The effects of seasonality and leaf dehydration on foliar water uptake rehydration kinetics in the mangrove Sonneratia alba, Daintree River, QLD, DP150104437 and DP180102969.

Full description

Abridged data specific methods (See publication for unabridged experimental methods: "Foliar water uptake via cork warts in mangroves of the Sonneratia genus" Plant, Cell and Environment, 2021.) Plant material was sourced between November 2017 and October 2019 from naturally occurring trees on Daintree River, Daintree National Park, Far North Queensland, Australia. Sonneratia alba material was collected closer to the estuary mouth (16deg 17'24.8"S 145deg 24'36.8"E). One branch was collected from each of 3-5 co-occurring trees of each species and transported to the lab in black plastic bags with moistened paper towel to prevent water loss.

Pathway kinetics and effect of season and dehydration.
Rehydration kinetics associated with FWU pathways were assessed in S. alba only due to the short, flattened petioles of S. caseolaris making it difficult to measure water potential in intact leaves. The effect of seasonality on leaf conductance to surface water was assessed in S. alba in wet season (Dec 2017) and again in dry season (August 2018). Branches from wet season (n = 3) and dry season (n = 4) were transported back to the lab in black plastic and allowed to air dry for 4-5 h, to achieve similar starting water potentials, -2.91 +/- 0. 16 MPa and -3.19 +/- 0.08 MPa, for the wet and dry season respectively (mean +/- SD, F = 0.069, P = 0.002, Two-tailed t-test). After dehydration branches were allowed to equilibrate in black plastic bags for 40 min. At 20:00 h, nine pairs of mature healthy leaves, each sharing a single node were selected from each branch. The Ψleaf of one leaf from each leaf pair was measured using a Scholander pressure chamber (1050D, PMS Instrument Albany, USA) as a proxy for its partner and the fresh weight of the opposite leaf was measured. Weighed leaves' petioles were wrapped in Nesco-film to preclude water entry, and were then hung with delicate clothes pegs on a dowel rod spanning a clear, 50 l polypropylene chamber. Leaves were subjected to a wetting treatment using a spraying bottle until all leaf surfaces and chamber walls were wet. Additionally, the chamber was filled with 5 cm of water with several wads of sponge placed semi-emerged in the water to increase evaporative surface area and maintain humidity. Rehydration kinetics were of leaves were assessed at eight intervals (t = 1, 2, 3, 4, 6, 8, 10, 12 h). Following wetting exposure, leaves were removed from the chamber, excess surface water was removed by blotting with a paper towel, then leaves were measured for change in fresh mass and change in Ψ. Leaf area was then measured using a flatbed scanner (LiDE scan 110, Canon, Sydney, Australia) and ImageJ (Schneider, Rasband & Eliceiri 2012). To maintain leaf surface wetting of leaves remaining in the chamber, leaf surfaces were re-misted seven times over a 12 h period, i.e. every time the chamber was opened for resampling. Foliar water uptake (FWU; mol H2O/ m^2) was calculated as: ((FWU= ((fm_f- fm_i ))/(LA * M ) ) where fmi and fmf are the initial and final leaf fresh mass respectively, LA is the two-sided leaf area and M is the molar mass of water (Limm, Simonin, Bothman & Dawson 2009). Leaf conductance to surface water (Ksurf; ∆ umol H2O /m^2/ s/ MPa) was calculated as: (K_surf=(C_leaf ln(Ψ_i/Ψ_f ))/t ) where Ψi and Ψf are the initial and final leaf water potentials respectively, Cleaf is FWU divided by the absolute change in Ψ (Ψf - Ψi) measured on individual leaves, and t is the duration leaf wetting (Brodribb & Holbrook 2003; Binks et al. 2019; Guzman‐Delgado et al. 2021).

The effect of leaf dehydration on leaf conductance to surface water was assessed in S. alba in leaves sampled in April 2019. Branches from five trees (n = 5) were subjected to three statistically distinct dehydration treatments differing in initial Ψleaf. -1.82 +/- 0.20, -2.26 +/- 0.09, -3.81 +/- 1.49 (mean +/- SD, F8 = 533.41, P < 0.001, One-way repeated measures ANOVA). Water relations between early and late dry season have been characterized by for S. alba at this study site previously (Bryant 2019). The dehydration levels selected in the present study span the expected points of bulk leaf turgor loss, measured as -2.9 +/- 0.1 MPa and -3.4 +/- 0.1 MPa during early and late dry season, respectively, as well as water potentials associated with 50% stomatal closure, -3.10 +/- 0.15 MPa, and approaching 88% stomatal closure, ~ -4.10 MPa (Bryant 2019). After dehydration, branches were allowed to equilibrate in black plastic bags for 40 min. Foliar water uptake rehydration kinetics were measured using the same protocol as seasonality FWU kinetics, however with only four leaf pairs from each branch arrayed over an 8 h period (t = 2, 4, 6, 8 h).

Notes

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Significance statement

Foliar water uptake (FWU) rehydration kinetics experiments for a novel pathways of leaf surface water uptake, the cork wart.
Experiments revealed a novel mode of FWU, with slow a steady rate of water uptake persistent over 12h durations. Leaf surface conductance to foliar water increased with longer durations of leaf wetting and was greater in leaves with more negative water potentials at the initiation of leaf wetting. Ksurf declined by 70% between wet and dry seasons.