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Autotrophic nitrification, heterotrophic nitrification, and gross nitrification rates in swine manure (SW)- and swine-manure-derived biochar (SWB)-amended soil

Autotrophic nitrification, heterotrophic nitrification, and gross nitrification rates in swine manure (SW)- and swine-manure-derived biochar (SWB)-amended soil

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Purpose Laboratory incubation experiments using ¹⁵N stable isotope labeling and acetylene suppression techniques were conducted to compare the autotrophic nitrification and heterotrophic nitrification rates with the addition of swine manure (SW) and swine-manure-derived biochar (SWB) in two paddy soils. Materials and methods SW and SWB were applie...

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... Most researchers have reported a stimulating effect of biochar on nitrification, as biochar promotes soil microbial activity, nutrient availability, and biochemical function due to its high specific surface area, hydrophilicity, and adsorption capacity [11]. Some researchers have also discovered an inhibitory effect of biochar on nitrification due to surface free radicals, increasing the soil pH, and reducing the bioavailability of NH 4 + -N [12,13]. Ammonia oxidation, catalyzed by ammonia-oxidizing bacteria (AOB) and ammoniaoxidizing archaea (AOA), is the rate-limiting step of autotrophic nitrification [14]. ...
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Biochar has been widely recognized as an effective and eco-friendly ameliorant for saline soils, but information about the mechanism of how biochar influences nitrification in salt-affected agroecosystem remains fragmented. An incubation experiment was performed on the salt-affected soil collected from a three-consecutive-year experiment at biochar application gradients of 7.5 t⋅ha−1, 15 t⋅ha−1 and 30⋅t ha−1 and under nitrogen (N) fertilization. Responses of the nitrification rate (NR), numbers of ammonia monooxygenase (amoA) gene copies, and community structures of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to biochar application were investigated. The results indicated that, under N fertilization, the NR and numbers of amoA-AOB and amoA-AOA gene copies negatively responded to biochar addition. Biochar application increased the community diversity of AOB but decreased that of AOA. Biochar addition and N fertilization shifted the AOB community from Nitrosospira-dominated to Nitrosospira and Nitrosomonas-dominated, and altered the AOA community from Nitrososphaera-dominated to Nitrososphaera and Nitrosopumilus-dominated. The relative abundance of Nitrosospira, Nitrosomonas and Nitrosopumilus decreased, and that of Nitrosovibrio and Nitrososphaera increased with biochar application rate. Soil SOC, pH and NO3−-N explained 87.1% of the variation in the AOB community, and 78.1% of the variation in the AOA community was explanatory by soil pH and SOC. The SOC and NO3−-N influenced NR through Nitrosovibrio, Nitrosomonas, Norank_c_environmental_samples_p_Crenarchaeota and amoA-AOB and amoA-AOA gene abundance. Therefore, biochar addition inhibited nitrification in salt-affected irrigation-silting soil by shifting the community structures of AOB and AOA and reducing the relative abundance of dominant functional ammonia-oxidizers, such as Nitrosospira, Nitrosomonas and Nitrosopumilus.
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