Changes of CO 2/H 2O exchange parameters were continually measured in winter wheat under different water stress stages.The results showed that photosynthesis rate and transpiration rate of winter wheat in water stress conditions were obviously lower than that in non stress conditions.After water stress,both of them slowly increased and even overtook that on sufficient irrigation treatment. Responses of winter wheat to water stress in different growth stages were different.To some extent, water stress can improve crop water use efficiency,speed up the process of milking.Under water stress condition,stomatal conductance limited diurnal changes of photosynthesis and transpiration in the morning but not in the afternoon.Transpiration is more sensitive to water stress than photosynthesis.
Studies on the effect of different levels root cutting on the photosynthesis rate,stomata conductance,aboveground biomass,grain yield,and water use efficiency of maize showed that moderate root cutting could improve its photosynthesis ability,and increase its aboveground biomass and WUE. On the contrary,when the roots were cut severely,the photosynthesis ability was weakened,and the biomass was decreased. Moderate root cutting could increase maize grain yield,but the effect was not significant.
