Rapid Plant Evolution Could Change Coastal Marsh Adaptability

American Association for the Advancement of Science (AAAS)

Rapid evolution of traits in dominant marsh plants’ root growth can result in ecosystem-level shifts in coastal wetland structure and function, including its resilience to sea level rise, researchers report. The findings suggest that evolutionary processes may play a larger role in regulating ecosystem function than previously thought and need to be accounted for when forecasting ecosystem responses to environmental change. In coastal marshes – which generally have low plant species diversity – dominant plants often act as ecosystem engineers by contributing to soil development and sediment accretion, which has allowed marshes to keep pace with changes in sea level for thousands of years. What’s more, these plants’ rapid growth, combined with the low decomposition rates in coastal marsh soils, result in the ecosystem’s ability to store large amounts of carbon. However, while a growing number of studies show how the traits and growth of dominant marsh plants contribute to these processes, the role of trait variation and evolution are largely overlooked in models that predict ecosystem response to ongoing environmental changes. According to the authors, this is due, in part, to a lack of empirical studies that demonstrate whether evolutionary processes are important drivers of ecosystem change. Here, Megan Vahsen and colleagues report a common garden study of 16 genotypes of the dominant marsh sedge, Schoenoplectus americanus, using plants “resurrected” from seed banks that span generations and neighboring marshes. Vahsen et al.’s study revealed considerable and ecologically meaningful heritable variation and rapid evolution in the allocation and distribution of belowground biomass. These findings, when incorporated into a costal marsh ecosystem model, altered predictions of carbon sequestration and soil surface accretion in costal marshes. According to the authors, the results suggest that these plants can evolve at a pace and magnitude that can have a sizeable downstream impact on ecosystem-level processes, including resilience to sea-level rise and atmospheric carbon storage potential. “Failure to account for heritable variation and rapid evolutionary change in ecosystem models might therefore mischaracterize the role that organismal response plays in ecosystem resilience to environmental change that could systematically alter ecosystem-level predictions.

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