Relationship Between Organic Carbon Stability And Erosion Resistance Of Degraded Red Soil At Different Vegetation Restoration Stages

In this study,Pingjiang River basin,which is located in Xingguo County,Ganzhou City,Jiangxi Province was selected as the research area.The soils in this region belongs to red soil developed from granite.The bare badlands after natural recovery was adopted as the control（CK）.In addition,four artificial forestlands with restoration ages of 5 years（LD₅）,15 years(LD₁₅),25 years(LD₂₅),and 35 years(LD₃₅)and orchards with 5 different planting years including 1 year（GY1）,5 years（GY5）,10 years（GY10）,15 years（GY15）,and 20 years（GY20）were selected as the research objects.Meanwhile,undisturbed forest land（CSL）was selected as the climax vegetation to investigate the recovery rates of soil organic carbon（SOC）storage after long-term vegetation restoration.Soil structural indexes and erosion resistance under different vegetation use types,restoration/planting years,and soil depth was analyzed.Accordingly,soil erosion resistance model was set up.Moreover,the storage and stability of soil total organic carbon（TOC）,aggregate organic carbon（POC）,light and heavy organic carbon（LFOC and HFOC）was investigated.Finally,the interaction path model between SOC and soil erosion resistance under different vegetation use,restoration/planting years,and soil depth was built up.The main conclusions are as follows:（1）The soils with different vegetation types,restoration/planting years,and soil depth were dominated by the macroaggregates（>2 mm）after dry sieving,while large aggregates（0.25-2 mm）were dominant after wet sieving.The soil mechanical stability of forest land increased with the restoration years,while that of orchards decreased.The water stability of forest land and orchard increased with the increase of years,but decreased with the increase of soil depth.Different vegetation restoration and utilization types have different corrosion resistance indexes.The soil corrosion resistance of forest land and orchard increased with the increase of years,but decreased with the increase of soil depth.（2）The contents and storage of soil organic carbon decreased first and then increased with the increase of restoration years.The organic carbon contents of orchard soils fluctuated around 4 g.kg^-1,and its storage increased first and then decreased with the planting years.The organic carbon content of forestland and orchard showed an exponential function relationship with soil depth,which decreased sharply with the increasing soil depth at 0-20 cm,and then decreased slowly.（3）The particulate organic carbon（POC）contents of forest and orchard increased with the decrease of particle size.The storage of particulate organic carbon in 1 m soil layer decreased first and then increased with the decrease of soil particle size.The stability of POC increased with the restoration years.POC of orchards increased steadily with planting years,but it was still lower than that of forestland.The content of POC in forest decreased first and then increased with soil depth.A gradual decrease occurred in POC content and storage of orchards with soil depth.Forest land is composed of carbon with high stability of chronic organic carbon and inert organic carbon.The sum of POC_0.05-0.25 and POC_<0.05 in different soil depths of forest was greater than 50%.POC_0.25-2 was the highest in orchard soil with poor soil stability,accounting for more than 50%of TOC.The content of heavy organic carbon in forest particles organic carbon was higher than that of light organic carbon in different restoration years.The contents of H_0.25-2 and L_0.25-2 increased with the restoration age.The contents of H_0.05-0.25 and H_<0.05 decreased first and then increased with the restoration years.The forest was dominated by heavy organic carbon.The stability of organic carbon decreased first and then increased with the restoration years,and the soil layer with high stability also increased gradually.（5）Principal component analysis was carried out on soil particles and soil corrosion resistance index to establish the optimized comprehensive model of corrosion resistance.Comprehensive expression of soil erosion resistance under different vegetation utilization patterns:Y=0.453F₁+0.398F₂+0.149F₃,the order of soil erosion resistance from the largest to the smallest is CSL>GY₁₅>CK>LD₁₅.Comprehensive expression of soil erosion resistance of forest with different restoration years:Y=0.562F₁+0.308F₂+0.131F₃,the order of soil erosion resistance is LD₃₅>LD₂₅>LD₅>LD₁₅.Comprehensive expression of soil erosion resistance in orchard with different planting years:Y=0.669F₁+0.228F₂+0.103F₃,the order of soil erosion resistance is GY₁₅>GY₁₀>GY₁>GY₂₀.The trend of soil erosion resistance in different soil layers was not obvious.The comprehensive expression of soil erosion resistance in different soil layers of woodland was as follows:Y=0.474F₁+0.293F₂+0.147F₃+0.087F₄.Comprehensive expression of soil erosion resistance in different soil layers of orchard:Y=0.464F₁+0.263F₂+0.133F₃+0.081F₄+0.059F₅.（6）The soil erosion resistance of different vegetation restoration was mainly related to the HFOC of different particle sizes.The erosion resistance of forestland soils under different restoration years and soil layers was mainly related to HFOC and light organic carbon of mineral particles.The soil erosion resistance in orchards was mainly associated with large aggregates and mineral particles in HFOC.In the forest soils with different vegetation use and restoration types,TOC influenced soil erosion resistance index by affecting POC_0.25-2,H_0.25-2,aggregates or soil particles.However,the indicators of soil aggregates or soil particles affected by HFOC are not the same,so the indicators of soil erosion resistance affected by HFOC are also different.To sum up,soil erosion resistance indicators and aggregates show the same change trends in forest lands and orchards.However,as an important cement of large aggregates,the storage and stability of SOC show the different variation trends.The stability of POC in forest lands increased with the recovery years.Moreover,the activity of POC in orchards was higher than those in forest lands.Further analysis of organic carbon components in POC shows that HFOC dominated in the forest lands,which increased steadily with the recovery period.The orchard is dominated by LFOC,with its content and stability increasing with the increase of planting years.The comprehensive indies of soil erosion resistance under different land use,restoration/planting years,and soil depths showed the same trend as SOC.Hence,this study uses soil particles as the media to establish relationships with soil aggregate properties,soil erosion resistance and SOC stability.The influence of SOC on soil erosion resistance through aggregates was clarified.The results provide a theoretical basis for quantitative regulation of soil ecological restoration process in degraded regions.