Regulation of Nitrogen Uptake at the Whole-plant Level: A Study in Almond Trees

It has been proposed that a pool of amino N, whose size is determined by aboveground N demand, cycles in the plant and regulates soil N uptake by exerting an inhibitory effect at the root level. Several experiments were carried out to study this hypothesis in almond trees [Prunus dulcis (Mill.) D.A. Webb]. Based on the evidence found, there is an association, at the whole tree level, between sap N content and soil N uptake. The data are consistent with the possibility that increased phloem sap amino acids result in decreased uptake of soil N.