Effects of Waterlogging on Water Relations of Actively-growing and Dormant Sitka Spruce Seedlings

Two-year-old Sitka spruce [Picea sitchensis (Bong.) Carr.] seedlings, either actively growing or dormant, were waterlogged in a growth room at 15 °C. Shoot and root growth, transpiration and leaf water potential were observed. In actively-growing plants shoot extension continued after waterlogging, though at a reduced rate, and shoots of dormant plants broke bud and extended during the waterlogging period. Root growth was suppressed by waterlogging in both types of plant. The 22 day waterlogging treatment eventually killed the actively-growing plants but plants which were dormant at the time of waterlogging were more tolerant. Changes in plant water relations after waterlogging were entirely different depending on the condition of the plants when the soil was flooded. Dormant plants showed a gradual reduction in transpiration and increased water stress over the waterlogging period; after the soil was drained leaf water potential increased to equal the value of control plants which had been maintained in a freely drained condition, but transpiration did not increase until root growth began. Actively-growing plants exhibited a more complex behaviour, characterized by a very rapid reduction in transpiration after waterlogging, accompanied by a brief period of water stress, followed by a period of increasing transpiration rate in the absence of water stress. Finally a second reduction in transpiration occurred and water stress increased as the seedlings died. The importance of the stage of activity of the root system to the response of plants to waterlogging is discussed.