High potential for foliar water uptake in early stages of leaf development of three woody angiosperms

Foliar water uptake (FWU) is a widespread mechanism that may help plants cope with drought stress in a wide range of ecosystems. FWU can be affected by various leaf traits, which change during leaf development. We exposed cut and dehydrated leaves to rainwater and measured FWU, changes in leaf water potential after 19 h of FWU (Delta Psi), minimum leaf conductance (g(min)), and leaf wettability (abaxial and adaxial) of leaves of Acer platanoides, Fagus sylvatica, and Sambucus nigra at three developmental stages: unfolding (2-5-day-old), young (1.5-week-old) and mature leaves (8-week-old). FWU and g(min) were higher in younger leaves Delta Psi corresponded to FWU and g(min) in all cases but mature leaves of F. sylvatica, where Delta Psi was highest. Most leaves were highly wettable, and at least one leaf surface (adaxial or abaxial) showed a decrease in wettability from unfolding to mature leaves. Young leaves of all studied species showed FWU (unfolding leaves: 14.8 +/- 1.1 mu mol m(-2) s(-1)), which may improve plant water status and thus counterbalance spring transpirational losses due to high g(min). The high wettability of young leaves probably supported FWU. We observed particularly high FWU and respective high Delta Psi in older leaves of F. sylvatica, possibly aided by trichomes.