Abstract
The effects of different agronomic practices, such as fertilization regimes, can be experimentally tested in long-term experiments (LTE). Here, we aimed to evaluate the effect of different nitrogen fertilizations on the bacterial microbiota in both rhizosphere and bulk soil of sugar beet, in the Giessen-LTE (Germany). Fertilization treatments included mineral-N, manure, mineral-N + manure and no N-amendment. Metabarcoding and co-occurrence analysis of 16S rRNA genes, qPCR of amoA, nirK, nirS, nosZ-I and nosZ-II genes and soil physico-chemical analyses were performed. The effect of the fertilization treatments was more evident in the bulk soil, involving 33.1% of the microbiota. Co-occurrence analysis showed a rhizosphere cluster, dominated by Proteobacteria, Actinobacteria and Verrucomicrobia (hub taxa: Betaproteobacteriales), and a bulk soil cluster, dominated by Acidobacteria, Gemmatominadetes and “Latescibacteria” (hub taxa: Acidobacteria). In the bulk soil, mineral N-fertilization reduced nirK, amoA, nosZ-I and nosZ-II genes. Thirteen Operational taxonomic units (OTUs) showed 23 negative correlations with gene relative abundances. These OTUs likely represent opportunistic species that profited from the amended mineral-N and outgrew the species carrying N-cycle genes. Our results indicate trajectories for future research on soil microbiome in LTE and add new experimental evidence that will be helpful for sustainable management of nitrogen fertilizations on arable soils.
Highlights
Long-term experiments (LTE) in agriculture help to assess the effects of different agronomical practices and soil managements on plant growth, crop yields, ecosystem response and soil biological parameters [1,2]
In the long-term fertilization experiment in Giessen (Germany), the different nitrogen fertilization regimes affected the soil microbiota differentially depending on the soil habitat
Bulk soil was the soil habitat most affected by different nitrogen fertilizations
Summary
Long-term experiments (LTE) in agriculture help to assess the effects of different agronomical practices and soil managements on plant growth, crop yields, ecosystem response and soil biological parameters [1,2]. Different fertilization regimes (especially mineral vs organic) have shown to optimize soil management, in order to reduce the input of chemicals into the soil [3,4,5] and to understand the soil microbiome dynamics [6]. The LTE “nutrient depletion trial” of the Justus-Liebig University of Giessen (Germany) was established in 1954 to test the effect of different fertilization regimes, namely mineral N, P, K (in different amounts and combinations) and manure (cattle) on the biomass yields of sugar beet, winter wheat and summer barley cultivated successively.
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