Stem and leaf traits as co-determinants of canopy water flux

Transpiration through stomata in tree canopies plays an important role in terrestrial water cycles. However, the empirical relationship between leaf stomata anatomy and canopy stomatal conductance (G(s)) is surprisingly rare, thereby the underlying biological mechanisms of terrestrial water flux are not well elucidated. To gain further insight into these mechanisms, we reanalyzed the dataset of G(s) previously reported by Gao et al. (2015) using a quantile regression model. The results indicated that the reference G(s) (G(sref), G(s) at 1 kPa) was negatively correlated with wood density at each quantile, which confirmed previous data; however, G(sref) was significantly correlated with stomatal density at the 0.6 quantile, i.e., 450 stomata mm(−2). This highlighted the potential of using stomatal density as a trait to predict canopy water flux. A conceptual model of co-determinants of xylem and stomatal morphology suggests that these traits and their coordination may play a critical role in determining tree growth, physiological homeostatic response to environmental variables, water use efficiency, and drought resistance.