Environmental gradients strongly affect functional composition and biomass C stocks within aquatic plant meadows

Abstract

Ecological succession provides a critical framework to evaluate and predict the effects of successional dynamics within plant communities on ecosystem functions, which has become increasingly relevant in recent years as humans adapt to a world that is progressively shaped by anthropogenic disturbances. To date, we lack a mechanistic understanding of how environmental gradients shape succession of functional diversity within aquatic plant communities, complicating our ability to predict the C sink potential of aquatic plant meadows. This makes it imperative to explore the factors underlying shifts in functional community structure and associated functions provided by aquatic plants across broad environmental gradients. We conducted a field survey in August–September 2023, where we sampled 20 soft-bottom sites along a strong (50 km) gradient of environmental variables (i.e., exposure and salinity) in the northern Baltic Sea. Spatial differences in the functional community structure and biomass-bound C stocks were influenced by an interplay between wave exposure, depth and salinity. The functional community structure of aquatic plant meadows shifted from more conservative strategies under high hydrodynamic forces to more acquisitive strategies under relatively benign environmental conditions. Functional trait variation across meadows was driven by both intraspecific variation (ITV) and species turnover, but their relative role was highly variable. Biomass-bound C stocks were mainly influenced by light availability. Overall, our study illustrates the importance of addressing ITV and that the functional community structure and biomass-bound C stocks of aquatic plant meadows were shaped by an interplay between wave exposure, depth, and salinity. This highlights the complexity in assessing ecosystem services provided by vegetated coastal ecosystems and the need to improve our understanding of the relationships among the environment, species traits, and ecosystem functioning for developing effective measures of ecosystem conservation.