Great and fast increase in soil CH4 uptake after reforestation in karst cropland area is linked to the environmental and microbial factors

• Published in: Agriculture, ecosystems & environment Vol. 347; p. 108367
• Main Authors: Liu, Fang, Wang, Shilu, Huang, Kerui, Yeager, Kevin M., Li, Yufeng, Lv, Lingling, Jia, Guikang, Ma, Bo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2023
• Subjects: CH4 oxidation kinetics; Karst landscape; Net soil CH4 fluxes; Reforestation; USCγ methanotrophs; USCγ methanotrophs; Reforestation; Karst landscape; Net soil CH4 fluxes; CH4 oxidation kinetics
• ISSN: 0167-8809; 1873-2305
• DOI: 10.1016/j.agee.2023.108367

Karst environments are an important but often overlooked global sink of atmospheric CH4. Little is known about methanotrophic bacterial communities in karst soils; consequently, the effects of land use change (LUC) and soil management practices on them and how they function as part of the soil CH4 sink are unclear. In this study, we compared net soil CH4 fluxes, kinetic parameters (Km and Vmax) of CH4 oxidation, and the pmoA gene of CH4 oxidizers at five test soil plots in karst areas that have different soil types and land use types. The maximum atmospheric CH4 uptake rate (−5.62 ± 3.14 kg ha-1 y-1) occurred in reverting scrublands just 10 years after they had been utilized for crop cultivation; followed by natural forest (−4.30 ± 4.02 kg ha-1 y-1) in limestone soils. The cultivated soils in the cropland emitted CH4 into the atmosphere. The difference in net CH4 fluxes (−8.21 kg ha–1 y–1) between soils in cropland and soils in reverting scrubland from cropland was 4–8 times higher than the global average values, suggesting that reforestation on limestone soils in karst cropland areas has much greater potential to enhance soil CH4 oxidation than in non-karst areas. Soil moisture is the most likely environmental factor to trigger the enhancement effect of reforestation. The remarkable corresponding relationships between Km, net soil CH4 fluxes, and methanotrophic compositions in these plots suggest that bacteria play an essential role in regulating the effects of LUC on soil CH4 oxidation rates. It is type Ⅰ methanotroph USCγ and JR3 (USCγ sensu lato), not type II methanotrophs USCα as in previous studies, that dominate in enhancing soil oxidation of atmospheric CH4 since reforestation on limestone soils. The specific unstable habitats in karst settings favor USCγ who, as r-strategists, can change rapidly to adapt to new conditions formed from LUC and then grow presumably at an exponential rate. This coupling of environmental and microbial factors can well explain the great and fast response of CH4 oxidation in limestone soils. Our study provides new insights that reforestation of cropland in karst areas may be a noticeably more efficient way to potentially mitigate atmospheric CH4 build-up and thus should be strongly encouraged. [Display omitted]