Response of the perennial legume Cullen australasicum to low water and phosphorus availability and the use of modelling to predict adaptation to the southern Australian wheatbelt

[Truncated abstract] Arable lands across Australia are often affected by phosphorus (P) and moisture limitations, and most exotic pasture species are not well adapted to these marginal soils. Under such scenarios, Australian native species may perform better since they evolved in nutrient-impoverished and dry landscapes. However, information on Australian native species is very limited, and thus it is difficult to predict the growth of native pasture species and make comparisons with exotic pasture species. However, once basic morphological and physiological characteristics of a prospective pasture species are known, those can subsequently be used as inputs for the development of pasture growth models. Plant growth models integrate the understanding of plant physiological processes within a mathematical framework that allows dynamic simulation of plant growth and development to estimate plant responses to genetic, environmental and management factors. Therefore, this PhD project aimed to study the growth and physiology of the Australian native perennial legume species Cullen australasicum when grown in moisture- and P-limited conditions. Since C. australasicum is considered to have potential as a pasture species, the aim was to develop a growth model for C. australasicum to estimate its performance under the conditions of the wheatbelt of Western Australia. First, an experiment was conducted under glasshouse conditions to understand the mechanisms and adaptations of C. australasicum and C. pallidum to grow at low-P and low-moisture availability (Chapter 2). The changes in shoot and root growth, root architecture, rhizosphere carboxylate dynamics, leaf photosynthesis, water use-efficiency and phenological development were studied. The results were compared with a widely cultivated exotic perennial pasture legume, Medicago sativa (lucerne).