High density invasion by the shrub Ardisia crenata in Florida, USA is associated with altered soil chemical properties and microbial communities

Invasive plants can reshape soil ecosystems by altering chemical conditions and microbial communities. However, field evidence for how these effects scale with invader density, and whether responses are nonlinear, remains limited. We examined whether local stem density of the invasive shrub Ardisia crenata is associated with shifts in soil chemistry and soil microbiomes. The local density of A. crenata , which reproduces clonally with apomictic seeds, forms a gradient from high density to low density across invaded stands. Our results show strong differences in soil ecosystems with invasion, including consistently lower soil moisture, pH, organic matter, total carbon, total nitrogen, and electrical conductivity. These changes were accompanied by shifts in the community composition of soil prokaryotes and fungi, such as increased abundances of Acidothermus and Saitozyma with higher density of A. crenata . While the exact mechanisms causing these changes could not be established, increases of more labile above- and below-ground litter, as well as A. crenata specific secondary metabolites, were possible causal factors. We conclude that strong changes in soil ecosystems can be caused by invasive plants in a mesic forest understory, especially when they occur at high densities. Hence, to maintain healthy soil ecosystems, it is recommendable to control aggressive invasive plants such as A. crenata before they reach high densities.