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Abstract Liming of acidic soils has been suggested as a strategy to enhance N 2 O reduction to N 2 during heterotrophic denitrification, and mitigate N 2 O emission from N fertilised soils. However, the mechanisms involved and possible interactions of key soil parameters (NO 3 − and O 2) still need to be clarified. To explore to what extent soil pH controls N 2 O emissions and the associated N 2 O/(N 2 O + N 2) product ratio in an acidic sandy soil, we set-up three sequential incubation experiments using an unlimed control (pH 4.1) and a limed soil (pH 6.9) collected from a 50-year liming experiment. Interactions between different NO 3 − concentrations, N forms (ammonium- and nitrate) and oxygen levels (oxic and anoxic) on the liming effect of N 2 O emission and reduction were tested in these two sandy soils via direct N 2 and N 2 O measurements. Our results showed 50-year liming caused a significant increase in denitrification and soil respiration rate of the acidic sandy soil. High concentrations of NO 3 − in soil (>10 mM N in soil solution, equivalent to 44.9 mg N kg−1 soil) almost completely inhibited N 2 O reduction to N 2 (>90%) regardless of the soil pH value. With decreasing NO 3 − application rate, N 2 O reduction rate increased in both soils with the effect being more pronounced in the limed soil. Complete N 2 O reduction to N 2 in the low pH sandy soil was also observed when soil NO 3 − concentration decreased below 0.2 mM NO 3 −. Furthermore, liming evidently increased both N 2 O emissions and the N 2 O/(N 2 +N 2 O) product ratio under oxic conditions when supplied with ammonium-based fertiliser, possibly due to the coupled impact of stimulated nitrification and denitrification. Overall, our data suggest that long-term liming has the potential to both increase and decrease N 2 O emissions, depending on the soil NO 3 − level, with high soil NO 3 − levels overriding the assumed direct pH effect on N 2 O/(N 2 +N 2 O) product ratio. Highlights • High soil NO 3 − content inhibits N 2 O reduction to N 2 regardless of soil pH value. • The direct pH effect on N 2 O/N 2 ratio was overridden by the effect of NO 3 − content. • Liming increased N 2 O emissions when NH 4 + fertiliser applied under oxic condition. • Liming decreased N 2 O emissions when NO 3 − fertiliser applied under anoxia. [ABSTRACT FROM AUTHOR]

Biochar has been shown to reduce nitrous oxide (N 2 O) emissions from soils, but the effect is highly variable across studies and the mechanisms are under debate. To improve our mechanistic understanding of biochar effects on N 2 O emission, we monitored kinetics of NO, N 2 O and N 2 accumulation in anoxic slurries of a peat and a mineral soil, spiked with nitrate and amended with feedstock dried at 105 °C and biochar produced at 372, 416, 562 and 796 °C at five different doses. Both soils accumulated consistently less N 2 O and NO in the presence of high-temperature chars (BC562 and BC796), which stimulated reduction of denitrification intermediates to N 2 , particularly in the acid peat. This effect appeared to be strongly linked to the degree of biochar carbonisation as predicted by the H:C ratio of the char. In addition, biochar surface area and pH were identified as important factors, whereas ash content and CEC played a minor role. At low pyrolysis temperature, the biochar effect was soil dependent, suppressing N 2 O accumulation in the mineral soil, but enhancing it in the peat soil. This contrast was likely due to the labile carbon content of low temperature chars, which contributed to immobilise N in the mineral soil, but stimulated denitrification and N 2 O emission in the peat soil. We conclude that biochar with a high degree of carbonisation, high pH and high surface area is best suited to supress N 2 O emission from denitrification, while low temperature chars risk supporting incomplete denitrification. • Biochar produced over 416 °C consistently reduced N2O accumulation during denitrification. • Denitrification response was soil dependent below this temperature. • Carbonisation degree, pH and surface area best explained the response. • Biochar affected total denitrification and not only the final conversion of N2O to N2. [ABSTRACT FROM AUTHOR]

A well-defined methodology for constructing appropriate atomistic representations of biochar will aid in visualizing the structural features and elucidating biochar behavior with molecular dynamics (MD) simulations. Such knowledge will facilitate engineering biochars tailored to specific applications. To achieve this goal, we adapted modeling strategies applied in coal science by employing multi-cross-polarization 13C nuclear magnetic resonance, ultimate analysis, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy to identify functional groups. Helium density, surface area, and porosity were used to assess structural features. Biochar's aromatic cluster size distribution was proposed based on data from the benzene polycarboxylic acid method. The computational framework reduces bias by incorporating chemical information derived from density functional theory, reactive MD simulations, and advanced characterization data. The construction approach was successfully applied to cellulose biochars produced at four temperatures, obtaining independent representations with a relative error on the atomic contents of <10 % for oxygen and nitrogen and <5 % for carbon and hydrogen. The atomistic representations were validated using X-ray diffraction, electron spin resonance data, and laser desorption/ionization Fourier-transform ion cyclotron resonance-mass spectrometry. The code will assist others in overcoming structural creation barriers and enable the utilization of the generated structures for further simulations. [Display omitted] • Available code for creating large-scale atomistic models, capturing chemical and physical features. • A novel approach proposes the aromatic cluster size distribution of biochar. • Atomistic representations are validated with experimental and theoretical data. • The arrangement of aromatic size distributions aids in surface area and pore development. [ABSTRACT FROM AUTHOR]

Iron is an essential nutrient. Its deficiency hinders the synthesis of ATP and DNA. We report that galactose metabolism is defective when iron availability is restricted. Our data support this connection because 1) galactose-mediated induction of GAL promoter-dependent gene expression was diminished by iron limitation, and 2) iron-deficient mutants grew slowly on galactosecontaining medium. These two defects were immediately corrected by iron replacement. Inherited defects in human galactose metabolism are characteristic of the disease called galactosemia. Our findings suggest that iron-deficient galactosemic individuals might be more severely compromised than iron-replete individuals. This work shows that iron homeostasis and galactose metabolism are linked with one another. [ABSTRACT FROM AUTHOR]

Sorption of nutrients such as NH 4 + is often quoted as a critical property of biochar, explaining its value as a soil amendment and a filter material. However, published values for NH 4 + sorption to biochar vary by more than 3 orders of magnitude, without consensus as to the source of this variability. This lack of understanding greatly limits our ability to use quantitative sorption measurements towards product design. Here, our objective was to conduct a quantitative analysis of the sources of variability, and infer which biochar traits are more favourable to high sorption capacity. To do so, we conducted a standardized remodelling exercise of published batch sorption studies using Langmuir sorption isotherm. We excluded studies presenting datasets that either could not be reconciled with the standard Langmuir sorption isotherm or generated clear outliers. Our analysis indicates that the magnitude of sorption capacity of unmodified biochar for NH 4 + is lower than previously reported, with a median of 4.2 mg NH 4 + g−1 and a maximum reported sorption capacity of 22.8 mg NH 4 + g−1. Activation resulted in a significant relative improvement in sorption capacity, but absolute improvements remain modest, with a maximum reported sorption of 27.56 mg NH 4 + g−1 for an activated biochar. Methodology appeared to substantially impact sorption estimates, especially practices such as pH control of batch sorption solution and ash removal. Our results highlight some significant challenges in the quantification of NH 4 + sorption by biochar and our curated data set provides a potentially valuable scale against which future estimates can be assessed. [Display omitted] • NH 4 + sorption capacity of biochar highly variable in literature. • Re-analysis showed analytical methods as key source of variability. • NH 4 + sorption capacity of biochar is more limited than previously believed. • Modification of biochar results in modest absolute increases in sorption capacity. [ABSTRACT FROM AUTHOR]