Abstract:

Leaf water status and photosynthetic characteristics were investigated in four evergreen species, i.e. Laurus nobilis, Ligustrum japonicum, Nerium oleander and Pittosporum tobira, grown under ambient conditions. The results reveal variations in photosynthetic traits in relation to the use of water, during the optimal period of growth, in the middle of the dry season, during the secondary growth period and in the middle of the cold and wet season. Photosynthesis was restricted by limitations of stomatal conductance, causing transpiration impairment in L. nobilis, L. aponicum and P. tobira; while, the opposite holds true for N. oleander . Stomatal conductance of N. oleander was higher than that of the three co-existing species, sustaining elevated rates of photosynthesis and transpiration, at the expense of water. As drought progressed, there was a reduction in photosynthesis and water use efficiency in L. japonicum and P. tobira . Leaf turgor of the four species was closely associated with leaf water potential and differences among species narrowed in the dry season. The results show that L. nobilis possess features that confer  advantage for the maintenance of this species in the driest sites, N. oleander maximises gas exchanges in the dry season by exhibiting a capacity for water acquisition, while L. japonicum
and P. tobira may be limited to the moist sites .