Field and glasshouse studies were undertaken to relate leaf photosynthesis rate as well as stomatal and non-stomatal behaviors to drought resistance and yield performance of wheat. Based on a two-year field trial, 11 wheat cultivars were divided into three groups of susceptible, intermediate and resistant, using stress susceptibility index (SSI) and then were further examined in a glasshouse experiment. Water stress decreased leaf photosynthesis rate (Pn), stomatal conductance (gs) transpiration rate (Tr) and mesophyll conductance (MC), and increased sub-stomatal CO2 concentration (Ci). Cultivars differed in their response to water stress. In general, resistant cultivars showed a higher Pn and gs and leaf water content under both moisture conditions comparing to susceptible ones. A greater reduction in gs and Tr and a smaller reduction in Pn under stress condition led to a remarkably higher photosynthetic water use efficiency of the resistant cultivars. A greater decrease in MC and a greater increase in Ci due to water stress of the susceptible cultivars exhibited the enhanced sensitivity of the photosynthetic apparatus to water stress.
