Sea Lavender Reimagined: Keystone Halophytes in Salt Marsh Blue Carbon Dynamics

Abstract Salt marshes are ecologically and socio‐economically valuable intertidal ecosystems that have suffered rapid losses worldwide. As a blue carbon ecosystem (BCE), they are efficient sinks and long‐term reservoirs of organic carbon (OC), with vital roles in the global carbon cycle. To accurately characterize salt marsh carbon sequestration dynamics, knowledge of halophyte below‐ and aboveground biomass (BGB, AGB) and their relation to the subsurface organic carbon content (OC) is fundamental, yet only vaguely defined. Herein, the biomass and subsoil dry bulk density (DBD), organic matter (OM), and OC of plots pertaining to seven different halophyte species were analyzed. The volume and partitioning of biomass were found to be species‐specific. The difference between the mean AGB in the lower marsh (425 ± 217 g m −2 ) and the upper marsh (1,616 ± 807 g m −2 ) was highly statistically significant. BGB, OM, and OC values peaked in the middle marsh zone (5,890 g m −2 ; 14.5%; 5.4%). DBD was negatively correlated with OM. The BGB, BGB/AGB ratio, OM and OC all had their maxima coinciding with Sea Lavender . As a nexus of unique attributes, Sea Lavender has remarkable potential as a keystone halophyte capable of enhancing and maintaining blue carbon reservoirs. Overall, these results affirm that the observed distribution of biomass and OC is an artifact of biogeomorphic feedbacks where phytomorphic and physiologic traits interplay with underlying soil chemistry, sediment supply, geomorphology, hydrodynamics and external forcings. This data set elucidates factors underpinning interdisciplinary frameworks focused on intertidal wetlands and the intertwined mechanisms that dictate salt marsh evolutionary trajectories.