Abstract
Winter climate change may result in reduced snow cover and could, consequently, alter the soil frost regime and biogeochemical processes underlying the exchange of methane ( CH 4 ) in boreal peatlands. In this study, we investigated the short‐term (1–3 years) vs. long‐term (11 years) effects of intensified winter soil frost (induced by experimental snow exclusion) on CH 4 exchange during the following growing season in a boreal peatland. In the first 3 years (2004–2006), lower CH 4 emissions in the treatment plots relative to the control coincided with delayed soil temperature increase in the treatment plots at the beginning of the growing season (May). After 11 treatment years (in 2014), CH 4 emissions were lower in the treatment plots relative to the control over the entire growing season, resulting in a reduction in total growing season CH 4 emission by 27%. From May to July 2014, reduced sedge leaf area coincided with lower CH 4 emissions in the treatment plots compared to the control. From July to August, lower dissolved organic carbon concentrations in the pore water of the treatment plots explained 72% of the differences in CH 4 emission between control and treatment. In addition, greater Sphagnum moss growth in the treatment plots resulted in a larger distance between the moss surface and the water table (i.e., increasing the oxic layer) which may have enhanced the CH 4 oxidation potential in the treatment plots relative to the control in 2014. The differences in vegetation might also explain the lower temperature sensitivity of CH 4 emission observed in the treatment plots relative to the control. Overall, this study suggests that greater soil frost, associated with future winter climate change, might substantially reduce the growing season CH 4 emission in boreal peatlands through altering vegetation dynamics and subsequently causing vegetation‐mediated effects on CH 4 exchange.