Search

Free-living diazotrophs play a critical role in nitrogen (N) supply to ecosystems. Land-use change and plant rhizosphere are two important factors influencing diazotroph populations, but their relative strength in determining the soil diazotrophic community is still unclear, especially in acidic soils. One natural vegetation (the dominant species is green foxtail) and three agricultural land-uses (maize, peanut and soybean, respectively) widely distributed in the acidic soil region of southern China were selected. Bulk and rhizosphere soils were collected from every land-use, and their properties were determined. Quantitative PCR and high-throughput sequencing were applied to investigate soil diazotrophic abundance, diversity and community composition. Land use conversion from natural vegetation to different agricultural land-uses significantly reduced diazotroph abundances in bulk soils, however, the rhizosphere had a positive effect on the abundances in agricultural land-uses. Statistical analysis showed that the rhizosphere exerted a stronger effect on diazotroph abundance than land-use change. Converting natural vegetation to agricultural land-uses also decreased diazotroph richness and land-use types differed significantly in community composition, but plant rhizosphere did not cause these effects. In particular, the community variations in leguminous plants were more distinct than maize. Land-use change also influenced some topological properties of the community network. In acidic soil, land-use change has noticeable effects on the richness and composition of diazotrophic community than the rhizosphere. The rhizosphere, however, has a more obvious effect in increasing the abundance of the diazotrophs. These results highlight the critical role of land-use change in manipulating soil diazotrophic community composition.

Although phosphorus (P) availability and plant cultivation affect diazotrophic populations, studies often consider individual factors rather than their combined effects. Their relative importance to diazotrophs remains poorly understood, especially in acidic soils with P deficiency. It is hypothesized that the influences of P fertilization and plant cultivation on diazotrophic communities differ in acidic soils. The objectives were to investigate these influences and identify the key determining factors. Maize was grown in an acidic soil that was supplemented with 0, 20, and 50 mg P kg− 1 for 42 days. Maize biomasses, plant nutrient contents, and soil physicochemical properties were determined. Based on the nifH gene, the abundances and community compositions of diazotrophs in the different plant/soil compartments (bulk soils, rhizosphere soils, and roots) were respectively investigated using quantitative PCR and high-throughput sequencing. P fertilization significantly improved the diazotrophic abundances in the bulk and rhizosphere soils, but not in the roots. The plant/soil compartments had stronger effects on the abundance and diversity of diazotrophs than did P fertilization. Furthermore, the plant/soil compartments influenced diazotrophic community composition, but P fertilization did not. However, in the same sampling site, P fertilization caused community variations in the bulk and rhizosphere soils, rather than in the roots. Although P fertilization affected the abundances and compositions of diazotrophic communities in the bulk and rhizosphere soils, the plant/soil compartments resulting from maize cultivation had more noticeable effects than did P fertilization. These findings improved the understanding of biological nitrogen fixation in acidic soils.

In acidic soil, plant aluminum (Al) tolerance and nitrogen (N) fertilizer form play the important roles in influencing plant growth. Diazotrophs as plant growth promoting rhizobacteria can contribute to plant available N, but the response to plant growth differences resulting from plant Al tolerance or N fertilizer form in acidic soil is poorly understood. Here, we investigated this response. Three maize cultivars with different Al-tolerance levels were grown in an acidic soil that was added with nitrate (NO3−-N) or ammonium (NH4+-N) fertilizers. After 42 days, maize biomasses and root morphologies as well as the physicochemical properties of bulk and rhizosphere soils were determined. Based on nifH gene, soil diazotroph abundance was determined by quantitative RT-PCR and community composition was assayed using high-throughput sequencing. For the same maize cultivar, application of NO3−-N fertilizer relative to NH4+-N fertilizer increased maize biomass, root length, root surface area, and rhizosphere pH, but not significantly affect rhizosphere nifH copy number and community composition. The nifH copy numbers did not show significant differences among rhizosphere samples of three maize cultivars, but community composition was obviously different between Al-tolerant and Al-sensitive cultivars. In acidic soil, maize cultivars depending on Al tolerance altered rhizosphere diazotrophic community composition, but this effect seemed to be not susceptible to N fertilizer forms.

Acid and alkaline phosphatase (ACP and ALP), encoded separately by the bacterial phoC and phoD genes, participate in the mineralization of organic phosphorus (P) to inorganic P. However, the influence of chemical fertilization on soil phosphatase activities and associated bacterial communities in acidic soils remains unclear. Here, we conducted a 27 year continuous chemical fertilization experiment consisting of the no-fertilizer control (CK), N and P fertilizer (NP), N and K fertilizer (NK), P and K fertilizer (PK), and N, P and K fertilizer (NPK) treatments, in order to investigate phosphatase activities and phoC- and phoD-harboring bacterial communities. Results demonstrated that ACP and ALP activities increased significantly in the NP (198.70 and 35.46 μg pNP g−1 soil h−1, respectively) and NPK treatments (199.62 and 36.51 μg pNP g−1 soil h−1, respectively) compared to CK (143.81 and 22.49 μg pNP g−1 soil h−1, respectively), while ALP activity was reduced for the NK treatment (13.86 μg pNP g−1 soil h−1). The abundance and diversity index of phoC- and phoD-harboring bacteria differed among treatments. The two bacterial community structures exhibited similar trends in terms of the significant differences between N-free (CK and PK) and N-containing (NP, NK and NPK) treatments (Adonis, p

Low soil nutrient availability severely constrains plant growth and productivity in acidic soil ecosystems. Diazotrophs and arbuscular mycorrhizal fungi (AMF) are the important microbial groups that improve the bioavailability of soil nitrogen (N) and phosphorus (P), respectively. Therefore, the objective was to investigate the biogeographic patterns and co-occurrence networks of the diazotrophic and AMF communities in the acidic soil ecosystem. We collected 52 soil samples from four long-term field observation stations with spatial distances of 961.3 km in the acidic soil region of southern China, and analyzed the community composition and biogeographic distributions of the diazotrophs and AMF using high-throughput sequencing of the functional gene amplicons. The variation partition analysis indicated that soil physicochemical factors provided more contributions than geographic distance, sampling stations and land-use types in the assembly of the diazotrophic and AMF community communities. Distance-decay relationships and Mantel tests showed that soil physicochemical factors had remarkable effects on both microbial community structures, whereas geographic distance only significantly affected the diazotrophic community variations. Co-occurrence network analysis revealed that AMF network was more complex and stable than the diazotrophic network. Furthermore, the dominant genera Bradyrhizbium and Glomus might be the more important keystone taxa in the diazotrophic and AMF networks, respectively. These findings suggest that the diazotrophic and AMF communities exhibit different assembly mechanisms and co-occurrence ecological networks in the acidic soil region of southern China, and both community assemblies were mainly driven by soil physicochemical factors.

The nitrogen (N) cycle process in agricultural soil is affected by fertilization. However, there is limited information on the abundance of N-cycling microbial community and its response to the different fertilization strategies in acidic soil. Using quantitative PCR, we investigated the microbial abundance involving 11 functional genes of the N cycle (nifH, chiA, aprA, archaeal and bacterial amoA, napA, narG, nirS, nirK, norB and nosZ) in an acidic agricultural soil. The soils were subjected to no fertilizer (Control), chemical NPK fertilizer (NPK), NPK combined with quicklime (NPKCa), NPK combined with crop residues (NPKS), NPK combined with quicklime and crop residues (NPKSCa), NPK combined with manure (NPKM) and only manure (M) fertilization for 27 years. Results showed that fertilization improved crop yield and soil nutrient availability, changed soil pH levels and affected the abundance of N-cycling functional genes. Manure application markedly increased the abundance of all genes and was associated with the largest shift in community structure. The variation of microbial community in the fertilization treatments (NPK, NPKCa, NPKS, NPKSCa, M and NPKM) resulted from the distinct contribution of functional genes, in which the nifH, napA and archaeal amoA genes highly contributed to the community variations between manure fertilization and Control. Soil variables, particularly pH, NO3−-N and AP, significantly affected the N-cycling microbial community structure. Overall, the different fertilization strategies demonstrated varying influential patterns on the N-cycling microbial abundance and community by altering soil properties and affecting specific functional gene abundance; in particular, manure treatments had a greater influence compared to chemical fertilizers.

This paper presents the modeling and analysis of the longitudinal dynamic of variable-sweep aircraft. The variable-sweep aircraft have complex nonlinear and time-varying characteristics. To capture the complicated characteristics of variable-sweep aircraft, a systematic modeling method of the longitudinal dynamics is investigated. By using Digital Datcom software, aerodynamic data of the morphing aircraft is obtained; then the nonlinear dynamic models of the variable-sweep aircraft is established. To facilitate future control design, a T-S fuzzy model was constructed based on the nonlinear model. Both models are simulated and analyzed. Comparison verifies the effectiveness of the T-S fuzzy model. The characteristics of the longitudinal dynamic are analyzed based on simulation results.