Increased snow depth and vascular plant species promote Arctic soil methane emissions

Abstract

Atmospheric temperatures are steadily rising on a global scale, with the Arctic region experiencing an alarming rate of increase, double that of the global average. This temperature surge not only signifies anticipated changes but also forecasts a consequential rise in winter precipitation. Within the context of climate change, this leads to a significant upturn in net methane (CH4) emissions. During winter, augmented snow depth enhances thermal insulation of the underlying soil, subsequently increasing soil moisture upon melting. This results in warmer and wetter soil conditions, fostering an anoxic environment that stimulates methanogenic activity. Furthermore, methane emissions are accelerated through plant-mediated CH4 transport. Studies propose a potential shift in vegetation communities, favoring vascular species with extensive aerenchyma under warming conditions. While projections suggest an increase in CH4 flux with greater winter precipitation, the combined effects of heightened snow cover and the presence of vascular plant species on CH4 production remain largely unexplored. This study, conducted using snow fences installed since 2017 in Council, Alaska, aims to unravel the legacy effect of deepened snow during winter and plant-mediated transport on soil CH4 emissions during the growing season (Jul–Aug, 2023). Our investigation involves the analysis of soil CH4 flux, soil chemical properties, and microbial abundance and communities in both control and high snow depth (HS) conditions, comparing bare soil and Eriophorum angustifolium dominant soil. Results indicate that deeper snow significantly increased the average CH4 emission rate from 2.65 to 16.6 mg m-2 day-1. The presence of E. angustifolium amplified CH4 emission strength in both control and HS conditions (63.4 and 116 mg m-2 day-1, respectively). Increased CH4 emissions in HS conditions were primarily driven by enhanced carbon source availability and higher ammonium concentrations. Deeper thaw depth in HS conditions increased carbon source availability, particularly in vegetated soils, promoting methanogenic activity. Higher ammonium concentrations in HS conditions contributed to inhibiting methanotrophs from oxidizing CH4. Consistent variations in soil characteristics were observed at a microbial scale, confirming increased methanogenic activity and decreased methanotrophic activity in HS conditions, for both bare and vegetated soil. These findings underscore the synergistic legacy effect of increased CH4 flux resulting from the complex interaction between deepened snow depth and the presence of vascular species, creating conditions conducive to elevated CH4 production during the growing season.