Effect Of Typical Artificial Vegetations On Soil Carbon Fluxes In The Loess Hills Of Central Gansu Province

The terrestrial carbon cycle is an important part of the biochemical cycle of the Earth system and a major driver of global warming.Loess Hills of Central Gansu Province is located in the hinterland of Asia and Europe,and is one of the sensitive areas affected by climate in China,which has become a hot spot for studying the carbon cycle of terrestrial ecosystems in the context of climate change due to its poor adaptive capacity to climate change and fragile ecological environment.Since the implementation of the "return of farmland to forest and grass" project,not only the physical and chemical properties of local soils have been changed,but also the content of different components of soil organic carbon and their transformation processes have been significantly altered,thus further affecting the carbon sink function of terrestrial ecosystems.Therefore,in this study,five kinds of typical artificial vegetations(Medicago sativa[MS],Xanthoceras sorbifolium[XS],Caragana korshinskii[CK],Hippophae rhamnoides[HR]and Leymus secalinus[LS])were selected to study the effects of vegetations on carbon fluxes in the Loess Hills area of Central Gansu Province.By studying the characteristics and temporal changes of soil physical and chemical properties,methane fluxes,and ecosystem respiration(ER)of different vegetations,and using redundancy analysis and structural equation modeling to analyze the soil characteristics affecting carbon fluxes,we investigated the dominant factors of different vegetations on carbon fluxes in loess hilly areas,and revealed the mechanisms of different vegetations on the carbon sequestration function of loess hilly ecosystems,so as to provide a scientific basis for the carbon balance of loess hilly ecosystems and their response to climate change.This will provide a scientific basis for the carbon balance of the Loess Hills ecosystem and its response to climate change.The main findings are as follows:(1)Under the five typical vegetations in Loess Hilly area of Central Gansu Province,vegetation type,soil depth,and the interaction term of the two significantly affected soil pH,bulk density,capillary water holding capacity,capillary porosity,total porosity,maximum water holding capacity,minimum water holding capacity,soil organic carbon,water-soluble organic carbon,easily oxidizable organic carbon,microbial carbon,total nitrogen(TN),total phosphorus,amylase,and sucrose enzyme(P<0.05).Soil organic carbon,water-soluble organic carbon(WSOC),easily oxidizable organic carbon(EOC),and microbial mass carbon content gradually decreased with increasing soil depth in the vertical profile of soil layers.(2)All five vegetation types are CH4 sinks in the Loess Hilly area.The cumulative CH4 uptake fluxes decreased in the order of LS,HR,CK,MS,XS.The cumulative ecosystem respiration was decreasing from HR,MS,LS,CK,XS.Throughout the study period,the maximum values of CH4 uptake and ecosystem respiration occurred in the growing season and the minimum values occurred in the non-growing season.The combined effect of soil temperature and moisture was an important controlling factor for the temporal variation of CH4 flux and ecosystem respiration.In the loess hilly area,LS was the vegetation with the highest CH4 uptake capacity among the five vegetations studied,and was also the more desirable vegetation for mitigating CH4 emissions;XS was the vegetation with the lowest ecosystem respiration among the five vegetation species studied,and was also potentially the more desirable vegetation for mitigating CO2 emissions.The temperature sensitivity index of ecosystem respiration varied greatly among vegetations and seasons.(3)Within the study area,the lowest Global Warming Potential(GWP)were found in the arborvitae forests of XS.Soil chemistry is the most critical factor limiting carbon fluxes in this area,with sucrose enzymes having the greatest impact.When considering only GWP,XS should be selected as the main type of vegetation restoration in this area.In the process of vegetation restoration in the Loess Hills region,the carbon sequestration capacity and ecological benefits of different vegetations should be considered in order to select the vegetation community most conducive to carbon neutrality.In summary,vegetation type has a significant effect on soil physicochemical properties and soil carbon fluxes in Loess Hills of Central Gansu Province.The most critical factor limiting carbon fluxes in this region is soil chemical properties.In the case of considering only the global warming potential,the arborvitae forest of the crown fruit should be used as the main afforestation type in the vegetation restoration process in this region.The research results,theoretically,provide technical parameters for scientific understanding and evaluation of carbon flux changes under vegetation in Loess Hills of Central Gansu Province of China,and provide theoretical basis for regulating carbon fluxes and improving the carbon sink function of semi-arid loess hills.