Mechanisms Of Filamentous Algae Affect Methane Production And Emissions In Wetlands

Greenhouse gas emission has been as a critical issue for ecosystem environment. Studying the sources of greenhouse gases have been as a hot topic in global biogeochemistry. Wetlands are key components in biogeochemical cycles. Studying greenhouse gases emissions from wetlands are important for our comprehensive understanding of freshwater ecosystem in global greenhouse gas emissions. Filamentous algae are important primary producers in freshwater ecosystems. However, their effects and mechanisms on methane(CH4) emission in wetland ecosystem are not fully understood. Considering the roles of filamentous algae in freshwater ecosystems, understanding the role of filamentous algae on CH4 emission in wetlands is necessary for correct estimate of CH4 in freshwater ecosystem.contribution.The main purpose of this study was to(1) study the effects of filamentous algae Spirogyra spp. on methane emission in a riverine wetland,(2) to characterize factors that responsible for these effect, and(3) to estimate the extracellular release of DOC by filamentous algae and the DOC composition. Sediment cores were sampled in riverine wetlands in Shanghai, China and inoculated with Spirogyra spp in laboratory for two months. CH4 fluxes and relative biotic and anbiotic environmental factors(dissolved CH4 concentrations, methanogen and methanotroph abundance, CH4 production and oxidation potentials, physicochemical characteristics of sediments and overlying water and stable carbon isotopic signatures), as well as the components and contents of algal extracellular material were analyzed during the experimental periods.The main results are as follows:1) Filamentous algal bloom significantly decreased CH4 fluxes in riverine wetlands. CH4 fluxes from the algal groups were ranged from 90±5 μmol m-2 h-1 to 119±5 μmol m-2 h-1, which were significantly lower than those in control groups(one ANOVA, P < 0.01, n = 6). Dissolved CH4 concentrations and potential CH4 production rates in sediments were also significantly lower than those of in controls(P < 0.01). Nevertheless, dissolved organic carbon(DOC) concentrations in porewater of algal sediment cores showed significant increasing compared to control groups, and the DOC concentrations in algal groups were increase and varies from 55.52 mg l-1 to 155.45 mg l-1.2) Results of partial east squares(PLS) and stepwise forward multiple regression analysis showed that sediment CH4 produce was the main factor that determines CH4 fluxes in test columns(Log CH4, flux=1.63+0.28 log CH4, production, P < 0.001, r2 = 0.72). In addition, TOC content and DOC concentration in sediment cores had significant relationships with potential CH4 produce rate.3) Variations of CH4 and CO2 stable isotope signatures and their apparent fractionation factors(?app) in pore water of test columns suggested that the ?13C-CH4 and ?13C-CO2 did not showed siginificant temporal variability, but the acetoclastic methanogensis was strongly dominated in all treatments, and increased in importance with the addition of algae.4) Considering the increasing of DOC concentrations and the increased acetoclastic pathway importance in algal sediment cores, we inferred that filamentous algae bloom could increase DOC concentration through secretion of algal extracellular materials. The algal extracellular materials may provide available carbon sources for microbial communities and affect the structure and function of microorganism in sediments. To identify the hypothesis, we incubated Spirogyra spp with hydroponic mediums and collected algal extracellular materials for qualitative and quantitative analysis. Results of qualitative analysis by GC-MS showed that algal extracellular materials mainly include organic acids, hydrocarbons, aldehydes, ketones and lipid, organic acids were the main components among the extracellular materials. Moreover, the organics acids components did not showed significant difference with temporal, but their contents were varied with different experimental duration,moreover, the algal extracellular materials significantly decreased potential CH4 production rates in sediments.