Soil Respiration Response to Experimental Warming in a Temperate Harwood Forest Varies With Species Composition

Under climate change, some forest ecosystems appear to be transitioning into net source of carbon dioxide (CO ₂ ), raising questions about the future role of soil respiration rate (R _s ), which depends on hydroclimatic conditions. The main objective of this study was to assess the effects of artificial warming on R _s 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 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. 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 slowdown 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 the another.