Enhanced soil methane oxidation in both organic layer and topsoil during the succession of subtropical forests

Although (sub)tropical forests account for 10–20% of the atmospheric methane (CH4) uptake by soils, the study of soil CH4 oxidation rates and the controlling factors during the chronosequences of forest succession remains poorly understood. The objectives of this study were to characterize the vertical distribution patterns and dynamics of CH4 oxidation among the early-, mid-, and late-successional stages of subtropical forests, and to investigate the main drivers of soil CH4 fluxes. Three successional forests soils were collected and the ambient and potential CH4 oxidation rates, the related enzymes as well as the key soil parameters were determined in the laboratory. The soils at mid- and late-successional stages functioned exclusively as a CH4 sink while the soil at early-succesional stage was either a CH4 source or sink. Soil CH4 oxidations showed significant vertical distributions along with the successional gradients. The highest rate of ambient CH4 oxidation was observed in the A-horizon of the mid-successional stage (forest age ∼ 100 years), increased by 26-fold compared to the early successional stage, while the highest rate of potential CH4 oxidation was detected in the O-horizon of the late-successional stages (forest age > 300 years), which increased the CH4 oxidation by 29% and 21% respectively compared to the early- and mid-successional stages. Soil CH4 oxidation enhanced with decreasing of soil nitrite and nitrate content but weakened with declining of soil moisture at the successional chronosequence. Collectively, subtropical forests have the potential to increase the soil sink capacity for CH4 oxidation along the successional gradient, and thereby providing the negative feedbacks to ecosystems under climate changing.