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Osmotic potential of Norway spruce [Picea abies (L.) Karst.] secondary phloem in relation to anatomy

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Abstract.

Variations in water status of secondary phloem of Picea abies (L.) Karst., caused by (1) radial and (2) vertical differences within the tree, (3) seasonal influences, and (4) tree class, and their relation to bark anatomy were investigated. The water status parameters measured were the osmotic potential at full saturation [Ψo (sat)], the in situ osmotic potential [Ψo (in situ)], the in situ water content (Cin situ), and the in situ relative water content (Rin situ). Ψo (sat) reached most negative values in the conducting part of the secondary phloem, whereas Ψo (in situ) was similar in conducting (PC) and non-conducting secondary phloem (PN). The remarkable discontinuity in the radial course of Cin situ and Ψo (sat) at the transition from PC to PN can be attributed to the degeneration of sieve cells and Strasburger cells. In PC, the vertical decrease of Ψo (sat) towards the crown was compensated by an increase in Rin situ, so that Ψo (in situ) did not change along the stem. With stem height, Ψo (sat) decreased and PC width increased. The determining factor for vertical gradients in Ψo (sat) was the distance to the sources; similar gradients were also measured in PN. Seasonal differences in Ψo (sat) could only be detected in PC, where they corresponded exactly to changes of Ψo (sat) in needles. Suppressed trees showed less negative Ψo (sat) values in PC, smaller annual secondary phloem increments and smaller radial lumen diameter of living sieve cells than predominant or dominant trees.

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Rosner, S., Baier, P. & Kikuta, S.B. Osmotic potential of Norway spruce [Picea abies (L.) Karst.] secondary phloem in relation to anatomy. Trees 15, 472–482 (2001). https://doi.org/10.1007/s00468-001-0131-9

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  • DOI: https://doi.org/10.1007/s00468-001-0131-9

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