Are Rain-Induced Ecosystem Respiration Pulses Enhanced By Legacies Of Antecedent Photodegradation In Semi-Arid Environments?

Ecosystem respiration (R_eco) is highly variable in semiarid ecosystems. After a period of drought, R_eco can jump to a high value in response to rain events, and afterward it decays exponentially with time. To better understand the timing, size, and duration of rain-induced respiration pulses, we examined 57 rain events from over 23 site-years of eddy covariance measurements at an open annual grassland, a woodland understory, and a peatland pasture in California, USA. To explain these findings, we conducted a factorial litter-watering experiment on grass and soil plots exposure to varying amounts of sunlight and water. To interpret and compare the population of rain-induced respiration pulses, we fitted the data with a two pool, 4-parameter exponential decay model.

At the field scale, the total amounts of CO₂ emission emanating from a single and sustained respiration pulse (mean ± standard deviation) were 44.4 ± 38.0, 24.2 ± 17.8, and 94.6 ± 45.8 gC m⁻² at the open grassland, the woodland understory, and the peatland pasture, respectively. The large variations in precipitation of these respiration-triggering rain events were associated with 73–84% of variation in the total amount of CO₂ emission.

Litter that experienced antecedent photodegradation tended to enhance respiration pulses. Biotic and abiotic processes involved in the dynamic of respiration pulses were pulse-specific, and we summarized them into two pulse scenarios. This study illustrates an emerging connection of ecosystem processes, and these findings may help to improve models on the dynamics of ecosystem CO₂ cycling.