[A-CG46] Biogeochemical Cycles in Land Ecosystem

[ACG46-01] Trends of soil CO₂ and CH₄ fluxes along with long-term warming experiment in a cool temperate forest in Northeastern Japan

*Sun Lifei¹, Sachinobu Ishida², Yoshiyuki Takahashi¹, Naishen Liang¹, Munemasa Teramoto³, Takashi Hirano⁴, Kentaro Takagi⁴, Masahiro Takagi⁵, Toshiaki Kondo⁶, Jun Koarashi⁷, Mariko Atarashi-Andoh⁷ (1.National Institute for Environmental Studies Japan, 2.Hirosaki University, 3.Tottori University, 4.Hokkaido University, 5.University of Miyazaki, 6.Japan International Research Center for Agricultural Sciences, 7.Japan Atomic Energy Agency )

Keywords:long-term warming experiment, heterotrophic respiration, methane uptake, cool-temperate forest

Increasing greenhouse gas (GHG) emissions have led to global temperatures rising over 1°C above pre-industrial levels, resulting in higher soil temperatures and impacting biogeochemical processes in terrestrial ecosystems. Forest soils play a crucial role in regulating atmospheric GHG concentrations. Heterotrophic respiration (RH) is a key component of soil CO₂ fluxes driven by the decomposition of soil organic carbon (SOC), which is a temperature-dependent process. Understanding the response of RH to global warming is important because SOC loss to the atmosphere would further accelerate global warming. Meanwhile, forest soil can act as either a net sink or source of atmospheric CH₄, depending on the balance between aerobic methanotrophic oxidation and anaerobic methanogenic production. Soil CH₄ fluxes are typically negative (CH₄ uptake) in unsaturated soils because drier conditions allow oxygen to diffuse more rapidly, which enhancing the rate of methane oxidation. Warming is expected to promote CH₄ uptake by reducing soil moisture, creating a negative feedback effect on global warming. Spatial variations in the warming effects on soil CO₂ and CH₄ fluxes link to soil microbial biomass carbon and soil moisture, respectively. However, interannual variations in these warming effects remain unclear due to the lack of long-term in situ experiments. In this study, we conducted a 12-year warming experiment in a 78-year-old cool-temperate broad-leaved deciduous forest to investigate the long-term responses of soil CO₂ and CH₄ fluxes to global warming. We used an automatic chamber system to measure the soil CO₂ fluxes during snow-free periods from 2011 to 2022. Fifteen chambers were divided into three treatments: 1) control plots (CT) for measuring total soil respiration (SR), 2) trenched plots (TC) for measuring heterotrophic respiration (RH), and 3) 2.5 ℃ warmed trenched plots (WT) for measuring warmed RH (RHW). The RHW was always higher than that of HR, and the warming effects on RHW tended to increase throughout the entire observation year. The interannual variation in warming effects on RHW were probably associated with precipitation. Soil CH₄ fluxes showed negative values among the three treatments in seasonal variation. Although soil CH₄ fluxes were lower due to the higher frequency of precipitation, warming effects of soil CH₄ fluxes were opposite. These results indicated that precipitation is an important factor for regulating the interannual variations of warming effects on CO₂ and CH₄ fluxes.