# Increased CH4 Oxidation in Arctic Tundra Ecosystems Caused by Vegetation‐Mediated Soil Drying

## TL;DR

Arctic tundra vegetation changes increase methane oxidation in drier areas, potentially reducing methane emissions as the climate warms.

## Contribution

The study reveals that vegetation-driven soil drying enhances methane oxidation in Arctic tundra ecosystems under warming conditions.

## Key findings

- Methane oxidation increased by 140.4% and 204.2% in dry ecosystems under warming.
- Methane emissions decreased by 91.2% in Tussock Tundra with warming.
- Vegetation changes and soil aeration, not just temperature and moisture, drive methane dynamics.

## Abstract

Arctic tundra soils can act as an important sink for atmospheric methane (CH4). However, the role and magnitude of this process, and how it will change during future climate scenarios, are poorly understood. The vegetation is changing with a warmer Arctic climate, with taller plants, more shrubs, and altered vegetation patterns. These changes are predicted to be strongest in moist to wet regions, areas usually associated with CH4 production. Additionally, these changes in growth patterns can increase evapotranspiration rates, leading to enhanced soil aeration, favouring CH4 oxidation. Here, we investigate CH4 dynamics within long‐term (> 25 years) passive air warming treatments, using five plant communities with contrasting soil moisture and nutrient regimes. These treatments reveal a strong increase in atmospheric CH4 oxidation in two dry ecosystems (140.4% ± 8.1% and 204.2% ± 19.3% for a Dry Heath and Dry Meadow, respectively), and a strong reduction of CH4 emissions (91.2% ± 18.6%) in a Tussock Tundra community. In contrast, our investigation of Mesic and Wet Meadows showed no significant treatment effects, with only limited CH4 exchange in the Wet Meadow. Furthermore, when inhibiting CH4 oxidation in the surface soil, we found evidence of CH4 production even at the driest site (Dry Heath), indicating a potential for CH4 production throughout the landscape. Although soil temperature and moisture have been put forward as strong regulators of CH4 fluxes, they did not consistently explain our observed changes. Instead, we argue for interactions between vegetation change and near‐surface soil characteristics. The observed shift in plant composition and increased vegetation height, along with warmer air temperatures, enhanced evapotranspiration and surface soil aeration, thereby stimulating methanotrophy and leading to increased CH4 oxidation. This vegetation‐induced climate feedback would aid the predicted temperature‐dependent increase of CH4 oxidation in the Arctic, potentially mediating CH4 emissions from the region.

In a warmer Arctic, vegetation changes can play a critical role in methane dynamics. Our results indicate that taller vegetation, shifts in species composition, and warmer air temperatures enhance soil aeration by increasing evapotranspiration, thereby promoting methane oxidation in surface soils. This results in an increased uptake of atmospheric methane in drier ecosystems, while moderating emissions from wetter ones. These vegetation‐driven responses, although not uniform among the plant communities investigated, might then mitigate the large methane emissions estimated from the region.