Abstract
Functional Diversity (FD) experiments are highly effective for investigating how a community interacts with its environment. However, such experiments using morphological and chemical traits have not been conducted for submerged aquatic plants and their insights would be highly valuable for understanding the ecology of these communities. We conducted a 15-week field experiment in the Baltic Sea where we manipulated the species composition of aquatic plant communities to investigate functional diversity. We constructed artificial triculture communities with different species compositions to change the Community Weighted Means (CWMs) and variability of traits. We measured 9 plant traits and tested how community productivity (CP) was related to FD, trait CWMs and community trait ranges. CP varied by more than four times across treatments and functional richness was significantly related to CP. Functional evenness and functional divergence were not significantly related to CP. Height, leaf area and δ¹³C were significantly related to CP. Leaf δ¹³C trends with CP suggested that the carbon supply is not replete, yet species composition was partly responsible for the relationship. Plant height likely had multifaceted benefits to CP because there was evidence of a competitive height interaction between the tallest and 2nd tallest species, therefore the effects of plant height to CP would have been disproportionally large. The height of the tallest species significantly drove the variability of the community height range, which was significantly related to CP and it had a relatively large influence on the calculation of FD indices. Leaf area, which was strongly correlated to plant height, was also significantly related to community productivity. The significant relationship between functional richness and CP was most likely driven by the presence of taller plants. FD likely enhanced CP, by selecting for extreme trait values which enhanced production (selection effect), while niche complementarity effects were not observed. This study provides experimental evidence and mechanistic insights into the role of FD and specific traits for CP in submerged aquatic plant communities. To conclude, FD was significantly related to CP of temperate aquatic plant communities likely by selecting for traits which enhanced light capture, with consequences for carbon supply.
Highlights
Functional diversity experiments are powerful tools for understanding how an ecosystem works (Tilman et al, 1997; Díaz and Cabido, 2001; Hooper et al, 2005; Mouillot et al, 2013; Gagic et al, 2015)
This study has provided evidence that the benefits of aquatic plant height to community production are multifaceted, because the height of the tallest species was significantly related to community productivity, and its height likely stimulated a competitive height response in the community (Figure 3, Hector et al, 1997)
We found that leaf area was significantly related to primary production and that it was significantly correlated with height, strengthening inferences for the potential generality of our findings
Summary
Functional diversity experiments are powerful tools for understanding how an ecosystem works (Tilman et al, 1997; Díaz and Cabido, 2001; Hooper et al, 2005; Mouillot et al, 2013; Gagic et al, 2015). It is likely that functional traits strongly influence ecosystem properties, as suggested by a consensus of literature (Hooper et al, 2005) They can support the biomass production of plants by many potential mechanisms (Pérez-Harguindeguy et al, 2013), for example by enhancing their ability to capture light (Díaz et al, 2004; Gustafsson and Norkko, 2019), to compete for resources against other plants (Gaudet and Keddy, 1988; Cadotte, 2017), or by increasing their access to nutrient pools (Campbell et al, 1991; Kembel et al, 2008; Angove et al, 2018). Species richness affects productivity in temperate submerged aquatic plant meadows (Salo et al, 2009; Gustafsson and Boström, 2011), as can functional traits (Gustafsson and Norkko, 2019) and perhaps these functional traits can be used to explain species effects (e.g., Hillebrand and Matthiessen, 2009)
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