[Response of Bacterial and Fungal Communities to Chemical Fertilizer Reduction Combined with Organic Fertilizer and Straw in Fluvo-aquic Soil].

To investigate the effects of chemical fertilizer reduction combined with organic fertilizer and straw on bacterial and fungal communities in fluvo-aquic soil under a wheat-maize rotation system in North China, a field-oriented fertilization experiment was performed at a trial base in Ninghe District of Tianjin. The differences in composition, diversity, and structure of bacterial and fungal communities were evaluated using five fertilization patterns (chemical fertilizer, F; chemical fertilizer reduction, FR; chemical fertilizer reduction combined with straw, FRS; chemical fertilizer reduction combined with organic fertilizer, FRO; chemical fertilizer reduction combined with organic fertilizer and straw, FROS) using Illumina high-throughput sequencing technology. Further, the main soil environmental factors driving the alteration of bacterial and fungal communities under different fertilization treatments were explored in combination with soil chemical analysis. The results showed that adding organic fertilizer (FRO) significantly increased the SOM content. In comparison with the FRS treatment, the TP content in the FROS treatment significantly increased by 13.33%. The AP content increased significantly after applying the FRO and FROS treatment, and it increased by 18.03%-33.45% and 22.69%-38.72%, respectively, as compared to that with the other treatments. The NH-N content of FRO and FROS treatments was significantly higher than that of chemical fertilizer treatments (F and FR), which was 2.14 and 2.23 times that of F treatment, and 2.23 and 2.33 times that of FR treatment, respectively. Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteria were the dominant bacterial phyla for all treatments, with Ascomycota being the dominant fungal phylum. Based on the chemical fertilizer reduction combined with organic fertilizer, the addition of straw (FROS) significantly decreased the relative abundance of Actinobacteria. Under the FRS and FROS treatments, a significant decrease in the relative abundance of Gemmatimonadetes was observed. Moreover, the FROS treatment caused a significant decrease in the relative abundance of Planctomycetes and Verrucomicrobia. As for the fungal community, the relative abundance of Ascomycota was significantly increased under the treatments applying organic fertilizer (FRO and FROS). In comparison with the FR treatment, the FROS treatment significantly decreased the relative abundance of Mortierellomycota and Olpidiomycota, and the FRS treatment also showed a significant inhibitory effect on the relative abundance of Mortierellomycota. The Shannon index of bacterial community of the FROS treatment was significantly reduced by 1.26% and 1.25% in comparison with the F and FR treatments, respectively; the Chao1 index increased by 4.51% as compared with that of the F treatment. The Shannon index of bacterial community exhibited a significantly positive correlation with available phosphorus as well as ammonium content (<0.05). In comparison to the FR treatment, the FRS, FRO, and FROS treatments significantly decreased the Shannon index of fungal community by 29.85%, 24.94%, and 25.73%, respectively. A significantly positive relationship between the Shannon index of fungal community and available phosphorus content was observed. The community structure of bacteria of the FROS treatment was significantly different from that of F, FR, and FRO treatments, with the soil moisture, total phosphorus, pH, and available phosphorus as the major driving factors; the fungal community structure of the FRO and FROS treatments showed significant difference from that of the F and FR treatments, and the fungal community structure was mainly altered by total nitrogen, available phosphorus, and total phosphorus. In summary, our results indicated that the bacterial and fungal communities in fluvo-aquic soil exhibited a relatively strong response to the chemical fertilizer reduction combined with organic fertilizer and straw; meanwhile, the fungal community was also significantly influenced by chemical fertilizer reduction with organic fertilizer. Therefore, the organic fertilizer and straw drive the changes in the bacterial and fungal community composition, while improving the soil physicochemical properties. The fluvo-aquic fungi were more sensitive to the organic materials than the bacteria. Soil P was a common important influencing factor for regulating the bacterial and fungal community structure, and it should be paid full attention during the agricultural cultivation of fluvo-aquic soil.