Soil pH fitness of residents contributes more to the invasion success of Ralstonis solanacearum than the invader itself

Exploring how abiotic environment affects microbial invasion is a key issue in microbial ecology. Soil pH, as an important environmental variable, plays a vital role in shaping the microbial community and regulating microbial multifunctionality. However, it remains unclear how pH determines microbial invasion success. Based on a series of experiments, we found that the pH fitness of the invader, a typical plant pathogen, was not consistently related to invasion success. Comparatively, the pH fitness of residential members highly affected the established pathogen abundance and plant disease outcome. Accordingly, in the in vivo experiment, compared to the observed soil pH, the underlying pH variation from the initial stable state played a more important role in explaining invasion success, mainly through decreasing the fitness of residential community, represented by community variation extent after pH disturbance. Overall, we demonstrated that invasion success is not only dependent on the environmental fitness of the invader itself, but also, more importantly, is determined by the environmental fitness of residents competing with the invader. Our results suggest the limitations of using observed environmental variables to explain invasion success and highlight the underlying role of environmental change, which highly affects the environmental fitness of residential community.