Abstract:

Microorganisms are key drivers of the carbon cycle, and soil erosion is a major force that causes carbon loss. Investigating the mechanisms of soil erosion on soil microorganisms and soil organic carbon (SOC) is of great significance for understanding the coupling mechanisms of erosion, microbial communities, and carbon cycling. We conducted a simulated erosion experiment using the “cutting-and-filling” method from 2012 in a typical mountain area. A completely randomized design with five soil erosion thicknesses (5, 10, 20, 30, and 40 cm) and a control (0 cm) was employed. Each treatment was performed in triplicate. Using phospholipid fatty acid (PLFA) and structural equation modeling (SEM) analysis, we found that 1) SOC and dissolved organic carbon (DOC) decreased in a quadratic pattern with the intensification of erosion, and there was a nonlinear relationship. The total PLFAs, fungal, bacterial (Gram-positive [G⁺], Gram-negative [G⁻]), actinomycete, and arbuscular mycorrhizal fungal (AMF) abundance significantly decreased with increasing erosion (p<0.05), whereas fungal/bacterial ratios and G⁺/G⁻ significantly increased (p<0.05). 2) Multi-response permutation procedure (MRPP) analysis confirmed significant differences in soil microbial communities under varying erosion intensity (δ=0.189, p=0.001), demonstrating that erosion intensity directly regulates microbial composition. 3) SEM revealed that erosion directly explained 89.0% of SOC loss, while the decline in DOC was jointly driven by the direct effect of erosion (69.1%) and microbial mediation (53.6%), with reduced bacterial and G⁻ gram positive GPLFAs serving as key indirect pathways. These findings indicate that SOC loss primarily results from erosion-induced reduction in soil mass, whereas DOC depletion is mainly mediated by the reduction in microbial PLFA content caused by soil erosion. This study provides a theoretical basis for soil erosion control and carbon management in southwestern China.

Key words: soil erosion, soil organic carbon, soil microbial diversity, phospholipid fatty acids (PLFA), carbon cycle

摘要：

微生物是影响碳循环的关键驱动者，土壤侵蚀是造成碳损失的驱动力。研究土壤侵蚀对土壤微生物和土壤有机碳（SOC）的影响机制，对理解侵蚀-微生物-碳循环的耦合机制具有重要意义。于2012年开始，在元江流域典型黄红壤区，采用“削土-配土”法开展模拟侵蚀实验。实验采用完全随机设计，设置5个土壤侵蚀厚度处理（5、10、20、30和40 cm）和对照（0 cm），每个处理设3次重复。结合PLFA和结构方程模型（SEM）分析发现，1）SOC和溶解性有机碳（DOC）随侵蚀加剧呈二次函数下降，并而呈非线性关系。总PLFAs、真菌、细菌、G⁺、G⁻、放线菌和AMF含量随侵蚀增加显著降低（p<0.05），真菌/细菌与G⁺/G⁻比值显著上升（p<0.05）。2）多响应置换过程分析（MRPP）证实了不同侵蚀程度的土壤，其微生物群落差异显著（δ=0.189，p=0.001），表明侵蚀厚度直接调控微生物组成。3）SEM揭示侵蚀直接解释89.0%的SOC损失，而DOC下降由侵蚀直接作用（解释率69.1%）和微生物介导（解释率53.6%）共同驱动，其中细菌与G⁻减少是关键间接路径。这表明SOC损失主因是土壤侵蚀厚度改变引起的土壤质量损失，但DOC的损失主要是由于土壤侵蚀引发的微生物PLFAs含量降低介导的。该研究为西南地区水土流失治理和碳库管理提供了理论依据。

关键词: 土壤侵蚀, 土壤有机碳, 土壤微生物多样性, 磷脂脂肪酸（PLFA）, 碳循环