Unifying soil respiration pulses, inhibition, and temperature hysteresis through dynamics of labile soil carbon and O₂

Abstract

Event-driven and diel dynamics of soil respiration (R s ) strongly influence terrestrial carbon (C) emissions and are difficult to predict. Wetting events may cause a large pulse or strong inhibition of R s . Complex diel dynamics include hysteresis in the relationship between R s and soil temperature. The mechanistic basis for these dynamics is not well understood, resulting in large discrepancies between predicted and observed R s . We present a unifying approach for interpreting these phenomena in a hot arid agricultural environment. We performed a whole ecosystem wetting experiment with continuous measurement of R s to study pulse responses to wetting in a heterotrophic system. We also investigated R s during cultivation of Sorghum bicolor to evaluate the role of photosynthetic C in the regulation of diel variation in R s . Finally, we adapted a R s model with sensitivity to soil O 2 and water content by incorporating two soil C pools differing in lability. We observed a large wetting-induced pulse of R s from the fallow field and were able to accurately simulate the pulse via release of labile soil C. During the exponential phase of plant growth, R s was inhibited in response to wetting, which was accurately simulated through depletion of soil O 2 . Without plants, hysteresis was not observed; however, with growing plants, an increasingly significant counterclockwise hysteresis developed. Hysteresis was simulated via a dynamic photosynthetic C pool and was not likely controlled by physical processes. These results help characterize the complex regulation of R s and improve understanding of these phenomena under warmer and more variable conditions.

Quantification and Controls of Wetland Greenhouse Gas Emissions

“…A second important outcome of the study was that the highest N2O fluxes occurred during the colder winter months. These data support a recent paradigm shift away from simple temperature response functions for gas flux predictions (Davidson and Janssens, 2006;Oikawa et al 2014) that are often used for CO 2 and CH 4 . Instead, the asynchronous fluxes of O2-sensitive CH 4 and N 2 O gases suggest seasonal wetland redox oscillations can be important in regulating the composition of wetland greenhouse gas emissions.…”

Merging a mechanistic enzymatic model of soil heterotrophic respiration into an ecosystem model in two AmeriFlux sites of northeastern USA

“…semi-arid, arid, and Mediterranean-type climate). To improve simulation of wet-up events, Oikawa et al (2014) applied the DAMM model in a hot arid agricultural environment after adding a third substrate pool that represented a proxy of transient labile-C pool, which accumulated C substrate during the dry period and was released upon rewetting of soil. Freeze-thaw cycle may also exert substrate limitation on aerobic soil R by strongly limiting diffusion of soluble C and O 2 across a narrow temperature range where soil water alters between ice and liquid water in soil pore space.…”

Dynamic interactions of ecohydrological and biogeochemical processes in water‐limited systems

“…Including microbial biomass and enzyme pools was found to be important to correctly predict pulses. Notably, the presence of a soluble pool that accumulates C during drying (when microbial uptake is low, but extracellular enzymes are still active) and is used rapidly upon rewetting provided the needed mechanism for the respiration pulse (Lawrence et al 2009, Manzoni et al 2014a, Oikawa et al 2014.…”