The Effect of Salinity upon Photosynthesis in Rice (Oryza sativa L.): Gas Exchange by Individual Leaves in relation to their Salt Content

Yeo, A. R., Caporn, S. J. M.and Flowers, T. J. 1985. The effectof salinity upon photosynthesis in rice (Oryza sativa L.): Gasexchange by individual leaves in relation to their salt content.—J.exp. Bot. 36: 1240–1248. The effect of salinity upon net photosynthesis and transpirationby individual leaves of rice has been investigated by gas exchangemeasurements in seedlings at the five to six leaf stage. Salinitydid not, initially, reduce net photosynthesis in the whole plantbut only in the older leaves in which sodium accumulated. Analysisof the course of events in leaf four following salinizationof the medium showed that net photosynthesis was inversely correlatedwith the sodium concentration in the leaf tissue. There wasno evidence of a threshold effect; net photosynthesis declinedlinearly with increasing leaf sodium concentration and was reducedby 50% at only 05 mmol sodium per gram dry weight. The relationshipbetween transpiration rate and leaf sodium concentration closelyparalleled that for photosynthesis; there was no effect of leafsodium concentration on the carbon dioxide concentration inthe intercellular spaces, showing that sodium accumulation inthe leaf affected stomatal aperture and carbon dioxide fixationsimultaneously. Photosynthesis was reduced by half at a sodiumconcentration in the leaf which did not reduce the concentrationof chlorophyll. The nature of the effect of salinity upon leafgas exchange is discussed. Key words: Salinity, rice, Oryza sativa L., photosynthesis, apoplastic salt load