Environmental control of gas exchange in some savanna woody species : I. Controlled environment studies of Terminalia sericea and Grewia flavescens.

The effects of temperature, radiation, water stress and humidity on net photosynthesis, transpiration and leaf resistances of the two savanna woody species, Grewia flavescens and Terminalia sericea were studied under controlled environmental conditions. Both species have developed morphological and physiological features resulting in low rates of transpiration even under non-stress conditions and are able to tolerate quite severe water stress. Grewia seemed particularly well adapted in this regard and prestressed plants of Grewia were able to photosynthesise down to leaf water potentials of-42 bars. The photosynthetic responses of both species to all the environmental parameters studied were predominantly under stomatal control. The mechanisms employed for maintaining production and conserving water are examined.