COS 60-1 - Functional traits of Schoenoplectus americanus reflect genetic variation and interspecific competition under conditions of sea-level rise

Background/Question/Methods

Plant traits like belowground biomass are critical for carbon sequestration and accretion in coastal wetlands. Trait expression is mediated by environmental conditions (e.g. sea-level rise, salinity), genetic variability, and community composition. We previously found that genetic variability in Schoenoplectus americanus, a common marsh sedge, explains a substantial proportion of variation in belowground biomass traits. This prompted us to ask, (i) does this variation in belowground traits influence community level changes in species composition, and (ii) does this, in turn, affect carbon cycling? Here, we used a resurrection ecology approach to study 26 genotypes of S. americanus, capturing spatial and temporal genotypic variation by using seeds collected from a soil-stored seed bank representing different sediment age cohorts (n = 2 levels) at two Chesapeake Bay marshes. To estimate the impact of environmental variation on the expression of belowground traits, we conducted a fully crossed sea-level rise manipulation experiment that exposed these genotypes to high and low flooding and salinity, in the presence and absence of Spartina patens, a co-occurring marsh grass. Belowground traits were measured to draw inferences about ecosystem consequences of S. americanus responses to corollaries of global change.

Results/Conclusions

We found that genotypic differences in belowground biomass reflected environmental conditions, species composition, and their interactions. Belowground biomass was significantly lower with higher flooding and salinity (p < 0.001). Specifically, belowground biomass was significantly lower under higher salinity conditions than lower salinity for both flooding frequencies (p < 0.001), with the lowest productivity being under high flooding and salinity. Species composition also interacted with environmental conditions to significantly impact belowground biomass. For instance, while higher salinity decreased belowground biomass regardless of species composition treatment (p < 0.001), a greater reduction was observed under conditions of elevated salinity and without the presence of S. patens (p = 0.005). Notably, mixed effects models with random intercepts for the site-age grouping of S. americanus increased the proportion of explained variance by 11% (marginal R2 = 0.34, conditional R2 = 0.45), suggesting that accounting for genetic variability can better explain belowground processes. Our findings indicate that both genetic variation and interspecific interactions drive trait diversity at a scale that can affect how ecosystems function under globally relevant conditions linked to climate change.