Vallisneria invasion into Myriophyllum community: differential responses of complete ammonia oxidation (Comammox) community in changing rhizosphere environment

AIMS: Species invasion is one of the key issues in global ecosystems. This study investigated the changes in the rhizosphere community structure of complete ammonia-oxidizing (Comammox) bacteria after the invasion of the long-rooted submerged macrophyte Vallisneria spiralis L. into the community of the short-rooted submerged macrophyte Myriophyllum spicatum L. METHODS AND RESULTS: Different planting ratios simulated varying invasion intensities. Increasing invasion intensity significantly altered rhizosphere factors, reduced dissolved organic carbon (DOC), and lowered pH, thereby causing distinct alterations in the rhizosphere environment. Comammox Clade A remained dominant with stable abundance, indicating strong adaptability. In contrast, Clade B abundance increased under low-moderate invasion but declined sharply under high intensity, suggesting a preference for mixed roots or low-intensity invasion. Higher pH and DOC provided a stable niche for Clade A. High invasion intensities elevated NH4+-N and NO3--N concentrations, which coupled with stronger oxidative conditions promoted AOB and certain Clade A subgroups, thereby suppressing the low-nitrogen-adapted Clade B. CONCLUSIONS: This study demonstrates that submerged macrophyte invasion reshapes the rhizosphere environment and drives Comammox community differentiation, offering new insights into plant invasion's ecological effects and nitrogen cycling regulation.