Clipping-and-burning alters carbon and nitrogen cycling through bacterial fixation pathways in the key Chinese karst...

Clip-and-burn is a forestry and land management technique common in China and other tropical regions worldwide to clear land for agriculture or to manage vegetation. However, the dynamics of carbon and nitrogen in karst regions following clip-and-burn practices remain largely unknown. Here, we evaluate the impact of clip-and-burn management practices on carbon and nitrogen cycling in the Karst region of China. The treatments included high-intensity fire (HIF), low-intensity fire (LIF), clipping and fire (CF), clipping (CP), and control (CK). Soil samples were collected one year after treatment application. Clipping-and-burning significantly influenced soil organic carbon (SOC), total nitrogen (TN), nitrate (NO₃^-), and ammonium (NH₄⁺) levels compared to the control. Clipping-and-burning treatments significantly (p < 0.05) reduced SOC, soil organic matter, TN, and NO₃^- compared to CK. In contrast, NH₄⁺ content increased substantially under clip-and-burn treatments compared to CK, suggesting it potentially affects soil fertility and the recovery of plant life in the post-fire environment. Clipping-and-burning treatments showed higher Acidobacteria and Proteobacteria, likely driving C and N cycling, with Proteobacteria involved in N transformations. The higher bacterial diversity in LIF indicates more active nutrient cycling, with Actinobacteria indicating the importance of organic matter availability and nutrient balance. Moreover, CP significantly (p < 0.05) enhanced the metabolic potential for various N cycle processes, including N fixation, N uptake, and assimilatory NO_3^- reduction. On the other hand, CP also showed higher gene levels for N fixation than other treatments, indicating its effectiveness in promoting N assimilation in the soil. In addition, microbial biomass C, microbial biomass N, and microbial biomass P were significantly (p < 0.05) increased (by 10.70 %, 11.90 %, 25.60 % respectively) under CP treatment compared to CK. The changes in bacterial composition and diversity could have important implications for soil fertility, nutrient availability, and ecosystem functioning, particularly in terms of C sequestration and N availability in plants in the karst landscape. It suggests that careful fire management and selective clipping could enhance soil health and ecosystem productivity.