Soil warming-induced reduction in water content enhanced methane uptake at different soil depths in a subtropical forest.

Global warming can significantly impact soil CH 4 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 CH 4 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 CH 4 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 0-10 and 10-20 cm depths. Our findings revealed that warming significantly enhanced soil net CH 4 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 (a type of MOB) and decreased the relative abundance of Methylocystis, but it did not significantly increase the pmoA gene copies. Our structural equation model analysis indicated that warming directly regulated soil CH 4 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 CH 4 uptake at different depths, with soil moisture playing a crucial role in this process. Under warming conditions, the drier soil pores allow for better CH 4 penetration, thereby promoting more efficient activity of MOB.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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