[Structure and Stability of Soil Organic Carbon Pools Along Depth in Forests and Grasslands in the Luya Mountains]

Organic carbon is the most important active component of the soil carbon pool and has an important influence on atmospheric CO₂ concentration. Soluble organic carbon （DOC）， labile organic carbon （LOC）， and recalcitrant organic carbon （ROC） are the main chemical components of the soil organic carbon （SOC） pool， which determine the stability of the carbon pool. Deep SOC accounts for more than half of the total soil organic carbon， but understanding of its structure and stability remains insufficient. In this study， we investigated the structure and stability of the organic carbon pools and their influencing factors in the 0-10， 10-20， 20-40， and 40-80 cm soil layers of typical subalpine forests and grasslands on Luya Mountain. The study produced several important results： ① ω（SOC） of forest and grassland showed a gradual decrease along the depth of the soil layer， within the ranges of 12.54-41.71 g·kg^-1 and 26.04-52.77 g·kg^-1， respectively. The SOC content of the 0-10 cm layer was the highest， and the SOC content of the 40-80 cm layer was significantly lower than that of the 0-40 cm layer. ② There were some differences in the components and stability of the organic carbon pools in forest and grassland soils. The SOC， LOC， and ROC contents in each soil layer of grassland soils were larger than those of forest， while the DOC content in each soil layer of forest soils was larger than that of grassland. ③ There was a highly significant positive correlation between the contents of SOC and ROC （P < 0.01）， and the remaining components of the organic carbon pools were also correlated with each other. Random forest analyses showed that soil physicochemical properties， microbial biomass， and enzyme activities together explained 78.24% and 80.99% of the variation in SOC in forest and grassland soils， respectively， and that total nitrogen， pH， S-ACP， S-NAG， and MBC were significant influencing factors. ④ The stability of SOC in the surface layer of forest and grassland was greater than that in the deep layer， and the ROC content decreased gradually faster with depth of the soil layer. In conclusion， the structure and stability of the deep organic carbon pools in subalpine forest and grassland soils were differentiated， with obvious epimerization characteristics， and biological factors played an important role in maintaining the structure and stability of the soil carbon pools. This study provides data support for the development of differentiated management measures for soil carbon pools in temperate subalpine forests and grasslands.