Realm Specific Adaptations Lead to Contrasting Global Patterns in Submerged and Emergent Aquatic Plant Height

ABSTRACT Aim This study aims to evaluate whether the trait–environment relationships known for terrestrial plant height extend to freshwater macrophytes, and to identify the primary environmental factors influencing global height patterns in emergent and fully submerged aquatic plants. Location Global. Time Period Species occurrence records and height measurements compiled from 1931 to 2022. Major Taxa Studied Freshwater plant species. Methods We compiled a global dataset of maximum plant height records for 1735 aquatic plant species, categorised by life form (partially emergent vs. submerged). Using generalised additive models, we tested how plant height varied along latitudinal gradients and how it was related to environmental predictors including temperature, relative inorganic carbon supply, and water depth (indicated by habitat availability). We explicitly analysed whether these relationships differed between the two life forms and validated these patterns using site‐scale species and environmental data from northern temperate lakes and streams. Results Species with emergent growth increase in height with warmer temperature. On the contrary, fully submerged species exhibit increased height with higher inorganic carbon availability and colder climates. At the local scale, submerged plant height is positively associated with relative inorganic carbon supply in lakes and streams of the northern temperate zone. Main Conclusions The relationships between environmental variables and plant height differ between emergent to completely submerged life forms, consistent with realm‐specific patterns in trait‐environment correlations. These differing patterns highlight that trait‐environment coupling in freshwater systems may not parallel those in terrestrial ecosystems and suggest that life form mediates species' responses to environmental variation.