| As an important part of the terrestrial ecosystem,forest area account for 30%of global land area,and the forest soil carbon content accounts for about 70%of the terrestrial soil carbon pool.Thus,the changes of forest vegetation and soils have a significant impact on global carbon cycle and carbon dynamic.As an important factor affecting vegetation distribution and soil physical and chemical characteristics,topography has been widely treated as an important factor affecting soil organic carbon distribution.Due to the variant hydrothermal conditions caused by different topography,the material circulation and energy flow in the soil show strong spatial variability,causing variations in soil quality.Studying the distribution of vegetation and the soil physical and chemical characteristics among different landscape positions can help us better understand the influencing factors of spatial variability of soil organic carbon and provide scientific mitigations to improve soil organic matter level.In addition,the study of soil organic carbon composition among different landscape positions has certain guiding significance for the prediction of forest soil carbon dynamics under global climate change.In this study,we collected soil samples from different slope positions(summit,middle slope,lower slope,and valley)and soil layers(0-10cm,10-20cm,and 20-40cm)in a lha permanent forest site in the Badagongshan National Nature Reserve,Hunan Province.Based on the field sampling and the laboratory experiments,we used the linear mixed-effects models to analyze the differences of soil physical and chemical characteristics among different landscape positions,and used the partial least squares path modeling to explore the factors affecting soil organic carbon components.In addition,the differences of soil organic carbon stability among different landscape positions were explored by laboratory incubation experiments.The main results are as follows:The summit position had a better vegetation condition than the valley position.The thickness of forest floor and the soil root biomass decreased gradually from the summit to the valley.Soil particle compositions were not significantly different among different slope positions,but the content of coarse particle(>2 mm)of the valley was significantly higher than that of summit.Soil pH showed a significant increase from the summit to the valley.There were no significant differences among slope positions for soil organic carbon and total nitrogen.But they respectively showed a decreasing and increasing trend from the summit to the valley.Soil carbon and nitrogen ratio showed a significant downward trend from the summit to the valley.In addition,the variability of soil attributes among the four slope positions occurs mainly in the surface soil.Although there was no significant difference in soil organic carbon content among the four slope positions,soil dissolved organic carbon(DOC,the active component of SOC)and particulate organic carbon(POC,non-protective component of SOC)showed that they had a significant decrease from the summit to the valley.Based on the results of partial least squares analysis,the variation of DOC content in 0-10cm soil layer is mainly controlled by the soil physical and chemical characteristics(pH,carbon and nitrogen ratio,iron-aluminum oxide and sand content).The variation of the DOC content in the middle soil layer is mainly controlled by the topsoil DOC content.In addition,the change of POC content in the 0-10cm and 10-20cm soil layer was mainly controlled by soil physical and chemical factors,and the change of POC in the 20-40cm soil layer was mainly affected by the upper layer POC content.The stability of soil organic carbon showed significant difference among slope positions only for topsoils.The summit had the lowest SOC stability.The results of partial least squares regression analysis showed that this change in 0-10cm was mainly affected by POC.But the stability of soil organic carbon in 10-20cm and 20-40cm was mainly affected by soil particle compositions. |
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