THE EFFECT OF FLUCTUATING SUBSTRATE SALINITY ON THE YIELD AND FLAG LEAF PHOTOSYNTHESIS OF WHEAT

The effects of constant and fluctuating substrate salinity on flag lea f photosynthesis and grain yield of wheat were investigated. Plants ex posed to salinity fluctuating around a mean integrated value of 25 mol m-3 NaCl (0-50 mol m-3) and around 50 mol m-3 NaCl (25-75 mol m-3) ha d yields 36 and 38% higher, respectively, than those receiving the cor responding constant salinity. Plants treated with salinity fluctuating from 50 to 100 mol m-3 NaCl had a 14% lower yield than those receivin g 75 mol m-3 NaCl. Flag leaf photosynthesis did not vary between treat ments and during salinity fluctuations, suggesting that differences in flag leaf longevity caused the observed differences in yeild. Results suggest plants grown under constant salinity are unlikely to behave i n the same way as those in field situations, where fluctuation rather than constant salinity occurs.