Degradation of Karst Ecosystem and Soil Organic Carbon Storage

During the process of karst ecosystem degradation (forest-shrub-grass cover change process), the total organic carbon storage of soil decreased significantly, indicating that karst soil changed from atmospheric CO₂ sink to carbon source, which had adverse effects on the atmospheric environment. The vegetation type also changed from C3 vegetation to C4 vegetation, which made soil organic carbon become heavier. The microbial biomass carbon in the active organic carbon component of soil also changed correspondingly, and the microbial biomass carbon in soil layer B decreased significantly, but the content of dissolved organic carbon in soil did not show a significant difference, which may be one of the reasons for the decline of soil organic carbon in degraded karst ecosystem. Therefore, effectively preventing the degradation of the karst ecosystem will significantly promote the role of the karst ecosystem as a sink of atmospheric CO₂ in global change. At the same time, it will play an important role in protecting the biodiversity of the karst ecosystem. The karst forest soil had a high carbon storage, and the organic carbon content in the top soil was as high as 87.12±35.10 g·kg⁻¹, and the organic carbon content in the whole profile was high, and the carbon content in the lower soil layer was higher than that in the lower soil layer of other vegetation types. The degradation of karst ecosystem had not significantly affected the DOC content in karst soil, but from the perspective of the content under the three vegetation conditions, the forest vegetation was the highest, while the shrub land was the lowest and grassland was the lowest. The stable isotope δ¹³C value of organic carbon in karst soil changed from 26.15 ‰ under forest to 25.44 ‰ under shrub, showing a relatively consistent phenomenon with the stable carbon isotope change of plant leaves. After changing into grassland system, the stable carbon isotope δ¹³C value of soil increased significantly, reaching -20.83‰, which also showed the same change as that of vegetation.