Exploring the impact of soil warming on methane uptake at different soil depths in a subtropical forest: unraveling the role of decreased water content

Global warming can significantly impact soil CH₄ uptake in subtropical forests due to changes in soil moisture, temperature sensitivity of methane-oxidizing bacteria (MOB), and shifts in microbial communities. However, the specific effects of climate warming and the underlying mechanisms on soil CH₄ uptake at different soil depths remain poorly understood. To address this knowledge gap, we conducted a soil warming experiment (+4°C) in a natural forest. From August 2020 to October 2021, we measured soil temperature, soil moisture, and CH₄ uptake rates at four different soil depths: 0-10 cm, 10-20 cm, 20-40 cm, and 40-60 cm. Additionally, we assessed the soil MOB community structure and pmoA gene (with qPCR) at the 0-20 cm depth. Our findings revealed that warming significantly enhanced soil net CH₄ uptake rate by 12.28%, 29.51%, and 61.05% in the 0-10, 20-40, and 40-60 cm soil layers, respectively. The warming also led to reduced soil moisture levels, with more pronounced reductions observed at the 20-40 cm depth compared to the 0-20 cm depth. At the 0-10 cm depth, warming increased the relative abundance of upland soil cluster α and decreased the relative abundance of Methylocystis, but it did not significantly increase the pmoA gene copies. Our structural equation model indicated that warming directly regulated soil CH₄ uptake rate through the decrease in soil moisture, rather than through changes in the pmoA gene and MOB community structure at the 0-20 cm depth. In summary, our results demonstrate that warming enhances soil CH₄ uptake at different depths, with soil moisture playing a crucial role in this process. Under warming conditions, the drier soil pores allow for better O₂ and CH₄ penetration, thereby promoting more efficient activity of MOB. This increased CH₄ uptake in subtropical forests has the potential to mitigate the effects of global warming.