Differential daytime and night-time stomatal behavior in plants from North American deserts

Night-time stomatal conductance (g night) occurs in many ecosystems, but the g night response to environmental drivers is relatively unknown, especially in deserts. Here, we conducted a Bayesian analysis of stomatal conductance (g) (N=5013) from 16 species in the Sonoran, Chihuahuan, Mojave and Great Basin Deserts (North America). We partitioned daytime g (g day) and g night responses by describing g as a mixture of two extreme (dark vs high light) behaviors. Significant g night was observed across 15 species, and the g night and g day behavior differed according to species, functional type and desert. The transition between extreme behaviors was determined by light environment, with the transition behavior differing between functional types and deserts. Sonoran and Chihuahuan C4 grasses were more sensitive to vapor pressure difference (D) at night and soil water potential (ψ soil) during the day, Great Basin C3 shrubs were highly sensitive to D and ψ soil during the day, and Mojave C3 shrubs were equally sensitive to D and ψ soil during the day and night. Species were split between the exhibition of isohydric or anisohydric behavior during the day. Three species switched from anisohydric to isohydric behavior at night. Such behavior, combined with differential D, ψ soil and light responses, suggests that different mechanisms underlie g day and g night regulation.