Are rain-induced ecosystem respiration pulses enhanced by legacies of antecedent photodegradation in semi-arid environments?

Ecosystem respiration (Reco) is highly variable in semiarid ecosystems. After a period of drought, Reco 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.

► The highlight of this study is to make a link between rain-induced respiration pulses and legacies of antecedent photodegradation by analyzing a dataset over 23 site-years of eddy covariance measurements, applying a factorial litter-watering experiment, and modeling labile carbon pools involved in respiration pulses.
► Our data show that litter, combined with precipitation, enhanced the size of respiration pulses.
► This study is done timely when photodegradation and its sequent effects on carbon fluxes start attracting the attentions of the carbon flux community.
► No one has reported the potential effects of antecedent photodegradation on ecosystem respiration pulses yet to our knowledge.