,提高土壤中硝态氮含量.建议在城市森林建设中应配置需氮能力强,特别是对硝态氮吸收偏好的地被植物,减缓城市森林中有效氮的流失及其引发的环境污染.

Effects of urbanization on soil nitrogen supply in Pinus elliottii plantations.

With the Pinus elliottii plantations along an urban-rural gradient in Nanchang City as test objectives, and by using ion-exchange resin (IER) bag, thi s paper studied the seasonal dynamics of soil available nitrogen in the plantati ons, and analyzed the effects of urbanization on soil nitrogen supply. The resul ts showed that the soil nitrogen supply in the plantations had an obvious season al fluctuation. Soil NH4+-N concentration was significantly higher in autum n and winter than in spring and summer, while soil NO3--N concentration, mi neral N concentration, and relative nitrification rate were in adverse (P＜0 05). The seasonal dynamics of soil available nitrogen was basically consistent with the growth rhythm of P. elliottii. The soil nitrogen availability and relative nitrification ratio along the gradient differed greatly, being signific antly higher in urban than in rural area (P＜005). Urbanization accelerate d soil N mineralization and nitrification, enhanced soil nitrogen supply capacit y, and increased soil NO3--N content. It was suggested that in the construc tion of urban forest, the plants with high N demand, especially with high NO3 -- N absorption capacity, should be introduced to mitigate the soil available N loss and its induced environmental pollution.