Beneficial effects of direct foliar water uptake on shoot water potential of five chasmophytes

Five chasmophytic species growing as wall-fissure plants on vertical retaining walls of a castle in the town of Patras, Greece, were examined for their ability to benefit from direct absorption of foliar surface water. Epifluorescence microscopy and application of an apoplastic tracer of water movement indicated that sprayed water on leaf surfaces penetrated into the mesophyll of all species, and in some cases was also detected within conducting tissues of the leaf. Water potential (Psi(w)) of sprayed detached shoots was improved compared with unsprayed controls when they were slowly losing water under laboratory conditions. The beneficial effect of leaf water absorption on Psi(w) was found either on leaves that were originally fully turgid or on leaves that had undergone a considerable water content reduction. Sprayed leaves maintained their Psi(w) above turgor loss point for a time period of 10-90 min depending on species and degree of water deficiency. The relevance of the results to the importance of dew uptake from chasmophytes growing under water shortage in wall fissures in inhabited areas is discussed.