Screening Of Nitrogen Efficient Germplasm And Preliminary Study On Its Phsiological Mechanism In Rapeseed

Rapeseed is an oil crop of many uses , high economic value and great potentialdevelopment. Both planting area and yield of rapeseed in china occupy 1/3 of the world.As rapeseed is a crop for higher nitrogen (N) requirement, the application of excessive Nfertilizers has caused great pressure on environment and economy. What is the best way tosolve the problem is to screen N-efficient rapeseed variety and exploit geneticimprovement on N utilization. In this study, a total of 100 rapeseed germplasms werescreened for N high-efficiency at seedling stage under low N stress (0.02 g N/kg) andnormal N (0.20 g N/kg) respectively, then five possible N high-efficient germplasm andfive possible N low-efficient germplasm were obtained. The candidated N-efficient andN-inefficient germplasms were then confirmed by maturity period screening under low N(0.067 g N/kg) and normal N (0.20 g N/kg) and at last one N high-efficient germplasmand one low-efficient germplasm were obtained by the two-step screening method. On thebasis of the screening, the N-efficient and N-inefficient germplasms were planted at theseedling period with solution culture under the conditions of low N stress (8.40 mg/L)and normal N (84.00 mg/L). During the culture period, the indexes related to uptake andutilization of N were analyzed, and then physiological mechanism of N-efficiency inrapeseed was commended. The main results obtained from the research were shown asfollowing.1. One N-efficient and one N-inefficient rapeseed germplasms were obtained throughseedling stage screening and maturity stage screening at first.2. There existed significant positive correlation relationship between N accumulation,N utilization indexes and shoot dry matter weight at seedling stage, this demonstrated thatshoot dry matter weight in the seedling stage could be used as an index for estimating Nuptake and utilization efficiency.3. Reasonable and reliable screening indexes were established: relative shoot drymatter weight could be used as a reliable index in seedling stage screening; relative shootN accumulation could be used as an auxiliary index and relative utilisation index couldonly be considered as a reference index. N efficiency coefficient (a ratio of seed yieldunder low N level to that under normal N level) and the seed yield under low N levelcould be used as the dependent index in maturity period screening. There is a significantpositive correlation relationship between the index of seedling screening and the one ofscreening in the maturity period, which suggested that the method of two-step screeningwas available. 4. Through the research on dry matter accumulation at different development stage ofthe candidated germplasms obtained at seedling stage screening, it was found that the drymatter accumulation increased significantly with increment of the applied N level. Thechange trend of the dry matter accumulation showed: the dry matter accumulationincreased with the development stage, which was the slowest at seedling stage and got thebiggest at maturity stage. The dry matter accumulation of different rapeseed germplasmshowed significant differences in the same N level at the same growth stage and thedifferences was higher between N-efficient and N-inefficient germplasms. Whether at lowN stress or normal N conditions, the dry matter accumulation of N-efficient germplasm 51was always higher at each growth stage than N-inefficient germplasm 88.5. N-accumulation of different rapeseed germplasms increased remarkably with theincrement of N level. The change trend of N accumulation under two different N levelswere to ascend firstly and descend lately, which showed a change curve of S-type duringthe whole growth period. Significant difference in N accumulation among differentrapeseed germplasms was found at the same N level at the same growth stage. The Naccumulation of N-efficient germplasm 51 at flowering and maturity stages was higherremarkably than that of N-inefficient germplasm 88.6. N use efficiency for plant biomass (NUEp) and for seed production (NUEg) ofdifferent rapeseed germplasms reduced with increasing of N level. Different rapeseedgermplasm showed significant differences at the same N level. Under low N stresscondition, the NUEp of N-efficient germplasm 51 were higher than that of N-inefficientgermplasm 88 at seedling, buding, flowering, silique, stages. But this was reversed atmaturity stage7. Based on the research on the N content in each growing period and transportcoefficient of different rapeseed germplasms, it was found that shoot N content of allrapeseed germplasms presented apical dominance. The low N stress accelerated thedifference in N-accumulation among organs or tissues. N-translocation and utilizationexisted difference in different germplasms in every growing period, and N-efficientgermplasm 51 showed higher translocation efficiency than N-inefficient germplasm 88 ineach growing period.8. With the study on the physiological and biochemical indexes related to uptake,utilization and transport of N between N-efficient germplasm 51 and N-inefficientgermplasm 88, the mechanism of N efficiency in rapeseed was deduced. Compared withN-inefficient germplasm under the condition of low N, N-efficient germplasm showedmore developed root morphology (longer axial root, bigger root volume) and higher root vigor (greater total uptake root area and active uptake area of root system). This resultedin accumulating more N in N-efficient germplasm, and then induced stronger N transportability, and N reduction and assimilation ability (higher nitrate reductase activity andglutamine synthetase activity). At last, N-efficient germplasm showed better adaptabilityto low N stress (higher biomass production and seed yield).