Annual methane emissions from degraded alpine wetlands in the eastern Tibetan Plateau

Grazing-oriented drainage of alpine/boreal wetlands has been broadly implemented to meet the increasing demand for animal products. However, the annual methane (CH₄) emissions from alpine fens degraded due to drainage for grazing have not been well characterized due to a lack of year-round observations. In this study, the year-round CH₄ fluxes from a degraded alpine fen that is typical in the Tibetan Plateau (TP) were measured. The temperature sensitivity of the CH₄ emissions during the nongrowing season (NGS) was different between the microsites with and without CH₄ uptake during the growing season (GS), showing apparent activation energy of 59-61 vs. 22-43 kJ mol^-1 (or variation folds induced by the 10-degree change (i.e., Q₁₀): 2.61-2.74 vs. 1.38-1.91). The CH₄ emissions amounted to 0.2-63.3 kg C ha^-1 yr^-1 (with -0.8 to 41.4 kg C ha^-1 and 0.9 to 21.9 kg C ha^-1 in the GS and NGS, respectively), which were significantly (P < 0.05) related to the distances to the drainage ditch or water tables across the six microsites. As a key factor, the water table determined the role of the CH₄ emissions during freezing/thawing. For cool/cold/alpine wetlands with no CH₄ uptake in the GS, a mean factor of 1.52 (within a range of 1.00-2.44 at the 95% confidence interval), corresponding to an NGS contribution of 34% (ranging from 0 to 59%), was recommended to upscale the GS emissions to annual totals. Degradation of the native peat marshes in the Zoige region (originally the largest area of alpine wetlands) due to intentional drainage has greatly reduced the quantities of CH₄ emissions. Additional studies are still needed to minimize the large uncertainties in CH₄ emissions estimates for the changes in alpine wetlands in this region and for the entire TP.

Shifts in soil bacterial and archaeal communities during freeze-thaw cycles in a seasonal frozen marsh, Northeast China

Diurnal freeze-thaw cycles (FTCs) occur in the spring and autumn in boreal wetlands as soil temperatures rise above freezing during the day and fall below freezing at night. A surge in methane emissions from these systems is frequently documented during spring FTCs, accounting for a large portion of annual emissions. In boreal wetlands, methane is produced as a result of syntrophic microbial processes, mediated by a consortium of fermenting bacteria and methanogenic archaea. Further research is needed to determine whether FTCs enhance microbial metabolism related to methane production through the cryogenic decomposition of soil organic matter. Previous studies observed large methane emissions during the spring thawed period in the Sanjiang seasonal frozen marsh of Northeast China. To investigate how FTCs impact the soil microbial community and methanogen abundance and activity, we collected soil cores from the Sanjiang marsh during the FTCs of autumn 2014 and spring 2015. Methanogens were investigated based on expression level of the methyl coenzyme reductase (mcrA) gene, and soil bacterial and archaeal community structures were assessed by 16S rRNA gene sequencing. The results show that a decrease in bacteria and methanogens followed autumns FTCs, whereas an increase in bacteria and methanogens was observed following spring FTCs. The bacterial community structure, including Firmicutes and certain Deltaproteobacteria, was changed following autumn FTCs. Temperature and substrate were the primary factors regulating the abundance and composition of the microbial communities during autumn FTCs, whereas no factors significantly contributing to spring FTCs were identified. Acetoclastic methanogens from order Methanosarcinales were the dominant group at the beginning and end of both the autumn and spring FTCs. Active methanogens were significantly more abundant during the diurnal thawed period, indicating that the increasing number of FTCs predicted to occur with global climate change could potentially promote CH₄ emissions in seasonal frozen marshes.