The ecophysiology of drought stress in Australian species of 'Acacia': water relations, solute composition and photosynthesis during drought and recovery

Abstract

In many plant species osmotic-adjustment (OA) is an important drought tolerance mechanism. Most research into OA has investigated cropping and forage species, by comparison little is known about the process in non-agronomic plants. The 'Acacia' genus is one of the most widespread and species rich taxons of woody plants in Australia. Members of the genus display morphological and physiological traits that augment their general utility; including rapid growth (enhanced carbon sequestration), nitrogen fixing capacity and above average drought/dehydration tolerance (reduced water consumption). A limited number of 'Acacia' species are cultivated on a global basis to provide a food source and raw materials for various industries. Given the potential of the genus and in the context of currently accepted climate change paradigms, a more complete knowledge of 'Acacia' ecophysiology is required. As water availability becomes progressively limited, a superior capacity to tolerate drought is evidently important. Capacity to recover from water deficit, however, and grow efficiently under conditions of restricted and often punctuated water availability is justifiably of greater significance. This study investigated the fundamental physiological responses of several 'Acacia' species to water stress and subsequent recovery. Particular attention was given to the drought tolerance mechanism of osmotic-adjustment and its relationship to the ecology of 'Acacia'. A separate section of this research surveyed seasonal and climate zone induced changes in leaf/phyllode solute composition and osmotic potential for a cohort of endemic Australian 'Acacia' species. These species were selected to cover a climatic gradient from semi-arid to sub-tropical/coastal habitats. Aspects including the degree of xeromorphy, the ecology and evolutionary heritage of the species and the influence of these factors on resultant physiological responses during drought and recovery were considered.