Soil aggregates determine the fertility and productivity of soils,and possess the ability to protect soil organic carbon by physical entrapment.The land use change will affect the capacity of the soil to act as both a source and a sink of organic matter and nutrients.However,limited literature on soil organic carbon in aggregates with different sizes under land use change were reported.The objective of the present study was to elucidate aggregate composition,organic carbon(OC)distribution and storage of orchard soil,dryland soil,paddy soil,and dryland and paddy rotation soil from Jianghan plain.The results showed that the percentage of soil micro-aggregates in the following order:2-20μm,<2μm and 20-50μm.Soil micro-aggregates in <50μm size group occupied 80.8%-94.1% of the total soil micro-aggregates.The organic carbon contents under different land uses was the highest in 200-2 000μm fractions of aggregates.Furthermore,OC contents in >50μm fraction were higher than those in <50μm fraction.However,69.8%-86.6% of the total organic carbon was mainly found in the aggregates with a size of <50μm.Especially,35.2%-45.9% of the total organic carbon was concentrated in the aggregates with sizes of 2-20μm.So the fine micro-aggregates possessed the high ability of carbon sink,and the organic carbon content in coarse micro-aggregates responded easily to land use change.The content of active soil organic carbon in 2-20μm fraction of different aggregates was the lowest,and their differences between <2μm and 20-50μm was slight.The content of active soil organic carbon was higher in paddy field than that under dryland cultivation.It was proposed that 2-20μm fraction of aggregates was regarded as characteristic aggregates due to its high retention of soil organic carbon.These results will help to reveal the regional soil organic carbon sequestration.