Diurnal Variations in Photosynthesis, Stomatal Conductance and Leaf Water Relation in Sorghum Grown with or without Silicon under Water Stress

ABSTRACT

Sorghum [Sorghum bicolor (L.) Moench] was grown hydroponically with or without 50 ppm silicon (Si), and exposed to water stress from 10 days after sowing (DAS). At 15 and 23 DAS, we measured dry weight and diurnal variations in photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (T), leaf water potential (ψ _L), and water uptake rate (23 DAS only). The reduction in dry weight at 23 DAS caused by water stress was ameliorated by silicon. Under water stress, silicon-treated seedlings showed higher g _s, P _N, and T than untreated ones. ψ _L remained almost constant within treatments throughout the daytime. Water uptake rate was reduced by water stress, but the reduction was ameliorated by silicon. We conclude that silicon enhanced water uptake and g _s, improving water supply to the leaves. These effects of silicon occurred soon after exposure to water stress.

Keywords:

• plant physiology
• photosynthesis
• drought

ACKNOWLEDGMENTS

The authors thank Dr. M. C. Saxena for his valuable comments. We are also very grateful for the support for this study by a grant for the 21^st Century Center of Excellence (COE) program from Japan Society for the Promotion of Science.