Vertical distribution patterns of soil organic carbon along elevational gradients and its environmental drivers in the montane forests of the western Tianshan Mountains,China
The organic carbon pool in forest soils plays a crucial role in maintaining ecosystem carbon balance.However,the vertical variation patterns of soil organic carbon(SOC)and its influencing factors in western Tianshan Mountain forests remain controversial.This study aimed to discern the elevational distribution pattern of forest SOC and identify the predominant factors that influence this pattern.Furthermore,we sought to quantify the spatial correlation between the SOC and these factors.This study aims to provide a better basis for regional forest conservation and management.In this study,fixed plots were established along two elevational gradients in the western Tianshan Mountains.Real-time microclimate monitoring coupled with GIS technology was employed to extract environmental variables,such as flat curvature(FC),profile curvature(PC),topographic relief(TR),surface roughness(SR),and normalized difference vegetation index(NDVI).A geographic weighted regression(GWR)model was utilized to simulate the spatial distribution characteristics of the SOC and to decipher the driving factors of the SOC spatial distribution.The results revealed that the surface layer(0-20 cm)SOC content in the western Tianshan mountain region was abundant(64.65-123.3 g/kg),exceeding that of other mid-latitude mountain ecosystems(20.61-83.72 g/kg)and the national average(42.4 g/kg).Along different altitudinal(ALT)gradients,the spatial distribution patterns of SOC varied inconsistently,with the western Tianshan and wild walnut gullies forming unimodal and linearly increasing spatial distribution patterns with elevation,respectively.Western Tianshan exhibited more pronounced vertical changes in the environment and vegetation,with SOC being influenced by complex factors.Soil nutrient content and microclimate factors play significant roles in the spatial distribution of SOC,which is primarily influenced by total potassium(TK),soil pH,ammonium nitrogen(NH4-N),and soil mean annual temperature(SMAT).Conversely,the Wild Walnut Gully,with a smaller altitudinal range,demonstrated that soil factors played a more crucial role in SOC distribution than environmental factors such as microclimate and vegetation.The main influencing factors were total nitrogen(TN),nitrate nitrogen(NO3-N),pH,TK.Overall,the results of our analysis show that the western Tianshan Mountains are rich in SOC,and the spatial distribution patterns of SOC along the ALT gradients in the western Tianshan Mountains are affected by a complex interplay of soil nutrient elements and microclimate,rather than a single environmental factor.The differences in the spatial distribution patterns of SOC between the two mountains were attributed to the different ALT ranges,indicating that SOC distribution is a multifaceted phenomenon influenced by a range of environmental variables.The results are helpful in understanding the characteristics of SOC distribution in the district and providing data on forest utilization and management.
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