Does invasive submerged macrophyte diversity affect dissimilatory nitrate reduction processes in sediments with varying microplastics?

Nitrogen removal is essential for restoring eutrophic lakes. Microorganisms and aquatic plants in lakes are both crucial for removing excess nitrogen. However, microplastic (MP) pollution and the invasion of exotic aquatic plants have become increasingly serious in lake ecosystems due to human activity and plant-dominant traits. This field mesocosm study explored how the diversity of invasive submerged macrophytes affects denitrification (DNF), anammox (ANA), and dissimilatory nitrate reduction to ammonium (DNRA) in lake sediments with varying MPs. Results showed that invasive macrophytes suppressed DNF rates, but DNRA and ANA were less sensitive than DNF to the diversity of invasive species. Sediment MPs increased the biomass of invasive species more than native species, but did not affect microbial processes. The effects of MPs on nitrate dissimilatory reduction were process-specific. MPs increased DNF rates and the competitive advantage of DNF over DNRA by changing the sediment environment. The decoupling of DNF and ANA was also observed, with increased DNF rates and decreased ANA rates. The study findings suggested new insights into how the invasion of exotic submerged macrophytes affects the sediment nitrogen cycle complex environments. The nitrate dissimilatory reduction process is vital for freshwater ecosystem stability. It is crucial to understand how the process will be affected by MPs pollution and invasive aquatic plants. We found that responses of nitrate dissimilatory reduction on invasive species diversity are process-specific. However, the MPs in sediments have been found to interfere with macrophyte impacts. Our finding indicates that MPs drive the evolution of sediment environments towards a suitable denitrification (DNF), thereby increasing DNF rates and competitive advantage over DNRA. These results contribute to a better understanding of the ecological effects of MPs and exotic submerged macrophyte diversity.