中文摘要：

利用太湖地区26年水稻土长期定位施肥试验,分析了长期不同施肥处理对土壤剖面有机碳分布和稳定性碳同位素自然丰度（δ13C）的影响,以及土壤中不同结合态腐殖质组成的变化.结果表明：长期施肥使水稻土表层土壤有机碳含量显著升高,不同处理土壤剖面有机碳含量与土层深度呈极显著指数负相关（P〈0.01）;施化肥处理10～30cm土层和施有机肥处理20～40cm土层有机碳含量变化相对稳定;随土层深度增加,土壤δ13C值逐渐升高,其变化范围在-24‰～-28‰,不同处理土壤剖面有机碳含量与δ13C值呈显著线性负相关（P〈0.05）;0～20cm土层,仅施有机肥处理（M0）、有机肥＋氮＋磷处理（MNP）、有机肥＋氮＋磷＋钾处理（MNPK）、有机肥＋秸秆＋氮处理（MRN）以及秸秆＋氮处理（CRN）的δ13C值明显降低;30～50cm土层,除CRN外,有机肥和化肥处理土壤的δ13C值均明显升高;不同处理土壤中结合态腐殖质均以紧结合态腐殖质（胡敏素）为主,其含量在50%以上,其余部分为松结合态和稳结合态腐殖质;长期施肥使土壤松结合态腐殖质含量及富啡酸（FA）与胡敏酸（HA）比值（HA/FA）升高.

英文摘要：

Soil samples were collected from an experimental paddy field with long-term （26 years） fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance （8 ~3C） in the soil pro- file, and on the humus composition. The results showed that long-term fertilization increased the or- ganic carbon content in top soil significantly, and there was a significantly negative exponential cor- relation between soil organic carbon content and soil depth （P 〈0. 01 ）. The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertili- zations was relatively stable. Soil 8 ~3C increased gradually with soil depth, its variation range being from -24%~ to -28%o, and had a significantly negative linear correlation with soil organic carbon content （P 〈0. 05 ）. In 0-20 cm soil layer, the 8 ~3C in treatments organic manure （M）, M ＋ NP, M ＋ NPK, M ＋ straw （R） ＋ N, and R ＋ N decreased significantly; while in 30-50 cm soil layer, the ~ ~3C in all organic fertilization treatments except R ＋ N increased significantly. Tightly com- bined humus （humin） was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably loosely combined humus and the combined humus. Long-term ratio of humic acid （HA） to fertilization increased the content of fulvic acid （FA）.