Characteristics Of Stable Carbon Isotope In Leaves,litter And Soil Of Typical Forests In Ningxia

The stable carbon isotope(δ13C)can indicate the distribution characteristics of organic carbon in ecosystems,and serve as a medium for the study of carbon turnover,and also provide key information for the study of soil carbon dynamics.The variation of stable carbon isotopes in leaves,litter and soil plays an important role in understanding the biogeochemical cycle of carbon.In this study,two kinds of forests,Picea Crassifolia and Pinus Tabulaeformis,were selected from different mountains(Helan,Luoshan and LiuPan Mountain)in Ningxia Hui Autonomous Region as research objects.Field sampling and laboratory analysis were used.The characteristics of stable carbon isotopes in leaves,litters and soil were studied,and the fractionation of stable carbon isotopes in leaves,litters and soil and the decomposition rate of soil organic carbon were calculated.In this study,we analyzed the variation characteristics of stable carbon isotopes of P.tabulaeformis and P.tabulaeformis in different mountainous regions(Helan,Luoshan and Liupan Mountain),and revealed the differences of organic carbon δ13C distribution patterns and their underlying mechanisms.The main research results are as follows:(1)The leaf δ13C of P.Crassifolia and P.Tabulaeformis in Helan is higher than that in Luoshan and Liupan Mountain.The leaf δ13C of Picea crassifolia in Helan and Liupan Mountain is lower than that of P.tabulaeformis.The homeostasis of N content was higher in the leaves of P.Crassifolia and P.Tabulaeformis,but the homeostasis of P content was weaker.The growth of P.Crassifolia and P.Tabulaeformis in Helan,Luoshan and Liupan Mountain was restricted by N.(2)The δ13C of litter of P.crassifolia and P.Tabulaeformis in typical stands of Helan was higher than those in Luoshan and Liupan Mountain.The δ13C of litter of Helan and Liupan Mountain were P.crassifolia>P.Tabulaeformis,while the δ13C of litter of Luoshan was P.Tabulaeformis>P.crassifolia,and the contents of C,N and P in the litter were lower than those in the leaf.The decomposition rate of P.crassifolia in Helan was higher than that in Luoshan and Liupan Mountain.The δ13C of litter was negatively correlated with the N content of litter.(3)The soil δ13C of Helan is the highest in the typical stands of Helan,Luoshan and Liupan Mountain in Ningxia.The comparison of the typical stands of the same mountain type shows that the soil δ13C changes in the three mountains are similar,and all of them are shown as P.tabulaeformis>P.crassifolia.In the three mountains,the carbon decomposition rate of the soil in qinghai is greater than the pine soil,and the organic carbon decomposition rate is the fastest,and the organic carbon decomposition rate is the slowest.(4)The proportion of silt and very fine sand in the typical stand of P.Crassifolia and P.Tabulaeformis in Ningxia ranged from 64.60%to 83.72%,while the proportion of clay was very small,indicating high stability of soil structure.Soil microorganisms in P.tabulaeformis were abundant and active,the turnover of soil carbon and nitrogen elements was fast,and the soil organic carbon and total nitrogen were in a slow accumulation process.Soil physical and chemical characteristics and biological characteristics of Ningxia typical stand all have influence on stable carbon isotope characteristics,among which bulk density,soil organic carbon,available nitrogen,microbial biomass carbon and soilδ13C and β are the main direct influencing factors.(5)The degree of carbon isotope fractionation from leaf to litter is small,which indicates that theδ13C of litter in arid and semi-arid regions is mainly related to the plants from the surface,and the degree of δ13C of litter and soil is the largest.Although litter are the source of forest soil organic carbon,the soil δ13C does not completely inherit the δ13C of litter.Sources of soil organic matter,also is mixed input of various plants,and in the litter into the process of soil organic matter in isotope fractionation,C3 vegetation shape tall at the same time,plant leaves and litter for whole plant of the contribution of soil organic carbon ratio is small,so the litter and soil between the degree of carbon isotope fractionation.In conclusion,the soil carbon sequeering potential of P.Crassifolia is higher than that of P.Tabulaeformis,so P.Crassifolia is more conducive to maintaining ecosystem stability.The growth of P.Crassifolia and P.Tabulaeformis is restricted by N.Therefore,it is suggested that appropriate input of N elements should be considered in the management and management of these forest areas to improve the soil quality of P.Crassifolia and P.Tabulaeformis.