中文摘要：

平衡状态时的土壤有机碳含量水平确定对于正确评价土壤的固碳潜力和制定合理的有机物质分配措施有重要意义。本文通过比较红壤典型地区不同时期水稻土有机碳含量变化、不同利用年限水稻土有机碳含量动态、以及有机碳输入输出量状况，分析红壤水稻土有机碳库的平衡值，进而估计较大区域内水稻土的固碳潜力。过去20余年来江西省余江县水稻土的有机碳含量总体呈上升趋势，但高产水稻土的有机碳含量稳定在18．5gkg^-1；水耕利用30a，土壤有机碳含量达到19．0（±1．20）gkg^-1，其后变化幅度很小；若使目前的较高形成量水平达到平衡，则土壤有机碳含量为19．2（±1．10）gkg^-1。综合分析，在较高生产力水平条件下，红壤水稻土有机碳的平衡值为18～20gkg^-1，平均为19．0±1．0gkg^-1。过去20余年来，江西省余江县水稻土有机碳储量增加了6955（±1116）kghm^-2。据此计算我国亚热带地区水稻土过去20年固定大气CO2量555．1（±88．7）Tg，其作为碳汇的作用是相当明显的。目前仍有相当面积的水稻土其有机碳含量低于平衡水平，估计还可平均固碳5150（±1063）kghm^-2。据此，若保持现实较高生产力水平，则我国亚热带地区水稻土未来可新固定大气CO2量411．0（±84．7）Tg。

英文摘要：

Determination of soil organic C content at steady state is of important significance for evaluating potential of C sequestration of the soil and developing a measure for rational organic material utilization. In this study, change in soil organic C content of paddy fields in a typical red soil region over a period of time, dynamics of the organic C content in the paddy soils across a chronosequence of cultivation, and the input and output of soil organic C, were investigated in order to determine the organic C content at steady state and then potential of C sequestration in the paddy soils of subtropical China. In the past 20 years or so, soil organic C content of the paddy fields in Yujiang County of Jiangxi Province increased generally but it remained stably at 18.5 g kg^-1 in paddy soils with high productivity. After 30 years of rice cultivation, soil C content of the paddy field reached to 19.0 （ ± 1.20） g kg^-1 and varied insignificantly afterwards. If the high level of soil organic C formed recently is settled in equilibrium, the soil organic C content will be 19.2 （ ± 1.10） g kg^- 1 . As a whole, at the present high level of productivity, the soil organic C content at steady state of paddy soils in subtropical China would be 18 - 20 g kg^-1 with an average of 19.0 （ ± 1.0） g kg^-1. In the past 20 years, the storage of organic C in the paddy soils of Yujiang County increased by 6 955 （ ± 1 116）kg hm^-2. Based on this, it was figured out that the paddy soils in subtropical China sequestrated 555.1（ ± 88.7）Tg of atmospheric CO2 in the past 20 years, demonstrating an important function as a sink of CO2. Today there are still large areas of paddy fields that have less soil organic C content than that at steady state. It is estimated that they could sequestrate on average 5 150（ ± 1 063）kg hm^-2 more of carbon. Therefore, at the present high level of productivity, the paddy soils in subtropical China would sequestrate an extra of 411.0（ ± 84.7）Tg of atmospheric CO2 in future.