Distributions and Influencing Factors of Soil Organic Carbon Fractions under Different Vegetation Restoration Conditions in a Subtropical Mountainous Area, SW China

Abstract

Vegetation type is known to affect soil organic carbon (SOC) storage. However, the magnitudes and distributions of SOC sequestration and driving factors for different vegetation types are still largely unknown. Thus, we studied the changes in SOC fractions along soil profiles for different vegetation restoration types and their relationships with soil properties. We selected five vegetation types and collected soil samples from depth intervals of 0–10, 10–30, 30–60, and 60–90 cm. Five soil carbon fractions and the soil properties were tested to evaluate the soil carbon fraction distributions and influencing factors. Our results demonstrated that the concentrations of total organic carbon (TOC) and five carbon fractions were strongly affected by vegetation types and soil depths. The concentrations of all five soil carbon fractions in 0–10 cm depth were higher than those in the other three soil depths and generally increased with vegetation complexity. The Pearson correlations and redundancy analysis showed that the fractions of soil glomalin-related soil protein (GRSP) and Fe oxides as well as the soil bulk densities, were the most significant related to soil TOC levels and carbon fractions, which suggests that soil biochemical and physicochemical processes are among the most important mechanisms that contribute to SOC persistence. Considering the sensitive indices of the soil carbon variables and PCA results, soil permanganate oxidizable carbon (POXC) was considered to be the most sensitive index for differentiating the effects of vegetation types. These results provide important information regarding the distributions and driving factors of the carbon fractions that result from different vegetation restoration types and will help to improve our understanding of soil carbon sequestration during vegetation restoration processes.