Acclimation of cold-stored jack pine and white spruce seedlings: effect of soil temperature on water relation patterns

Cold-stored jack pine (Pinusbanksiana Lamb.) and white spruce (Piceaglauca (Moench) Voss) seedlings were planted in a controlled environmental chamber providing an air temperature of 22 °C and soil temperatures of 22, 16, or 10 °C. After 21 days, observation of root growth for white spruce seedlings was limited at all soil temperatures, whereas jack pine seedlings showed limited root growth at a soil temperature of 10 °C but not at 22 °C. During 21 days of observation after removal from cold storage, stomatal response patterns changed during the transition phase from darkness to first light. Jack pine seedlings showed increasing stomatal opening at first light with greater stomatal opening for seedlings in the 22 °C root-temperature treatment, while all white spruce seedlings exhibited a greater stomatal closure during darkness. In both species, seedlings at lower soil temperatures experienced greater initial water stress than seedlings at higher soil temperatures, the difference being associated with a greater water-flow resistance through the soil-plant-atmosphere continuum (SPAC). In both species, xylem pressure potentials increased with time at all temperatures; a change attributable to a decline in water-flow resistance through the SPAC. The decline in water-flow resistance was possibly due to either a change in the permeability of older suberized roots or, as in jack pine at the higher soil temperature, a significantly greater development of new unsuberized white roots.