Evaluating the role of evolutionary change in the growth of wetland plants over the last century

Background/Question/Methods

The impact of anthropogenic CO₂ production on terrestrial primary production depends on the complex pools and fluxes of the global carbon budget. In coastal salt marshes, the growth of plants, which is mediated by CO₂ and indirect effects of CO₂ such as sea level rise, has a large impact on ecosystem processes.  We investigated the growth performance of an ecologically important C₃ coastal sedge, Schoenoplectus americanus across much of its range and over the past 100 years. Previous studies have shown that biomass allocation to different tissues within this species affect its competitive success and the ecosystem function of the salt marsh as a whole, but did not consider how evolution might alter tissue allocation over time. We hypothesized that genetically determined plant growth rates and tissue allocation would vary over space and in place over time. We grew replicated clones of individuals from across the species’ Atlantic Coast range and of individuals revived from sediments in a Maryland salt marsh deposited over the last 100 years under controlled CO₂ and salinity levels both alone, and in competition with their natural competitor, the C₄ grass, Spartina patens. We measured growth rates and biomass allocation to above and below ground tissues, to determine the extent to which observed genetic changes in this species correspond to changes in carbon storage potential through time.

Results/Conclusions

As expected, plants grown in elevated CO₂ were larger in final mass across all pools examined. We also found significant differences in growth among populations and through time in response to CO₂ and salinity. Our competition treatment was too weak to demonstrate a significant growth response. Overall, genetic changes significantly affected the performance of this species over time and space, illustrating the potential for evolution to alter ecosystem dynamics over centennial scales.