Impact Of Vegetation Recovery Of Abandoned Lands In Loess Hilly Region On Soil Organic Carbon And Stability Of Soil Aggregates

Vegetation recovery is the measure which is mainly adopted by loess hilly regions in western Shanxi to protect ecological environment and reduce water and soil erosion.This study chooses the typical sample areas with different recovery periods in the vegetation recovery process in typical loess hilly regions of western Shanxi as the research object,and it uses Yoder method and Le Bissonnais method to classify the soil,and measures the soil organic carbon and the components and the Glomalin related proteins,and studies the changing rule of the soil organic carbon pool and soil structure,and on this basis,explores the protection mechanism of the soil organic carbon.The main conclusions are as follows:(1)Vegetation recovery can improve the stability of soil aggregates,and the law of average weight diameter(MWD)and geometric mean diameter(GMD)increases with the increase of vegetation restoration years.MWD and GMD of three treatments of LB method in the same soil layer shows that SW > FW > WS,which means that the main reason for the soil degradation in loess hilly regions is dissipation function and mechanical disturbance caused by the explosion of gas sealing.MWD and GMD obtained from the three treatments of LB method show: farmland returning to grassland and forest for 30 years >15 years> 5 years,which can be seen that,with the natural succession of vegetation,the quantity of vegetation is increased and the stability of soil aggregates is improved.(2)In the process of vegetation recovery,the soil organic carbon content shows an increasing tendency,that is: farmland returning to grassland and forest for 30 years > 15 years > 5 years > slope cropland,and the soil organic carbon content of slope cropland is relatively low.With the deepening of soil layer in the section,the organic carbon shows a decreasing tendency,and its content is the lowest in 70-100 cm.The changing trend of total organic carbon content of aggregates of the same grade is that slope cropland< farmland returning grassland and forest 5 years < 15 years < 30 years.The effect of the years of farmland returning grassland and forest on the organic carbon of each particle size is2-0.25 mm.In the same soil layer,the total organic carbon content of farmland returning grassland and forest for 30 years is the highest,followed by 15 years and 5 years,while the total organic carbon content of slope farmland is the lowest.(3)With the increase of vegetation recovery years,the organic carbon component content of aggregates shows an increase tendency.The change of easily oxidized organic carbon,particulate organic carbon and soluble organic carbon is that farmland returning to grassland and forest for 30 years>15 years > 5 years > slope farmland.The organic carbon component of aggregates with a different particle size shows that the overall content is larger than 2 mm,and the organic carbon component of aggregates of 2-0.25 mm is higher than 0.25-0.053 mm,and less than 0.053 mm,showing that vegetation recovery mainly affects the organic carbon contentof larger than 0.25 mm.In the process of vegetation recovery,the content of easily oxidized organic carbon,particulate organic carbon and soluble organic carbon of aggregates with a different particle size is the highest from 2 to 0.25 mm.(4)In the process of vegetation recovery,the content of total glomalin and coccidiomycindecreases with the increase of soil depth.Under 4 vegetation recovery stages of same soil layer,the content of total glomalin and coccidiomyc in always shows an increase tendency with the increase of farmland returning to grassland and forest years,that is:farmland returning to grassland and forest for 30 years >15 years> 5 years >slope farmland.The content of total glomalin and coccidiomycin of soil aggregates with different size shows a decreasing tendency with the increase of soil layer.Each vegetation restoration stage in the same soil layer first increases and then decreases with the reduction of soil aggregates,namely,the content of total glomalin and coccidiomycin in 2-0.25 mm and 0.25-0.053 mm of soil aggregates is higher.In the same soil layer,the content of total glomalin and coccidiomycin in the same soil aggregates shows that farmland returning to grassland and forest for 30 years >15 years > 5 years > slope farmland.(5)There is a significant positive correlation between the content of coccidiomycin and total glomalin in different vegetation restoration stages and MWD and GMD.At the same time,there is a significant positive correlation between the content of total glomalin and coccidiomycin in each soil layer and the content of easily oxidized organic carbon,particulate organic carbon and dissolved organic carbon in organic carbon composition.