Foliar Water Uptake in Trees: Negligible or Necessary?

Identifying the pathways for foliar water uptake in beech (Fagus sylvatica L.): a major role for trichomes

“…Foliar water uptake (FWU) has known an increasing scientific interest over recent years resulting in a growing body of evidence supporting the general occurrence of this mechanism (Dawson and Goldsmith, 2018;Berry et al, 2019;Schreel and Steppe, 2020). FWU can occur during leaf wetting events, such as fog, rain, snow and morning dew, and has been indicated as a global phenomenon, ranging from redwood forests (Burgess and Dawson, 2004) to dryland ecosystems (Breshears et al, 2008) and mangrove forests (Steppe et al, 2018).…”

“…Of the nine species studied by Schreel et al (2019a), beech (Fagus sylvatica L.) was identified as one of the species that would benefit most from FWU during drought. Because droughts are projected to become more frequent and severe as a result of climate change in the upcoming century (IPCC, 2018), investigating the underlying mechanisms for FWU in beech will increase our understanding of tree functioning during these extreme events (Schreel and Steppe, 2020).…”

“…Although the importance of FWU during drought is becoming more clear, the pathways used for foliar absorption are species dependent (Eller et al, 2016;Dawson and Goldsmith, 2018) and, for most species, unidentified (Schreel and Steppe, 2020). The four most commonly accepted pathways are: (i) diffusion through the cuticle (Ketel et al, 1972) and (ii) absorption by hydathodes (Martin and von Willert, 2000), (iii) stomata (Burkhardt et al, 2012) or (iv) trichomes (Ohrui et al, 2007).…”

“…Subsequent ultrastructural and (immuno)histochemical analyses were carried out to identify structural and chemical features that may facilitate trichome water uptake. The proposed methodological framework is generic and can be applied to other species to further unravel the yet poorly understood FWU pathways (Schreel and Steppe, 2020).…”

Foliar water uptake as a source of hydrogen and oxygen in plant biomass

“…Introductory biology lessons around the world typically teach that plants absorb water through their roots (McElrone et al, 2013), but, unfortunately, absorption of water through leaves and subsequent transport and use of this water for biomass formation remains a field limited mostly to specialists (Roden et al 2000). Recent studies have identified foliar water uptake as a significant but still unquantified net water source for terrestrial plants (Eller et al, 2013;Goldsmith et al, 2013;Dawson & Goldsmith, 2018;Berry et al, 2019;Schreel & Steppe, 2020). The growing interest in the development of a new model that includes foliar uptake of liquid water to explain hydrogen and oxygen isotope ratios in leaf water and tree rings requires a method for distinguishing between these two water sources.…”