Oscillations in plant transpiration

Abstract

Plants take up water via the root system and transpire water vapor through stomatal openings in the leaves. Surrounding guard and subsidiary cells control the magnitude of the openings, enabling transpiration but also CO2 transport for photosynthesis. Rhythmic transpiration reflects rhythmic cellular control by these cells and shows a range of short-term periods (typically from a few minutes to some hours). Hydraulic feedback models of water regulation and rhythmic transpiration via the stomatal cells have been developed, either for single or for coupled stomata oscillators. Coupling between stomata over a leaf is necessary to obtain overall transpiration rhythms. Modeling has been strongly extended in later years. The chapter concentrates on experimental findings of overt transpiration rhythms as well as on oscillatory events in the guard cells. Results on the occurrence of rhythms, their period, amplitude, and modulation are discussed. The impact of external environmental parameters on the rhythms is dealt with, e.g., humidity, light, osmotic changes, and ions. The relevance of hydraulic feedback models is discussed as well as the possibilities of calcium oscillations in the guard cells to participate in generating the transpiration rhythms. The overall transpiration pattern can be complicated in space and time: Patchy transpiration can occur over a leaf surface, and period-doubling and period-n patterns have been recorded in the rhythms. There are indications that the control system can be chaotic and the advantages of such a system are shortly discussed. The behavior of transpiration rhythms reveals many dynamic features of the stomatal control system. Some comments and a short discussion on water-use efficiency (WUE) of plants and vegetation end the chapter.