SEASONAL WATER-USE CHARACTERISTICS OF TALL WHEATGRASS [AGROPYRON ELONGATUM (HOST) BEAUV.] IN A SALINE ENVIRONMENT

It is essential to characterize the water use of plants that have pote ntial for the stabilization of rising saline groundwater which could l ead to increases in soil salinity, In this study, several techniques w ere used to determine the seasonal water use characteristics of the pe rennial grass Agropyron elongatum (tall wheatgrass) growing in a moder ately saline, dryland environment with a fluctuating shallow groundwat er table varying in electrical conductivity between 0 and 10 dS m(-1). Soil conditions were examined in terms of water potential measurement s, plant water sources were identified using a stable isotope of water (deuterium, H-2) and evapotranspiration was estimated using hydrologi cal and ventilated chamber methods, Seasonal changes in soil water pot ential were caused by salt accumulation and soil moisture leading to c hanges in plant water availability, particularly in the surface soil r egion over summer and autumn, Evapotranspiration in A, elongatum was h igh over summer during the peak period of growth (4 mm d(-1)), with ev idence of water use from groundwater and from specific regions of the soil profile, Evapotranspiration was low during the period that A, elo ngatum was partially senescent in autumn (< 0.5 mm d(-1)) and the lowe st leaf water potential of -3 MPa that was measured occurred during th is period of moderate water stress, Intermediate levels of water use ( 1.5 mm d(-1)) were measured during winter when the entire soil profile was available for water uptake, Based on physiological characteristic s, including aspects of summer water use, root morphology and salt tol erance in A, elongatum, we conclude that this species is suitable for stabilizing the level of moderately saline groundwater in parts of sou thern Australia, which could reduce the potential for soil salinizatio n.