Abstract
Abstract Aquatic plant meadows are important coastal habitats that sustain many ecosystem functions such as primary production and carbon sequestration. Currently, there is a knowledge gap in understanding which plant functional traits, for example, leaf size or plant height underlie primary production in aquatic plant communities. To study how plant traits are related to primary production, we conducted a field survey in the Baltic Sea, Finland, which is characterized by high plant species and functional diversity. Thirty sites along an exposure gradient were sampled (150 plots), and nine plant morphological and chemical traits measured. The aim was to discern how community‐weighted mean traits affect community production and whether this relationship changes along an environmental gradient using structural equation modelling (SEM). Plant height had a direct positive effect on production along an exposure gradient (r = 0.33) and indirect effects through two leaf chemical traits, leaf δ15N and leaf δ13C (r = 0.24 and 0.18, respectively) resulting in a total effect of 0.28. In plant communities experiencing varying exposure, traits such as root N concentration and leaf δ15N had positive and negative effects on production, respectively. Synthesis. Our results demonstrate that the relationship between aquatic plant functional traits and community production is variable and changes over environmental gradients. Plant height generally has a positive effect on community production along an exposure gradient, while the link between other traits and production changes in plant communities experiencing varying degrees of exposure. Thus, the underlying biological mechanisms influencing production differ in plant communities, emphasizing the need to resolve variability and its drivers in real‐world communities. Importantly, functionally diverse plant communities sustain ecosystem functioning differently and highlight the importance of benthic diversity for coastal ecosystem stability.
Highlights
There is general consensus that species identity and the functional traits of species are key to understand the role of biodiversity for ecosystem functioning and how ecosystems respond to environmental disturbance (Díaz & Cabido, 2001; Lavorel & Garnier, 2002)
In contrast to the various terrestrial studies that have focused on continuous plant functional traits (e.g., leaf nitrogen concentration (Leaf N), Specific leaf area (SLA)) and the links to ecosystem functioning (Garnier et al, 2016), this is to our knowledge, the first study that explores the relationship between continuous aquatic plant traits and primary production along an environmental gradient
Our results demonstrate that the relationship between plant traits and production is variable and context-dependent, and this further emphasizes the importance of trying to resolve variability in real-world communities
Summary
There is general consensus that species identity and the functional traits of species are key to understand the role of biodiversity for ecosystem functioning and how ecosystems respond to environmental disturbance (Díaz & Cabido, 2001; Lavorel & Garnier, 2002). The species composition and dominance changes between the archipelago zones with marine, biomass-storing species, such as Zostera marina and Ruppia spp., being common in the more exposed, saline outer areas, while limnic canopy-forming species, for example, Potamogeton spp. and Myriophyllum spp. occur more frequently in sheltered, less saline inner areas (Kautsky, 1988; Pitkänen, Peuraniemi, Westerbom, Kilpi & von Numers, 2013) Some of these species such as Stuckenia pectinata show significant morphological phenotypic plasticity, which may reflect in certain traits exhibiting high intraspecific variability, for example, root:shoot ratio or leaf area (Garnier et al, 2016; Kautsky, 1987). The gradient approach taken in this study further allows us to better understand how the changes in the species composition and dominance patterns and the potential plastic responses in intraspecific trait values might affect community primary production differently along an exposure gradient, and we predicted the links between plant effect traits and primary production to change between archipelago areas. Despite some traits potentially changing along the gradient (response traits) and overlapping with the measured effect traits (Lavorel & Garnier, 2002; Suding et al, 2008), our study aimed at solely evaluating the link between effect traits and production
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