16年間3℃温めた泥炭土壌でCO2放出が2倍以上に～炭素を多く含む土壌が温暖化をさらに進める可能性を示唆～

Global warming is increasingly recognized as a critical driver of carbon release from terrestrial ecosystems, yet the magnitude and persistence of this effect remain uncertain. This study investigates the impact of sustained warming on soil carbon decomposition by measuring soil heterotrophic respiration (R_h) in a sub-boreal forested peatland in northern Hokkaido, Japan, over a 16-year period. We compared three treatments: root-trenched (R_h), root-trenched with +3 °C warming at 5 cm depth (warmed R_h), and a control allowing root invasion. We evaluated interannual variations in R_h, temperature sensitivity (Q₁₀), and basal respiration rate at 10 °C (R₁₀). Our results reveal a remarkably strong and persistent warming effect on R_h, averaging an 111% increase over 16 years (p < 0.001). This amplified response is attributed to the peatland’s substantial soil organic carbon (SOC) stocks in this site (17.7 kg C m⁻² in the top 30 cm). Although there was no significant difference, we also observed that warming reduced soil water content by 6.5% over 2011–2022 (p = 0.529), which could enhance aerobics and further contribute to increased R_h. Furthermore, warming significantly increased bacterial abundances at 20–30 cm soil depth by 39% and fungal abundances at 10–20 cm depth by 84%, which also played a role in accelerating SOC decomposition. Despite a negative correlation between the seasonal average soil temperature and the warming effect (p = 0.05) observed in the later 11 years of the experiment (2012–2022), long-term warming led to a 116% increase of in R₁₀, corresponding with the significant increase in microbial abundance. Our findings highlight the potential for peatlands to transition to large carbon sources through synergistic effects of high SOC stocks, warming-induced soil moisture loss, and increase in soil microbial abundance.