Abstract

Diazotrophs that carry out the biological fixation of atmospheric dinitrogen (N2) replenish biologically available nitrogen (N) in soil and are influenced by the input of inorganic and organic substrates. To date, little is known about the effects of combined organic substrate addition and N fertilization on the diazotroph community composition and structure in purple soils. We investigated the effects of N fertilization and straw mulching on diazotroph communities by quantifying and sequencing the nifH gene in wheat rhizosphere. The abundance and richness of diazotrophs were greater the higher the fertilization level in the mulched treatments, whereas in the nonmulched treatments (NSMs), richness was lowest with the highest N fertilization level. The abundance and α-diversity of diazotrophs correlated with most of the soil properties but not with pH. At the genus level, the relative abundances of Azospirillum, Bacillus, and Geobacter were higher in the NSMs and those of Pseudacidovorax, Skermanella, Azospira, Paraburkholderia, Azotobacter, Desulfovibrio, Klebsiella, and Pelomonas in the mulched treatments. The differences in community composition between the mulched and the NSMs were associated with differences in soil temperature and soil organic carbon and available potassium contents and C:N ratio. Overall, straw mulching and N fertilization were associated with changes in diazotroph community composition and higher abundance of nifH gene in alkaline purple soils.

Highlights

  • Nitrogen (N) is an essential element that plays a crucial role in agroecosystems (Feng et al, 2018)

  • The abundance, diversity, and community composition of soil diazotrophs have been associated with various factors such as soil physicochemical characteristics and management strategies (Reardon et al, 2014)

  • We assessed the response of diazotrophs to straw mulching and N fertilization by quantifying and sequencing the nifH gene and noticed that the variation in diazotroph communities was more associated with straw mulching than with N fertilization

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Summary

Introduction

Nitrogen (N) is an essential element that plays a crucial role in agroecosystems (Feng et al, 2018). N transformation processes in the N cycle, e.g., N fixation (dinitrogen fixation), nitrification, and organic N mineralization, provide inorganic N to fulfill the requirements of plants (Luo et al, 2018; Pereg et al, 2018). Microbes play an important role in the soil N cycle by regulating N availability and transformation (Canfield et al, 2010). N2-fixing bacteria and archaea, diazotrophs, convert atmospheric N to bioavailable N (Levy-Booth et al, 2014; Chen et al, 2021). Diazotrophs may promote the growth of cereals, even though this has been mostly attributed to their other plant growth-promoting abilities instead of N fixation (Rosenblueth et al, 2018). Diazotrophs are highly diverse and include members of several bacterial phyla, e.g., Proteobacteria, Firmicutes

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