Carbon dioxide fluxes reflect plant zonation and belowground biomass in a coastal marsh

Coastal wetlands are major global carbon sinks; however, they are heterogeneous and dynamic ecosystems. To characterize spatial and temporal variability in a New England salt marsh, greenhouse gas (GHG) fluxes were compared among major plant‐defined zones during growing seasons. Carbon dioxide ( CO 2 ) and methane ( CH 4 ) fluxes were compared in two mensurative experiments during summer months (2012–2014) that included low marsh ( Spartina alterniflora ), high marsh ( Distichlis spicata and Juncus gerardii ‐dominated), invasive Phragmites australis zones, and unvegetated ponds. Day‐ and nighttime fluxes were also contrasted in the native marsh zones. N 2 O fluxes were measured in parallel with CO 2 and CH 4 fluxes, but were not found to be significant. To test the relationships of CO 2 and CH 4 fluxes with several native plant metrics, a multivariate nonlinear model was used. Invasive P. australis zones (−7 to −15 μmol CO 2 ·m −2 ·s −1 ) and S. alterniflora low marsh zones (up to −14 μmol CO 2 ·m −2 ·s −1 ) displayed highest average CO 2 uptake rates, while those in the native high marsh zone (less than −2 μmol CO 2 ·m −2 ·s −1 ) were much lower. Unvegetated ponds were typically small sources of CO 2 to the atmosphere (