Soil Organic Carbon Stability On Eroded Slope Land In The Hilly Loess Plateau

The impact of erosion on soil organic carbon(SOC)sequestration and release of terrestrial ecosystem is highly uncertain,which hinders people in scientifically learning about the potential of soils to mitigate climate change.Identify the stability mechanism of SOC in the process of slope erosion-sedimentation has great practical and scientific significance for assessing the carbon sequestration potential,environmental effects under soil erosion and global carbon budgets.In this study,soil on the slopes with different SOC levels(C1,C2,C3,C4,C5)in the loess hilly region were taken as objects,in which the physical,chemical and biological properties were analyzed to quantify the multi-factor effect influencing the stability of SOC and identified the change of SOC stability and its main influencing factors in the surface layer(0-10 cm)of the erosion slope by continuously monitoring of soil temperature,humidity and CO2 flux in this area and combining soil sample analysis.The main conclusions are as follows:1.Rainfall erosion changed the soil physical and chemical properties of slope erosion-deposition area,which led to the heterogeneity of soil temperature and humidity in different parts of the slope,and the degree of differentiation was related to the SOC level of the slope.The soil bulk density(BD)of the erosion zone(0-10cm)is smaller than that of the sedimentary zone,and the higher the SOC level on the slope,the smaller the BD,the better the aeration,while the sedimentary zone has no obvious regularity.Generally speaking,the water stable soil aggregates(WSA)of >0.25 mm shows that the erosion zone is larger than that in the deposition zone.Under the low SOC level,the mean weights diameter(MWD)of the WSA in the sedimentary area is larger than that in the eroded area.Under the high SOC level,the MWD of the WSA in the eroded area is larger than that in the sedimentary area.The sedimentary area has a lower temperature and a higher humidity than that in the eroded area.Before and afterthe rainy season,the soil temperature difference in the erosion-deposition area decreases,and the higher the SOC level,the greater the difference.The difference in soil moisture in the erosion-deposition area is also related to the SOC level.When in a low SOC level(C1-C3),the difference is increased,and when in a high level(C4-C5),the difference is reduced.In addition,when the SOC level on the slope is low(C1-C3),the SOC in the erosion-deposition area is not obvious.When the level is high(C4-C5),the difference is relatively obvious.The SOC in the eroded area is 28.6%~37.5%.2.Fractions of SOC on slope erosion-deposition area differ at spatial-temporal scales,and exhibit various responses to SOC levels,soil temperature and humidty.At the end of the rainy season,the soil microbial biomass carbon content(SMBC)increased by 91.1%~286.8% compared with that before the rainy season,which showed an obvious seasonal variation.The SMBC in the slope sedimentary area was larger than that of the erosion area,and with the increase of SOC level.The difference of SMBC between sedimentary area and erosion area are increased.Moreover,the spatial differentiation also increased.The SMBC in the eroded and sedimentary areas before the rainy season is mainly affected by soil moisture.The eroded area at the end of the rainy season is mainly affected by SOC,and the sedimentary area is mainly affected by soil temperature.The difference in sensitivity of SMBC to influencing factors is mainly due to the restrictive conversion of different factors.The soil light fraction organic carbon content(LFOC)of the slope is mainly affected by the SOC level,and its distribution ratio is greatly affected by seasonal changes.The LFOC in the erosion and sedimentary areas is mainly affected by SOC,which can explain 58.9% and86.9% of the variation,respectively,while the distribution ratio of LFOC is more sensitive to seasonal changes,which can explain 41.2% and 35.3% of the variation.3.The soil respiration rate(Rs)of the erosion slope has obvious spatial and temporal differences.The stability of SOC in the slope erosion-deposition area is mainly related to SOC level,soil temperature and humidity.The Rs of slopes under different SOC levels was higher than that of non-erosion seasons,Rs at high carbon levels were higher than low carbon levels,and sedimentary areas greater than that in erosion areas.The soil moisture and temperature two-factor model can explain the Rs variation in the slope erosion-sedimentation area from 44.3% to 73.9%,and the higher the SOC level,the greater the degree of interpretation of the model.Accordingly,when at high levels of SOC in the soil,Rs was mainly impacted by soil water and temperature,with the increasing accuracy of soil water and temperature two-factor model.Compared with the control area,the soil carbon emission in the slope sedimentary area increased,which reduced the SOC stability;the SOC stability in the erosion area was related to the slope organic carbon level,and the lower or higher the carbon level(C1 Or C5),the SOC stability was reduced,and the SOC is more stable at the medium level of C2-C4.4.The stability of SOC in eroded slope soil is affected by many factors,and the influence of different factors on the stability of SOC varies.SOC stability in eroded and sedimentary areas is affected by multiple factors.The SOCstability in the eroded area is mainly affected by the content of >0.25 mm water-stable aggregates,with an interpretation of 88.9%.The sedimentary area was mainly affected by the content of >0.25 mm of WSA and BD,with interpretations of 56.1% and 41.7%,respectively.The Rs on the eroded slope is mainly affected by the organic carbon level,which can explain the variation of 66.4%.The LFC and SMBC can explain the Rs variation of 7.2%and 0.3%,respectively.The effect of erosion-induced changes LFOC on SOC mineralization rate is more important than SMBC.