Ecosystem multifunctionality and stability are enhanced by macrophyte richness in mesocosms

Diverse communities are more productive than less diverse ones because of two overyielding mechanisms: a selection effect and a complementarity effect, which operate in different ways. Moreover, ecosystem multifunctionality is expected to increase and become more stable with increasing species diversity. However, it is unclear how the aforementioned processes operate in aquatic ecosystems, where the overyielding mechanisms, ecosystem multifunctionality, and stability have been poorly explored. Here, we conducted an experimental study manipulating three levels of macrophyte richness to test two hypotheses: (i) the positive macrophyte richness effect on community biomass production is the result of the species complementarity effect; (ii) ecosystem multifunctionality and its stability increase with macrophyte richness. We found that macrophyte species increased their biomass production in high richness treatment, evidencing overyielding, which occurred through a significant complementarity effect. Macrophyte richness also enhanced ecosystem multifunctionality, and made it more stable over time, but only in high richness treatment. Our study shows that preserving high macrophyte richness is essential to preserving the ability of aquatic communities and ecosystems to sustain their functioning.