Diazotrophs associated with non-legumes grown in sandy soils

This study was carried out to monitor the effect of introducing single and multiple strains of diazotrophs to plant systems (wheat and barley) under gnotobiotic conditions. The relative scarcity of nutrient supply and maintenance requirements under the present experimental conditions resulted in slower growth and much longer doubling time compared to those found in their respective batch cultures. Single inoculations significantly enhanced the efficiency of nitrogen fixation in both plant systems compared to non-inoculated controls. Among tested diazotrophic strains, cells of Azospirillum spp. and Azotobacter spp. were superior in their ARAs, being higher with barley than with wheat seedlings. Increases in total dry weight of plants between 16.8% and 78% were achieved in the wheat system and between 54.5% and 68% in the barley system, with the highest-value being for Azospirillum spp. and Pseudomonas spp. treatments, respectively. It was observed that the type of plant host has a pronounced effect on cell growth and the type of interactions between the two diazotrophic candidates inoculated jointly into wheat and barley systems. Similar to dual inoculation, the doubling time of each candidate increased when inoculated as a mixed inoculum of three or four diazotrophs into the wheat system, and decreased in the barley system.