Comparison of N uptake of maize inoculated with two diazotrophic bacterial species grown under two N levels.

We investigated how plant inoculation with two diazotrophic bacteria would influence the modulation of root architecture and parameters associated with N uptake rate under high and low NO₃⁻ availability. The treatments were arranged in a 2 × 3 factorial design, the first factor being N dose (0.3 and 3.0 mM, or low and high N, respectively) and the second being inoculation with Herbaspirillum seropedicae strain ZAE94 (Hs-ZAE94), Azospirillum brasilense strain Sp245 (Ab-Sp245) and an uninoculated control. The parameters evaluated were: root architecture, mineral N in the growth solution, soluble metabolites, and activities of two N enzymes, dry mass, N accumulation, and the ratio of plant dry mass to N accumulation (NUE). Plant parameters improved with higher N availability. Only under high N, the inoculation with Ab-Sp245 brought about a change in root architecture with an improvement in root surface area, which was in agreement with an increased plant dry matter, N accumulation, and NUE, which was not always observed on either sampling date, 24 and 32 days after transfer to the hydroponic system. The shift in root architecture and the maintenance of N uptake per unit of root area by inoculation with Ab-Sp245 was likely the main effect. [ABSTRACT FROM AUTHOR]