Abstract:

By investigating and comparing the vertical distribution pattern of soil carbon with different densities along the soil profile in the subtropical forest ecosystem, this study analyzed the important role of different types of soil in the decomposition, fractionation, deposition and preservation of carbon elements with varying densities in the forest ecosystem. This study was carried out in the subtropical moist evergreen broad-leaved primary forest ecosystem in Ailao Mountains of Yunnan Province. It took the primary soil of the upstream forest ecosystem and the warp soil of the downstream grassland ecosystem as the research soil types. With the stratified sampling method, we collected soil samples, and observed the vertical distribution pattern of soil organic carbon with different densities in the root layer (0-45 cm) in the soil profile. The study further compared and analyzed the differences between the soil carbon density fractionation method and the potassium dichromate oxidation method for determining soil total carbon. The results showed that the light carbon, middle carbon, heavy carbon and soil total carbon all were distributed in a decaying exponential pattern in the six soil profiles and two soil types, and the contents of the four measurement indicators in each soil layer of the warp soil profile were significantly higher than those of the primary soil profile in the corresponding depth of the soil layer, indicating that the unit volume of warp soil played a greater role in depositing soil carbon than the primary soil. Among the three kinds of soil carbon with different densities, the light carbon content was the lowest, the middle carbon content was the second, and the heavy carbon content was the highest. This finding indicated that most of the soil carbon formed soil aggregates with minerals and could not be directly used by soil microorganisms, soil animals and plant roots. Among the proportions of the three soil carbons with different densities in total soil carbon, the proportions of light carbon and middle carbon decreased with the increase of soil depth, and the proportion of heavy carbon increased with the increase of soil depth, indicating that different soil layers played different roles in depositing and preserving soil carbon with varying densities. The results of this study expand the scope and dimension of the research on the deposition rate and storage of soil carbon with different densities in various types of soil profiles in tropical and subtropical forest ecosystems.

Key words: soil profile, soil light carbon, soil middle carbon, soil heavy carbon, sodium polytungstate, subtropical moist evergreen broad-leaved forest in Ailao Mountains, primary soil