WATER RELATIONS OF A TROPICAL VINE-LIKE BAMBOO (RHIPIDOCLADUM-RACEMIFLORUM) - ROOT PRESSURES, VULNERABILITY TO CAVITATION AND SEASONAL-CHANGES IN EMBOLISM

The occurrence of root pressure, the vulnerability of xylem vessels to drought-induced cavitation, and the seasonal changes in hydraulic conductivity due to embolism were studied in the culms of Rhipidocladum racemiflorum (Steud.) McClure, a tropical vine-like bamboo from central Panama. Positive hydrostatic potentials up to 120 kPa occurred only during the wet season when the transpiration rate of the plant was low, i.e. at night or during rain events. Although the xylem vessels were large and efficient for conducting water, they were highly resistant to cavitation. Xylem water potentials lower than -4.5 MPa were required to induce 50% loss of hydraulic conductivity in culms. The minimum water potential reached -3.75 MPa at the end of the 1993 dry season, so loss of hydraulic conductivity due to embolism remained <10%. The species is adapted to drier habitats both by way of a low vulnerability to xylem cavitation and by root pressures in the wet season that could refill vessels that became embolized during a severe dry season.