Function of the methanogenic community in mangrove soils as influenced by the chemical properties of the hydrosphere

Abstract

Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH 4) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH 4 emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH 4 fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH 4 production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179-289 mS m −1 , pH (H 2 O): 7.45-8.10] compared with aerobic conditions [water content: 38.9-109.2%, EC: 187-299 mS m −1 , pH (H 2 O): 6.86-7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH 4 production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9-109.2%, EC: 533 mS m −1 , pH (H 2 O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH 4 emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH 4 production require a particular hydrospheric salt concentration and soil pH.

Spartina alterniflora invasion drastically increases methane production potential by shifting methanogenesis from hydrogenotrophic to methylotrophic pathway in a coastal marsh

“…The 12‐year invasion by S. alterniflora also significantly increased rates of acetoclastic and hydrogenotrophic methanogenesis, along with the abundance of acetoclastic and hydrogenotrophic methanogens, thus suggesting that both forms of methanogenesis were not completely inhibited by sulphate reducers with an increasing sulphate concentration. This result and interpretation are consistent with those of sulphate‐rich mangroves (Arai et al, ), estuarine and marine sediments (Sela‐Adler et al, ; Treude et al, ), and oilfield fluids (Lv et al, ). It has been suggested that the co‐existence of methanogenesis and sulphate reduction is possible on competitive substrates and is primarily controlled via organic C input levels (Egger et al, ).…”

Effects of Organic Phosphorus on Methylotrophic Methanogenesis in Coastal Lagoon Sediments With Seagrass (Zostera marina) Colonization

“…Methylotrophic methanogens were able to outcompete SRB by virtue of excess substrate by which they maintained higher activity in the surface layer sediments; thus, it was reasonable that phytate phosphorus would not affect methane production to a great extent. In contrast to the surface layer sediments, the bottom layer sediments lack some essential substances for microbial life in Arai et al (2016) , so methylotrophic methanogens may not be unfavored for methane production with increasing sediment depths ( Lee et al, 2015 ). However, when phytate phosphorus was added to the bottom layer sediments, methane production rate was significantly increased, meaning that OP may be a source of phosphorus rather than the substrate for methanogens in deeper sediments ( Broman et al, 2017 ).…”

Dynamics of Methane in Mangrove Forest: Will It Worsen with Decreasing Mangrove Forests?

“…Recent studies have reported a significant amount of CH 4 flux from mangrove sediment [42][43][44][45][46][47][48][49] and have claimed that the contribution of CH 4 flux to global warming was non-negligible in estuarine mangrove forests, which could account for 18% to 22% of blue C burial rates [13] and 9% to 33% of plant CO 2 sequestration [50]. However, observed CH4 flux from mangrove soils is mostly negligible compared to CO 2 emissions from sediment but is highly variable [38][39][40][41][51][52][53][54][55][56][57][58], particularly for non-polluted mangrove sediment [21,49,[59][60][61][62]. To confirm this observation, the authors compared incubation experiments with mangrove sediment collected from the Vietnamese Mekong delta and the Indian Sundarbans forest [39].…”

“…The gas species has become the second most important greenhouse gas in the atmosphere, contributing approximately 20% to global warming since the pre-industrial era [38]. The risk of further methane emission is due to mangrove sediment exposed to the above-mentioned anthropogenic impacts by stimulating related methanogens (i.e., CH 4 -producing microorganisms) and/or by inhibiting methanotroph (i.e., CH 4 -oxidizing microorganisms that contribute to lower the emission from the ecosystem) activity [39][40][41].…”