Organic Carbon And Carbon Cycle Enzyme Activity Of Black Soil Affected By Erosion-deposition Process

The combination of high-intensity non-stop mechanical farming and slope erosion in the northeast black soil area accelerates the migration and depletion of black soil organic carbon(SOC),and the degradation of black soil quality threatens regional ecological environment safety and national food security.Taking slope cultivated land with different reclamation years(30 a?40a?60a)in typical black soil area as the research object,based on Stewart physical-chemical grouping method.Firstly,we quantified the storage and spatial distribution characteristics of carbon reservoirs with different stable mechanisms(Unprotected,Physical,Chemical,Biochemical)in the erosion and sedimentary areas of sloping farmland.Secondly,The carbon sequestration potential of erosion-defix regions,topsoil(0 to 30cm)and subsoil(30 to 50cm)is estimated by quantifying the organic carbon density and carbon saturation levels of the sedimentary region.Finally,the relationship between the different stable mechanism of organic carbon and the activity of carbon cycling enzyme activity(conversion enzymes,cellulase,?-glucoglycoside enzymes)is further clarified by determining the activity of enzyme related to carbon cycling in the erosion-deposition zone.And the main findings are as follows:1)The results showed that long-term cultivation and associated erosion simultaneously resulted in significant accumulation of SOC in the foot-slope deposition areas,and the contents of four OCPs in the foot deposition area were significantly higher than those in top-slope eroded areas.SOC of sloping farmland is dominated by chemically protected carbon and biochemically protected carbon(>90%);furthermore,the top-slope erosion areas and foot-slope deposition areas mainly accumulate chemically protected organic carbon(84.6%)and biochemically protected organic carbon(51.4%),respectively.With increasing cultivation years,the accumulation rate of four OCPs increased according to the stability degree of SOC,that is,biochemical protection carbon pool(48%)>chemical protection carbon pool(42.2%)>physical protection carbon pool(6.4%)>free unprotected carbon pool(3.4%).The proportion and accumulation rate of the free unprotected organic carbon pool were the smallest,but they were most sensitive to external interference.Thus,free unprotected organic carbon requires more attention when considering management of black soil.2)The total organic carbon,the organic carbon density,and the carbon saturation level in lower-slope deposition areas and in the topsoil layer were significantly greater than those in upper-slope eroded areas and subsoil layer,respectively.All their maximum values were found to occur on sloping farmland with 30 years of reclamation.The carbon sequestration potential of upper-slope eroded areas(1.24?2.89 kg·m-2)and subsoil(0.83?3.59 kg·m-2)was significantly higher than that of lower-slope deposition areas(0.79?1.04 kg·m-2)and topsoil(0.6-2.53 kg·m-2),respectively.The potential of carbon sequestration was significantly lower in farmland with 30 years of reclamation than that in farmlands with 40 years and 60 years of reclamation.It will take 20?181 a and 13-66 a to achieve carbon sequestration potential in upper-slope eroded areas and lower-slope deposition areas of sloping farmland(30?60 a)in black soil(0?50 cm),respectively.Therefore,more attention should be paid to the spatial-temporal variability of carbon sequestration potential on sloping farmland in the process of agricultural operation and restoration management,to realize the sustainable potential of black soil resources.3)Three types of carbon-circulating enzyme activity(conversion enzyme activity,cellulase,beta-glucoglycoside enzyme activity)have similar spatial distribution characteristics with SOC,all showing that the sedimentary region is larger than the erosion area,the topsoil is greater than the subsoil;Beta-glucosinase was significantly positively correlated,the activity of three carbon circulatory enzymes in the topsoil was positively correlated with physically protected organic carbon in the erosion region,negative correlation in the sedimentary region,and the activity of beta-glucoglycoside enzyme was significantly negatively correlated with biochemical protection organic carbon,and was significantly positively correlated with chemically protected organic carbon.Microenvironment can affect the relationship between soil enzyme activity and soil organic carbon,and future research should combine a variety of environmental factors to explore the mechanism of effect of soil enzyme activity on carbon turnover.This study provides a theoretical basis for the study of carbon dynamic change mechanism in sloped farmland in black soil area,and suggests that carbon dynamics under soil erosion-desposition should be further studied from the basin scale and integrated various environmental factors in the future.