Phylogenetic and biogeographic controls of plant nighttime stomatal conductance

The widely documented phenomenon of nighttime stomatal conductance gₛₙ 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 gₛₙ 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 gₛₙ. We measured gₛₙ 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 gₛₙ and further assessed the degree to which gₛₙ co‐varied with leaf functional traits and daytime gas‐exchange rates. Closely related species were more similar in gₛₙ than expected by chance. Herbaceous species had higher gₛₙ 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 gₛₙ. Our results reveal the highest gₛₙ rates in species from environments where neighboring plants compete most strongly for water, suggesting a possible role for the competitive advantage of gₛₙ.