漓江流域喀斯特森林土壤有机碳空间分布格局及其驱动因子

Spatial Distribution Patterns of Soil Organic Carbon in Karst Forests of the Lijiang River Basin and Its Driving Factors

喀斯特森林生态系统脆弱,为了探明漓江流域喀斯特森林土壤的碳储潜力,揭示漓江流域喀斯特森林土壤有机碳(SOC)的空间分布格局,探寻各驱动因子对土壤有机碳空间分布的驱动作用途径及贡献,为评估该区域喀斯特森林的碳循环功能提供科学依据.以漓江流域喀斯特森林土壤为对象,研究漓江不同流域段(上、中、下游)、不同深度土层的森林土壤有机碳的空间分布特征,通过相关性分析和构建分段结构方程模型,揭示漓江流域喀斯特森林土壤有机碳空间分布的驱动因子及其作用途径,并量化了各类因子的直接或间接作用比例.结果表明,漓江流域喀斯特森林土壤整体土层较浅,土壤有机碳具有表聚性.在不同流域段土壤有机碳含量的分布为:上游>下游>中游,易氧化有机碳(ROC)和可溶性有机碳(DOC)的分布与之相一致,而微生物碳(MBC)的分布为:上游>中游>下游.各类驱动因子对流域喀斯特森林土壤有机碳空间分布驱动作用途径和贡献不同,其贡献按从大到小排序为:土壤理化因子>土壤有机碳活性组分>样地海拔>样地物种多样性,总效应分别为:1.148、0.574、0.284和-0.013.其中,样地海拔对土壤有机碳仅有间接影响,土壤有机碳活性组分对土壤有机碳仅有直接影响.各驱动因子中,土壤总氮、土壤易氧化有机碳、样地物种丰富度和土壤可溶性有机碳均可作为漓江流域喀斯特森林土壤有机碳含量变化的重要预测因子.因此,有必要建立有效的覆盖全漓江流域的生态环境保护机制,减少并控制人为干扰的影响(特别是漓江中游城市段),并通过提升和保护流域喀斯特森林的物种多样性,改善土壤理化性质,改善并提升土壤有机碳活性组分含量等有效途径,提升漓江流域喀斯特森林土壤有机碳储量,促进区域森林碳汇功能的提升.

The aim of this study was to explore the carbon storage potential of karst forest soils in the Lijiang River Basin,reveal the spatial pattern of soil organic carbon(SOC),investigate the contributions and pathways of each driving factor to the spatial distribution of soil organic carbon,and provide a scientific basis for assessing the carbon cycle function of karst forests in the region.We employed structural equation modeling(SEM)and correlation analysis to investigate the spatial distribution characteristics of forest soil organic carbon in different basin sections(upper,middle,and lower reaches)and soil layers at different depths of the Lijiang River.Additionally,the direct and indirect ratios of each factor were quantified.The results showed that the overall soil layer of karst forest soils in the Lijiang River Basin was shallow,and soil organic carbon was phenoconcentric.The distribution of soil organic carbon content in different watershed sections was upstream>downstream>midstream,and the distribution of readily oxidizable carbon(ROC)and dissolved organic carbon(DOC)was consistent,whereas the distribution of microbial biomass carbon(MBC)was upstream>midstream>downstream.The contribution of various biotic and abiotic factors to the spatial distribution of soil organic carbon in karst forests in the watershed was different,and their contributions were ranked in descending order as:soil physicochemical factors>soil organic carbon active fraction>sample elevation>sample species diversity,with the total effects of 1.148,0.574,0.284,and-0.013,respectively.Among them,the sample site elevation had only an indirect effect on soil organic carbon,and the soil organic carbon active fraction had only a direct effect on soil organic carbon.Among the driving factors,total soil nitrogen,soil oxidizable organic carbon,sample site species richness,and soil soluble organic carbon could be used as important predictors of soil organic carbon content in karst forests in the Lijiang River Basin.Therefore,it is necessary to establish an effective eco-environmental protection mechanism covering the whole Lijiang River Basin,to reduce and control the impact of anthropogenic disturbances(especially in the middle urban section of the Lijiang River Basin),and to enhance and protect the species diversity of karst forests in the basin in order to improve soil physicochemical properties,improve and enhance the content of the soil organic carbon active fraction,and enhance the soil organic carbon stocks of karst forests in the Lijiang River Basin through other effective ways,as well as to promote the enhancement of the regional forest carbon sink function.