STOMATAL OSCILLATIONS IN THE MANGROVE AVICENNIA-GERMINANS

1. The mangrove Avicennia germinans, maintained under semi-steady-stat e glasshouse conditions, exhibited stomatal oscillations. 2. Continuou s, simultaneous measurements of transpiration, photosynthesis, leaf te mperature and water potential indicated that cycling was synchronized throughout the plant and was rapidly propagated by changes in water po tential. 3. The frequency of cycling ranged from 30 to 48 min, usually with large amplitudes, and resulted in considerable fluctuations in t ranspiration and photosynthesis. 4. Cyclic variation in water potentia l lagged behind those in conductance and transpiration by 2-7 min. 5. Oscillations were induced by increases in vapour pressure deficit (VPD ) and osmotic potential of the substrate and eliminated by decreases i n VPD, substrate osmotic potential, root temperature and root resistan ce. 6. Oscillatory behaviour appeared to be induced by any factor that brought about rapid changes in hydraulic flow through the plant. 7. T hese results are discussed in relation to feedback mechanisms that reg ulate stomatal movement.