WATER RELATIONS PARAMETERS OF LOWLAND AND UPLAND BLACK SPRUCE - SEASONAL-VARIATIONS AND ECOTYPIC DIFFERENCES

Weekly values of water relations parameters of four black spruce (Pice a mariana (Mill.) B.S.P.) populations growing in a common garden north of Quebec City were obtained by pressure-volume curve analysis from m id-May to mid-October 1991. Two of the four populations originated fro m the province of Quebec, and two were from Ontario. Within each geogr aphical location, one population was from a lowland site (peat soil) a nd the other from an upland site (well-drained sandy soil). Difference s between upland and lowland populations were small but statistically significant for the majority of water relations parameters in the Onta rio pair. No significant differences could be found between population s in the Quebec pair. In the Ontario pair, trees from the lowland site exhibited some traits that could be associated with water-stress tole rance, such as lower relative water content at turgor loss point, lowe r maximum modulus of elasticity, lower osmotic potential at turgor los s point, and higher osmotic amplitude for turgor maintenance. The seas onal pattern of water relations parameters was similar among the four populations and also similar to patterns that have been reported for o ther species. The seasonal variations in water relations parameters fo llowed phenological changes that were driven by seasonal shifts in env ironmental parameters.