Temperature Sensitivity Of Organic Matter Anaerobic Degradation In Low Temperature Wetland Soil Of China And Methanogenesis Facilitated Via Nanofe₃O₄

Zoige wetland in Tibetan plateau, permafrost, wetland and paddy field in Northeastern China represent cold environment where significant methane emission has been observed. However, it remains unknown how the production and emission of CH4from these wetlands will respond to a warming climate. Here we determined the temperature sensitivity of methanogenesis in these four wetlands under the laboratory incubation conditions. We found that the response of methanogenesis to temperature could be separated into two phases, a high sensitivity in the low temperature range (<20℃) and a modest sensitivity under mesophilic conditions (20℃-35℃), respectively. The aceticlastic methanogens Methanosarcinaceae were the main methanogens at low temperatures, while hydrogenotrophic Methanobacteriales, Methanomicrobiales and Methanocellales were more abundant at higher temperatures. The total abundance of mcrA genes increased with temperature indicating that the growth of methanogens was stimulated. Determination of carbon isotopic signatures indicated that methanogenic pathway was shifted from mainly aceticlastic methanogenesis to a mixture of hydrogenotrophic and aceticlastic methanogenesis with the increase of temperature. Collectively, the shift of temperature responses of methanogenesis in these four wetlands was in accordance with the changes in methanogen composition and methanogenic pathway.Syntrophic interaction occurs during anaerobic fermentation of organic substances forming methane as the final product. H2and formate are known to serve as the electron carriers in this process. Recently, it has been shown that direct interspecies electron transfer (DIET) occurs for syntrophic CH4production from ethanol and acetate. Here, three zoige wetland soil enrichments were constructed to determine the involvement of DIET in syntrophic acetate, propionate, butyrate oxidation and CH4production. The results showed that CH4production was significantly accelerated in the presence of nanoFe3O4in all continuous transfers. This acceleration was dismissed when nanoFe3O4was coated with silica that insulated the mineral from electrical conduction. Amendment of nano-graphite at similar concentration also shortened the lag phase compared with the control, but the stimulatory effect was lesser compared with nanoFe3O4. Molecular approaches, including DNA-based stable isotope probing, revealed that the bacterial Syntrophomonas and the archaeal Methanobacteriaceae were involved in the syntrophic butyrate oxidation and CH4production; the bacterial Pelotomaculum and the archaeal Methanobacteriaceae were involved in the syntrophic propionate oxidation and CH4production; and the archaeal Methanosarcinaceae were involved in acetate cleavage and CH4production. Collectively, no proof of DIET involvement, our study demonstrated that the nanoFe3O4facilitate CH4production from acetate, propionate and butyrate.