Abstract
Little has been reported on the effects of long-term fertilization on rhizosphere soil microbial diversity. Here, we investigated the effects of long-term continuous nitrogen (N) fertilization on the diversity and composition of soil bacteria using data from a 10-year field experiment with five N application rates (0, 120, 180, 240, and 360 kg N hm–2). The results revealed varying degrees of reduction in the numbers of bacterial operational taxonomic units (OTUs) in response to the different N application rates. The highest wheat yield and number of proprietary bacterial OTUs were found in the N input of 180 kg N hm–2. In terms of average relative richness, the top seven phyla of soil bacteria in the rhizosphere of wheat after long-term nitrogen application were Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Gemmatimonadetes, and Patescibacteria. Among these, Proteobacteria and Gemmatimonadetes were found to be unaffected by the nitrogen fertilizer and soil environmental factors (pH, C/N ratio, and NO3– concentration), whereas Acidobacteria and Actinobacteria showed significant positive and negative correlations, respectively, with soil pH. The richness of Actinobacteria significantly increased in the N180 treatment. Patescibacteria and Bacteroidetes showed significant positive correlations with soil NO3– and wheat yield, and the average relative richness of these two phyla was high under long-term application of the N180 treatment. These findings indicate that the relative richness of Patescibacteria and Bacteroidetes can affect wheat yield. In conclusion, the results of our 10-year field experiments clearly show that long-term N fertilization can significantly affect most of the dominant soil bacterial species via changing the soil pH. The richness of Actinobacteria can serve as an indicator of a decreased soil pH caused by long-term N fertilization.
Highlights
Wheat is an essential commodity grain and strategic grain reserve in China
Throughout the study period, we detected no significant changes in the number of bacterial species under the N0 treatments, whereas after 10 years, the number of operational taxonomic units (OTUs) in the soils treated with N120, N180, N240, and N360 had decreased by 3.84, 7.42, 3.50, and 2.05%, respectively
This, in turn, has the effect of inhibiting the activities of the soil bacteria and causing a rapid decline in the diversification of rhizosphere soil bacterial communities (De Carvalho et al, 2016). These effects were well demonstrated in the present study, in which we found that the number of bacterial OTUs in the rhizosphere soils treated with N120 and N180 increased to different degrees compared with the no N fertilizer input, whereas in response to an N fertilizer input of 360 kg hm−2, we observed a marked decrease in the number of bacterial OTUs
Summary
Wheat is an essential commodity grain and strategic grain reserve in China It plays an extremely important role in ensuring national food security (Hu et al, 2016). Nitrogen (N) fertilizer, as the basis of the sustained high grain yields, plays a decisive role in agricultural production (Islam et al, 2015), with the appropriate application of N fertilizer contributing to increases in the absorption area and the activity of crop root systems and promotion of the emergence of productive tillers. High N inputs may result in lower yields and tend to be conducive to the emergence and frequency of pests and diseases and, can have detrimental environmental effects, such as water eutrophication (Tesoriero et al, 2009), increased greenhouse gas emissions (Luo et al, 2016), and increases in soil acidity and salinity (Han et al, 2017). Appropriate N fertilizer inputs are the key to balancing high crop yields and environmental compatibility
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