NO₃^--N pulse supply caused by biodegradable plastics exacerbates Trifolium repens L. invasion

The exacerbation of plant invasion by microplastics attracted widespread attention. Pulse resource hypothesis is popular theory to elucidate plant invasion. Our previous work demonstrated biodegradable microplastics (BMPs) could increase the arbuscular mycorrhizal fungi (AMF) colonization rate. Reportedly, AMF can enhance rhizobia colonization. Therefore, we infer the coexistence of BMPs with legumes may lead to an increased colonization of rhizobia with negative feedback regulation of N fixation. This could result in NO₃^--N pulse supply, thereby exacerbating plant invasion. Subsequently, a 60-day pot experiment was conducted using Trifolium repens L. as invasive plant and Oxalis corniculata L. as native plant, with 1% or 5% wt BMPs. AMF colonization, BMPs degradation, NO₃^--N content and pulse supply, rhizobia colonization, relative competitive intensity, replacement diagrams and NO₃^--N utilization were determined. The mechanism was clarified through heat map and structural equation model. The results reveal the greater the NO₃^--N consumption by BMPs, the more AMF promoted rhizobia colonization in T. repens, thereby the larger the pulse amplitude of NO₃^--N supply, then, the higher the NO₃^--N utilization rate of T. repens. It exacerbates T. repens invasion. This study clarifies effects of BMPs on rhizobia's N fixation, and enriches the evidence on mechanism of BMPs exacerbating plant invasion.