Mechanisms of Biodiversity-Ecosystem Functioning Shift With Flooding Stress

Disentangling how biodiversity facets link to ecosystem functioning is challenging, given the diverse mechanisms involved, including selection effect and niche complementarity along with competition and facilitation. The impact of flooding stress on these mechanisms has further been little explored. We evaluated the contribution of plant richness and identity, functional diversity and competition to community biomass under flooding relative to field capacity. One forb (Asclepias incarnata), one legume (Melilotus officinalis) and two grasses (Alopecurus pratensis and Phalaris arundinacea) were grown under these two water regimes alone or in mixtures. Community-weighted means (CWMs) and variances (CWVs) based on eight plant traits were related to biomass, and net biodiversity, complementarity and selection effects. Aboveground biomass, net biodiversity and selection effects increased with species and functional group richness only at field capacity. Melilotus officinalis increased biomass at field capacity, and P. arundinacea under flooding. Higher contribution of CWVs to biomass was observed at field capacity, and of CWMs under flooding. Flooding strongly influenced plant diversity-ecosystem productivity relationships by limiting species richness effect, modifying the identity of key species and changing the magnitude of complementarity and selection effects. Overall, promoting not only species but also functional diversity could help maintain ecosystem resilience in flood-prone environments.