Response of soil phosphorus fractions and bioavailability to native aquatic vegetation restoration in different types of degraded lakeside wetlands.

Phosphorus (P) fundamentally limits productivity and drives eutrophication in lakeside wetlands, yet these P-sensitive ecosystems are increasingly threatened by native vegetation degradation and exotic plant invasion. We hypothesized that restoring native aquatic vegetation would enhance bioavailable P in nutrient-depleted degraded bare lands but reduce it in nutrient-rich invaded wetlands. To test this hypothesis, we conducted a one-year in-situ experiment in two degraded lakeside wetlands (degraded bare land and Myriophyllum aquaticum-invaded land), applying two native plants (Myriophyllum spicatum and Ludwigia peploides) alongside unplanted controls. Soil samples were collected in summer and winter. Using Partial Least Squares Path Modeling (PLS-PM) and Random Forest analysis, we evaluated the impacts of soil physicochemical properties, extracellular enzymes, and microbial biomass on P fractions. Results showed that, compared to unplanted controls, native restoration in bare land significantly improved soil physicochemical properties, significantly increasing bioavailable P by 39.57%, a surge driven directly by reduced soil pH and elevated acid phosphatase (AP) activity. Conversely, relative to the unmanaged invaded baseline, replacing M. aquaticum with native plants significantly decreased bioavailable P by 31.96%, directly resulting from diminished microbial biomass and AP secretion associated with the loss of the invader. PLS-PM revealed that soil physicochemical properties indirectly regulated P bioavailability by reshaping nutrient stoichiometry, with labile inorganic P being the fraction most significantly altered by restoration treatments. These findings emphasize that native vegetation restoration exerts degradation-type-dependent effects on soil P cycling, providing crucial data-supported mechanisms for targeted wetland rehabilitation and precise soil P management.