Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

ABSTRACT

On the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH₄ fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH₄ uptake, α_soil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that α_soil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ¹³C–CH₄ was similar (−55.3 ± 5.5 ‰ and −53.0 ± 5.5 ‰) in two bogs separated by >1000 km but was lower (−63.4 ± 6.3 ‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ¹³C–CH₄ include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH₄ consumption pathways in grasslands and the biome type-specific consistency in CH₄ production pathways in wetlands.

KEYWORDS:

• Carbon-13
• grassland
• isotope ecology
• isotope fractionation
• methane oxidation
• methane production
• Qinghai–Tibetan Plateau
• soil C/N
• wetland

Acknowledgements

The authors thank Assoc. Prof. S. Toyoda in the Department of Environmental Science and Technology, Tokyo Institute of Technology and Ms. N. Suzuki and other members in Prof. N. Yoshida’s laboratory in the Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, for providing help and instruments for isotope measurements of the CH₄ gas. The authors also thank Assoc. Prof. M. Hirota, University of Tsukuba and Prof. S. Mariko, Hosei University, for providing the instruments and advice to measure CH₄ gas concentrations.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Tomomichi Kato http://orcid.org/0000-0003-3757-3243

Additional information

Funding

This study was supported by a JSPS grant-in-aid for Scientific Research (Kiban-A, No. 19201006) from the Ministry of Education, Science, Culture, Sports and Technology of Japan.