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The leaf economic spectrum of freshwater plant communities
Lindsay Louise Trottier, Francisca Aguiar, Janne Alahuhta, Lukács Balázs András, Lars Båstrup-Spohr, Vincent Bertrin, Sebastian Birk, Sébastien Boutry, Christian Chauvin, Frauke Ecke, Tõnu Feldmann, Cindy Gao, Jorge García-Girón, Daniel Gebler, Gana Gecheva, Gerben J. van Geest, Willem Kaijser, Pierre Maud, Yingji Pan, Maija Toivanen, and Lars L. Iversen
Freshwater ecosystems are of worldwide importance for maintaining biodiversity and sustaining the provision of a myriad of services to modern societies. In the terrestrial plant realm, the leaf economic spectrum has bridged the gap between biodiversity gradients and ecosystem functions, providing a framework for the underlying mechanisms driving ecosystem and biodiversity change. However, it is still unclear to what extent such a framework applies to aquatic plant communities and how unique adaptations to life in water shape the functional biogeography of freshwater organisms. Here, we show that variation in leaf phenotypes of aquatic plant communities is a product of selection from both general and system-specific trait-environment relationships. Using community data from 6687 European aquatic plant communities, we find that species with an emergent component in their life history follow trait-environment relationships comparable to terrestrial species. For emergent species, high phosphorus concentrations and high mean annual temperatures select for communities with acquisitive leaf traits (low leaf investment and fast growth). In contrast, acquisitive leaf traits in plant communities entirely composed of submerged species were linked to bicarbonate and phosphorus availability, but not temperature. We attribute these differences to freshwater-specific adaptations, where fast-growing species are found in nutrient-rich environments with alternative carbon sources available for photosynthesis (bicarbonate). Alternatively, freshwater plants with an emergent life history invest more in leaf structure, decoupling them from growth-related limitations due to carbon availability in water. These findings highlight the importance and potential of a system-specific approach when linking plant functional traits to freshwater ecosystem functioning and biodiversity.
