Sustained large stimulation of soil heterotrophic respiration rate and its temperature sensitivity by soil warming in a cool-temperate forested peatland

We conducted a soil warming experiment in a cool-temperate forested peatland in northern Japan during the snow-free seasons of 2007–2011, to determine whether the soil warming would change the heterotrophic respiration rate and its temperature sensitivity. We elevated the soil temperature by 3°C at 5-cm depth by using overhead infrared heaters and continuously measured hourly soil CO₂ fluxes with a 15-channel automated chamber system. The 15 chambers were divided into three groups each with five replications for the control, unwarmed-trenched and warmed-trenched treatments. Soil warming enhanced heterotrophic respiration by 82% (mean of four seasons (2008–2011) observation±SD, 6.84±2.22 µmol C m⁻² s⁻¹) as compared to the unwarmed-trenched treatment (3.76±0.98 µmol C m⁻² s⁻¹). The sustained enhancement of heterotrophic respiration with soil warming suggests that global warming will accelerate the loss of carbon substantially more from forested peatlands than from other upland forest soils. Soil warming likewise enhanced temperature sensitivity slightly (Q ₁₀, 3.1±0.08 and 3.3±0.06 in the four-season average in unwarmed- and warmed-trenched treatments, respectively), and significant effect was observed in 2009 (p<0.001) and 2010 (p<0.01). However, there was no significant difference in the basal respiration rate at 10°C (R ₁₀, 2.2±0.52 and 2.8±1.2 µmol C m⁻² s⁻¹) between treatments, although the values tended to be high by warming throughout the study period. These results suggest that global warming will enhance not only the heterotrophic respiration rate itself but also its Q ₁₀ in forests with high substrate availability and without severe water stress, and predictions for such ecosystems obtained by using models assuming no change in Q ₁₀ are likely to underestimate the carbon release from the soil to the atmosphere in a future warmer environment.