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Convergent xylem widening among organs across diverse woody seedlings

Zhong, Mengying, Castro‐Díez, Pilar, Puyravaud, Jean‐Philippe, Sterck, Frank J., Cornelissen, Johannes H. C.
Thenew phytologist 2019 v.222 no.4 pp. 1873-1882
Angiospermae, Mediterranean climate, allometry, leaf area, leaves, life history, mature plants, models, plant organs, seedlings, trees, vegetation, woody plants, xylem
Xylem conduit diameter (Dₘₐₓ) of woody angiosperm adults scales with plant size and widens from the stem apex downwards. We hypothesized that, notwithstanding relative growth rate (RGR), growth form or leaf habit, woody seedling conduit Dₘₐₓ scales linearly with plant size across species; this scaling should be applicable to all vegetative organs, with consistent conduit widening from leaf via stem to main root and coupling with whole‐leaf area and whole‐stem xylem area. To test these hypotheses, organ‐specific xylem anatomy traits and size‐related traits in laboratory‐grown seedlings were analyzed across 55 woody European species from cool‐temperate and Mediterranean climates. As hypothesized, conduit Dₘₐₓ of each organ showed similar scaling with plant size and consistent basipetal widening from the leaf midvein via the stem to the main root across species, independently of growth form, RGR and leaf habit. We also found a strong correlation between Dₘₐₓ and average leaf area, and between stem xylem area and whole‐plant leaf area. We conclude that seedlings of ecologically wide‐ranging woody species converge in their allometric scaling of conduit diameters within and across plant organs. These relationships will contribute to modeling of water transport in woody vegetation that accounts for the whole life history from the trees’ regeneration phase to adulthood.