Measurement design: We randomly selected 12 high-diversity plots, each containing 16 or 24 species, which allowed us to compare as many species as possible across relatively short distances. The aim of our study was to establish links between stomatal control and functional leaf traits.

We recorded daily courses of stomatal conductance for all species in a particular plot by taking repeated measurements on the same leaf from the same individual. Each sampled leaf was fully developed, undamaged, and fully exposed to the sun each day, and leaves were marked with colored plastic ties to ensure the same leaf was measured each day. To provide comparable environmental conditions, all measurements were taken in summer dur- ing dry spells and only on sunny days. Stomatal con- ductance was measured using an SC1 porometer (Decagon), which is based on steady-state technology. It measures the gradient of relative humidity at two dis- tances from the leaf and then calculates vapor flux from the stomata and stomatal conductance per area and time. Only stomatal conductance of the abaxial leaf side was measured as none of the species displayed adaxial sto- mata. For each measurement of stomatal conductance, we also recorded air temperature and relative humidity using a T2 thermo-hygrometer (Trotec) as well as photosyn- thetically active photon flux density (PPFD) using a HD2102.2 PAR Logger (DELTA OHM). The field studies took place in August to October 2010, May/June 2011 and August to October 2011 and only included continuous periods of sunny days to ensure radiation was not limiting photosynthesis and stomatal conductance.

Main Experiment, Site A and B, high diversity plots

08/2010 - 09/2011

39 tree species of the experimental sites

hot sunny humid to dry

stomatal conductance and vapour pressure deficit