Foliar water uptake in Pinus species depends on needle age and stomatal
wax structures
Abstract
The uptake of water through leaves is commonly referred to as foliar
water uptake (FWU). The phenomenon has been documented in many species
and is increasingly recognized as a non-trivial factor in plant-water
relations. However, it remains unknown whether FWU is a wide-spread
phenomenon in Pinus species, and how it may relate to needle
traits such as the form and structure of stomatal wax plugs. Here we
studied these questions in current-year and one-year old needles of
seven Pinus species. We analyzed the surface and stomatal
structure with cryo-scanning electron microscopy. Additionally, we
considered the effect of artificial wax erosion by application of the
surfactant Triton TM X-100, which is able to alter wax
crystals. The results show for all species 1) that FWU occurred, 2) that
FWU is higher in old needles compared to young needles, and 3) that
there is substantial erosion of stomatal wax plugs in old needles.
Additionally, FWU in young needles was enhanced by the surfactant
treatment, and was highest in P. canariensis showing a thin wax
plug. The results of this study provide evidence 1) for widespread FWU
in Pinus and 2) for the influence of age-related needle surface
erosion on FWU.