Phylogenetic and biogeographic controls of plant nighttime stomatal conductance

The widely documented phenomenon of nighttime stomatal conductance g(sn) could lead to substantial water loss with no carbon gain, and thus it remains unclear whether nighttime stomatal conductance confers a functional advantage. Given that studies of g(sn) have focused on controlled environments or small numbers of species in natural environments, a broad phylogenetic and biogeographic context could provide insights into potential adaptive benefits of g(sn). We measured g(sn) on a diverse suite of species (n = 73) across various functional groups and climates-of-origin in a common garden to study the phylogenetic and biogeographic/climatic controls on g(sn) and further assessed the degree to which g(sn) co-varied with leaf functional traits and daytime gas-exchange rates. Closely related species were more similar in g(sn) than expected by chance. Herbaceous species had higher g(sn) than woody species. Species that typically grow in climates with lower mean annual precipitation - where the fitness cost of water loss should be the highest - generally had higher g(sn). Our results reveal the highest g(sn) rates in species from environments where neighboring plants compete most strongly for water, suggesting a possible role for the competitive advantage of g(sn).