Evergreen conifers, including spruce and pine, are now well documented to take up liquid water directly through their needles and branch surfaces when those surfaces are wet (dew, fog, rain, melting snow). The mechanism is “foliar water uptake,” and in conifers it is usually from liquid films on the surface rather than from water vapour at normal humidities.
Classic experiment: Ponderosa pine needles absorbing water and redistributing it (Stone 1956)
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Seedlings of Pinus ponderosa were exposed so that only the needles were wetted (shoots enclosed, soil kept dry or isolated).
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Needle water content and plant water potentials were measured over time.
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The seedlings gained water even though the soil was dry, and that water was traced moving internally from wetted needles into stems and other tissues.
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This showed that pine needles can absorb water from external wetting and that the absorbed water is integrated into the xylem stream, not just sitting on the surface.
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Modern pine work: foliar water uptake depends on needle traits (Roth‑Nebelsick et al. 2022, Annals of Botany)
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Seven Pinus species were tested by wetting needles and monitoring mass gain (gravimetric FWU).
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All species showed measurable foliar water uptake, but the rate depended strongly on needle age and stomatal wax structure.
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Younger needles, and those with less-complete wax “plugs” over stomata, absorbed more water.
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This directly links pine needle micromorphology to their capacity to absorb liquid water from the surface.
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Spruce and other conifers: branch/needle uptake and redistribution (Mayr et al. 2021, alpine treeline study on Picea abies and Larix decidua)
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Branch segments were experimentally wetted (simulating melting snow, fog, or rain) while monitoring water potentials and xylem conductivity.
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Both species took up significant amounts of water through the branch surface (needles and bark) and redistributed it along the crown during winter, helping reverse embolism and improve hydraulic status.
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Prior work cited in that study identifies Picea abies needles and partially open stomata plus high cuticular conductance as key pathways for water entering from external wetting.
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Greenhouse and fog‑chamber work on western conifers (Weisgrau 2020, Humboldt State M.Sc. thesis)
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Four western conifers were tested, including Picea sitchensis (Sitka spruce).
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Two methods were compared: submersion of foliage and exposure to water vapour/fog in a chamber.
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All species, including spruce, showed capacity for foliar water uptake; uptake rates from fog were about three times higher than from submersion, indicating that fine water droplets and films on the needles are particularly effective.
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The absorbed water could then be hydraulically redistributed, helping maintain water status under drought.
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General foliar uptake in conifers and other plants (Limm et al. 2009; Liu et al. 2021)
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Surveys in foggy redwood forests found many species, including conifers, increased leaf water content by 2–11% after fog events due to foliar uptake.
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Isotope‑labelled precipitation experiments on the conifer Platycladus orientalis showed that water deposited on foliage entered the leaf, then moved along a water potential gradient from leaves to branches and roots, even under soil drought.
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These studies confirm that foliar uptake is not an oddity but a common strategy in woody plants, including conifers.
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Mechanisms at the needle scale
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Wetting requirement: The dominant evidence is for uptake of liquid water (dew, fog droplets, rain, melting snow) on the needle surface, rather than direct condensation from unsaturated air.
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Pathways:
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Partly open stomata and regions of relatively high cuticular conductance allow water to cross the outer surface.
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Aquaporins (water-channel proteins) increase in needle endodermis and phloem during spring recovery in spruce, consistent with enhanced radial water movement from surface to xylem.
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Conditions favouring uptake:
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Low soil water potential (drought or frozen soil) and high atmospheric humidity/wetting events.
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Cool, moist conditions (fog, dew, snowmelt on needles) that reverse the usual water potential gradient, allowing water to move inward.
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Clarifying “from the air”
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In the strict sense of absorbing water directly from water vapour at typical humidities, evidence is sparse and largely indirect; what is well documented is absorption from surface water that originates from the air (dew, fog, cloud water, drizzle) once it has condensed or deposited on the needles.
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In field terms, this still functions as an atmospheric water source: canopy wetting can materially increase needle water content and support xylem function when roots cannot supply enough water.
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In summary, both spruce and pine needles demonstrably absorb externally supplied water under natural conditions, especially from dew, fog, and snowmelt on the foliage. This water can move into the xylem, be redistributed within the tree, and partially offset soil water limitations. The mechanism relies on wet surfaces and microstructural features (cuticle, stomata, aquaporins), so it is best described as foliar uptake from liquid water derived from the atmosphere, rather than direct uptake of water vapour from unsaturated air.
