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Woody biomass is the most common natural carbon source applied in solid-phase denitrification (SPD). However, its denitrification ability is low in the SPD process due to its poor carbon availability. In this study, sawdust samples were pretreated to various degrees, and then filled into SPD bioreactors to reveal the relationship between carbon availability and denitrification behaviors. The behaviors include the denitrification process, internal effects of major factors (carbon availability, pH and temperature), and the presence of bacterial communities. Results shown that the long-term denitrification rate of pretreated sawdust was increased by 4.5–4.8 times over that of untreated sawdust (29.3 mg N L−1 sawdust d−1). However, despite improving the pretreatment degree of the sawdust in the bioreactor, the long-term denitrification rate shown no further increase. The denitrification rate was most influenced by the temperature, followed by the pH, and then the sawdust pretreatment degree. The denitrification rate increased with decreasing pH and rising temperature of the pretreated sawdust. The removed nitrate was rarely converted into nitrite or nitrous oxide, but ammonium was produced at high pH and temperature for the pretreated sawdust. The adverse effects of ammonium and dissolved organic carbon (DOC) reduced when the pH of the pretreated sawdust was lowered to 6.5. Hydrolytic and denitrifying bacteria formed the main SPD bioreactor bacteria, whose abundances increased with increasing sawdust pretreatment degree. The results were beneficial to reduce the hydrolytic retention time and adverse products for the SPD system using woody carbon source. Image 1 • Nitrate removal rates increased by 4.5–4.8 times with pretreated sawdust. • Bioreactors with pretreated sawdust maintained a high nitrate removal rate. • Denitrification efficiency improved with lowering pH for pretreated sawdust. • Functional bacteria abundances increased with rising sawdust pretreatment degree. [ABSTRACT FROM AUTHOR]

Few long-term fertilization experiments have been performed in forests, even though the effects of nitrogen (N) addition on soil microbial biomass are a cause for concern. Our objective was to examine the effects of repeated fertilization for 36 years on soil microbial biomass in two forest stands. We measured soil chemical properties and microbial biomass carbon (C) and N in soils in fertilized and non-fertilized plots in a birch stand (Betula maximowicziana Regel) and a fir stand (Abies sachalinensis Fr. Schmidt). We also performed lime amendments and a 21-day laboratory incubation, and measured microbial biomass to clarify the effects of acidification due to fertilization. Soil pH was significantly lower in fertilized plots in both stands, and soil microbial biomass C and N were lower (significantly so in the fir stand) in the fertilized plots after 36 years of repeated fertilization. In the laboratory incubation, lime amendment did not significantly affect the microbial biomass C, N, or C:N ratio, despite an increase of about 1 unit in soil pH. Our results therefore indicate that factors other than soil pH also have important effects on soil microbial biomass in repeatedly fertilized forest stands. [ABSTRACT FROM AUTHOR]

Wood ants maintain a stable, high temperature in their nests from spring to autumn. Much of the heat is generated by the nest's microbial community, which might be differently affected by the addition of available carbon (C) sources in spring, when the nest temperature increases, than in summer, when the nest temperature is maintained at a high level. We used an incubation experiment to examine the effects of honeydew and resin on microbial activity and biomarkers' contents in ant nest and forest floor substrates. The effects of resin lasted longer than those of honeydew. Microbial activity was higher in the ant nest substrate than in the forest floor substrate, indicating that the microorganisms in the ant nest substrate were better adapted to utilize both C sources. Although bacteria were expected to be dominant after honeydew addition, this was not the case probably because the available C from honeydew had been depleted by the end of the incubation. Fungal biomarkers dominated at 10 °C with both C sources probably because fungi are better able than bacteria to remain active at low temperatures. [ABSTRACT FROM AUTHOR]

Based on continuous anaerobic co-digestion of cow manure with available carbon slowly released corn straw, the effect of adding available carbon quickly released fruit and vegetable waste (FVW) was explored, meanwhile microbial community variation was studied in this study. When the FVW added was 5% and 1%, the methane production of the cow manure and corn straw was improved, and the start-up process was shortened. With higher proportion of FVW to 5%, the performance was superior with a mean methane yield increase of 22.4%, and a greater variation of bacterial communities was observed. FVW enhanced the variation of the bacterial communities. The microbial community structure changed during fermentation and showed a trend toward a diverse and balance system. Therefore, the available carbon quickly released FVW was helpful to improve the anaerobic co-digestion of the cow manure and available carbon slowly released corn straw. [ABSTRACT FROM AUTHOR]

For a long time, farmers in the red soil region of southern China have returned crop residues to the soil, but how various crop residues influence nitrous oxide ( N2 O) emissions is not well understood. We compared the influence of returning different crop residues [rapeseed cake (RC), maize straw, rice straw and wheat straw (WS)] in combination with different levels of nitrogen ( N) fertilizer (nil, low and high) on red soil N2 O emissions. Results confirmed the inverse relationship between cumulative N2 O emissions and residue C:N ratio in red soil under different levels of N fertilizer. However, N-fertilizer application did not significantly influence N2 O emissions in the WS (which had the highest C: N ratio) and corresponding control treatments, while it enhanced N2 O emissions in the RC (which had the lowest C: N ratio) treatment and displayed significantly higher cumulative N2 O emissions with low N fertilizer application. This phenomenon may be attributed to the poor nutrient content in red soil, which leads to 'Liebig's Law of the Minimum' on available C. N fertilizer application provided sufficient available N, while the readily available C, which was mainly dependent on the degradability of the residue, became the crucial factor influencing N2 O emissions. Additional experiments, which showed that the addition of glucose and sucrose could increase N2 O emissions when N ( [ABSTRACT FROM AUTHOR]

Wood ant nests are hotspots of nutrients and microbial activity in nutrient-limited coniferous forest ecosystems, as ants accumulate honeydew and nutrients in their nests due to foraging and building activities. In this study we carried out a microcosm experiment focussing on the role of bacteria and protozoa on carbon and nitrogen turnover in nutrient-rich and nutrient-poor litter materials. Two types of litter material, (i) ant nest material or (ii) surrounding forest floor material were sterilized and inoculated either with bacteria alone (B treatment) or with bacteria and protozoa in combination (BP treatment). The litter materials were subsequently incubated in laboratory microcosms for 21 days. Respiration of the microcosms was measured during the whole incubation period and leachates were sampled every week and analysed for ammonium and nitrate. Our results showed lower ammonium leaching and increased respiration in the BP treatment, which could be explained by higher microbial biomass in this treatment. The negative effect of protozoa on ammonium leaching was independent of the type of litter material suggesting that available carbon in nest material supported fixation of nitrogen in the bacterial biomass. Our data show that protozoan grazing can play a critical role in retaining nitrogen in ant nests by increasing microbial activity and biomass, and thereby preventing nitrogen leaching. [ABSTRACT FROM AUTHOR]

The effect of glucose, chicken manure, and filter mud on the ammonium and nitrate concentrations, ammonia-oxidizing bacterial community and bacterial community in latosolic red soils during the incubation of microcosms was investigated. The soil nitrate concentration was significantly lower in the glucose-treated soil than in the filter mud or chicken manure-treated soil from days 2 and 5 to 21 of incubation. The ammonia-oxidizing bacteria community composition, measured by terminal restriction fragment length polymorphism analysis, was different among the treatments 9 days after incubation, suggesting that the control soil without external fertilization had a low 283-bp ( Nitrosospira) fragment relative abundance (27 %) compared with the glucose-treated (62 %), filter mud (73 %) and chicken manure (78 %) samples. Additionally, 491-bp fragments ( Nitrosomonas) were detected in all the soil treatments except for the control soil, and 48-bp fragments (from different Nitrosomonas) were detected in the chicken manure-treated soil. The bacterial community structure was markedly changed in the glucose-treated soil on day 9 and in the filter mud-treated soil on day 31, indicating that the effect of filter mud on the bacterial community is delayed compared to the effect of glucose. The chicken manure-treated soil showed less change, similar to that of the control soil. Glucose fertilization greatly increased the soil bacterial abundance and functional diversity; however, the chicken manure and filter mud did not stimulate soil bacterial activity on day 9. These results indicated that nitrification may have been somewhat suppressed in the glucose-treated soils, which was possibly related to the improving ammonia-oxidizing bacterial community, bacterial community and activity via the available carbon application. The filter manure and chicken manure treatments demonstrated fewer effects. These results suggest that organic carbon quality, e.g., increasing the available carbon, regulates the nitrification process and is beneficial to reducing soil nitrogen losses. [ABSTRACT FROM AUTHOR]

Development of techniques utilizing waste without any additional energy or rare catalysts is a starting point for becoming sustainable. In the present work, the complex utilization of greenhouse residues was studied on a commercial scale. Only the energy produced by the process (8%) was used to run the technology, thanks to multilevel heat recuperation and high methane yields (over 340 m3 volatile solid t−1). Manifestations of labile carbon in relation to available nitrogen, methane yields, and the formation of inhibitors were investigated in detail. The results sweep away many false beliefs about the ratios of carbon to nitrogen and highlight the role of the availability of carbon in phytomass utilization. [ABSTRACT FROM AUTHOR]

To estimate the availability of nonexchangeable NH−N for soil microorganisms four incubation experiments were conducted under controlled conditions. The following results were obtained: Incorporating glucose as a source of readily oxidizable organic material favored the release of nonexchangeable NH−N. Mobilization of NHfrom the interlayers of the clay minerals was decreased by the application of K, while Ca, which is supposed to expand the lattice of the clay minerals, had no influence on the release of NH. Soil temperature had no effect on microbiological mobilization of NH. It is assumed that, generally, the influence of nitrifying bacteria on the mobilization of nonexchangeable NH−N is negligible. However, in soils with abundant amounts of available carbon promoting the activity of heterotrophic soil microorganisms, the release of NHfrom clay minerals is favored under fallow conditions. [ABSTRACT FROM AUTHOR]

• NO 3 ––N removal of >60% from groundwater was achieved with a straw-based PRB. • Biodenitrification occurred with waste-straw material. • No secondary pollution, as measured by chromaticity and nitrogen, was observed. • Agricultural straw is a suitable alternative to woodchip as a PRB filler. Large amounts of straw produced each year are currently wasted. A potential use of this resource in permeable reactive barriers (PRBs) for the denitrification of polluted groundwater has not previously been reported. In this study, a field PRB filled with straw-based materials was installed to reduce nitrogen transport in the Huaihe River Basin. In initial laboratory-scale experiments, wheat straw, corn straw, corncobs, and woodchip substrates were investigated through elemental analysis, leaching experiments, and their functional gene abundance. The carbon and nitrogen contents of the substrates were 39.62–48.17% and 0.64–1.07%. Corn-straw (15.12 mg g–1) and wheat straw (8.04 mg g–1) exhibited higher leaching of total organic carbon (TOC), in the presence of denitrification functional genes. All agricultural waste released chromaticity (up to 750 degree) and nitrate, nitrite (<0.05 mg g–1), and ammonium (<0.30 mg g–1) ions. The field PRB filled with processed straw materials as substrates exhibited nitrate removal rates of 60–90% and minimal secondary pollution, due to biochemical coupling reactions. Hence, straw waste is a suitable alternative to woodchip for in situ PRB fillers. [ABSTRACT FROM AUTHOR]