Studies Of The Characters Of Soil Structure And Soil Carbon During Vegetation Restoration In Secondary Forest Areas Of Loess Plateau

Secondary decidous broad-leaved forest in Ziwuling Mountain was restored from abandoned land after local population emigration in 1866. It is peculiar natural forest in hinterland of Loess plateau. Slope land, abandoned land, grassland, shrubberyland and forest land in Ziwuling Mountain secondary forest area was selected as representative site within vegetation restoration course in this study. Physical method was adopted to fractionate soil organic carbon and aggregate organic carbon. The change law of soil structure character, soil organic carbon pool, fractions of soil organic carbon pool (Particulate organic carbon, Mineral associated organic carbon, Light fraction organic carbon and Heavey fraction organic carbon) and distributing character of soil organic carbon & fractions of soil organic carbon in aggregates during vegetation restoration course was studied. Furthermore, this study could offer reference to discuss SOC sequestration mechanism in Ziwuling mountain area. The main results and conclusions were presented as follows:(1)Influence of vegetation restoration on SOC and fraction of SOC contentThe SOC, POC, MOC content of 0-100cm soil profile follow the order slope land, abandoned land < grassland, shrubbery land < forest land during vegetation restoration course. The weighted mean value of SOC, POC, MOC content of 0-100cm soil layer in forest land is 6.15, 2.24, 3.90 mg/g, increase 73.6%, 173.6%, 43.5% compare with slope land, respectively.The LFOC content of 0-20cm soil profile follow the order slope land, abandoned land < grassland, shrubbery land < forest land during vegetation restoration course. The weighted mean value of LFOC of 0-20cm soil layer in forest land is 2.20mg/g, increase 218.8% compare with slope land.The HFOC content of 0-20cm soil profile follow the order slope land < abandoned land < grassland, shrubbery land < forest land during vegetation restoration course. The weighted mean value of HFOC of 0-20cm soil layer in forest land is 12.59mg/g, increase 101.8% compare with slope land.The content of SOC and fractions of SOC (POC, MOC, LFOC, HFOC) in different soil layers increase gradually with vegetation restoration. Effect of vegetation on SOC and fraction of SOC weaken with incrment of soil layer. The effect of vegetation on SOC and fraction of SOC in 0-5cm layer is strongest in all of the soil layers. The content of SOC, POC, MOC, LFOC, HFOC in slope land 0-5cm soil layer is 8.75, 4.32, 1.04, 4.43, 7.17mg/g, these values in forest land increase 192.7%, 310.3%, 366.3%, 78.0%, 170.2% compare to slope land.(2)Influence of vegetation restoration on stability of soil structureThe content of >5, 5-2, 2-1mm aggregate of ohter vegetation restoration phases increase with big extent compare with slope land in 0-5 and 5-10cm soil layer, the content of 1-0.5 and 0.5-0.25mm aggregate of other vegetation restoration phases change unconspicuous compare with slope land in 0-5 and 5-10cm soil layer. The content of >5, 5-2, 2-1, 1-0.5 and 0.5-0.25mm aggregates of other vegetation phase is higher than those of slope land in 10-100cm soil layer, the increase extent of >1mm aggregate content reduce with vegetation restoration, the increase extent of 1-0.5 and 0.5-0.25mm aggregate content improve with vegetation restoration.Natural vegetation restoration in Ziwuling Mountain could improve >0.25mm water stable aggragate content, reduce aggregate destruction rate and water stable aggregate fractal dimension, improve soil structure. The stability of soil structure improve gradually with vegetation restoration except the stability of soil structure in shrubbery land lower than that in grassland, the stability of soil structure in forest land is highest in all of the vegetation restoration phases.The relationship between >0.25mm water stable aggregate content, aggregate destruction rate, water stable aggregate fractal dimension and SOC is highly significant logarithm. When the SOC content is less than 20.9 mg/g, the content of >0.25 mm water stable aggregates increasing and the aggregates destruction rate and water stable aggregates fractal dimension decreasing significantly with the SOC content increasing,while the three indices don't change significantly, it is to say that the soil structure reach stable state in grassland and forest land 0-5cm soil layer.(3)Influence of vegetation restoration on the content and distribution of aggregate SOC and fraction of aggregate SOCThe SOC, MOC, HFOC content of all size aggregates increase with vegetation restoration except the SOC, MOC, HFOC content of all size aggregates in abandoned land is nonsigficant different with those in slope land, those in shrubbery land lower than those in grassland in 0-5 and 5-10cm soil layer.The POC and LFOC content of all size aggregates increase with vegetation restoration except the POC and LFOC content of all size aggregates in shrubbery land is nonsignificant different with those in grassland in 0-5 and 5-10cm soil layer.(4)Influence of vegetation restoration on the contribution rate of aggregate SOC and fraction of aggregate SOCThe contribution of >1mm aggregate to SOC increase gradually with vegetation restoration, the contribution of <1mm aggregate to SOC decrease gradually with vegetation restoration in 0-5, 5-10 and 10-20cm soil layer.The contribution of >1mm aggregate to POC and FLOC increase gradually with vegetation restoration, the contribution of <1mm aggregate to POC and FLOC decrease gradually with vegetation restoration in 0-5 and 5-10 cm soil layer. The contribution of >0.5mm aggregate to POC and FLOC increase gradually with vegetation restoration, the contribution of <0.5mm aggregate to POC and FLOC decrease gradually with vegetation restoration in 10-20 cm soil layer.The contribution of >1mm aggregate to MOC and HLOC increase gradually with vegetation restoration, the contribution of <1mm aggregate to MOC and HLOC decrease gradually with vegetation restoration in 0-5 and 5-10 cm soil layer. The contribution of >0.25mm aggregate to MOC and HLOC increase gradually with vegetation restoration, the contribution of <0.25mm aggregate to MOC and HLOC decrease gradually with vegetation restoration in 10-20 cm soil layer.