Different short-term responses of greenhouse gas fluxes from salt marsh mesocosms to simulated global change drivers

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Salt marshes are valued as important greenhouse gas (GHG) sinks, but global changes in climate, nitrogen (N) pollution, and exotic species invasion may alter this marsh function. With the goal of better understanding the potential responses of coastal marsh GHG fluxes to interacting global changes, a multifactorial experiment was conducted. Two climate treatments (present-day and end-of-century temperatures and carbon dioxide (CO2) concentrations) and two N treatments (non-enriched and simulated eutrophic estuary conditions) were applied to mesocosms containing either invasive Phragmites australis (Cav. Trin. Ex Steud.) or native Spartina patens (Aiton) Muhl. vegetated soil cores. Fluxes of CO2, methane (CH4), and nitrous oxide (N2O) were measured in each mesocosm before and after treatment using cavity ring-down spectrometry, along with vegetation growth, edaphic conditions, and pore water chemistry. Methane emissions increased in P. australis but not in S. patens mesocosms under climate change conditions, while CO2 fluxes were similar between vegetation types and treatments. Nitrous oxide emissions increased with N loading from both S. patens and P. australis mesocosms, but were decreased in N-enriched S. patens mesocosms under climate change conditions. These findings demonstrate complex GHG flux responses to global change and suggest the potential for vegetation community-specific responses, though further research is needed to test mechanisms underlying observed GHG flux patterns.

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