| Phosphorus (P) is one of the necessary nutrient elements. Brassica napus was sensitive to P deficiency. The aim of this study was to understand and unveil P-efficient physiological mechanism of Brassica napus, and to afford some bases for studying the molecular biology of P-efficiency in Brassica napus.P-efficient cultivar 97081 and P-inefficient cultivar 97009 were used to study oil rape growth, root character, uptake and utilization of P, acid phosphase activity, and inorganic P fraction of rhizosphere and bulk soils with pot culture, root box culture and solution culture, respectively. And the main results were as follows:1. P-efficient cultivar 97081 had the biological character to adapt P deficiency. Growth statuses of the two cultivars in seeding and bolting stage with pot culture and root box culture were investigated, respectively. The growth statuses of 97081 were better than those of 97009 under different P levels. P-efficient cultivar 97081 had more leaves, larger leaf area, root system, higher stem, bolting earlier and accumulated much weightier dry weight than P-inefficient cultivar 97009, and the growth rate of 97081 was faster than 97009, and had shorter growth period. Therefore, 97081 had the biological character to adapt P deficient condition well, and showed P efficiency.2. P-efficient cultivar 97081 had stronger ability to absorb and utilize P. Samples from different parts of the two cultivars in seeding stage and bolting stage with pot culture and bolting stage with root box culture were harvested, and then P content in these samples was determined. The results showed that P content in 97081 was lower than that of 97009, but 97081 can produce more dry biomass production using unit P absorbed than 97009, which suggested that 97081 had higher P utilization efficiency than 97009. Although P content in 97081 was lower than that of 97009, 97081 accumulated more P. The differences in P uptake and accumulation at seeding stage were more significant than at other stage. The results of bolting stage with pot culture and root box culture were different, which probably due to the effect of environment temperature on plant P uptake.It suggested that environment temperature was an important factor for plant to absorb P and grow normally.3. P-efficient cultivar 97081 had stronger ability to reutilize P. Total P in samples from a nutrition solution culture was fractionated into soluble P and insoluble P. Soluble P proportion in total P in old leaves was higher than young leaves in both two cultivars under P deficiency. However, soluble P proportion in total P in roots, young leaves and old leaves of 97081 was higher than of 97009, which suggested that relative mobilizable P in 97081 was more than that in 97009, P in old leaves could recycle to provide P for young leaves. And P-efficient cultivars 97081 had a higher ability to reutilize P.4. P-efficient cultivar 97081 had higher acid phosptase (APase) activity. Samples from solution culture were used to to determine APase activity, and we found that APase activity improved significantly with decreased P level in solution. The activity of different parts in plant was different: APase activity in root was higher than in old leaves, APase activity in old leaves was higher than in young leaves. APase activity in root was highest, which was propitious to excrete into medium in order to hydrolyze and absorb more organic P. APase activity in 97081 was higher than in 97009, and the increased degree of the APase activity in 97081 was higher than that in 97009 from P sufficiency to P deficiency, which suggested that 97081 can more highly improve P mobilization in plant than 97009. These results were coincident with the results of P fractions of plant.5. P-efficient cultivar 97081 had stronger ability to activate and utilize insoluble P in soil. The soil from root box culture was parted into rhizosphere and bulk soil. We determined available P content and inorganic P fractions. The content of available P, Al-P and Fe-P in rhizosphere soil for planting P-efficient cultivar 97081 was lower than that for planting P-inefficient cultivar 97009, respectively, which suggested that 97081 probably had a stronger ability to mobilize and absorb Al-P and Ca-P in soil than 97009. Compare to the results of P accumulation in plants, P-efficient cultivar 97081 had a stronger ability to activate and absorb insoluble P was proved again. But the mechanism and the difference in P fraction in bulk soil were expected to study further.
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