Abstract
To study nitrogen contribution to cucumber derived from nitrogen fixation of Paenibacillus polymyxa WLY78. The nif gene cluster deletion mutant (ΔnifB-V) of Paenibacillus polymyxa WLY78 was constructed by a homologous recombination method. The effects of plant-growth promotion were investigated by greenhouse experiments. The nitrogen fixation contribution was estimated by 15N isotope dilution method (also being called the 15N natural abundance technique). Deletion of nif gene cluster of P. polymyxa WLY78 resulted in complete loss of nitrogenase activity. Greenhouse experiments showed that inoculation with P. polymyxa WLY78 could significantly enhance the lengths and dry weights of cucumber roots and shoots, but inoculation with ΔnifB-V mutant could not. 15N isotope dilution experiments showed that cucumber plants derive 25.93% nitrogen from nitrogen fixation performed by P. polymyxa WLY78, but the ΔnifB-V mutant nearly could not provide nitrogen for plant growth. This present study demonstrated that nitrogen fixation performed by P. polymyxa WLY78 contributes to plant growth.
Highlights
Nitrogen is one of the most important nutrients in plant growth, but plants can not directly use nitrogen in the atmosphere
Deletion of nif gene cluster of P. polymyxa WLY78 resulted in complete loss of nitrogenase activity
Greenhouse experiments showed that inoculation with P. polymyxa WLY78 can significantly enhance the lengths and dry weights of cucumber roots and shoots, but inoculation with ΔnifB-V mutant can not. 15N isotope dilution experiments showed that cucumber plants derive 25.93% nitrogen from nitrogen fixation performed by P. polymyxa WLY78, but the ΔnifB-V mutant nearly can not provide nitrogen for plant growth
Summary
Nitrogen is one of the most important nutrients in plant growth, but plants can not directly use nitrogen in the atmosphere. Biological nitrogen fixation (BNF) is a process in which nitrogen-fixing microorganisms reduce nitrogen in the air to ammonia through nitrogenases. Associative nitrogen-fixing bacteria can colonize root surface cells, invade plant roots, and form close contact with plants, thereby promote plant growth (Baldani et al 1997). Associative nitrogen-fixing bacteria promote the absorption of nitrogen by non-legume plants (Geddes et al 2015). Biological nitrogen fixation reduce the use of nitrogen fertilizer, and improve soil fertility and the absorption of nutrients by crops (Farrar et al 2014)
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