Pine root structure and its potential significance for root function

Actively growing roots of pouch-grown Pinus banksiana Lamb. are known to have three anatomically distinct zones, i.e., white, condensed tannin, and cork (in order of increasing distance from the root tip). Roots of pouch and pot-grown Pinus taeda L., and field-grown P. banksiana also develop these three zones. The terminal region of a dormant root resembles the condensed tannin zone, with the addition of a suberized metacutis partially surrounding the apical meristem. White roots are anatomically suited for efficient ion uptake due to the presence of a living cortex. The condensed tannin zones of both growing and dormant roots have a dead cortex but retain passage cells in their endodermal layers, through which some ion uptake could occur. The effect of the maturation from white to condensed tannin zone on water uptake is difficult to predict, but some uptake would occur through the endodermal passage cells. In the young cork zone, no ion and little water absorption should occur. The discrepancies between results of separate anatomical and physiological investigations of tree roots need to be resolved by correlative studies incorporating both approaches in individual experiments.