Genetic variation in traits affecting the water relations of balsam poplar along a latitudinal transect in Northwestern Ontario

Genetic variation In traits potentially affecting the waterrelations of balsam poplar (PopuIus balsamifera L.) clones from four provenances along a transect from northern Wisconsin to Pickle Lake in northwestern Ontario was examined both in the field and In the greenhouse. Traits measured were transpiration rates, stomatal conductance, internode length, average single-leaf abaxial area and oven-dry weight, specific leaf weight, and stomatal density and length. Additional traits measured In the greenhouse provenance trial were shoot length, number of leaves per plant, total abaxial leaf area per plant, total oven-dry root, shoot and leaf weight, and oven-dry root/shoot weight ratio. Most of the observed variation in traits was attributable to clones within provenances and to ramets within clones. As much as eighty-five percent of the observed variation was attributable to variation among and within clones within provenances. The provenance effect had a significant Influence on leaf size and morphology traits, with an apparent north-south clinical trend. Leaves from northern sources were smaller In area, lighter In weight, and were thicker than leaves from southern sources. As expected stomatal conductance was positively correlated with measured transpiration rates. The only other trait significantly correlated with transpiration rates was stomatal length, and this only occurred in the greenhouse provenance trial. Larger stomata were associated with higher rates of transpiration