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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 4 + -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 ( P <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.

In order to evaluate the potential risk of planting transgenic corn on soil nitrogen-fixing microorganisms, in 2015, rhizosphere and non-rhizosphere soil samples were collected at the jointing stage, tassel stage, milky stage, and ripening stage, and the effects of transgenic maize with the cry1Ab and epsps genes on the abundance and diversity of soil nitrogen-fixing bacteria were studied by real-time quantitative PCR and T-RFLP. The results showed that the copy number of the diazotrophic nifH gene in the rhizosphere and non-rhizosphere soil of transgenic maize with the cry1Ab and epsps genes (C0030.3.5) and its parental maize (DBN318) showed a trend where it first increased and then decrease with the growth stages, ranging between 2.99×10 7 and 7.02×10 7 copies·g -1 . The abundance of the diazotrophic nifH gene in the rhizosphere soil and non-rhizosphere soil gene showed no significant difference between TM and PM in the same growth stage ( P >0.05). The correlation analysis showed that the abundance of the diazotrophic nifH gene was positively correlated with the content of organic matter, but negatively correlated with water content. T-RFLP analysis yielded 14 T-RFs of different lengths, and 43-bp and 155-bp fragments were the dominant population. The community composition of nitrogen-fixing bacteria was the same as that of TM and PM in the rhizosphere soil and non-rhizosphere soil, and there was no significant difference between the TM and PM populations in the same growth period ( P >0.05). The Shannon index and Evenness index of the diazotrophic nifH gene showed a trend where they first increased and then decreased with the growth period, and there was no significant difference in the Shannon index and Evenness index in the same growth stage between the rhizosphere and non-rhizosphere soil samples. Principal component analysis(PCA) indicated that the composition of nitrogen-fixing bacteria was not different between TM and PM. Redundancy analysis (RDA) showed that soil ammonium, nitrogen, and pH were significantly correlated with composition of nitrogen-fixing bacteria.

The variation characteristics of the content and components of soil active organic carbon under different fertilizer application were investigated in samples of calcareous fluvo-aquic soil from a field experiment growing winter wheat and summer maize in rotation in the North China Plain. The results showed that RF (recommended fertilization), CF (conventional fertilization) and NPK (mineral fertilizer alone) significantly increased the content of soil dissolved organic carbon and easily oxidized organic carbon by 24.92-38.63 mg x kg(-1) and 0.94-0.58 mg x kg(-1) respectively compared to CK (unfertilized control). The soil dissolved organic carbon content under OM (organic manure) increased greater than those under NPK and single fertilization, soil easily oxidized organic carbon content under OM and NPK increased greater than that under single chemical fertilization. OM and NPK showed no significant role in promoting the soil microbial biomass carbon, but combined application of OM and NPK significantly increased the soil microbial biomass carbon content by 36.06% and 20.69%, respectively. Soil easily oxidized organic carbon, dissolved organic carbon and microbial biomass carbon accounted for 8.41% - 14.83%, 0.47% - 0.70% and 0.89% - 1.20% of the total organic carbon (TOC), respectively. According to the results, the fertilizer application significantly increased the proportion of soil dissolved organic carbon and easily oxidized organic carbon, but there was no significant difference in the increasing extent of dissolved organic carbon. The RF and CF increased the proportion of soil easily oxidized organic carbon greater than OM or NPK, and significantly increased the proportion of microbial biomass carbon. OM or RF had no significant effect on the proportion of microbial biomass carbon. Therefore, in the field experiment, appropriate application of organic manure and chemical fertilizers played an important role for the increase of soil active organic carbon content and the effective control of its key components.