The "Nitrogen Fixation-Nitrogen Preemption" Mechanism of thomson kudzu in Suppressing the invasive weed Mikania micrantha: Nitrogen Cycle Remodeling and Light-Nitrogen Synergistic Suppression

Aims This study investigated how the native legume thomson kudzu and non-legume sweet potato suppress the invasive weed M. micrantha, focusing on nitrogen fixation's role in competitive outcomes. Methods We conducted controlled experiments measuring biomass, nitrogen content (using ¹⁵N natural abundance method), PNUE and microbial communities (via high-throughput sequencing). Competitive indices and random forest modeling identified key success factors. A 12-month field validation experiment was conducted to assess long-term suppression efficacy under natural conditions. Results Thomson kudzu showed superior suppression: (1) Thomson kudzu planted with M. micrantha significantly increased soil nitrogen levels, elevating total nitrogen, ammonium nitrogen, nitrate nitrogen, and microbial biomass nitrogen by 16.88%, 25.87%, 8.98%, and 37.63% respectively, whereas sweet potato planted with M. micrantha reduced these indicators by 3.4%, 14.4%, 12.3%, and 15.6%. (2) Co-planting with M. micrantha markedly enhanced nodulation in thomson kudzu, increasing nitrogenase activity by approximately 253%. (3) Thomson kudzu exhibited significantly higher phosphorus-nitrogen utilization efficiency (PNUE) than M. micrantha. (4) Thomson kudzu demonstrated stronger competitive ability (with a competitive index of 0.76, substantially higher than sweet potato's 0.36). (5) Field validation confirmed the sustained suppression of M. micrantha growth (coverage < 1%). Conclusions Thomson kudzu's "nitrogen amplification-preemption" strategy effectively controls invasives through nitrogen cycling optimization and multidimensional competition, offering an eco-friendly alternative to chemical control.