Control of Water Loss by Actively Growing Sitka Spruce Seedlings after Transplanting

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Abstract
The roots of actively growing Sitka spruce seedlings were disturbed and damaged to different degrees by transplanting treatments carried out in a growthroom. The treatments stopped root extension and after 2–4 h the transpiration rate of treated plants declined, indicating closure of the stomata, and transpiration continued to decrease for a few days. The hydraulic conductivity of the root system was reduced slightly by the treatment but leaf water potential increased or remained unchanged, therefore no water stress occurred to account for closure of the stomata. Measurements on detached shoots indicated that the water storage capacity was too small to accommodate changes in the vascular water supply without reducing leaf water potential. The measured responses of the plant were not affected by girdling the base of the stem prior to root treatment. It is suggested that the transpiration rate of treated plants was reduced as a result of a chemical stimulus originating in the root and acting on the stomata.