Effects of sulfur nutrition on the growth and photosynthesis of rice

Rice plants (Oryza sativa L. cv. IR72) were grown hydroponically in 1.0 mM SO₄ ^2- for one week and transferred to 0, 0.01, 0.03, 0.1, 0.3, or 3 mM SO₄ ^2-. An increase in the sulfate concentration in the medium up to 0.03 mM resulted in a significant increase in the relative growth rate (RGR) due to the increase in the net assimilation rate (NAR). The leaf blade and leaf sheath showed a linear increase in the total S content at 0 to 0.1 mM SO₄ ^2- in the growth solution. Total S content in the roots continued to increase with increased S supply. Changes in the soluble S content followed the same pattern as the total S content but increased proportionally in the leaf sheath and roots. Total N content and N allocation to the leaves also decreased below 0.1 mM S. However, the decrease in the N content was not appreciable, compared with that of the S content. S-deficiency strongly decreased the leaf photosynthesis, which was caused by large decreases in the contents of chlorophyll and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) below 0.1 mM SO₄ ^2- in the growth solution.