Rapid evolution might better enable species to cope with pressures arising from climate change, such as greater inundation and salinity exposure from sea level rise. Soil-stored seed banks are a largely untapped resource for assessing whether at-risk populations evolve in response to climate change corollaries. Prior work has shown that temporal patterns of population genetic variation can be reconstructed from plants ‘resurrected’ from the century-long seed banks of the foundational coastal marsh sedge Olney’s bulrush (Schoenoplectus americanus). In this study, we ‘resurrected’ plants to test the hypothesis that S. americanus exhibits heritable variation in salinity and inundation tolerance, and that tolerance has shifted since the early 20th century. This involved recovering and germinating seeds from radionuclide dated sediment to create ancestral (ca. 1900) and descendant (ca. 2000) cohorts for a common garden exposure experiment. Ancestral and descendant cohorts were each composed of nine genotypes that were cloned out for a multi-factorial set of 24 experimental treatments corresponding to an inundation stress gradient spanning a 60 cm range of elevation, fully crossed with contrasting salinity conditions (15 vs 0 ppt), and competition with a naturally co-occurring species (Spartina patens).
Results/Conclusions
Mean aboveground biomass production differed significantly between the ancestral cohort and descendant cohort, with descendant plants exhibiting greater production. Descendant plants also competed better than ancestral plants, producing greater biomass in competition treatments. Ancestral plants exhibited a higher mortality rate when compared to descendants, with mortality peaking at the deepest inundation level. A factorial ANOVA revealed that interactions between salinity, competition and inundation had the largest effect on biomass. Cohort identity also registered as a key factor in biomass responses to stressor exposure. For example, biomass variance differed by cohort for all stressors, with ancestral plants exhibiting greater variance. These findings indicate that S. americanus exhibits heritable variation in stressor response, and that descendant plants exhibit greater tolerance to pressures related to sea level rise. Though further comparisons are warranted to confirm these findings, this study illustrates that rapid evolution should be accounted for when modeling marsh plant- and by extension, marsh ecosystem- responses to sea level rise and perhaps other climate change corollaries.