Abstract: Using the typical wheat varieties with low P(phosphorus) efficiency(L),high P absorption efficiency(H1),high P utilization efficiency of P(H2) and hybrid F1-1(L×H1),F1-2(L×H2) as the experimental materials to study their photosynthesis and physiological mechanisms.The results showed that under Pideficiency condition,with the growing process of the flag leaf,the CO2 conductance parameters,stomatal conductance(Gs),mesophyll conductance(Gm) and carbonic anhydrase(CA) activity,the chlorophyll content(Chl) and the photosynthetic rate(Pn),as well as the inorganic phosphorus(Pi) concentration in the chloroplast,Mg2+-ATPase activity,soluble protein content(SP) and RuBPCase activity,were all decreased.All captioned physiological parameters in H1 and H2 were higher than those in L.Compared with parents,almost all heterosis values(super-average value of parents) of captioned physiological parameters in F1-1 and F1-2 were higher,indicating the improvement of photosynthesis in the wheat varieties with high P efficiency and the hybrid F1 resulted from their higher light harvesting capacity,lower stomatal limitation and non-stomatal limitation of CO2 conductance,and higher dark reaction rate of photosynthesis;thereinto,the high supplication of Pi to the chloroplast in the wheat varieties with high P efficiency and in the hybrid F1 maybe played an important role in maintaining the structure and function of photosynthetic organ under Pi stress condition,by which to some extent physiological process of the photosynthesis was improved.In this study,though H1 and H2 showed dramatic differences on P absorption and P utilization characteristics,their photosynthetic characteristics and physiological mechanisms were very similar,indicating the gene locus for P absorption and utilization are probable not tightly linkage to that for structure and function of photosynthetic organ.Under Pi-deficient condition,it seems that sufficient utilizing heterosis advantage of hybrid F1 on photosynthesis has latent application value to promote P absorption and utilization and increase grain yield of wheat.