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

Abstract

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 0–10 and 10–20 cm depths. 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 (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 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 CH4 penetration, thereby promoting more efficient activity of MOB.