关键词: 固氮施氏假单胞菌A1501, 氮高效利用玉米, 根际联合固氮, 生物固氮效率, 15N稳定性同位素稀释法

Abstract: Compared to symbiotic nitrogen fixation in legumes, associative nitrogen fixation is widely existed in the rhizosphere of non-leguminous food crops such as rice and maize, which potentially plays major role in reducing the use of synthetic nitrogen fertilizer in agriculture and increasing plant yield. Pseudomonas stutzeri A1501,  a model associative/endotrophic nitrogen-fixing bacterium, was isolated from the rhizosphere of rice. Inoculation with wild-type A1501 could promote the growth of rice and maize plants. In order to further elucidate the relationship between the biological nitrogen fixation (BNF) in rhizosphere and the plant-growth promotion, an efficient associative nitrogen fixation system consist of excretion-ammonium mutant strain (1568/pVA3) and transgenic nitrogen efficient maize genotype was constructed, and used for the evaluation of promoting effect and BNF quantification under greenhouse condition. After 60 d, inoculation of two maize genotypes (transgenic nitrogen efficient maize and the control) with 1568/pVA3 and wild-type A1501 all significantly increased the plant biomass of aboveground and underground, compared with the control without inoculation. However, in all the conditions assayed, transgenic nitrogen efficient maize inoculated with 1568/pVA3 or wild-type strains showed no significant difference between plant biomass and the control genotype. In the efficient associative nitrogen fixation system,  the biomass of the transgenic nitrogen efficient maize inoculated with 1568/pVA3 significantly increased by 25.5%, compared with the N fertilization treatment control, 39% total N content compared with the control without inoculation. According to the estimation by 15N-isotopic dilution method, individual maize plant could obtain  N 0.8 g·plant^-1 from BNF. Meanwhile,  the biomass of the transgenic nitrogen efficient maize inoculated with wild-type A1501 significantly increased by 24.8%, compared with the N fertilization treatment control. Accordingly, individual maize plant could obtain  N 0.64 g·plant^-1 from BNF. Therefore, the efficient associative nitrogen fixation system used in this study contained transgenic nitrogen efficient maize genotype and associative diazotrophs especially the excretion-ammonium engineering bacteria performed better in terms of nitrogen fixation rate and plant biomass. It was estimated that 23% synthetic fertilizer could be reduced in this efficient associative nitrogen fixation system, against than 7.5% in the control system.

Key words: Pseudomonas stutzeri A1501, nitrogen efficient maize genotype, associative nitrogen fixation, biological nitrogen fixation rate, 15N-isotopic dilution method