Soil CO₂ and CH₄ response to experimental warming under various tree species compositions in a temperate harwood...

Under climate change, some forest ecosystems appear to be transitioning into net source of carbon dioxide (CO₂), raising questions about the future role of soil respiration rate (R_s), which depends on hydroclimatic conditions. Conversely, well-drained forest soils could become more significant sinks of methane (CH₄) under warming. The main objective of this study was to assess the effects of artificial soil warming on R_s and CH₄ fluxes in a sugar maple forest at the northern limit of Quebec temperate deciduous forests in eastern Canada, and to evaluate the effect of species composition on soil response to warming. We measured R_s and CH₄ fluxes during the snow-free period of 2021 and 2022 in 32 plots distributed across three forest types, half of which were artificially heated by approximately 2 °C with heating cables. Forest soils were a very consistent sink for CH₄ and it did not respond to artificial soil warming nor was it sensitive to variations in soil moisture, ionic activity in soil solution and forest types. However, we observed an increase in R_s in response to warming in the heated plots, but only up to a threshold of about 15 °C, beyond which R_s started to slow down in respect to the control plots. We also observed a weakening of the exponential relationship between R_s and soil temperature beyond this threshold. This trend varied across the forest types, with hardwood-beech stands being more sensitive to warming than mixedwoods and other hardwoods. This greater response of hardwood-beech stands to warming resulted in a more significant downshift of R_s, starting from a colder temperature threshold, around 10-12 °C. This study highlights a potential plateauing of R_s despite rising soil temperature, at least in eastern Canada's temperate deciduous forest, but this trend could vary from one forest type to another.

The online version contains supplementary material available at 10.1007/s44378-025-00045-4.