Phylogenetic and biogeographic controls of plant nighttime stomatal conductance

Summary 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 .