Minimum leaf conductance and bark water vapor conductance in 14 deciduous tree species

Abstract

How well trees handle drought varies among species, and it is well-known that trees can use different strategies to survive drought stress. One main strategy is to avoid desiccation by limiting water losses through stomatal closure. Two less studied pathways of water loss in trees is the water that is leaving the leaf through other parts of the leaves than the stomata, leaf minimal conductance (gmin), and through the bark, bark water vapor conductance (gbark). Although the amounts of water loss through these processes are small compared to the tree’s total water loss when water availability is high, recent studies have shown that they can be more important for tree health than previously known during droughts. The aim of this study was to investigate: 1) the interspecies variation in gmin and gbark among 14 deciduous tree species, including species that are commonly used in Swedish cities today and ones that may be planted in the future, and 2) if gmin and gbark are linked and if gmin co-varies with stomatal conductance (gsw) and other leaf properties. The gmin and gbark were estimated based on measurements of the weight loss of detached leaves and branch pieces collected from well-watered trees using the “bench drying” method. To facilitate comparison between gmin and gsw, stomatal conductance was measured for attached leaves during both well watered and drought conditions. Significant interspecies differences in gmin and gbark were found. Also, species with high LMA were observed to have low gmin, while no significant relationship was found between gmin and gsw or leaf water content. In addition, gmin and gbark were not significantly correlated. However, the observed among-species differences in gmin and gbark suggest that these traits may be useful for identifying species that are well suited for growth in situations where water availability is limited.