Response Of Soil Carbon Pool Composition And Stability To Priming Effect Of Organic Carbon In The Restoration Of Robinia Pseudoacacia Forest

In the process of vegetation restoration,the content of soil organic carbon changes with the quantity and quality of litter and root exudates.Under the global changing environment,the balance of soil carbon pool and the dynamic mechanism of soil organic carbon will face severe challenges.When fresh organic matter(such as glucose,root exudates,etc.)is input in the soil,it may promote or inhibit the decomposition of original organic matter in the soil,which is called the priming effect.In this study,artificial Robinia pseudoacacia forests(14years,20 years,30 years,and 45 years)and adjacent sloping farmland were selected as the research objects in the loess hilly area.The characteristics of the priming effect of soil organic carbon during the restoration of Robinia pseudoacacia forests were studied by using¹³C stable isotope labeling technology in laboratory cultivation experiment.At the same time,the changes of the physical,chemical and biological components of soil organic carbon and the stability of carbon pool were analyzed to explain the influence of vegetation restoration on the components and stability of soil organic carbon pools.Finally,combining with the characteristics of vegetation community,the basic physical and chemical properties of the soil and extracellular enzymes activities,the influence of the composition and stability of soil carbon pool on the priming effect in the restoration of the Robinia pseudoacacia forest was explored.The specific results are as follows:(1)In the restoration of Robinia pseudoacacia forest,the input of exogenous carbon causes a positive priming effect and promoted the decomposition of soil organic matterIn the restoration process,the input of exogenous carbon promoted the mineralization of soil organic carbon,which showed a positive priming effect.With the increase of restoration years,the priming effect increased at first and then decreased,and reached the highest value in 20 years of Robinia pseudoacacia,and the priming effects of organic carbon in Robinia pseudoacacia forest was greater than that of farmland.In addition,during the cultivation process,the priming effect of soil organic carbon of the Robinia pseudoacacia forests showed a rapid increase in the early stage of cultivation,and a slow growth rate in the middle and later stages,and finally tended to be stable,with a variation range of 38.68-83.66mg CO₂-C·kg^-1 soil.(2)In the restoration of Robinia pseudoacacia forest,the contents of soil organic carbon and it components increased gradually,and the stability of soil carbon pool was enhancedDuring the restoration process of Robinia pseudoacacia forest,the contents of soil organic carbon,labile organic carbon,recalcitrant organic carbon,and microbial biomass carbon all increased significantly with the restoration years,and the range of change was2.98-7.73 g·kg^-1 and 0.77-1.82 g·kg^-1,2.21-5.91 g·kg^-1,60.27-521.54 mg·kg^-1,respectively.Among the different aggregate components,the organic carbon content of micro-aggregates(0.053-0.25 mm)was the highest and changed significantly during the recovery years,ranging from 5.65-9.59 g?kg^-1.With the increase of restoration years,soil carbon pool index and carbon pool management index gradually increased,while carbon pool activity and carbon pool activity index decreased gradually,indicating that vegetation restoration promoted the enhancement the stability of the soil carbon pool.(3)In the restoration of Robinia pseudoacacia forest,the priming effect was significantly correlated with the organic carbon associated with clay-silt fractions,and was synergistically regulated by the activities of soil enzymesWith the increase of the recovery years of Robinia pseudoacacia,vegetation coverage,biomass,soil total nitrogen,available nitrogen,microbial biomass content,and hydrolase(?-glucosidase,cellobiohydrolase)activity showed a significant increase trend,while oxidase(peroxidase,polyphenol oxidase)activity showed a trend of first increasing and then decreasing with the increase of forest age.Through regression analysis,it was found that the increase in organic carbon associated with clay-silt fractions and carbon pool management index would promote the soil priming effect,while the organic carbon associated with micro-aggregate,recalcitrant organic carbon,microbial biomass carbon content and carbon pool index were positively correlated with priming effect intensity.Through the partial least squares path model,it was found that the plant community regulate the priming effect of soil organic carbon in two ways.One is that litter organic carbon directly influences the activity of extracellular enzyme involved in soil carbon cycle and has a significant positive impact on the priming effect.The second is by influencing the stability of soil nutrient content and change of soil carbon pool and indirectly affect the priming effect.In general,compared with the latter,soil extracellular enzyme activity was the key process affecting the priming effect of vegetation community characteristics.In summary,returning farmland to forests in loess hilly areas with fragile ecological environment and converting slope farmland into artificial Robinia pseudoacacia forest will help increase the biomass and coverage of above-ground vegetation,and gradually improve soil structure and nutrient quality.The increase in the amount of exogenous organic matter from plant residues and root exudates will cause a positive priming effect.The results of this study have a certain reference value for the study of the influence of external carbon input on the soil carbon pool in the loess hilly area,and are of great significance for clarifying the impact of vegetation restoration on the soil carbon cycle and its response to global changes.