Microbial communities drive geochemical cycles in soils. Relatively few studies have assessed the long-term impacts of different types of soil amendments under field conditions in long-term experiments. The response of soil microbial organisms in a Mollisol cultivated with maize for 35 years was examined. Treatments involved the use of N, P, and K fertilizers and two doses of straw residue in isolation or combined. Real-time PCR and Illumina MiSeq sequencing methods were used to characterize the microbial community. The results showed that addition of nitrogen fertilizers decreased soil pH, but this was mitigated when a high dose of straw was also incorporated. Long-term application of inorganic fertilizers was able to alter the abundance of functional soil microbial population. Application of inorganic N fertilizer resulted in distinctive changes on N-cycle microorganisms. Phosphate-solubilizing functional genes abundance was lower in plots with no phosphate fertilizer. Sequencing analysis showed that the presence or absence of N in the fertilizer mix is a key factor affecting bacterial community diversity of agricultural soil, and pH, total organic C, and total N show a high correlation with bacterial community composition. Nitrogen addition increased the N concentration in the soil, which could cause changes in the soil pH and change the soil bacterial community. Our findings proved that interaction of N fertilizer with other fertilizers can affect microbial communities.

In this study, a combination of indoor culture and high-throughput sequencing was used to analyze changes in nutrients and fungal communities in black soil after the addition of biomass charcoal. The following conclusions were drawn: 1) After six months of constant temperature, black soils containing biomass carbon changed in physicochemical properties. For example, soil pH, organic matter, water content, available phosphorus, and available potassium increased compared with CK treatment (P<0.05). 2) It was observed from high-throughput sequencing that the fungal diversity of black soil also changed. High-throughput sequencing detected five fungal phyla, including Ascomycota, Basidiomycota, Chytridiomycota, Zygomycota, and Aspergillus (Glomeromycota), in which Ascomycota was the predominant group of fungi, which accounted for about 70.6% of the total number of OTUs. The sequencing also detected 67 known genera, among which the dominant genus included the genus Geomyces and sickle Fusarium, Chaetomium, Penicillium, Humicola. The analysis of fungal diversity concluded that the abundance and diversity of fungi in the black soil after adding biomass carbon increased. In the redundancy analysis (RDA), environmental factors had a great influence on the abundance and community composition of fungi. Therefore, adding biomass carbon could not only improve the soil nutrients but also were significant in maintaining the diversity of soil fungal communities.