| The experiments were carried out in Feng-qiu Agricultural Experiment station of CAS. The types of winter wheat were Zhoumai 18 (ZM18) and Jimai 20 (JM20). Wheat of experiment A was grown in PVC pipes, water treatments were carried out during the key growing stages. Wheat of experiment B was grown in plots, water treatments were carried out after flowering. The experiments were originally designed with three different water treatments, they were: abundant water treatment with water content keeping at 18～20%; light water stress with water content keeping at 14～16%; severe water stress with water content keeping at 10～12%. Photosynthesis, RuBPCase activity, accumulation and transformation of dry matter and process of grain filling after flowering under different water treatments were observed, the mechanisms of increase of Pn and activation of RuBPCase were investigated, and accumulation and transformation of photosynthetic product were researched, in order to offer theoretical foundation for modulating and increasing yield through water. The main results were as follows:The results of experiment A were shown that, at all growth stages, Pn, RuBPCase activity, sucrose content, soluble protein content and chlorophyll content of leaves exhibited the initial increase followed by the reduction, reaching the highest values at flowering. Different stages and water treatments had effected photosynthesis and physiological characteristics, influences of severe stress on physiological characteristics were greater than that of light water stress, and effects of water stress on JM20 were bigger than that on ZM18.Before grain filling stage, Pn of abundant water and light water stress treatments had been mainly effected by stomatal limitation; at primary severe water stress, ZM18 was from jointing to booting, JM20 was at jointing, Pn was effected by stomatal limitation, then non-stomatal limitation acted as a main factor. At grain filling, non-stomatal limitation acted as a dominant role.Relations were found that under different water treatments, RuBPCase content, RuBPCase activity and Pn were significantly correlated. Under water stress, RuBPCase activity and Pn had been inhibited by accumulation of sucrose of wheat leaves. There were great significant positive correlations between grain yield and water potential, soluble protein content, chlorophyll content of leaves, and significant positive correlations between grain yield and Pn, RuBPCase activity.There was a great significant positive correlation between photosynthate accumulation after tasseling and grain yield. Remobilization of fore-flowering assimilate from sheathes, stems to seeds had been enhanced by water stress, but smaller sink capacity and insufficient photosynthate supplement were the main factors of water stress treatment limiting yield. Grain yield of abundant water treatment could be improved by larger sink capacity and enhancing photo-productivity.The results of experiment B were shown that, after flowering, Pn, RuBPCase activity and soluble protein content of wheat leaves decreased, that of light water stress (WB-2) of ZM18 were in the highest level, the second was abundant water (WB-1) treatment, severe water stress (WB-3) treatment was lowest, WB-1 treatment of JM20 was in the highest level; during grain filling, the main cause of Pn decrease was non-stomatal limitation.Pn increased with enhanced CO2 concentrations, but the increase was reduced gradually; Carboxylation efficiency (CE) and CO2–saturated maximum net photosynthetic rate (Vm) of WB-1 and WB-2 treatments of ZM18 were significantly enhanced compared to WB-3 treatment, CO2 compensation points (CCP) and respiratory rate (R1) were significantly decreased compared to WB-3; CE, Vmof abundent water treatment of JM20 were significantly improved compared to water stress treatmets, and CCP, R1 were significantly decreased.The process of grain filling was S curve, it could be described by Logistic equation. During accumulation of dry matter of grain, WB-3 treatment had the lowest dry matter accumulation of grains and grain filling rate, WB-2 treatment of ZM18 and WB-1 treatment of JM20 were in the highest levels; there were 3 stages during grain filling, they were gradual increasing stage, rapid increasing and slow increasing stage. WB-2 treatment of ZM18 and WB-1 treatment of JM20 had the highest theory maximum of grain weight (a), dry matter accumulation of grain ((W|—)) and average filling rate ((V|—)), and filling duration((D|—)) had been delayed.Spikelets per panicle, 1000-grain weight, sink capacity, grain yield and harvest index were compared, WB-2 treatment of ZM18 and WB-1 treatment of JM20 were in the highest levels, sink capacity, grain yield and harvest index were increased by increasing 1000-grain weight and spikelets per panicle. During grain filling, there were great significant correlations among RuBPCase content, RuBPCase activity and Pn. Accumulation of sucrose of wheat leaves was disadvantaged to increase Pn and RuBPCase activity; grain weights were mainly influenced by Pn, RuBPCase activity, soluble protein content and grain filling rate.
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