城乡梯度森林土壤有效氮季节动态

Seasonal Variation in Soil Nitrogen Availability in Forest along an Urban-to-Rural Gradient

亚热带地区土壤中有效氮主要以铵态氮(NH4+-N)和硝态氮(NO3--N)形式存在,是限制林木生长的主要因子。以位于南昌市城乡生态界面的湿地松(Pinus elliottii)人工林为研究对象,开展城区、郊区、乡村3个不同梯度土壤有效氮月份动态监测。结果表明:不同月份对土壤有效氮的影响差异极显著(P<0.001),土壤有效氮具有明显的季节波动;城乡梯度对土壤有效氮、硝态氮占矿质氮的比例(相对硝化速率)的影响差异极显著(P<0.001),其中土壤铵态氮的年平均含量为城区>郊区=乡村,而硝态氮、矿质氮和相对硝化速率均为城区>郊区>乡村。可见,城市化过程不仅影响森林土壤有效氮的总量,还影响其形态组成;硝态氮是城区和郊区森林土壤中有效氮的主要形式,而铵态氮是乡村森林土壤中有效氮的主要形式。因此,在城市森林管理中应加强土壤硝态氮的养分管理。

Available nitrogen existing as ammonium nitrogen （ NH4^＋ - N） and nitrate nitrogen （ NO3^- - N） in soil is the important factor restricting the growth of trees in subtropical area. The monthly dynamic changes of soil available nitrogen were monitored from such three gradients as urban, suburb and rural based on Pinus elliottii plantations along an urban -rural transect in Nanchang City. The results showed that months had extremely significant influence on soil available nitrogen with an obvious seasonal fluctuation （P 〈 0.001 ）. And the impact of urban - rural gradient on available nitrogen and the relative rate of nitrification was extremely remarkable （P 〈 0.001 ）. Annual average of ammonium nitrogen content in soil on different ecological transect is ： urban 〉 suburb = rural, but nitrate nitrogen, available nitrogen and relative rate of nitrification all. are ： urban 〉 suburb 〉 rural. So, urbanization process affects not only the total amount of available nitrogen in forest soil but also its form composition. Nitrate nitrogen is the main form of available nitrogen in urban and suburb forest soil, but ammonium nitrogen in rural. Therefore, in urban forest management, more efforts should be made to manage the nutrient of nitrate nitrogen in soil.