Seasonal variation in photosynthetic capacity with respect to plant water status of five species of the mediterranean climate region of South Africa

Abstract

The seasonal variation in net photosynthetic rates of five plant species of the mediterranean climate region of South Africa (fynbos) was investigated. The following species, representing the major fynbos elements, were chosen for intensive investigation: Erica plukenetii (ericoid element), Thamnochortus lucens (restioid element), Protea laurifolia, Leucadendron salignum (proteoid element) and Metrosideros angustifolia , a shrub of riparian habitat. The shallow-rooted restioid and ericoid species showed the lowest net photosynthetic rates of all the species studied and they also exhibited the greatest summer declines in net photosynthesis. Photosynthetic rate generally decreased with increasing water stress. Those plant species which maintained relatively high photosynthetic rates throughout the year (the proteoid species) and those which were able to control excessive water loss ( E. plukenetii ) were more efficient at utilizing water as a resource than T. lucens which exhibited the lowest water-use efficiency.