Background and aims The benefits of biological nitrogen fixation (BNF) for blue lupin (Lupinus angustifolius L.) are well known. However, it is unclear how multiple microorganisms, other than plant growth promoting rhizobacteria, affect this legume's BNF and growth. Therefore, we evaluated the impact of mycorrhizal fungi and a yeast on growth and nutrition of nodulated blue lupin. Methods We isolated Cryptococcus laurentii from the rhizosphere of blue lupin. Nodulated L. angustifolius seedlings, treated with either C. laurentii (CL) or mycorrhizal fungi (MF) or with both symbionts (CLMF), were cultivated in sterile silica sand in a glasshouse for one month. The treatments' effects were investigated by analyzing the plants' biomass parameters, symbiotic colonization and mineral nutrition. Results The MF treatment had no effect on the plants, while growth, BNF efficiency and the nutrition of CL treated plants were improved. CLMF treated plants demonstrated increased growth and nodule relative growth rate, while utilizing nitrogen resources efficiently for growth.Conclusions Growth and nutritional physiology of L. angustifolius were affected via different mechanisms. Improved growth of CL treated plants was underpinned by increased BNF efficiency; while greater nodulation and efficient growth on nitrogen resources supported the increased biomass of CLMF treated plants.

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