Isoprene fluxes from warm temperate and tropical seagrass communities

Isoprene is an important biogenic volatile organic compound (BVOC), with a contribution to annual greenhouse gas emissions similar to that of methane in terms of carbon equivalent. Isoprene is mostly produced by terrestrial vegetation, although marine ecosystems also play an important role in isoprene production. Here, we report isoprene fluxes from warm temperate seagrass communities dominated by specific seagrass species (Posidonia australis, Zostera muelleri and Halophila ovalis) in Wallis Lake, NSW, Australia, and from tropical seagrass communities (H. ovalis/Halodule uninervis mixed patches) on Lizard Island, QLD, Australia. P. australis and Z. muelleri were net isoprene sinks (-0.6 ± 0.1 and -3.4 ± 2.0 nmol m-2 h-1, respectively), whereas H. ovalis (2.4 ± 0.2 nmol m-2 h-1) and mixed patches of H. ovalis/H. uninervis (13.2 ± 3.2 nmol m-2 h-1) were a net source of isoprene, indicating that seagrass communities can be both a source of and a sink for isoprene on a local scale depending on species. Overall, isoprene effluxes were more than 5 times higher on Lizard Island than in Wallis Lake, likely due to higher temperatures and prolonged sunlight on Lizard Island during the time of measurement. Wallis Lake and Lizard Island seagrass communities emit isoprene to the water column at an average rate of -0.3 and 8 mg m-2 yr-1, respectively. Seagrass communities are a benthic source of isoprene in coastal waters, but only make a small contribution (2.3 Gg C yr-1) to the global marine isoprene flux (11.6 Tg C yr-1).