DIURNAL AND SEASONAL-VARIATIONS IN GAS-EXCHANGE AND WATER RELATIONS OF LOWLAND AND UPLAND BLACK SPRUCE ECOTYPES

Gas exchange and water relations were measured on seedlings from two p airs of upland and lowland black spruce (Picea mariana (Mill.) BSP) po pulations. The seedlings were planted under natural atmospheric condit ions in exterior sand beds. Measurements were carried out on eight sep arate days during the summer of 1992. Diurnal and seasonal responses o f gas exchange and water relations parameters to natural changes in en vironmental factors were analyzed for possible ecotypic differences. D ifferences were found among the four populations and within one of the two upland-lowland pairs. However, no differences could be linked sig nificantly to an upland-lowland ecotypic differentiation. The physiolo gical responses are discussed with respect to diurnal and seasonal cha nges in environmental factors and to similarities with results from an earlier experiment involving mature trees from the same four populati ons.