A survey of root pressures in vines of a tropical lowland forest
Ewers F; Cochard H; Tyree M
Pre-dawn xylem pressures were measured with bubble manometers attached near the stem bases of 32 species of vines on Barro Colorado Island Panama to determine if pressures were sufficient to allow for possible refilling of embolized vessels. Of 29 dicotyledonous species 26 exhibited only negative xylem pressures even pre-dawn during the wet season. In contrast three members of the Dilleniaceae exhibited positive pre-dawn xylem pressures with a maximum of 64 kPa in Doliocarpus major. A pressure of 64 kPa is sufficient to push water to a height of 6.4 m against gravity but the specimens reached heights of 18 m. Thus in all 29 dicotyledons examined the xylem pressures were not sufficient to refill embolized vessels in the upper stems. In contrast two of the smaller non-dicotyledonous vines the climbing fern Lygodium venustrum and the viny bamboo Rhipidocladum racemiflorum had xylem pressures sufficient to push water to the apex of the plants. Therefore a root pressure mechanism to reverse embolisms in stem xylem could apply to some but not to most of the climbing plants that were studied.