Wheat Cultivar Differences in Photosynthetic Response to Low Soil Water Potentials. I. Maintenance of photosynthesis and leaf water potential.

Abstract

Although many studies have shown cultivar differences in photosynthetic response to water deficit, the understanding of detailed mechanisms is not sufficient. We examined the mechanisms of water stress-resistance in terms of photosynthetic performance under low soil water potential (Ψsoil) with sixteen cultivars of wheat (Triticum aestivum L.) from different habitats, which had shown different drought resistance on a grain yield basis. Cultivar differences in photosynthetic maintenance in response to decrease of Ψsoil (water stress resistance), were found at ail seedling, booting, and grain filling stages. Cultivars with high drought resistance based on grain yield also showed high water stress resistance in photosynthetic performance. Water stress resistance (Rws) was caused more by tolerance (Tws, maintenance ability of photosynthesis in response to decrease of leaf water potential, ΨL)in some cultivars, which maintained relatively high photosynthesis (PN) in spite of decreases in ΨL, while it was caused more by water stress avoidance (Aws, maintenance ability of ΨL in response to decreases in Ψsoil) in other cultivars, which showed a relatively high PN by maintaining a relatively high ΨL under the same low Ψsoil. However, there was a positive correlation between Rws and Tws or between Rws and Aws. It is suggested that avoidance and tolerance usually occur simultaneously in adaptation to low Ψsoil, although water stress resistant cultivars varied in the water stress resistance mechanism.