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The Effect of the Autumn Senescence of Leaves on the Internal Cycling of Nitrogen for the Spring Growth of Apple Trees

P. MILLARD and C. M. THOMSON
Journal of Experimental Botany
Vol. 40, No. 220 (November 1989), pp. 1285-1289
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23692426
Page Count: 5
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The Effect of the Autumn Senescence of Leaves on the Internal Cycling of Nitrogen for the Spring Growth of Apple Trees
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Abstract

The internal cycling of nitrogen (N) has been studied in apple rootstocks grown in sand culture and subjected to a constant N supply, or defoliation, or withholding the N supply in the autumn in order to manipulate the amount of N stored over the winter. The trees subsequently received either no N or 8.0 mol N m-3 (labelled with 15N to 4.98 atom%) with the irrigation the following spring in order to determine the effect of the current N supply on the remobilization of N for leaf growth. Provision of an autumnal N supply delayed leaf senescence and reduced the amount of N withdrawn from leaves from 156 mg N plant-1 to 91 mg N plant-1. Loss of protein ribulose 1,5-bisphosphate carboxylase/oxygenase (RUBISCO) accounted for 83—87% of the soluble protein N lost during leaf senescence, there being a preferential loss of RUBISCO compared with other soluble leaf proteins. Remobilization of N from perennial woody tissues (stems and roots) in the spring was used predominantly for leaf growth. The amount of N remobilized depended upon the size of the N store, but was unaffected by the current N supply, demonstrating that fertilization of trees does not alter the efficiency with which they cycle N. Degradation of RUBISCO in the autumn accounted for between 32% and 48% of the N subsequently remobilized for leaf growth the following spring, suggesting that RUBISCO has a role as a summer store for N.

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