Effects of Biochar Application on Soil Nitrogen Conversion and Microbial Community Composition

In northeastern China, successive years of cultivation have led to a decline in soil quality, a process that is exacerbated by the over-application of chemical fertilizers to ensure staple food production. The large amount of straw produced by cultivation is difficult to effectively use in recent years. There has been an increasing amount of research on the transforming straw into biomass char, but it has often focused on the effects of biomass char addition on soil physicochemical properties, without further exploring the mechanisms of this process and its effects on soil microorganisms. Microorganisms are an important part of the soil system and the process of how biomass char addition affects microorganisms through its effect on soil physicochemical properties should not be overlooked. In this study， the effect of biochar application at different preparation temperatures (300°C, 400°C and 500°C) and addition contents (0.1% and 1%) on ammonia, nitrate and total nitrogen in soil leachates were investigated. The effect of microbial sequencing on the dynamics of carbon and nitrogen was also investigated to reveal the mechanisms contributing to the changes in nitrogen forms. The results showed that biochar had a better adsorption ability on ammonia nitrogen, and biochar promoted the conversion of ammonia nitrogen to nitrate nitrogen by nitrifying bacteria. The addition of 1% biochar (prepared at 500°C) increased nitrate-nitrogen leaching by 86.52% compared to the control treatment. The sequencing of microorganisms also revealed that biochar changed the structure and abundance of the soil microbial community, especially increasing the relative abundance of the Helicobacter nitrification phylum by 2.02%. These results indicates that biochar facilitated the adsorption of ammonium nitrogen and the conversion of nitrate nitrogen, and solving the problem of low nitrogen fertilizer utilization while promoting the formation of beneficial bacteria in the soil.

Effects of Elevation and Distance from Highway on the Abundance and Community Structure of Bacteria in Soil along Qinghai-Tibet Highway

In recent years, highway construction in the Qinghai-Tibet Plateau (QTP) has developed rapidly. When the highway passes through grassland, the soil, vegetation, and ecological environment along the line are disturbed. However, the impact on soil bacteria is still unclear. Soil bacteria play an important role in the ecological environment. The Qinghai-Tibet Highway (QTH) was selected as the research object to explore the changes in bacterial community structure, vegetation, soil, and other indicators. The results showed that the highway-related activities increased the degradation of vegetation along the road, significantly changed the physical and chemical properties of soil, and caused heavy metal pollution. These environmental factors affected the diversity and community structure of soil bacteria. This kind of disturbance shows a trend of gradually increasing from near to far from the highway. Gemmatimonas, Terrimonas, Nitrospira and Bacillus are more tolerant to environmental changes along the highway, while Barnesiella, and Blastococcus are more sensitive. The content of nitrate decreased and the content of ammonium nitrogen increased in the disturbed area, increasing the abundance of nitrifying bacteria. Therefore, the main factor of the disturbance of the QTH on the grassland is the decline of soil nutrient content, and the supplement of soil nutrients such as carbon and nitrogen should be taken into account in the process of ecological restoration of grassland along the line.

Effect of the Oxidative Phosphorylation Uncoupler Para-Nitrophenol on the Activated Sludge Community Structure and Performance of a Submerged Membrane Bioreactor

In this work, the metabolic uncoupler para-nitrophenol (pNP) was applied to suppress excess sludge production and to investigate its effects on the system’s performance and activated sludge community structure. The COD removal efficiency decreased from 99.0% to 89.5% prior to and after pNP addition, respectively. Application of pNP transiently reduced NH4+-N, NO3−-N and NO2−-N removal efficiencies, suggesting partial inhibition of both nitrifying and denitrifying activity. However, no changes in the relative abundance of the nitrifying bacteria occurred. Phosphorus removal efficiency was sharply reduced after pNP addition, as the consequence of hydrolysis of stored cell reserves. Tetrasphaera, a key polyphosphate accumulating organism, was also affected by the addition of pNP, a fact that highly influenced system’s ability to remove phosphorus. A drastic drop in Soluble Microbial Products (SMP) and Extracellular Polymeric Substances (EPS) was also detected shortly after the introduction of the uncoupler. On the other hand, MBR’s physicochemical parameters were restored to initial values a week after the addition of pNP. Moreover, remarkable changes in beta-diversity were noted after pNP addition. An increase of Bacteroidetes, Gammaproteobacteria and Firmicutes over Actinobacteria and Alphaproteobacteria was also observed after pNP addition.

16S Metagenomics of Nitrifying Bacteria and Archaea Inhabiting Maize Rhizosphere and the Influencing Environmental Factors

The maize rhizosphere soil is unique with diverse microorganisms. Nitrifying bacteria and archaea are ubiquitous and can transform ammonia locked up in soil or manure into nitrate; a more soluble form of nitrogen. However, nitrifying bacteria and archaea inhabiting maize rhizosphere are yet to be identified. We elucidate the diversity and abundance of nitrifying bacteria and archaea associated with maize rhizosphere across different growth stages using 16S metagenomics sequencing. Also, the influence of environmental factors on the nitrifying communities was evaluated. The maize rhizosphere soil was collected from North-West University, Molelwane, South Africa. DNA was extracted using Nucleospin Soil DNA extraction kit and the V3-V4 hypervariable region was sequenced on Illumina Miseq platform. MG-RAST was used to analyze the raw sequences. The environmental factors were measured using standard procedure. The result revealed 9 genera of nitrifying bacteria; Nitrospira, Nitrosospira, Nitrobacter, Nitrosovibrio, Nitrosomonas, Nitrosococcus, Nitrococcus, unclassified (derived from Nitrosomonadales), unclassified (derived from Nitrosomonadaceae) and 1 archaeon Candidatus Nitrososphaera. The Nitrospirae phyla group which had the most nitrifying bacteria was more abundant at the tasselling stage (67.94%). Alpha diversity showed no significant difference. However, the Beta diversity showed significant difference (P=0.01, R=0.58) across the growth stages. The growth stages had no significant effect on the diversity of nitrifying bacteria and archaea, but the tasselling stage had the most abundant. A correlation was observed among some of the environmental factors. The research outcome can be put into consideration while carrying out a biotechnological process that involves nitrifying bacteria and archaea.

Summer Mixed Seeding For Green Fodder As A Preceder For Winter And Spring Grain Crops

Mixed summer crops are used to obtain green forage in the late autumn period and are very effective precursors for winter and spring crops. The use of summer crops as a precursor for winter and spring crops saturated with legumes, which, thanks to a well-developed, deeply penetrating root system, raise available nutrients into the arable horizon, structure the soil and leave biological nitrogen for forage after harvesting, using nitrifying bacteria in the rhizosphere.

Isolation and identification of nitrifying bacteria from tilapia (Oreochromis sp.) pond in Sleman Yogyakarta Indonesia

This research aims to isolate and identify autochtonous nitrifying bacteria from tilapia pond in Sleman Yogyakarta Indonesia for future application in aquaculture practices in the region. Bacteria were isolated using a nitrification medium. Bacterial characterization was carried out by non-pathogenic test to tilapia (Oreochromis sp.), and nitrification activity test in a single bacterial fermentation medium for 9 days. Bacterial identification was carried out based on the colony and cell morphologies, biochemical tests, and molecular analysis using the 16S rRNA and gyrB genes. A total of 15 isolates of nitrifying bacteria were obtained. Four non-pathogenic isolates obtained the highest nitrification activity on the sixth day of incubation, with nitrate production of 17.26-21.54 ppm. Two selected bacteria, isolates A2 and A3, have colony morphology that is milky white, smooth surface, circular shape, entire edge, and convex elevation. Both bacteria are short rods, Gram-negative, non-motile, produce catalase, fermenting glucose, sucrose, and lactose, and do not produce oxidase, ornithine decarboxylase, indole, and H2S. Molecular analysis showed that the two isolates had the highest similarity (99.28% and 99.34%) to Klebsiella spp.