| Abstract: | The roots of actively growing Sitka spruce seedlings were disturbedand damaged to different degrees by transplanting treatmentscarried out in a growthroom. The treatments stopped root extensionand after 24 h the transpiration rate of treated plantsdeclined, indicating closure of the stomata, and transpirationcontinued to decrease for a few days. The hydraulic conductivityof the root system was reduced slightly by the treatment butleaf water potential increased or remained unchanged, thereforeno water stress occurred to account for closure of the stomata.Measurements on detached shoots indicated that the water storagecapacity was too small to accommodate changes in the vascularwater supply without reducing leaf water potential. The measuredresponses of the plant were not affected by girdling the baseof the stem prior to root treatment. It is suggested that thetranspiration rate of treated plants was reduced as a resultof a chemical stimulus originating in the root and acting onthe stomata. |
