Abstract: A rainproof and water controlling experiment was conducted to study the effects of phased drought and re-watering on the photosynthetic characteristics and grain yield of winter wheat. Four treatments, i.e., 70%±5% soil moisture content from turning green to maturity (S₀), 55%±5% soil moisture content from turning green to anthesis together with 70%±5% soil moisture content from anthesis to maturity (S₁), 70%±5% soil moisture content from turning green to anthesis together with 55%±5% soil moisture content from anthesis to maturity (S₂), and 55%±5% soil moisture content from turning green to maturity (S₃), and two planting densities, i.e., 525 and 675 basic seedlings per square meter, were installed. In treatment S₀, the flag leaf chlorophyll content, chlorophyll fluorescence parameters, and photosynthetic characteristic parameters and the grain yield were higher than those in other three treatments, and the photosynthetic characteristic parameters and grain yield were significantly higher than those in treatments S₃ and S₂. Though the photosynthetic characteristic parameters in treatment S₁ increased to some extent, showing an overcompensation effect, the grain yield presented a slight decrease, as compared to that in treatment S₀. The water use efficiency in treatments S₁, S₂, and S₃ was 143.2%, 86.5%, and 97.3% of that in treatment S₀, respectively. It was suggested that to maintain 55% moisture content in 0-40 cm soil layer from turning green to anthesis and maintain 70% moisture content in this soil layer from anthesis to maturity could be the optimal water management way for obtaining definite grain yield of winter wheat while high efficiently saving water. Due to the interaction between water and plant density on the grain yield of winter wheat, the optimal water management way suggested above and the plant density of 675 basic seedlings per square meter could be the optimum combination for winter wheat with the consideration of watersaving and highyielding.

Key words: cold-terra rice, CO₂ and temperature, OTC, CERES-Rice crop model.