Thermal Compensatory Response of Soil Heterotrophic Respiration Following Wildfire

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 (Rh) 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 Rh will help maintain C stocks in forest
ecosystems after wildfires in a warming world.