'The functional equilibrium', nibbling on the edges of a paradigm.

Abstract

Mechanisms underlying the functional equilibrium between aboveground and belowground organs of higher plants are discussed with reference to maize, potatoes, wheat, cucumber and Plantago lanceolata. Evidence is presented that the alternative path contributes to a significant extent in root respiration and as this path is only engaged when the supply of carbohydrates to a sink exceeds its demand, it is suggested that root growth is not limited by the supply of carbohydrates. The close correlation between carbohydrate supply to the roots and root growth cannot be explained by a limitation of root growth by carbohydrates but a satisfactory alternative explanation is not provided. Translocation of N from the leaves to the roots of wheat at both opt. and limiting nitrate supply is described. The proportion of N translocated to the leaves and then retranslocated to the roots was highest with limiting N. It is suggested that leaves are unable to incorporate all imported N under N-limiting conditions and that the excess N is then translocated back to the roots. (Abstract retrieved from CAB Abstracts by CABI’s permission)