Diazotroph abundance and community composition in an acidic soil in response to aluminum-tolerant and aluminum-sensitive maize (Zea mays L.) cultivars under two nitrogen fertilizer forms

In acidic soil, plant aluminum (Al) tolerance and nitrogen (N) fertilizer form play the important roles in influencing plant growth. Diazotrophs as plant growth promoting rhizobacteria can contribute to plant available N, but the response to plant growth differences resulting from plant Al tolerance or N fertilizer form in acidic soil is poorly understood. Here, we investigated this response. Three maize cultivars with different Al-tolerance levels were grown in an acidic soil that was added with nitrate (NO3 (-)-N) or ammonium (NH4 (+)-N) fertilizers. After 42 days, maize biomasses and root morphologies as well as the physicochemical properties of bulk and rhizosphere soils were determined. Based on nifH gene, soil diazotroph abundance was determined by quantitative RT-PCR and community composition was assayed using high-throughput sequencing. For the same maize cultivar, application of NO3 (-)-N fertilizer relative to NH4 (+)-N fertilizer increased maize biomass, root length, root surface area, and rhizosphere pH, but not significantly affect rhizosphere nifH copy number and community composition. The nifH copy numbers did not show significant differences among rhizosphere samples of three maize cultivars, but community composition was obviously different between Al-tolerant and Al-sensitive cultivars. In acidic soil, maize cultivars depending on Al tolerance altered rhizosphere diazotrophic community composition, but this effect seemed to be not susceptible to N fertilizer forms.