Foliar water uptake via cork warts in mangroves of the Sonneratia genus

Foliar water uptake (FWU) occurs in plants of diverse ecosystems; however, the diversity of pathways and their associated FWU kinetics remain poorly resolved. We characterized a novel FWU pathway in two mangrove species of the Sonneratia genus, S. alba and S. caseolaris. Further, we assessed the influence of leaf wetting duration, wet-dry seasonality and leaf dehydration on leaf conductance to surface water (K-surf). The symplastic tracer dye, disodium fluorescein, revealed living cells subtending and encircling leaf epidermal structures known as cork warts as a pathway of FWU entry into the leaf. Rehydration kinetics experiments revealed a novel mode of FWU, with slow and steady rates of water uptake persistent over a duration of 12 hr. K-surf increased with longer durations of leaf wetting and was greater in leaves with more negative water potentials at the initiation of leaf wetting. K-surf declined by 68% between wet and dry seasons. Our results suggest that FWU via cork warts in Sonneratia sp. may be rate limited and under active regulation. We conclude that FWU pathways in halophytes may require ion exclusion to avoid uptake of salt when inundated, paralleling the capacity of halophyte roots for ion selectivity during water acquisition.

Automated summary

A novel foliar water uptake pathway was characterized in Sonneratia species, with slow and steady rates of water uptake over a 12-hour period. Leaf conductance to surface water (K-surf) increased with longer leaf wetting durations and more negative leaf water potentials at the start of wetting, but declined by 68% between wet and dry seasons. Results suggest that foliar water uptake via cork warts may be rate limited and regulated in Sonneratia sp.