Gas Exchange and Growth in Wheat and Barley Grown in Salt

Abstract

By measuring a range of gas exchange and growth variables, attempts were made to select key indicators of response to salinity in a wheat (Q61) and a barley (Beecher). A second wheat (WW15, Anza) was included in the growth measurements.

Plants were grown to anthesis in gravel culture flushed with 0, 75 or 150 mol m^-3 NaCl, and under the high radiation and evaporative conditions of summer. Salinity increased leaf chloride contents and reduced peak photosynthesis, the initial slope of the light response curves, and dark respiration of young leaves at ligule emergence, but dark respiration of slightly older leaves was increased by salinity as were the CO₂ compensation points. Short-duration changes in salinity could modify photosynthesis rates by no more than 15% though dark respiration rates moved quickly towards those of plants held continuously at the new salinity level.

While Q61 wheat appeared superior to Beecher barley at moderate salinity using these gas exchange indicators, it died at 150 mol m^-3 NaCl; Beecher and WW15 survived. Carbon and water budgets are used to propose that the demise of Q61 could have been partially due to its marginally poorer water-use efficiency and its higher specific leaf weight, i.e. its higher requirement for carbon and water to produce each unit area of leaf. It is suggested that measurements of relative leaf expansion rate, specific leaf weight, and water use efficiency would be basic requirements in a salinity screening program. Measurements of ion contents and gas exchange variables are of little benefit when used alone.