Nitrofixing cyanobacteria: diversity, cultivation and biostimulant potential in consortia

Abstract

The nitrogen-fixing cyanobacteria consortia are an alternative to the indiscriminate use of chemical fertilizers due to their ability to fix atmospheric nitrogen. It can be used as plant growth promoters, biofertilizers and soil conditioners. The objective of this research was to develop consortia of cyanobacteria isolated from the rhizosphere and roots of Carica papaya, applying biotechnological methods. Two stable growth consortia were obtained: C1 (Nostoc commune, Aphanothece minutissima, Planktothrix sp.) and C2 (N. commune, Calothrix sp., A. minutissima). The biostimulant properties of each consortium were determined using Cucumis sativus L. var. Market plus seeds, obtaining with the C2 consortium a higher percentage of germination (>90%), longer root length (>6 cm) and higher vigour index I (513), II (13.02). The effects of static magnetic field (SMF) on consortium growth and biochemical composition were also investigated in C2, using two ranges of magnetic induction (40-50 mT and 100-200 mT). It was demonstrated different effects depending of the inductions range. At 40-50 mT, it was obtained the maximal concentration of chlorophyll a and carotenoids, proteins, and carbohydrates; SMF induced cells structural changes. At 100-200 mT, the biomass yield, lipid content, and total organic carbon content were increased. Otherwise, the effect of SMF in germination and development of C. sativus L. seedlings showed that the cyanobacterial consortium without treatment and those treated with the magnetic induction range of 40-50 mT stimulated the germination, promoting root length, vigour index, and stem length. This research contributes to expanding the spectrum of rhizosphere’s microorganisms with biostimulant potential.