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 extreme longevity when growing on cliffs of the Niagara Escarpment, Ontario, Canada. To test whether these features could result from sectored radial architecture, dye-infusion experiments were performed on trees in four different age/size categories. Safranin and/or crystal violet were infused for up to 2 wk into young lateral roots. Plants were then harvested, serial-sectioned, and photographed. When two dyes were infused simultaneously, different lateral roots were used. Trees were also infused with dye, wounded, and then resupplied with dye to determine whether hydraulic pathways were altered as predicted by commonly accepted models. The results showed rapid radially sectored dye uptake in trees older than 1 yr. Individual roots tended to supply dye to only part of the crown. Wounding had no influence on the pattern of dye distribution. Stem segments with opposing, overlapping, and adjacent saw cuts had hydraulic conductance values near zero. The results indicate that T. occidentalis has sectored radial architecture that almost completely isolates the hydraulic pathways to particular parts of the stem and crown. The results indicate that the survival, morphology, and longevity of this species are related to the capacity of this species to sector productivity and mortality in resource-patchy environments.