Microplastics promote the invasiveness of invasive alien species under fluctuating water regime

Abstract Microplastic (MP) pollution and alien plant invasions are two important threats to terrestrial ecosystems. Microplastics alter the physical and chemical characteristics of soil, potentially affecting the performance of alien plants. However, previous studies have overlooked the impact of weather on invasive plants in areas polluted by MPs. With the global increase in extreme rainfall events, it is imperative to redefine the correlation between MPs and invasive plants. Here, we conducted an experiment in a climate chamber to examine the effects of MPs on the growth and development of both native and invasive alien plants under constant and fluctuating water regime (FWR). The FWR simulated extreme water pulses during the 2016–2020 growing seasons in Wuhan, China. Our results indicated that biomass accumulation and root development were influenced by water conditions and MP pollution in both invasive and native species. The extent of the effects varied between the two groups of plant species. FWR promoted plant growth and fine root development in invasive plants but reduced the maximum quantum efficiency of photosystem II ( F v / F m ) and nonphotochemical quenching ( NPQ ) indices of native plants. Moreover, FWR attenuated the negative effects of polybutylene succinate (PBS, degradable MPs) on biomass and root characteristics (length, surface area and tips). FWR compensated the negative impacts of MPs on the total and below‐ground biomass of the invasive species Paspalum dilatatum and Sphagneticola trilobata , but not on the native species. Consequently, invasive species showed better performance than native species in the fine root development of biomass growth and chlorophyll fluorescence under the combined effects of MPs and FWR. Synthesis and applications . Our findings suggest that MP pollution enhances the competitiveness of invasive alien species over the native species when exposed to pronounced dry–wet water cycle conditions, potentially affecting the composition and biodiversity of the ecosystems. Thus, controlling MP pollution should be a part of the management strategy to conserve biodiversity and ecosystems.