Survey of root pressure in tropical vines and woody species
International Journal of Plant Sciences
Observations on root pressure were made for 109 species in Costa Pica, Mexico, and Florida during the rainy season. Native and naturalized species, as well as a few outdoor cultivated specimens, were used. Predawn guttation was observed in 15 species. Predawn root pressure, as evidenced by xylem sap exudation from cut stems, was observed in 61 species. Root pressures, measured with a bubble manometer, ranged from 2 kPa to a maximum of 148 kPa in Cissus (Vitaceae). A broad range of climbing monocotyledons, dicotyledons, and one fern (Lygodium) displayed root pressure. Root pressures of selected shoots were followed over consecutive days and were highest in the nighttime, especially at sunrise. The maximum observed root pressure can raise a capillary water column, assuming no resistance, to a height of 14.8 m. Although root pressure alone could not refill embolized xylem vessels in tall trees and vines, the reduction of xylem sap tension would facilitate the dissolving of gas bubbles and the reestablishment of vessel function, at least in the lower parts of the plant or throughout shorter plants.