Water Relations of Tropical Epiphytes

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Abstract
The water relations of five species of tropical vascular epiphytes native to Malaysia were studied. The species were ferns: Pyrrosia adnascens (Forst.) Ching. and Pyrrosia angustata (Sw.) Ching.; orchids: Eria velutina Lindl., Dendrobium tortile Lindl. and Dendrobium crumenatum Sw. Leaf resistance as a function of leaf water potential was measured for the two ferns. The critical water potential at which stomata closed was found to be high in each case; −0.75 MPa and −0.5 MPa respectively. The components of water potential were estimated with the pressure chamber as functions of relative water content. For each species cell sap was found to be dilute, pressure potential low at full turgor, and the change in relative water content between full turgor and wilting point small. Small values of solute potential at full turgor were also found for the ferns and E. velutina using a vapour pressure osmometer. Values of the bulk modulus of elasticity of the leaf tissue for each species lay within the range of published data. The significance of these results for the epiphytic way of life is discussed.