Vegetation restoration affects the carbon cycle of terrestrial ecosystems by changing the rate of carbon input and conversion. In order to explore the evolution characteristics of soil active organic carbon components and carbon pool management index during vegetation restoration in karst areas, the soil of a grassland sequence(5, 10, 15, and 20 a), shrub sequence(5, 10, 15, and 20 a), and garden sequence(5, 10, and 15 a) in a karst area was taken as the research object, and the adjacent farmland was taken as the control(CK). The effects of different vegetation restoration years on the evolution of soil organic carbon(SOC), readily oxidizable organic carbon(ROC333, ROC167, and ROC33 were all soil active organic carbon that could be oxidized by 333, 167, and 33 mmol·L-1 KMnO4), microbial biomass carbon(MBC), dissolved organic carbon(DOC), and carbon pool management index(CPMI) were analyzed. The results showed that compared with that of CK, the average grassland, shrub, and garden SOC contents in the 0-40 cm soil layer increased by 70.77%, 114.40%, and 50.17%, respectively. In the 0-20 cm soil layer, with the increase in restoration years, the SOC content of the grassland sequence and garden sequence increased first and then decreased, and that of the shrub sequence increased first, then decreased, and then increased again. ROC333, ROC167, and ROC33 were consistent with the SOC change trend of the corresponding sequence. In the 20-40 cm soil layer, the change trend of ROC333, ROC167, and ROC33 of each sequence was inconsistent with the SOC of the corresponding sequence. In the 0-40 cm soil layer, the MBC content of the grassland sequence decreased first, then increased, and then decreased, and the maximum value of MBC in each soil layer was in G15. The shrub sequence in the 0-10 cm soil layer increased first, then decreased, and then increased, and in the 10-40 cm soil layer it increased first and then decreased. The garden sequence increased first and then decreased in the 0-30 cm soil layer and gradually increased in the 30-40 cm soil layer. Kos of the three sequences decreased first, then increased, and then decreased, whereas L and LI showed the opposite of Kos. CPI increased first and then decreased; the CPMI of the grassland and garden sequences increased first and then decreased, whereas the CPMI of the shrub sequence increased first, then decreased, and then increased again. The contents of SOC, ROC333, ROC167, ROC33, and MBC and the annual growth of Kos were shrub>grassland>orchard, and the annual growth of DOC and CPMI were orchard>grassland>shrub. The contents of SOC and its components in the three sequences decreased with the increase in soil layer and had obvious surface aggregation. Redundancy analysis showed that alkali-hydrolyzable nitrogen(AN) was the main environmental factor affecting soil active organic carbon components and soil organic carbon pool under the vegetation restoration in the karst area. In summary, soil active organic carbon components and CPMI evolved with vegetation restoration years. Different vegetation restorations could increase the content of SOC and its components in karst areas to a certain extent, and shrub restoration promotes the accumulation of SOC.
Keywords: active organic carbon components; carbon pool management index(CPMI); evolution characteristics; karst region; soil; vegetation restoration.