Objectives Inefficient P supply often limits crop yield potential in arid and semiarid regions. Here, we studied the effects of P application frequency on photosynthetic efficiency and endosperm cell division of flag leaf and ear parts of wheat after anthesis under different water conditions to provide a theoretical basis for scientific application of phosphorus fertilizer.

Methods Field experiments were carried out with winter wheat cultivars of Xindong23 (a middle yield level cultivar) and Xindong20 (a high yield level cultivar) in Gansu Province of China. The two water conditions were drought stress (DT, total irrigation amount of 5625 m³/hm²) and suitable water irrigation (WT, total irrigation amount of 9000 m³/hm²). Under each water condition, three P fertilization times were set: P1 (applying all P fertilizer at wheat regreening stage of winter wheat), P2 (applying 50% P fertilizer at regreening stage and 50% at jointing stage), and P3 (applying 40% at regreening stage, 30% at jointing stage and 30% at grain filling stage). The chlorophyll and DNA contents in flag leaves were measured at 7, 14, 21, 28 and 35 days after anthesis, and the DAN content and starch accumulation in grains were measured at the same time. Yield and yield components were measured at maturity stage.

Results The chlorophyll content of flag leaves in P1 was higher (P<0.05) than that in P2 and P3 under DT condition. In contrast, The chlorophyll content of flag leaves in P3 was higher (P<0.05) than that in P1 and P2 under WT condition. Under DT condition, DNA contents in the flag leaves and grains of Xindong20 and Xindong23 were higher (P<0.05) in P1 and P2 treatments, respectively. Under WT conditions, we recorded the highest DNA content in the flag leaves and grains of both cultivars in P3. The total starch accumulation of the grains was higher in P1 under DT condition. The 1000-grain weight of the two cultivars was the highest in P3 regardless of water condition.

Conclusions No matter the high or middle yield potential of wheat cultivar, under drought stress, applying all the phosphorus fertilizer at regreening stage can achieve the highest chlorophyll and DNA contents in flag leaves, and the highest grain DNA content and starch accumulation, which is conducive to the accumulation of photosynthetic products and cell differentiation, and ultimately result in higher yield. While under suitable water condition, split applying phosphorus fertilizer into three times shows satisfactory results in the chlorophyll and DNA contents in flag leaves, and the DNA content and starch accumulation in grains. Therefore, the application method of phosphate fertilizer should be based on the water condition.