{"title":"Anoxic seagrass leaf environments as potential hotspots for toxin production and N2O emission","authors":"","doi":"10.1016/j.marpolbul.2024.117113","DOIUrl":null,"url":null,"abstract":"<div><div>Epiphytes on seagrass leaves can render parts of the leaf phyllosphere anoxic in darkness owing to leaf/epiphyte respiration and O<sub>2</sub> 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.</div><div>We used microsensors to measure O<sub>2</sub>, NO, N<sub>2</sub>O and H<sub>2</sub>S concentration gradients, as well as NO and O<sub>2</sub> dynamics within epiphytic biofilms on seagrass (<em>Zostera marina</em>) leaves under changing environmental conditions. The bacterial community composition of epiphytic biofilms was analyzed with 16S rRNA gene amplicon sequencing.</div><div><em>Flavobacteriaceae</em> and <em>Rhodobacteraceae</em> were dominant bacterial community members accounting for ˃50 % of the relative abundance, and sulfate-reducing bacteria (<em>Desulfobacterota</em>) were omnipresent in the epiphytic biofilms. We found pronounced production of NO, N<sub>2</sub>O and H<sub>2</sub>S in anoxic parts of the seagrass phyllosphere, with NO and H<sub>2</sub>S reaching maximal concentrations of 1.0 and 4.4 μmol L<sup>−1</sup>, respectively, under slow flow and hypoxic seawater conditions, while the highest N<sub>2</sub>O concentration in the epiphytic biofilms reached 5.9 μmol L<sup>−1</sup> in hypoxic, nitrate-rich seawater. Part of the phytotoxic NO and H<sub>2</sub>S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N<sub>2</sub>O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N<sub>2</sub>O m<sup>−2</sup> day<sup>−1</sup>. Such release of the potent greenhouse gas N<sub>2</sub>O from seagrass leaves with epiphytic biofilms under eutrophic conditions could potentially offset the carbon burial capacity of seagrass meadows.</div><div>Ocean eutrophication can thus stimulate denitrification and sulfate reduction within anoxic leaf microenvironments, negatively impacting seagrass fitness and ecological function.</div></div>","PeriodicalId":18215,"journal":{"name":"Marine pollution bulletin","volume":null,"pages":null},"PeriodicalIF":5.3000,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Marine pollution bulletin","FirstCategoryId":"93","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0025326X24010907","RegionNum":3,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENVIRONMENTAL SCIENCES","Score":null,"Total":0}
引用次数: 0
Abstract
Epiphytes on seagrass leaves can render parts of the leaf phyllosphere anoxic in darkness owing to leaf/epiphyte respiration and O2 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 O2, NO, N2O and H2S concentration gradients, as well as NO and O2 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, N2O and H2S in anoxic parts of the seagrass phyllosphere, with NO and H2S reaching maximal concentrations of 1.0 and 4.4 μmol L−1, respectively, under slow flow and hypoxic seawater conditions, while the highest N2O concentration in the epiphytic biofilms reached 5.9 μmol L−1 in hypoxic, nitrate-rich seawater. Part of the phytotoxic NO and H2S diffused into the seagrass leaves, while no NO escaped the biofilm. In contrast, N2O emission from the biofilm in hypoxic and eutrophic seawater reached 9.6 μmol N2O m−2 day−1. Such release of the potent greenhouse gas N2O 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.
期刊介绍:
Marine Pollution Bulletin is concerned with the rational use of maritime and marine resources in estuaries, the seas and oceans, as well as with documenting marine pollution and introducing new forms of measurement and analysis. A wide range of topics are discussed as news, comment, reviews and research reports, not only on effluent disposal and pollution control, but also on the management, economic aspects and protection of the marine environment in general.