Water relations, gas exchange and growth of cool-season grain legumes in a Mediterranean-type environment

The aim of this study was to identify the physiological characteristics which may affect the yield of six cool-season grain legume species grown in a water-limited Mediterranean-type climate in Western Australia. The rate of net photosynthesis, stomatal conductance and water relations were measured from flowering to complete leaf senescence in white lupin, chickpea, faba bean, field pea, grass pea and lentil. In irrigated plants, the midday leaf water potential was about -0.6 MPa in all species, while the maximum rate of leaf photosynthesis was 30 μmol m^-2 s^-1 for chickpea and white lupin, and below 20 μmol m^-2 s^-1 for the other species. With the development of water deficits, the leaf water potential in rain-fed plants decreased to about -3 MPa in chickpea and lentil and -2 MPa in the other species. Photosynthesis and stomatal conductance decreased markedly as the leaf water potential decreased below -0.9 MPa in all six species, including chickpea and lentil, which showed a high degree of osmotic adjustment. Despite the similarity in water use, restricted to the top 40 cm of soil, and water relations characteristics, yields varied markedly among species. Yields were strongly correlated with early biomass production and early pod development.