Effects of Land Utilization Methods on Soil Organic Carbon and Its Labile Fractions in Karst Peak-Cluster Depression

By studying the response characteristics of soil organic carbon and its labile fractions to land utilization methods in karst peak cluster depressions, the result could provide the theoretical basis for the maintenance of soil carbon pool stability, ecological restoration and reconstruction in karst areas.

Based on long-term field positioning experiments, five common land use methods were selected in karst peak cluster depression areas, including enclosure, burning, cutting, grass planting, and maize planting, to study the effects of different land utilization methods on soil organic carbon (SOC) and its labile fractions, namely particulate organic carbon (POC), light fraction organic carbon (LFOC), easily oxidizable organic carbon (EOC), and microbial biomass carbon (MBC).

The SOC content under different land utilization methods showed as follows: enclosure>burning>cutting>grass planting>maize planting, and the SOC content in maize planting as significantly lower than other land utilization methods (P<0.05). The trend of changes in soil POC content was consistent with that of SOC, but the decrease in POC content among land utilization methods was greater than that of SOC; the content of LFOC and EOC in soil was highest in the enclosure, and lowest in maize planting; compared with enclosure, the burning significantly increased soil MBC content. Soil POC was the main labile fraction of soil organic carbon in different land utilization methods in the study area. The POC/SOC ratio ranged from 39.3% to 58.6%, with enclosure>cutting>burning>grass planting>maize planting. The ratios of LFOC/SOC and EOC/SOC were lower in enclosure and burning, but the highest were observed under maize planting. Correlation analysis showed a highly significant positive correlation (P<0.01) between POC, EOC, MBC and SOC in karst areas soil, which could sensitively reflect soil SOC dynamics. SOC, POC, EOC, and MBC were all significantly positively correlated with TN, AN, Ca²⁺, and Mg²⁺ (P<0.01), and significantly negatively correlated with clay particles (P<0.05); SOC, LFOC, POC, EOC, MBC were significantly negatively correlated with silt particles (P<0.05) and significantly positively correlated with sand particles (P<0.05); SOC, EOC, and MBC were significantly positively correlated with TP (P<0.05). Redundancy analysis indicated that AN, Ca²⁺, TP, as well as silt and clay particles in soil, were the most significant contributing factors to changes in SOC and its labile fractions content. This suggested that the changes in soil physical and chemical properties under different land utilization methods were closely related to changes in SOC and its labile fractions content.

Strategies such as enhancing vegetation coverage and reducing high-intensity utilization were beneficial for increasing organic carbon content and maintaining its stability in karst peak cluster depressions, while measures such as long-term tillage that cause significant soil disturbance increased the risk of organic carbon and fraction loss.