Changes in soil respiration Q10 during drying–rewetting along a semi-arid elevation gradient

Wetting induced increases in soil CO2 efflux (R) from dry soils have been repeatedly reported, however little is known about the sensitivity of the pulse to temperature. To address this knowledge gap changes in temperature sensitivity of soil CO2 efflux (Q10) during repeated drying–rewetting (DW) events were experimentally quantified for soils collected both under canopy and interspace microenvironments at three elevations on Santa Rosa Mountain in southern California. Five field-replicated surface soil samples for each location were incubated at 13, 19, 25 and 31 °C. At each temperature, three consecutive DW cycles were performed by adding water to 40% water holding capacity. Instantaneous R was measured immediately after wetting and repeatedly until the soils were dry (< 2% of added water). Soil R responses were averaged above and below 20% WHC and considered as wet and dry fluxes, respectively. Wet and dry soil R responses were separately modeled using the Arrhenius equation and activation energy (Ei) was determined using non-linear mixed-level modeling. Soil R at 25 °C (flux25) increased with elevation gradient with a decrease in required Ei values. Negative relationship between flux25 and Q10 supported the carbon-quality hypothesis, whereas, Q10 values > 2 supported a temperature sensitive metabolic pulse throughout repeated DW events for soils across the mountain. Including variation in Arrhenius temperature kinetics with precipitation patterns has the potential to improve predictions of the precipitation pulse induced C loss across large spatiotemporal scales.

Research highlights
► Precipitation induced soil respiration pulses have a strong temperature sensitivity.
► Microenvironment influences Q10 change over drying at higher elevations.
► Inclusion of pulse induced Q10 variation is critical for global flux modeling.