Multi-functional trait-based community stability reveals climate-driven environmental filtering on riverine...

Understanding how climate-driven environmental changes shape the community stability of phytoplankton in rivers is crucial for maintaining freshwater ecosystem services and functions. Here, a novel evaluation framework of phytoplankton community stability was developed based on 21 functional traits of eight categories relevant to climate-driven environmental gradients. The proposed framework was applied to evaluate the compositional stability of phytoplankton communities in 16 rivers flowing through a transitional climate zone of China. The results indicated that both species and functional trait compositions significantly differed between communities from the northern (semi-humid) and southern (humid) slopes of the Qinling Mountains across seasons. Algae with large cell volume, defense, and photosynthesis traits were present at higher abundances on the northern slope, while algae with medium cell volume and mobility traits preferentially occurred on the southern slope. Community stability analysis revealed that in contrast to species composition, functional trait composition was less stable on the northern slope than on the southern slope. Due to stronger environmental filtering on the northern slope, closer associations emerged between species and functional traits within phytoplankton communities, reducing functional redundancy and thus compromising trait composition stability. The findings underscore the importance of integrating functional traits with species-based methods in comprehensive evaluation of phytoplankton community stability in rivers. Our new framework provides a powerful tool to unravel the impacts of climate-driven environmental filtering on the stability of riverine phytoplankton communities through a functional trait lens.