UC Davis

Frequent wildfires pose a serious threat to carbon (C) dynamics of forest ecosystems under a warming climate. Yet, how wildfires alter the temperature sensitivity (Q₁₀) of soil heterotrophic respiration (R_h) as a critical parameter determining the C efflux from burned landscapes remains unknown. We conducted a field survey and two confirmatory experiments in two fire-prone regions of China at <1, 3, 6, and 12 months after wildfires (n = 160 soil samples). We found that wildfire generally reduced the Q₁₀ for soil organic and mineral horizons within the first year after wildfire mainly due to substrate depletion, which was confirmed by a uniform inoculation experiment. Mineral protection of organic matter in the mineral horizon rich in iron/aluminum (hydr)oxides and a near-neutral pH in organic horizons of postfire soils further suppressed the Q₁₀. Decreased Q₁₀ persisted in organic horizons even after removing substrate limitation, reflecting the dominance of a thermally adapted, r-strategist microbial community in postfire soils. Moreover, fire-induced low C quality increased Q₁₀, which supported the C quality-temperature hypothesis, but a C-limited condition restricted this stimulatory effect. This study illustrates that a thermal compensatory response of R_h will help maintain C stocks in forest ecosystems after wildfires in a warming world.