Transpiration and stomatal control: a cross-species study of leaf traits in 39 evergreen and deciduous broadleaved subtropical tree species

Using an extensive dataset for 39 subtropical broadleaved tree species, we found traits of the leaf economics spectrum to be linked to mean stomatal conductance but not to stomatal regulation. The aim of our study was to establish links between stomatal control and functional leaf traits. We hypothesized that mean and maximum stomatal conductance (g (s)) varies with the traits described by the leaf economics spectrum, such as specific leaf area and leaf dry matter content, and that high g (s) values correspond to species with tender leaves and high photosynthetic capacity. In addition, we hypothesized that species with leaves of low stomata density have more limited stomatal closure than those with high stomata density. In order to account for confounding site condition effects, we made use of a common garden situation in which 39 deciduous and evergreen species of the same age were grown in a biodiversity ecosystem functioning experiment in Jiangxi (China). Daily courses of g (s) were measured with porometry, and the species-specific g (s)similar to vpd relationships were modeled. Our results show that mean stomatal conductance can be predicted from leaf traits that represent the leaf economics spectrum, with a positive relationship being related to leaf nitrogen content and a negative relationship with the leaf carbon: nitrogen ratio. In contrast, parameters of stomatal control were related to traits unassociated with the leaf economics spectrum. The maximum of the conductance similar to vpd curve was positively related to leaf carbon content and vein length. The vpd at the point of inflection of the conductance similar to vpd curve was lower for species with higher stomata density and higher for species with a high leaf carbon content. Overall, stomata size and density as well as vein length were more effective at explaining stomatal regulation than traits used in the leaf economics spectrum.