Responses of soil respiration to rainfall addition in a desert ecosystem: Linking physiological activities and rainfall pattern.

The tight linkage between photosynthesis (A) and soil respiration (R) has been verified in many terrestrial ecosystems. However, it remains unclear whether this linkage occurs in desert ecosystems, where water is considered an important trigger of carbon cycling. A field experiment was performed under seven simulated rainfall amounts (0, 3, 5, 10, 15, 25, and 40 mm) with two co-existing desert plants (Reaumuria soongorica and Nitraria sphaerocarpa) in June (early growing season, EGS) and August (middle growing season, MGS) in 2016. A, R, predawn water potential (Ψ), soil temperature (T) and soil moisture (S) were measured for each treatment or control plot for 3 weeks. Our objective was to examine the effects of rainfall pattern on R and physiological responses of the two plants and the relationships between R and biotic and abiotic factors. No obvious variations in Ψ or A were found under small rainfall events. However, when the rainfall amount exceeded 10 mm, both plants responded strongly, and the response patterns of R showed trends similar to those of A, which varied between species and seasons. Moreover, rain additions of 3-40 mm significantly increased R, and the relative changes in R (ΔR) of both species were much larger in the EGS than in the MGS. Importantly, abiotic factors may have controlled the variations in R under small rain events while A played a more important role in regulating the variations in R when the rainfall amount exceeded 10 mm for both species, suggest that the rainfall pattern-driven changes in R composition interact with physiological activity and abiotic factors to regulate the response of R to rainfall variability in desert ecosystems. Thus, climate change in the coming decades may lead to carbon sequestration by desert plants, which may cause desert ecosystems to act as carbon sinks.