Burn intensity regulates post-fire effects on soil N2O emissions: A grassland soil pyrocosm study

Low-intensity burns in Southern California grassland soil pyrocosms tripled post-fire N2O emissions over 18 weeks, while high-intensity burns left N2O fluxes similar to unburned controls.

• Why it matters: Post-fire NO and N2O fluxes vary widely, and natural differences in burn intensity may be a key driver of the underlying soil chemistry and microbial processes.
• What they did: Using a pyrocosm with grassland soil, the study compared Control, Low- (100.1 {+/-} 20.0 oC peak at 5 cm), and High-intensity (243.8 {+/-} 7.4 oC peak at 5 cm) burns, tracking NO and N2O fluxes plus pH, NO3-, NH4+, net nitrification, C pools, microbial biomass C, and five extracellular enzyme activities.
• The result: Low burns increased denitrification, supported by higher soil pH and labile C and an 88% reduction in net nitrification, whereas high burns constrained denitrification via losses of microbial biomass, soil C, and NO3- alongside time-rising enzyme activities consistent with C limitation.

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