Seasonal carbon fluxes from vegetation and soil in a Mediterranean non-tidal salt marsh

Abstract. Salt marshes are important ecosystems for carbon sequestration. However, while studies of atmospheric carbon exchange fluxes have been broadly performed in tidal salt marshes, they are scarce in non-tidal salt marshes. In this study we measured, throughout one year, instantaneous net CO₂ exchange rates from four halophytes (Sarcocornia fruticosa, Halimione portulacoides, Elytrigia atherica and Salicornia patula), which are dominant species of their corresponding habitat (an halophilous scrub, a salt meadow and a glasswort sward) of a Mediterranean non-tidal salt marsh. Soil CO₂ and CH₄ fluxes from these habitats were also measured. E. atherica, a perennial herbaceous species, showed the highest photosynthetic rates during the entire year, but S. patula, an annual succulent herb, had also remarkable photosynthetic rates in summer. Interestingly, the woody fraction of the two perennial shrubs, S. fruticosa and H. portulacoides, showed CO₂ uptake during most of the daily measurements. Regarding the studied habitats, the halophilous scrub and the salt meadow showed higher soil CO₂ emissions than the glasswort sward, being these values, in general, higher than those reported for tidal salt marshes. Both soil absorption and emission of CH₄ were detected. In particular, CH₄ emissions were remarkably high, similar to those found in low-salinity marshes, and, in general, higher than those reported for salt marshes with a high water table salinity. Soil mineralization quotients of the halophilous scrub and the salt meadow were lower than those measured at the glasswort sward, suggesting a higher soil carbon sequestration potential of the first two habitats.