Anoxic seagrass leaf environments as potential hotspots for toxin production and N2O emission
Year: 2024
Type: article
Abstract: Epiphytes on seagrass leaves can render parts of the leaf phyllosphere anoxic in darkness owing to leaf/epiphyte respiration and O 2 diffusion constraints. In such anoxic microenvironments, anaerobic microbes can potentially produce phytotoxins and greenhouse gases, but the actual occurrence of such processes in seagrass epiphytic biofilms remain uncertain. We used microsensors to measure O 2 , NO, N 2 O and H 2 S concentration gradients, as well as NO and O 2 dynamics within epiphytic biofilms on seagrass ( Zostera marina ) leaves under changing environmental conditions. The bacterial community composition of epiphytic biofilms was analyzed with 16S rRNA gene amplicon sequencing. Flavobacteriaceae and Rhodobacteraceae were dominant bacterial community members accounting for ˃50 % of the relative abundance, and sulfate-reducing bacteria ( Desulfobacterota ) were omnipresent in the epiphytic biofilms. We found pronounced production of NO, N 2 O and H 2 S in anoxic parts of the seagrass phyllosphere, with NO and H 2 S reaching maximal concentrations of 1.0 and 4.4 μmol L −1 , respectively, under slow flow and hypoxic seawater conditions, while the highest N 2 O concentration in the epiphytic biofilms reached 5.9 μmol L −1 in hypoxic, nitrate-rich seawater. Part of the phytotoxic NO and H 2 S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N 2 O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N 2 O m −2 day −1 . Such release of the potent greenhouse gas N 2 O from seagrass leaves with epiphytic biofilms under eutrophic conditions could potentially offset the carbon burial capacity of seagrass meadows. Ocean eutrophication can thus stimulate denitrification and sulfate reduction within anoxic leaf microenvironments, negatively impacting seagrass fitness and ecological function. • Costal eutrophication stimulates seagrass leaf epiphytes and oxygen consumption. • Anoxic leaf conditions enable anaerobic production of greenhouse gas and toxins. • Epiphytes can turn seagrass phyllospheres into hotspots for N 2 O production/emission. • Epiphytes also lead to toxic NO and H 2 S production in anoxic leaf microenvironments. • Stimulation of denitrification can negatively impact seagrass ecosystem services.
Source: Marine Pollution Bulletin
Institutions: University of Copenhagen, Roskilde University
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
SDG: Life below water
Open Access status: hybrid
Estimated APC paid: $3,630
OpenAlex ID: W4403505096