Vegetation type and Fe and Al oxides are important factors influencing the spatial distributions of soil organic carbon and mineral-associated organic carbon in mountain ecosystems

Abstract

In mountain ecosystems, changes in elevation can lead to alterations in regional microclimates, thereby affecting the distribution and transformation of soil organic carbon (SOC). Mineral-associated organic carbon (MOC) plays a crucial role in preserving SOC. However, research on the distribution of SOC and MOC content in mountain ecosystems is limited. Therefore, we conducted correlation analysis to analyze the effects of environmental factors (mean annual temperature and precipitation, elevation, and vegetation) and soil oxides (SO) on the contents of SOC and MOC in the Wuling Mountain. Selective dissolution methods have been used to further extract soil carbon (C) associated with Al and Fe minerals, as well as extractable Al and Fe. The results indicated that temperature and precipitation are important drivers of changes in the SOC and MOC contents. Moreover, the changes in the SOC and MOC contents were the result of the combined effects of multiple factors, such as climate, elevation and vegetation. There was a significant difference in the organic C stock among the different vegetation types: mixed coniferous broad-leaved forest > subalpine meadow > broad-leaved forest > shrubland-grassland. Not only were the Fe₂O₃ and Al₂O₃ contents in SO significantly correlated with SOC and MOC contents, but the extractable Fe and Al contents were also positively correlated with the extractable C content. The extractable Al and Fe contents increase with soil depth, whereas the MOC content decreases and the MOC/SOC ratio increases. Therefore, we speculated that the content of minerals such as Al and Fe in surface soils determines the MOC content, whereas in deeper soils the content of organic matter determines the content of MOC. Our research results emphasize that Fe and Al minerals promote SOC sequestration in mountain soils, which is important for understanding soil C cycling and predicting changes in SOC stocks in mountain soils.