Effect of Interruption of Flow Path on Stomatal Conductance ofAbies amabilis

Wounding of root or stem water conduction systems or cooling of roots in Abies amabilis produced rapid stomatal closure independent of evaporative demand or leaf water potential. The response also occurred in a branch if its xylem was only partially cut, but did not occur if the branch was completely severed. Removing part of the root system or cooling the roots produced the same effect as partial severing of the stem. The speed and uniformity of stomatal closure indicated that the stimulus was physical, linked to water flux in the xylem, and not caused by release of a chemical stimulus at the point of xylem flow disruption. The results suggested that stomatal closure could be rapidly induced with a change in the flux of water through the soil-plant-atmosphere continuum.