COS 12-2 - CANCELLED - Complex eco-evolutionary interactions drive coastal marsh plant responses to global change

Background/Question/Methods

Coastal marshes provide vital ecosystem services and are often dominated by plants that act as ecosystem engineers, influencing key attributes like marsh surface soil building and carbon sequestration. Thus, in order to best predict the fate of coastal marshes in a rapidly changing climate, it is imperative to understand how plant traits shift in response to global change. Increasing evidence indicates that complex interactions between global change factors drive trait change. Additionally, evidence of the rapid evolution of functional traits in Schoenoplectus americanus (a common marsh sedge) suggests that evolutionary processes may regulate trait shifts in response to global change. Here, we conducted a large mesocosm experiment using S. americanus to assess the relative role of plastic (i.e., “ecological”) and genetically-based (i.e., “evolutionary”) responses of its functional traits to global change factors. We exposed replicates of 32 genotypes ‘resurrected’ from soil-stored seed banks, derived from two provenances and within two age cohorts (ancestral: ca. 1900-1950; descendant: ca. 2000-2020), to either ambient or elevated CO2 and varying levels of sea-level, across two sites with different salinities. We also tested for the effect of the presence of a naturally co-occurring marsh grass, Spartina patens, on S. americanus traits.

Results/Conclusions

We found significant higher order interactions between global change factors and the age or provenance of S. americanus genotypes (e.g., four-way and three-way interactions) for traits such as aboveground biomass and root-to-shoot ratio, which are traits important in mediating ecosystem processes. For example, a stimulating effect of elevated CO2 on aboveground biomass at low elevations only existed for ancestral genotypes in brackish conditions and for descendant genotypes in more freshwater conditions (CO2 × elevation × salinity × age cohort, F1,182.6 = 7.06, p = 0.009). Accounting for evolutionary processes in statistical models explained an additional 9-28% of observed trait variation compared to models that accounted for plastic trait responses alone. Interestingly, the complex eco-evolutionary responses of traits found when S. americanus was in isolation were dampened when grown in competition with S. patens (CO2 × elevation × salinity × age cohort × competition, F1,243.9 = 5.23, p = 0.023). Our work suggests that evolutionary processes mediate complex ecological interactions indicating that evolutionary dynamics should be integrated into predictive models of near-term ecosystem dynamics.