THE EFFECT AND REGULATING MECHANISM OF NITROGEN NUTRITION ON CANOPY PHOTOSYNTHETIC CARBON ASSIMILATOIN IN WHEAT

During spring growth stages of wheat, the dynamic changes of canopy photosynthetic rate(CPR) showed one type curve with single peak. The maximum CPR were occured at booting stage or flowering stage. The application amount of nitrogen had important influence on the value, time of initiation and duration of the peak of CPR. Per canopy leaf photosynthetic rate(CPR pa ) was significantly negative correlated with the application amount of nitrogen. The increase of CPR in high amount treatments of nitrogen was mainly related to their increase of leaf area index(LAI) and light interception of canopy. Leaf area index(LAI) gradually increased with the increase of the amount of nitrogen, but the decline of LAI during late growth stages(booting to early ripening) in high nitrogen treatments were fast. CPR was significantly correlated with the LAI of same growth stage and next or last stage, which indicated that there were mutual effect between them. The diurnal changes of CPR basically showed one type curve with single peak. The population dry matter accumulation(PDW) at each nitrogen treatment were similar to its CPR, and at each growth stage, there were significantly positive correlations between CPR with PDW of the same and next growth stage. The changes of the canopy leaf source capacity(CLSC) showed a parabable curve, and peaked at the treatment of N 225kghm-2, which has a same trend as the CPR of flowering stage and the senescing rate of CPR and LAI from flowering stage to ripening stage. It is suggested that increasing the canopy photosynthetic rate and delaying the senescence of CPR during late growth stage have important influence on population carbon assimilating capacity of spring growth stage.