| Revegetation, which is one of the important measures of ecological environmentconstruction in Loess Plateau, has changed the unreasonable way of land use and promotedthe regional ecological balance by making full use of functions of soil-plant composite system.This study selects natural revegatation（Stipa grandis P.Smirn, Stipa bungeana Trin Ledeb,Artemisia sacrorum Ledeb, Thymus mongolicus Ronnm, Hierochloe odorata Beauv.Communities, Abandoned grazed grassland） and artificial revegetation（the25-year-oldCaragana Korshinskii Kom., the15-year-old Caragana Korshinskii Kom. Natural Grassland,and the slope cropland） on Ningxia Loess Plateau as the research objects, use wet sieving togain different size of soil aggregate. The effects of different revegetation types oncomposition of water-stable aggregate, the stability of soil aggregates, as well as carbon andfractions in soil aggregates were studied, soil organic carbon and fraction’s micro-response todifferent revegetation types are discussed. All of the study aimed at providing the basic datafor the discussion on the mechanism of soil carbon sequestration under different revegetationtypes, and providing scientific basis for eco-efficiency evaluation and soil quality assessment.The main results are as follows:（1） The results show the distribution of soil aggregates has a "V" distribution under avariety of revegetation. Small （<0.25mm） and large （>5.0mm） particle sizes form the mostaggregates. The next largest aggregate size classes were5–2mm and1–0.25mm, while the2–1mm size class had the fewest aggregates. Among natural revegatation, in the0–20cm soillayers soil aggregate stability is in this order: Hi. O>A. G> Th.M.> At. S.> St. B> St. G, andin20–40cm soil layers soil aggregate stability for At. S. Th.M and St. G was higher than A.G, while soil aggregate stability of St. B and Hi. O is lower than A. G. Among artificialrevegetation types, soil aggregate stability of N. G and C.K.25is relative better, C.K.15isfollowed, and Cr. is the worst.（2） The contents of organic carbon under natural revegetation are from10.1to29.7g·kg-1, while the contents under artificial revegatation are a little lower, from7.4to17.7g·kg-1.Under natural revegatation, the contents of soil organic carbon reduce in the following turn: St. G, St. B. Th. M., Hi. O., At. S., A.G in0-20cm soil layers; in artificial ones, the contentsof organic carbon for N. G are the highest, C.K. wood land is as followed, Cr. is the lowest.（3） The contents of soil microbial biomass carbon is from294.6mg·kg-1to1255.4mg·kg-1, accounting for2.9%-6.1%of the total organic carbon, among all theserevegatation, the contents of microbial biomass for Th.M. are higher; the contents of readilyoxidizable carbon was from3.0g·kg-1to6.9g·kg-1, accounting for15.3%-53.6%of totalorganic carbon and the contents of readily oxidizable carbon for At. S. was the highest; thecontents of light fraction organic carbon was between0.8g·kg-1and3.8g·kg-1, accounting for2.2%-22.9%of total organic carbon, and the contents of light fraction organic carbon for St.G, St. B. and Hi. O was relatively higher, At. S. and Th.M. was as followed, the contents oflight fraction organic carbon for Ab.G was the lowest; the contents of particulate organiccarbon was from2.2g·kg-1to15.5g·kg-1, accounting for22.3%-77.1%of total organiccarbon, Ab. G was the lowest. while other natural revegatation was1.7-4.4times as A. G; thecarbon content of humus was1.2and4.9g·kg-1; the content of humic acid carbon was0.5and2.0g·kg-1; and the fulvic acid was0.6and3.0g·kg-1for the0–20cm and20–40cm soil layers,respectively.（4） The soil microbial biomass carbon contents under artificial revegetation types,accounting for0.7%-4.8%of total organic carbon, and the contents of microbial biomasscarbon for Cr. was the lowest, other artificial revegetation was2.9-8.3times as Cr; thecontents of readily oxidizable carbon was from1.53g·kg-1to2.68g·kg-1, accounting for19.9%-44.8%of total organic carbon and the contents of readily oxidizable carbon for N. Gwas much higher than other artificial revegetation types; the contents of light fraction carbonwas between0.1g·kg-1and2.3g·kg-1, accounting for1.2%-13.6%of total organic carbon,and N.G was the highest, C.K.15was followed, while C.K.25and Cr. was relatively low; thecontents of particulate organic carbon was from0.9g·kg-1to4.7g·kg-1, accounting for13.6%-45.1%of total organic carbon, Cr. was the lowest. while other artificial revegatation was1.5-4.7times as Cr; the carbon content of humus was0.9and2.5g·kg-1; the content of humicacid carbon was0.2and0.6g·kg-1; and the fulvic acid was0.6and1.9g·kg-1for the0–20cmand20–40cm soil layers, respectively.（5） Most of the soil organic carbon content was concentrated on intermediate sizedaggregates （2–5mm,1-2mm,0.25–1.0mm）, and so was soil microbial carbon, readilyoxidizable carbon, particulate organic carbon, humus. Light fraction organic carbon wasconcentrated on the2-0.25mm size aggregates, especially in the0–20cm soil layers.（6） The more total of microbial biomass, the more soil organic, but the oxidation stabilityof soil organic was unchanging. During the revegetation, soil aggregate stability was was strengthen with organic carbon sequestration, but when soil organic carbon was higher than18.13g·kg-1, soil mean weight diameter was decreasing, and the soil aggregate stability wasweakened. Composition of water-stable aggregate influenced accumulation of soil organiccarbon, the more the certain size aggregate （>5mm,5-2mm,1-0.25mm）, the more soilorganic carbon, and when1-0.25mm size of the aggregates increased and0-0.25mm size ofsoil aggregates reduced, the contents of soil microbial biomass carbon, humus, and fulviccarbon were increased. |
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