Soft plant traits predict variation in underwater photosynthesis along an inundation gradient in salt marshes

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Authors: De Battisti D.1*, Ravaioli E.1, Comandini P.1, Airoldi L.1,2, A. Barausse1,2
Affiliations:
1Chioggia Hydrobiological Station “Umberto D’Ancona”, Department of Biology, University of Padova, Chioggia, Italy
2National Biodiversity Future Center (NBFC), Piazza Marina 61, 90133 Palermo, Italy

Abstract

A central goal in trait-based ecology is to develop predictive models of community assembly along environmental gradients. However, progress is limited because relationships between traits and environmental factors remain poorly demonstrated in many ecosystems.
Here, we address this gap in salt marshes by testing whether easily measurable (i.e., soft) plant traits can predict variation in underwater photosynthesis, a key functional (i.e., hard) trait that directly determines plant performance under inundation. We quantified underwater photosynthesis in dominant species from contrasting marsh zones along an inundation gradient of the Venice Lagoon－a recognized biodiversity hotspot in the Mediterranean Sea. Photosynthesis was measured based on oxygen fluxes under controlled laboratory conditions and related to leaf area, specific leaf area, leaf dry matter content, and plant height.
All species consumed oxygen underwater, but some exhibited reduced consumption under light, indicating that underwater photosynthesis partially offset respiration. This ability was not confined just to pioneer-low marsh species and, while unrelated to leaf area and specific leaf area, was negatively correlated with leaf dry matter content and plant height.
Our results confirm that underwater photosynthesis occurs in salt marsh plants but suggest that species adopt different strategies to cope with inundation. Smaller species (e.g., Salicornia veneta) rely on resistance via underwater photosynthesis, whereas taller species (e.g., Spartina maritima) adopt an escape strategy, maintaining contact with the atmosphere. Overall, soft traits can help predict variation in underwater photosynthesis, a hard trait underlying species responses to inundation, thereby improving mechanistic models of community assembly and biogeochemical processes in salt marshes.