RADIALLY SECTORED HYDRAULIC PATHWAYS IN THE XYLEM OF THUJA-OCCIDENTALIS AS REVEALED BY THE USE OF DYES

Thuja occidentalis shows slow growth, strip-bark morphology, and extre me longevity when growing on cliffs of the Niagara Escarpment, Ontario , Canada. To test whether these features could result from sectored ra dial architecture, dye-infusion experiments were performed on trees in four different age/size categories. Safranin and/or crystal violet we re infused for up to 2 wk into young lateral roots. Plants were then h arvested, serial-sectioned, and photographed. When two dyes were infus ed simultaneously, different lateral roots were used. Trees were also infused with dye, wounded, and then resupplied with dye to determine w hether hydraulic pathways were altered as predicted by commonly accept ed models. The results showed rapid radially sectored dye uptake in tr ees older than 1 yr. Individual roots tended to supply dye to only par t of the crown. Wounding had no influence on the pattern of dye distri bution. Stem segments with opposing, overlapping, and adjacent saw cut s had hydraulic conductance values near zero. The results indicate tha t T. occidentalis has sectored radial architecture that almost complet ely isolates the hydraulic pathways to particular parts of the stem an d crown. The results indicate that the survival, morphology, and longe vity of this species are related to the capacity of this species to se ctor productivity and mortality in resource-patchy environments.