中文摘要：

在野外采样和试验分析的基础上,研究了上海市土地利用方式及其变化对土壤有机碳、总氮含量及土壤有机碳密度的影响.结果表明：上海不同土地利用方式下的土壤有机碳、总氮含量及有机碳密度均存在显著差异.不同土地利用方式下的土壤有机碳密度大小依次为：水稻田（3.86 kg.m-2）〉旱地（3.17 kg.m-2）〉林地（3.15 kg.m-2）〉撂荒地（2.73 kg.m-2）〉城市草坪（2.65 kg.m-2）〉园地（2.13 kg.m-2）〉滩涂（1.38 kg.m-2）.通过相邻样地法,分析了水田转变为旱地、农田撂荒及水田转变为人工林地等3种土地利用变化对土壤有机碳、总氮的影响.由水田转化为旱地将导致土壤有机碳、总氮含量及有机碳密度显著降低;在水热充足、土壤肥沃、农田管理水平较高的长三角平原地区,农田撂荒并不是一种提高土壤有机碳储量的有效方式;水田转变为人工林地4～5年后,林地土壤有机碳、总氮含量及有机碳密度均低于相邻的水稻田,表明水田转变为林地并未引起土壤碳、氮的增加,从短期来看,人工林土壤有机碳的汇集效应因植被生产力水平的限制还处于较低水平.

英文摘要：

By the methods of field sampling and laboratory analysis,this paper studied the variations of soil organic carbon（SOC） and total nitrogen（TN） contents and SOC density under different land use types in Shanghai.Significant differences were observed in the test parameters among different land use types.The SOC density was the highest in paddy field（3.86 kg·m-2）,followed by in upland（3.17 kg·m-2）,forestland（3.15 kg·m-2）,abandoned land（2.73 kg·m-2）,urban lawn（2.65 kg·m-2）,garden land（2.13 kg·m-2）,and tidal flat（1.38 kg·m-2）.The assessment on the effects of three types of land use change on the test parameters showed that the conversion of paddy field into upland resulted in a significant decrease of SOC and TN contents and SOC density;the abandonment of farmland was not an effective way in improving SOC storage in the Yangtze Delta region with abundant water and heat resources,high soil fertility,and high level of field management;while the 4-5 years conversion of paddy field into artificial forestland decreased the SOC and TN contents and SOC density,suggesting that in a short term,the soil carbon sequestration effect of the conversion from paddy field to forestland was at a low level,due to the limitation of vegetation productivity.