Abstract:

P is an important nutrient element in plant, and P deficiency is one of the major factors limiting crop production. P recycling and distribution are remarkable in plant growth, especially under P deficiency condition. In this paper, the photosynthetic and transpiration rates of flag leaf, dry matter and P distribution in each organ, final yield of grain and P uptake efficiency were studied using large-spike cultivar CA9325 and multi-spike cultivar JM2, by remaining or removing tillers. The wheat plants were grown in spots with quartz sand, and watered with nutrient solution (KCl replaced KH₂PO₄ in P-deficiency treatment). The results were as follows: (1) Photosynthetic and transpiration rates of the flag leaf in two wheat cultivars were decreased and their photosynthetic functional periods were shortened after a short time of P deficiency. Those in plants without tillers were higher than those with tillers, and those in normal P treatment were higher in JM2 than in CA9325 (Fig.1,2). (2) In P-deficiency treatment, the dry matter weight and P accumulation in almost all organs and whole plant of both cultivars were decreased, especially in grains and whole plants. The percentages of dry matter and P in grains of the plants without tillers to whole plant were higher than those with tillers, which showed that P deficiency stimulated the transportation of dry matter and P from vegetative organs to grains (Table 1,2). With or without P in the nutrient solution, the percentages of dry matter and P of grains to whole plant in two wheat cultivars were about 40% and 65%, respectively, which showed dry matter and P allocations to grains were not synchronous. (3) The accumulations of dry matter and P in main shoot and the percentages of which to whole plant were higher in CA9325 than in JM2, but those in tiller were higher in JM2 than CA9325 because of their different spike types (Table 1,2). (4) 1000-grain weight, grain yield and P content and spike number per plant in two wheat cultivars were decreased under P deficiency at the flag leaf expanding stage. In the treatments with or without P, 1000-grain weight in plant without tillers was significantly higher than those with tillers in the same wheat cultivar. In the plants with tillers, grain yields were less in CA9325 than in JM2, but it was on the contrary in the plant without tillers. 1000-grain weight and P content of grains were higher in CA9325 than in JM2, no matter the tillers were kept or removed. P uptake efficiency was higher in CA9325 than in JM2 when the tillers were not removed; while these were no significant difference between them when the tillers were removed (Table 3). The possible mechanisms of P distribution and utilization were also discussed.

Key words: P deficiency, Sink strength, Winter wheat, Photosynthetic characteristic, P distribution