Effect Of Vegetation Restoration On Soil Carbon Sequestration And Carbon Fractions In Northern Shaanxi

The essential problem of ecological environment in the Loess Plateau mainly is soilerosion, degradation and improverishment caused by human activities. This area waslaunched a large area of artificial vegetation restoration from last century60s, has formedseveral main recovery types including forests, shrubs, and abandoned land with differentrecovery stages. This paper focused on Robinia pseudoacacia, Caragana korshinskii,Hippophae rhamnoides and natural grassland with different recovery years, and study thechanges of soil organic carbon pools as well as its mechanism, and seak the law of spatial andtemporal variations of soil organic carbon pools after vegetation restoration, and disscuss theprofile characteristics of oxidizable organic carbon fractions in different land uses, aimed toprovide a scientific basis for evaluating the effect of soil carbon sequestration duringvegetation restoration. The primary conclusions were as follows:(1) Total organic carbon (TOC)，oxidizable organic carbon (OC) and black carbon (BC)showed similar results, which significantly reduced in0-20cm soil layer. Soil carbonsequestration of Grain to green engineering was mainly long-term effect, their content andstorage significantly increased with increasing restoration years after restoration for10a, andHippophae rhamnoides showed significantly adding carbon sink effect. Comparison results ofdifferent restoration types showed that Hippophae rhamnoides exhibited the hightest contentand storage in topsoil (0-10cm), their contend and storage in subsoil of Caragana korshinskiiand abondoned cropland changed with restoration years, they were higher than that in Robiniapseudoacacia and Caragana korshinskii after restoration for20a. OC and BC showedsignificantly positive correlation with TOC. TOC and BC storage of0-20cm and0-100cmshowed significantly positive correlation relationship with each other, TOC and BC storage in0-20cm increased linerly with restoration years.(2) The first fraction of OC (C1) significantly decreased only in0-20cm soil depth, andthe longer restoration the greater they decreased. The first and second fraction of OC (C1andC2) began to increase signifcantly after restoration for10a, which showed the fastestincreasing rate in Hippophae rhamnoides. Comparision result of OC in different restorationtypes showed that C1content of Hippophae rhamnoides hold the hightest value in the topsoil,and C1content in subsoil of Caragana korshinskii and abondoned cropland increased with restoration years, which was significantly higher than Robinia pseudoacacia and Caraganakorshinskii after restoration for20a. Carbon management index (CMI) increased significantlyduring restoration of20-30a, and Hippophae rhamnoides showed the hightest CMI in topsoilat restoration year of5,10and20a. Significantly positive correlation relationship was foundbetween C1and C2, and C1showed positive relationship to OC and TOC.(3) Water soluble organic carbon (WSOC) showed the highest content in0-10cm soillayer, WSOC/TOC significantly increased with increasing soil depth. WSOC content began toincrease significantly after restoration for10a, and WSOC content in topsoil of Hippophaerhamnoides increased fastest. Comparision result of WSOC in different restoration stylesshowed that WSOC in0-20cm of Hippophae rhamnoides hold the hightest value atrestoration year of10a and20a, and WSOC/TOC in10-50cm soil layers showed the hightestvalue at20a. WSOC was significantly correlated with TOC, and this relationship was greatestin Caragana korshinskii and Hippophae rhamnoides, followed by Robinia pseudoacacia,which in abandoned cropland was weakest.(4) Microbial biomass carbon (MBC) dropped significantly only in0-20cm soil depth.MBC content of topsoil in Caragana korshinskii, Hippophae rhamnoides and Robiniapseudoacacia began increased significantly after restoration for10a, and MBC content ofHippophae rhamnoides increased fastest.Comparision result of OC in different restorationtypes showed that MBC content of Hippophae rhamnoides hold the hightest value at5a and20a, and MBC content in subsoil of Caragana korshinskii and abondoned cropland increasedwith restoration years. MBC showed significantly positive correlation with TOC.(5) Soil depth significantly affected C1, C2and C4content, C1and C2sharply decreasedin0-0.2m soil layer, and maintained from0.2m to5.0m for most land uses, and showed greatvariability in forest land, shrublands and natural grassland, C4represented significantvariability in terraced cropland (Setaria italica) and terraced cropland (Zea mays). Amongland use types, natural grassland, Caragana korshinskii and forestland with Robiniapseudoacacia significantly increased C1and C2content in0-0.1m soil layer compared toterrace cropland (Setaria italica) and sloped cropland (Setaria italica). Natural grasslandsignificantly increased C1and C2content in0-0.6m soil layer, artificial grassland notablelyimproved C1and C2content in1.5-5.0m soil layers, natural grassland and Hippophaerhamnoides significantly increased C4content in1.5-5.0m soil layers. Natural grasslandshowed the highest SOC lability index and carbon management index (CMI) value in0-0.4msoil layers. Conclusion:The results indicate that land use significantly affect oxidizableorganic carbon fractions in deep soil, and suggest natural grassland, forestland and shrublandsas ideal choice for their great potential to improve the lability, quality and sequestration of SOC in the Loess Plateau.