Coastal marshes keep pace with sea-level rise through vertical accretion, whereby the elevation of the marsh surface increases through the deposition of inorganic sediment and accumulation of organic matter. Both processes are mediated by marsh vegetation, therefore it is important to determine the factors that govern plant traits such as growth, density, and biomass allocation to roots and shoots. It is known that environmental factors such as sea-level rise, salinity, and atmospheric CO2 influence marsh plant productivity, which in turn modifies accretion rate. Further, a growing body of work across a variety of ecosystems suggests that intraspecific genetic variation and diversity in plant populations can influence ecosystem-level processes by mediating plant functional traits such as productivity. We conducted a common garden experiment to assess whether productivity differs according to intraspecific genetic variation and diversity of a dominant marsh sedge, Schoenoplectus americanus. Genotypes used in the experiment were seeds “resurrected” from varying depths in marsh soil profiles, and were then divided by depth into modern and ancestral cohorts. There is compelling evidence that the genetic structure of S. americanus populations has changed considerably over the past century. Thus, our experimental design allowed us to ask whether modern genotypes are better adapted to current climatic conditions compared to ancestral genotypes, as this would suggest populations may have evolved via adaptation in response to global climate change.
Results/Conclusions
We found considerable differences in productivity across genotypes, with genotypic identity explaining 40% of observed variability in aboveground biomass. At the extreme, one genotype produced nearly twice as much biomass as another, on average. However, there were not consistent differences in productivity between ancestral and modern cohorts, and diverse experimental plots performed similarly, on average, to plots composed of clones of a single genotype. While these findings illustrate that there is heritable variation in plant productivity, it will also be important to determine whether there are environmental conditions that amplify or dampen differences among genotypes. Quantifying the intraspecific differences in plant functional traits is important for understanding marsh accretion and contributes to the greater effort of forecasting the uncertain fate of coastal marshes.