Effect of Land Use Patterns on Soil Aggregate Stability and Aggregate-associated Organic Carbon

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To provide scientific evidence for coordinating regional land use and soil carbon pool management,it is essential to reveal the distribution of different sizes of soil aggregates and the aggregate-associated organic carbon after the Grain to Green Program.Eucalyptus grandis and Metasequoia glyptostroboides were the main afforestation species in the Grain to Green Program in Chengdu.Four typical land use patterns,namely,E.grandis,M.glyptostroboides plantations,the natural secondary forest of Pinus massoniana and the adjacent slope farmland,were selected as sampling plots to study the effects of land use change on aggregate stability and the aggregate-associated organic carbon in different soil layers(0-20 cm,20-40 cm and 4060 cm).The results showed that the macro-aggregates( 0.25 mm) dominated in the soil aggregate structure.The content of organic carbon in soil aggregates decreased with the increase of aggregate size.The proportion of the 0.25 mm fraction of soil aggregates,the mean weight diameter(MWD) of soil aggregates and the content of organic carbon in soil aggregate size increased after the Grain to Green Program.And the increase of content of organic carbon was largest in the 2 mm fraction of soil aggregates in the top 40-cm soil layer.Compared with those in the slope farmland,the proportion of organic carbon storage in the size of 2 mm soil aggregates increased by 5.96%-47.57% in other land use patterns,but decreased by 0.95%33.28% in the size of 0.053 mm soil aggregates.The natural secondary forest of P.massoniana had the highest total organic carbon storage of soil aggregates,while the farmland had the lowest total organic carbon storage among all land use patterns.The results indicated that E.grandis and M.glyptostroboides plantations have higher soil aggregate stability and organic carbon storage than the slope farmland,though still lower than the natural forest.