ADDITIVE AND ANTAGONISTIC EFFECTS OF OZONE AND SALINITY ON THE GROWTH, ION CONTENTS AND GAS-EXCHANGE OF 5 VARIETIES OF RICE (ORYZA-SATIVA L)

Five varieties of rice (Oryza sativa L.) of varying salinity resistanc e were grown in non-saline and in saline conditions, with and without a repeated exposure to ozone at a concentration of 88 nmol mol(-1) giv ing an AOT40 (cumulative exposure above 40 nmol mol(-1)) of 3600 nmol mol(-1) h. Salinity caused a substantial reduction in shoot and root d ry weight in all varieties, but the effect on root growth was proporti onately less than on shoot growth. Ozone reduced root dry weight but t he treatment used did not significantly affect shoot dry weight. Both salinity and ozone reduced plant height. The potassium concentration i n the leaves of all five varieties was reduced by salinity, and by ozo ne in both saline and non-saline treatments. Ozone reduced the sodium concentration in plants grown at 50 mM NaCl but had no effect upon the chloride concentration. Carbon dioxide assimilation, transpiration an d stomatal conductance were all reduced by salinity and by ozone and t here was close quantitative similarity between the effects of ozone an d/or salinity upon assimilation, stomatal conductance and transpiratio n. There were some antagonistic effects but there were additive effect s of salinity and of ozone on root dry weight, plant height, shoot pot assium concentration, photosynthesis, transpiration and stomatal condu ctance. The possible basis of the additive effects of salinity and ozo ne on gas exchange and mineral uptake are discussed. Copyright (C) 199 6 Elsevier Science Ltd