中文摘要：

【目的】土壤固碳与生产力的协同是农业土壤碳循环研究的热点,而提高土壤固碳容量又是农业固碳减排的重要途径。本文研究中国南方4种典型水稻土长期定位试验条件下的固碳趋势及其外源碳输入对土壤固碳的贡献。【方法】选取西南紫色丘陵水稻土、东南红壤丘陵水稻土、太湖平原水稻土和沿海平原水稻土的长期试验,分析其不同施肥处理下耕层土壤（0～20cm）有机碳变化与外源碳输入（作物输入碳＋肥料输入碳）以及肥料氮输入的关系,并进一步探讨不同施肥处理下的土壤饱和固碳量。【结果】不同施肥处理下的土壤固碳速率线性依存于年均碳输入增量,单位碳输入增加下以紫色水稻土和红壤性水稻土的固碳速率相对较高。良好施肥下的饱和固碳量以富氧化铁的红壤性水稻土最高,其次为富黏粒的沿海平原水稻土。统计分析表明,施肥下不同类型水稻土的固碳效率（即碳输入增量与土壤固碳的线性关系斜率）与初始有机碳含量表现为明显的线性负相关关系,而与黏粒之间的相关性不明显。看来,不同类型水稻土的饱和固碳量与土壤中丰富的游离氧化铁以及降水量有着密切的关系。另外,施肥下的稻田土壤固碳与氮素农学效率之间亦存在着正相关的趋势,并且以红壤性水稻土中的相对最弱,这可能主要归因于不同类型水稻土饱和固碳水平的负影响。【结论】施肥措施主要通过增加外源碳输入来促进土壤的有效固碳,并且土壤固碳与氮素利用效率之间存在着明显的碳-氮耦合效应。水稻土中活跃的氧化铁可能对土壤碳储量的提高起着积极的促进作用,而黏粒有可能并非土壤固碳的驱动因子。气候因子可能是影响水稻土碳储量变化的另一主导因子,这还有待于进一步的分析探讨。

英文摘要：

【Objective】 The coupling of soil C sequestration with productivity is a hotspot in soil C cycling;moreover the increase of saturation capacity is a key approach in agricultural C sequestration and mitigation.The objective of this study was to clarify the saturation capacity of soil C sequestration and its cooperation with C input（crop source and organic fertilizer source C） and N input.【Method】Data from four sites of long-term soil agro-ecosystem experiments of fertilizations from South China was collected,with which the soil cover four types of paddy soils derived from sandstone（PP） in Sichuan Basin,from Quaternary red earth（RP） in red soil region of Jiangxi,from lucustrine deposit（TP） in Tai Lake region of Jiangsu and from lagoon deposit（SP） in costal area of Zhejiang respectively）.Changes in crop yields and topsoil SOC content,and the relationship of topsoil SOC with C and N input was analyzed and further the saturation capacity of soil C sequestration was explored with different fertilization treatments.【Result】A significant linear correlation was found of annual soil C sequestration with C input under different fertilization treatments.SOC accumulation resultant from C input was high in PP and RP compared to that in TP and SP.The saturation capacity of C sequestration under good fertilization managements was shown highest in RP,followed by SP over TP and PP.Statistic analysis exhibited a negative linear correlation of C sequestration efficiency（C sequestered per unit of C input） with the initial SOC content but with the clay content.However,the saturation capacity of C sequestration was in a positive linear correlation with free iron oxyhydrates and annual precipitation for the soils studied.In addition,a positive correlation of N use efficiency on crop yields with soil C sequestration rates was observed though it was less distinctive for SP probably due to the high N stock.【Conclusion】Well designed fertilization could promote soil C sequestration from the increased