Differences in the regulation of soil carbon pool quality and stability by leaf-litter and root-litter decomposition

Litter plays a crucial role in soil ecosystems. However, the differences in decomposition between leaf-litter and root-litter and their relative contributions to soil carbon pools and stability are not yet clear. Therefore, we conducted a 450-day in situ decomposition experiment in a semi-arid grassland to investigate the effects of soil biophysical and chemical properties on litter decomposition and to elucidate the dynamics of soil carbon pools during the decomposition process. The results showed that the decomposition rate (K) of leaf-litter was significantly higher than that of root-litter, and litter quality was the most important factor affecting the K of leaf-litter (58%) and root-litter (63%). Leaf-litter decomposition was more effective in promoting the increase in soil leucine aminopeptidase and β-1,4-glucosidase activities, as well as the accumulation of microbial biomass carbon (MBC), particulate organic carbon (POC), and dissolved organic carbon (DOC), compared to root-litter. However, the difference in the impact of leaf-litter and root-litter on soil organic carbon (SOC) was not significant. The decomposition of leaf-litter contributed more significantly to enhancing the soil carbon pool management index (CPMI) compared to root-litter, with increases of 39% and 25%, respectively. In contrast, leaf-litter decomposition significantly reduced the mineral-associated organic carbon (MAOC) and the MAOC/POC ratio, while root-litter decomposition significantly increased the MAOC and MAOC/POC. Random forest, partial correlation, and path analysis indicated that the effects of leaf-litter and root-litter decomposition on CPMI were mainly regulated by decomposition time and soil carbon components, while the effects on MAOC/POC were mainly controlled by litter quality. The results demonstrate that both leaf-litter and root-litter can enhance soil carbon storage and CPMI, but root-litter may be more beneficial for soil carbon pool stability. These results further contribute to the understanding of the continuous system of litter-soil carbon pools.