Abstract
(1) Recent studies suggested that stem photosynthesis could favor bark water uptake and embolism recovery when stem segments are soaked in water under light conditions, but evidence for this phenomenon in drought-resistant Mediterranean species with photosynthetic stems is missing. (2) Embolism recovery upon immersion in water for 2 h–4 h under light was assessed (i) via a classical hydraulic method in leafless Fraxinus ornus and Olea europaea branch segments stressed to xylem water potentials (Ψxyl) inducing ca. 50% loss of hydraulic conductivity (PLC) and (ii) via X-ray micro-CT imaging of the stem segments of drought-stressed potted F. ornus saplings. Hydraulic recovery was also assessed in vivo in intact drought-stressed F. ornus saplings upon soil re-irrigation. (3) Intact F. ornus plants recovered hydraulic function through root water uptake. Conversely, the soaked stem segments of both species did not refill embolized conduits, although Ψxyl recovered to pre-stress levels (between −0.5 MPa and −0.2 MPa). (4) We hypothesize that xylem embolism recovery through bark water uptake, even in light conditions, may not be a common phenomenon in woody plants and/or that wounds caused by cutting short stem segments might inhibit the refilling process upon soaking.
Highlights
Most terrestrial plants rely on root-level water absorption to maintain their hydration status
The soaked stem segments of both species did not refill embolized conduits, Ψxyl recovered to pre-stress levels. (4) We hypothesize that xylem embolism recovery through bark water uptake, even in light conditions, may not be a common phenomenon in woody plants and/or that wounds caused by cutting short stem segments might inhibit the refilling process upon soaking
We tested the hypothesis that the immersion of photosynthesizing stem segments in distilled water for some hours in the presence of light would induce hydraulic recovery through bark water uptake in the embolized branches of two droughtresistant Mediterranean tree species (F. ornus and O. europaea)
Summary
Most terrestrial plants rely on root-level water absorption to maintain their hydration status. Water can be absorbed from the surface of aboveground plant organs under particular biophysical conditions, i.e., when liquid water is wetting plant surfaces or the water potential of the surrounding atmospheric boundary layer is higher than that of cells [1] This occurs when water vapor pressure in the air is at (or close to) saturation and, most importantly, when liquid water forms or falls on a plant surface due to fog, rain or snow melting, allowing local rehydration and partial xylem tension relief, especially when plants are experiencing a soil water deficit [2]. In two species without leaf trichomes or hydathodes, open stomata have been observed to play a major role in water uptake over cuticles when exposed to fog [7]. Leaf water absorption can be involved in the recovery of leaf [8] and stem [9,10] hydraulic functions after drought- or frost-induced xylem embolism
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