DYNAMIC CHANGES IN LEAF BULK WATER RELATIONS DURING STOMATAL OSCILLATIONS IN MANGROVE SPECIES - CONTINUOUS ANALYSIS USING A DEWPOINT HYGROMETER

Plants of the mangrove species Pelliciera rhizophoreae and Avicennia g erminans exhibit pronounced oscillations in stomatal aperture under ce rtain climatic conditions. During these oscillations, changes in trans pirational water loss were closely followed by those in leaf water pot ential (Psi(1)) as indicated by continuous monitoring with an in situ dewpoint hygrometer. With this instrument, it was possible to measure dynamic changes in Psi(1) for several days under constant conditions. Subsequently, the leaf was detached from the shoot and a pressure-volu me (PV) curve was established by repeatedly weighing the leaf, still a ttached to the hygrometer during short interruptions of the water pote ntial recordings. The pressure-volume relationship was then used to de rive other water relations parameters from these water potential data. Thus, the procedure described herein allows a continuous analysis of the relevant components of bulk leaf water relations. Oscillations in water potential were also measured with single leaves using a pressure chamber. Water relations data obtained with these two different metho ds were in good agreement. In addition, osmotic potentials derived fro m the PV-analysis were well within the range of those determined cryos copically using extracted cell sap.