Gas storage of peat in autumn and early winter in permafrost peatland

The carbon (C) balance of permafrost peatlands in autumn and winter, which affects the annual C budget estimation, has become a hotspot of studies on peatlands C cycle. This study combined the static chamber method, in situ soil profile measurements, and incubation experiments to investigate release and storage of C during autumn and early winter in a permafrost peatland in the Da Xing'an Mountains, Northeast China. Our results showed that the peak values of CH₄ fluxes (30 August 2016) lagged behind those of CO₂ fluxes (24 July 2016). At the onset of soil freezing, CH₄ fluxes slightly increased, while CO₂ fluxes decreased. During soil freezing in autumn, gases were found to be mainly stored in the soil as dissolved CH₄ and CO₂ and dissolved C concentrations (CH₄, CO₂, and DOC (dissolved organic carbon)) increased with depth. DOC concentrations were closely related to dissolved C gases, implying that the stored dissolved C gases might be derived from DOC decomposition. The CO₂: CH₄ ratio decreased sharply from the freezing of the surface layer to the total freezing of the soil, indicating larger CH₄ storage in totally frozen soil. The incubation experiments also showed larger CH₄ storage in the frozen soils and the stored C gases could influence the assessment of C emissions during thawing. These findings have important implications for clarifying the gas storage of permafrost peatland in autumn and early winter. The results may also clarify the key link of C emissions between the growing season and the nongrowing season.