Ammonia Abundance Research Articles

Effects of Biochar Addition Under Different Water Management Conditions on N2O Emission From Paddy Soils in Northern Hainan

Alternating dry and wet conditions affect the main processes of N2O production, such as nitrification and denitrification. Such conditions are very common in tropical rice-growing areas, such as Hainan. As a type of soil amendment, biochar is widely used to improve physical and chemical properties of soil and to reduce soil greenhouse gas emissions. However, there is a lack of existing in-depth research on the emission reductions of biochar when used in tropical soils that undergo frequently alternating dry and wet conditions. In this experiment, typical paddy soil from northern Hainan was used as the test soil, and corn stalk biochar, carbonized under anaerobic conditions at 400℃, was used as the test biochar. This experiment explored the effects of adding biochar on soil greenhouse gas emissions and microbial-related functional genes under different water management conditions. The experiment comprised a 30 d culture, kept in the dark at 25℃, and a total of six treatments:alternating dry-wet conditions without adding biochar (AWD1), alternating dry-wet conditions with 2% biochar (AWD2), alternating dry-wet conditions with 4% biochar (AWD3), continuous flooding without adding biochar (CF1), continuous flooding with 2% biochar (CF2), and continuous flooding with 4% biochar (CF3). The results showed that:① the addition of biochar under different moisture conditions can reduce N2O emissions in acidic paddy soil (P<0.05, the same below), as the total N2O emissions with the AWD3 treatment were 0.43 mg ·kg-1, which indicates an approximate reduction of 68%, relative to the AWD1 treatment; ② Corn stalk biochar can significantly increase the soil pH under different water management conditions. Compared to the no-biochar treatment, the soil pH increased by 0.5 units on average after cultivation with the addition of biochar, and as the soil NH4+-N content increased, it led to a decrease in Eh. ③ Corn stalk biochar significantly reduces the abundance of ammonia oxidizing bacteria and significantly increases the nosZ gene abundance. However, it decreases the ratio of (nirK+nirS)/nosZ, inhibits the nitrification process, and promotes the reduction of N2O in the denitrification process. Thereby, the addition of corn stalk biochar can reduce N2O emissions. These results show that alternating dry-wet conditions, combined with the addition of corn stalk biochar, are beneficial for reducing N2O emissions in paddy soil, which may have further application in the reduction of agricultural greenhouse gas emissions in northern Hainan.

Effects of biochar and biochar compound fertilizer on the communities of nitrifier and denitrifier in a reclaimed soil from coal-mining area

As a new soil amendment strategy, the effects of biochar application on soil microbial community have been reported in literature, but little information is available on the response of nitrogen-related microbial communities to biochar application in the reclaimed soil from coal-mining area. Through an outdoor pot experiment with reclaimed soil from coal-mining area of Huaibei, the effects of biochar and biochar compound fertilizer on nitrifier and denitrifier communities were investigated by real time PCR (qPCR) and terminal-restricted fragment length polymorphism (T-RFLP). There were five treatments: control (CK), NPK fertilizer (CF), biochar compound fertili-zer (BF), 2% biochar and NPK fertilizer (LB), 4% biochar and NPK fertilizer (HB). Results showed that compared with the CK, the treatments CF, BF, LB and HB significantly increased the abundance of ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB), nirK and nirS genes of denitrifier. Compared with the CF treatment, BF, LB and HB significantly increased the abundance of AOB and nirK genes by 42.9%-82.1% and 33.5%-62.7%, respectively. Results of redundancy analysis showed that soil organic carbon, pH, NH4+-N and available potassium significantly affected AOB community structure, while soil organic carbon concentration, pH and NO3--N concentration significantly altered nirK-denitrifier community structure. Therefore, the application of biochar and biochar compound fertilizer could improve soil quality of the reclaimed soil from coal-mining area, and increase the abundances of nitrifier and denitrifier and alter community structure of AOB and nirK-denitrifier.

Impacts of silver nanoparticles on enzymatic activities, nitrifying bacteria, and nitrogen transformation in soil amended with ammonium and nitrate

Silver nanoparticles (AgNPs) are effective antimicrobial compounds that are used in a myriad of applications. Soil microorganisms play crucial roles in nitrogen cycling, but there is a lack of comprehensive understanding of the effects of AgNPs on enzymatic activity in the nitrogen cycle, nitrifying bacteria, and nitrogen transformation in soil. Herein, enzyme activities were determined following the addition of different forms of nitrogen, ammonium nitrogen ((NH4)2SO4), nitrate nitrogen (KNO3), and amide nitrogen (urea, CO(NH2)2) at 200 mg N kg–1, into the soil amended with AgNPs at 0, 10, 50, and 100 mg kg–1. After 7 d of incubation with 10 mg kg–1 AgNPs, the activities of urease, nitrite reductase (NiR), nitrate reductase (NaR), and hydroxylamine reductase (HyR) were reduced by 12.5%, 25.0%, 12.2%, and 24.2%, respectively. Of particular note, more than 53.5%, 61.7%, and 34.7% of NaR, NiR, and HyR activities, respectively, were inhibited at 100 mg kg–1 AgNPs. The abundance (most probable number) of ammonia- and nitrite-oxidizing bacteria (AOB and NOB, respectively) was measured using real-time quantitative polymerase chain reaction (qPCR) and the Cochran method. The abundance of AOB and NOB decreased when AgNPs were present in the soil. The NH4NO3 amendment increased copy numbers of bacterial and archaeal amoA nitrification functional genes, by 38.3% and 12.4%, respectively, but AgNPs at 50 mg kg–1 decreased these values by 70% and 56.4%, respectively. The results of 15N enrichment (atom% excess) of NH4+ and NO3– experiments illustrated the influence of AgNPs on soil nitrogen transformation. According to the 15N atom% excess detected, the conversion of 15N-labeled NH4+ to NO3– was significantly inhibited by the different levels of AgNPs in soil. The reduced gross nitrification rate further confirmed this finding. Overall, this study revealed considerable evidence that AgNPs inhibited nitrogen cycle enzyme activity, the number of nitrifying bacteria, the abundance of the amoA gene, and the gross nitrification rate. Silver nanoparticles inhibited nitrogen transformation, and the rate of nitrification was also negatively correlated with AgNP levels.

Nitrogen removal processes coupled with nitrification in coastal sediments off the north East China Sea

Denitrification and anaerobic ammonia oxidation (anammox) play key roles in nitrogen (N) loss, and nitrification can supply substrates of NO2– and NO3– for denitrification and anammox. Coupled nitrification-denitrification/anammox processes are thus crucial for N removal in coastal ecosystems. This study aims to examine the spatial-temporal variations of ambient, coupled, and uncoupled N removal rates in the coastal sediments off the north East China Sea, and to clarify the controlling factors and microbial mechanisms of coupled nitrification-denitrification/anammox. The rates of ambient, coupled, and uncoupled denitrification and anammox in coastal sediments off the north East China Sea were quantified using the continuous-flow experiments combined with 15N isotope pairing technique. The quantitative polymerase chain reaction method was used to determine the abundances of nitrifiers, denitrifiers, and anammox bacteria, with the functional genes of amoA and nirS, and 16S rRNA gene, respectively. Ambient denitrification rates varied between 0.43 and 7.39 μmol N m−2 h−1, and ambient anammox rates ranged from 0.05 to 0.62 μmol N m−2 h−1. Coupled nitrification-denitrification was the dominant N removal pathway. The rates and coupling of N removal processes with nitrification varied distinctly between nearshore and offshore sites, which were driven by diverse environmental factors. Redundancy analysis suggested that nitrate and sulfide were important factors controlling the coupled and uncoupled N removal rates, and nitrate was proved to be the key factor influencing the ratio between coupled and uncoupled N removal via an integrated analysis. Abundances of ammonia oxidizing bacteria (AOB) correlated significantly with coupled denitrification rates and abundances of denitrifiers, suggesting the importance of AOB in coupled nitrification-denitrification. This study investigated the ambient, coupled, and uncoupled denitrification and anammox rates in coastal sediments off the north East China Sea. Nitrate was proved to be the critical factor influencing the ratio between coupled and uncoupled N removal, and AOB may play important role in coupled nitrification-denitrification. These results emphasized that nitrification is crucial for N removal with important implications on N loss in coastal ecosystems.

15N natural abundance of vehicular exhaust ammonia, quantified by active sampling techniques

Vehicular exhaust has been identified as an important ammonia (NH3) emission source in urban areas using the stable isotope tracer technique (δ15N); however, its δ15N signature remains poorly constrained due to difficulties in concentrating and speciating NHx (NH3 + particulate NH4+). In this study, we deployed two active sampling techniques, MCIs (Multi-nozzle Cascade Impactor sampler; “particle-gas” order) and CCSCs (ChemComb Speciation Cartridge sampler; “gas-particle” order), to collect vehicular exhaust NHx in a long urban tunnel in Shenyang, China, and quantified the 15N from the collected NH3 and NH4+. While no significant difference in tunnel NH3 concentrations between the two samplers was observed (n = 21), the δ15N-NH3 was slightly higher using the MCIs (6.3 ± 1.6‰) compared to the CCSCs (4.8 ± 2.3‰) during the tunnel operation period. This minor absolute difference of 1.5 ± 2.8‰ may derive from denuder-saturation used within the CCSCs that lead to NHx speciation ambiguity, which also caused significant δ15N-pNH4+ differences between the two sampling approaches. Our results suggest that both active samplers can well characterize the δ15N-NHx in the ambient environment, but the “particle - gas” sampling approach performs better in elevated NH3 concentration environments. We recommend that the δ15N value of 6.3‰ is used as the isotope end member for vehicle NH3 when performing NH3 source apportionment.

Amendment with biodiesel co-product modifies genes for N cycling (nirK, nirS, nosZ) and greenhouse gas emissions (N2O, CH4, CO2) from an acid soil

When applied to soils, ‘biodiesel co-product’ (BCP) functions as a labile source of organic C for microorganisms and promotes immobilisation of inorganic N (otherwise susceptible to leaching). However, the effects on biological N transformations and greenhouse gas (GHG) emissions, have not yet been investigated. Therefore, we investigated these effects with BCP amendment of soils at water contents ranging from 40 to 100% water holding capacity (WHC). The BCP applications significantly increased soil microbial biomass C, N, and ATP contents at all soil moistures, but maximally at 60% WHC. Amendment with BCP increased the abundance of nosZ genes coding for N2O reductase, and temporarily increased emissions of N2O up to day 3, but from day 7 onwards, emissions of N2O at all water contents almost stopped. Consequently, BCP suppressed total N2O emissions from waterlogged soil (100% WHC) by about 40% at 56 days, while the greatest emissions of N2O were still observed at 80% WHC. BCP significantly increased the abundance of ammonia oxidising archaea (AOA) and ammonia oxidising bacteria (AOB) at lower moisture contents (40% and 60% WHC) at day 7. In summary, our results suggest that BCP disproportionately increased the genetic capacity for the final reactions of denitrification by nosZ compared with those genes more implicated in early reactions of denitrification (nirS and nirK).

Dissolved oxygen concentrations affect the function but not the relative abundance of nitrifying bacterial populations in full-scale municipal wastewater treatment bioreactors during cold weather

This study aimed to understand the effect of different dissolved oxygen (DO) concentrations on the abundance and performance of nitrifying bacteria in full-scale wastewater treatment bioreactors, particularly during the winter when nitrifying bacterial activity is often negligible. Biomass samples were collected from three parallel full-scale bioreactors with low DO concentrations (<1.3 mg/ L) and from two full-scale bioreactors with higher DO concentrations (~4.0 and ~2.3 mg/ L). The relative abundance of nitrifying bacteria was determined by sequencing of PCR-amplified 16S rRNA gene fragments. In the three bioreactors with low DO concentrations, effluent ammonia concentrations sharply increased with a decline in temperature below approximately 17 °C, while the bioreactors with high DO concentrations showed stable nitrification regardless of temperature. Even with the decline in nitrification during the winter in the three low DO bioreactors, the relative abundance of ammonia oxidizing bacteria (mostly Nitrosomonas spp.) was curiously maintained. The relative abundance of nitrite oxidizing bacteria was similarly maintained, although there were substantial seasonal fluctuations in the relative abundance values of Nitrospira spp. versus Nitrotoga spp. This research suggests that nitrification activity can be controlled during the winter via DO to produce better effluent quality with high DO concentrations or to reduce aeration costs with a concomitant decline in nitrification activity.

A gelatinized lipopeptide diet effectively modulates immune response, disease resistance and gut microbiome in Penaeus vannamei challenged with Vibrio parahaemolyticus

Penaeus vannamei is one of the most economically vital shrimp globally, but infectious diseases have hampered its proper production and supply. As antibiotics pose a huge threat to the environment and humankind, it is essential to seek an alternative strategy to overcome infection and ensure proper culture and production. The present study investigates the effect of an anti-infective biosurfactant derivative lipopeptide MSA31 produced by a marine bacterium on the growth performance, disease resistance, and the gut microbiome of P. vannamei when challenged with pathogenic Vibrio parahaemolyticus SF14. The shrimp were fed with a commercial and lipopeptide formulated diet for 60 days and the growth performance was analyzed. The lipopeptide fed shrimp group showed enhanced growth performance and specific growth rate with improved weight gain than the control group. The challenge experiment showed that the survival rate was significant in the lipopeptide fed group compared to the control group. The results revealed 100% mortality in the control group at the end of 12 h of challenge, while 50% of the lipopeptide diet-fed group survived 24 h, which indicates the enhanced disease resistance in shrimp fed with a lipopeptide diet. The test group also showed higher levels of digestive and immune enzymes, which suggests that the lipopeptide diet could positively modulate the digestive and immune activity of the shrimp. The gut microbiome profiling by Illumina high-throughput sequencing revealed that the most abundant genera in the lipopeptide diet-fed group were Adhaeribacter, Acidothermus, Brevibacillus, Candidatus, Mycobacterium, Rodopila, and Streptomyces, while opportunistic pathogens such as Streptococcus, Escherichia, Klebsiella, Neisseria, Rhizobium, and Salmonella were abundant in the control diet-fed shrimp. Also, lipopeptide diet-fed shrimp were found to have a high abundance of ammonia and nitrogen oxidizing bacteria, which are essential pollutant degraders. Therefore, the study reveals that the dietary supplementation of lipopeptide in shrimp aquaculture could positively modulate the gut microbiome and enhance the shrimp's overall health and immunity in an eco-friendly manner.

荒漠孑遗植物四合木对土壤古菌群落的影响

土壤是植物定居的场所，也是植物-微生物互作的重要界面。古菌是土壤微生物重要组份，在碳、氮、硫、铁等元素的生物地球化学循环和植物的生长发育、适应生境中发挥重要作用。植物定居对土壤古菌群落的影响研究鲜有开展，孑遗植物在研究植物-微生物-环境互作中具有独特的优势。采用扩增子高通量测序技术，研究以荒漠孑遗植物四合木为建群种或优势种的四合木-红砂-珍珠-针茅群落、四合木-针茅群落和四合木群落等三种荒漠植物群落类型中，四合木根区土壤和光板地土体土壤古菌群落特征，揭示四合木定居对土壤古菌物种数量、多样性、群落组成及功能的影响。结果表明，荒漠孑遗植物四合木定居不仅增加了根区土壤古菌的物种数量，提高了根区土壤古菌群落多样性，而且改变了土壤古菌群落组成，减少了奇古菌门Nitrososphaeraceae科未分类的属氨氧化古菌（unclassified_f_Nitrososphaeraceae）和暂定Nitrososphaera属氨氧化古菌（Candidatus Nitrososphaera）相对丰度，增加了Nitrososphaeraceae科暂定Nitrocosmicus属氨氧化古菌（Candidatus Nitrocosmicus）和广古菌门海洋古菌类群Ⅱ中未分类的属（norank_o_Marine_Group_II）相对丰度，广古菌门热原体纲未分类的属（unclassified_c__Thermoplasmata）相对丰度变化显著。植物群落演替对四合木根区土壤和光板地土体土壤古菌群落均无显著影响。Nitrososphaeraceae科氨氧化古菌是三种不同荒漠植物群落类型中土壤古菌的核心微生物组。四合木定居也显著改变土壤古菌群落的功能，减弱了高丰度功能，增强了低丰度功能，对有氧呼吸、核苷酸合成、氨基酸合成等途径影响显著。荒漠孑遗植物四合木定居改变了土壤古菌群落物种数量、多样性、组成、功能等特征。;Soil is the place where plants colonize and an important interface between plant and microorganism interaction. Archaea is an important component of soil microorganism and plays an important role in the biogeochemical cycle of carbon, nitrogen, sulfur and iron, and in the growth, the development and adaptation to the environment of plants. It is rarely reported the influence of plant colonization on the archaeal community in soil. The relict plants have special advantages in the study of interaction among plant, microbe and environment. In this paper, the archaea in rhizosphere soil in relict plant Tetraena mongolica and barren soil obtained from three different communities of desert plants including the community of Tetraena mongolica, Reaumuria songarica, Salsola passerine and Stipa capillata, the community of Tetraena mongolica and Stipa capillata and the community of Tetraena mongolica where Tetraena mongolica is the dominant species or constructive species were studied to explore the effect of relict plant Tetraena mongolica colonization on the number, the diversity, the composition and the function of archaeal community using the high-throughput sequencing method. The results showed that the diversity and the number of species in archaeal community of rhizosphere soil increased with relict plant Tetraena mongolica colonization. Meanwhile, the composition of archaeal community in soil were changed with relict plant Tetraena mongolica colonization. The relative abundance of ammonia oxidizing archaea of genera unclassified_f_Nitrososphaeraceae of phylum Thaumarchaeota and ammonia oxidizing archaea of Candidatus Nitrososphaera of phylum Thaumarchaeota in rhizosphere soil decreased, while the relative abundance of ammonia oxidizing archaea of genera Candidatus Nitrocosmicu of phylum Thaumarchaeota and norank_o_Marine_Group_II of phylum Euryarchaeota in rhizosphere soil increased. There was no obvious change on the relative abundance of unclassified_c__Thermoplasmata of phylum Euryarchaeota. However, the succession of plant communities had no significant effect on the archaea communities in the rhizosphere soil of relict plant Tetraena mongolica and barren soil. Ammonia oxidizing archaea of family Nitrososphaeraceae is the core microbiome of archaeal communities in soil obtained from three different communities of desert plants. Furthermore, the relict plant Tetraena mongolica colonization greatly changed the function of archaeal community in soil. The high abundant function of archaeal community in soil was weakened and the low abundant function of was enhanced. There was significant effect on aerobic respiration, the pathway of nucleotide biosynthesis and the pathway of amino acid biosynthesis.The relict plant Tetraena mongolica colonization has changed characteristics of archaeal community in desert soil including the number of species, the diversity and the species composition, the function, etc.

Microplastic Addition Alters the Microbial Community Structure and Stimulates Soil Carbon Dioxide Emissions in Vegetable-Growing Soil.

Microplastic pollution has become an increasingly pervasive issue worldwide, but little is known about its effects on the soil environment. A soil microcosm experiment was conducted using low-density polyethylene microplastics to estimate the effect of microplastic pollution on soil nutrient cycling and the soil microbial community structure. The results showed that microplastic addition significantly promoted soil carbon dioxide emissions but not soil nitrous oxide emissions. Soil pH, dissolved organic carbon, ammonia nitrogen, the contents of total phospholipid fatty acid (PLFA), and the ratios of gram-positive bacteria to gram-negative bacteria and saturated to monounsaturated PLFAs significantly increased. In addition, nitrate nitrogen and the ratios of fungi to bacteria, total iso-branched fatty acids to total anteiso-branched fatty acids, and cyclopropyl to precursor significantly decreased with increasing microplastic addition. The addition of microplastics decreased the abundance of ammonia oxidizing bacteria and nitrite reductase (nirS) but had little effect on the functional genes of ammonia oxidizing archaea, nitrite reductase (nirK), and nitrous oxide reductase. A principal coordinate analysis of the bacterial 16S ribosomal RNA gene and fungal internal transcribed spacer in the microplastic addition treatments revealed that the bacterial and fungal communities formed an obvious cluster. The average abundance of some microbial species with tolerance and degradability to microplastics, such as Nocardioidaceae, Amycolatopsis, Aeromicrobium, Cytophagaceae, Betaproteobacteria, Rhodoplanes, and Mortierella, in the microplastic addition treatments was significantly higher than that of the control treatment. The results suggested that microplastics have obvious influences on microbial communities and may affect global carbon and nitrogen cycles. Environ Toxicol Chem 2021;40:352-365. © 2020 SETAC.

Soil extracellular enzyme activities and the abundance of nitrogen-cycling functional genes responded more to N addition than P addition in an Inner Mongolian meadow steppe

Nitrogen (N) and phosphorus (P) availability in soils commonly limit belowground biological processes in terrestrial ecosystems. Soil extracellular enzyme activities (EEAs) and microbial functional groups play critical roles in soil biological processes and nutrient cycling, yet their response to nutrient addition are poorly understood. To address this issue, we applied six fertilization treatments composed of combinations of N (0, 1.55, 13.95 g N m−2 yr−1) and P (0, 5.24 g P m−2 yr−1) for two years in a meadow steppe of Inner Mongolia. Soils were collected from each plot in July and August and analyzed for abundances of N-cycling genes and EEAs, and their relationships with treatments. The addition of N significantly increased C-acquisition enzyme activity and enzyme C:N and C:P ratios. Enzymatic stoichiometry indicated that N addition alleviated microbial demand for N, while it increased microbial C limitation. Microbial C and N limitation were significantly correlated with NH4+–N in July, yet they were correlated with soil water content (SWC) in August. The abundance of amoA significantly increased with N addition and was positively related to mineral-N accumulation. The abundance of denitrifier genes and gaseous N loss potential were accelerated by N addition in July, while a neutral effect was observed in August. Nitrate leaching potential was significantly increased by N addition, yet it declined with P addition in July. P addition also suppressed amoA abundance of ammonia oxidizing bacteria. Partial least squares path modelling indicated that N addition positively affected microbial-C limitation, soil N-loss potential and negatively affected microbial-N limitation. P addition negatively affected soil N-loss potential. Ultimately, this study highlights the importance of soil N availability in regulating microbial metabolism and soil N-loss potential, and enhances our understanding of the mechanisms responsible for variation in microbial nutrient cycling in meadow steppe soils.

Progress in the effects of warming on soil N2O and CH4 emission and the underlying micro-bial mechanisms

Global warming has received widespread concern. The increasing concentration of greenhouse gases (GHG) is one of the major factors contributing to global warming. Soil is a major source of GHG. Global warming could feed back on soil GHG emission. Warming influences the growth of plants, animals, microbes and their interactions, as well as the cycling of soil matters (especially nitrogen and carbon). Consequently, warming has the potential to affect soil GHG emission. We summarized the effects of warming on soil N2O, and CH4 emissions and the underlying mechanisms. In general, warming increased the emission of these two greenhouse gases, which are mainly related to the effects of temperature on the abundance and composition of ammonia oxidizing bacteria, denitrification functional genes, methane-producing bacteria and methane-oxidizing bacteria. Soil GHG emissions are affected by plant species characteristics, nutrient uptake and community composition, as well as soil nutrient element content, water content, pH and other physical and chemical properties. Further studies are needed to elucidate the microbial mechanisms of GHG emission. In addition, various warming patterns should be considered in the study of GHG emissions, and more attention should be paid on the interactive effects between warming and other environmental factors. It will provide solid theoretical basis for the prediction of global climate change and GHG emissions.

Gross nitrogen transformations in tropical pasture soils as affected by Urochloa genotypes differing in biological nitrification inhibition (BNI) capacity

Several tropical grasses, particularly Urochloa humidicola (Rendle) Schweick.) (Syn. Brachiaria humidicola), have been associated with low soil nitrate content and reduced nitrogen (N) losses from pasture systems. Previous studies have detected that root exudates of certain Urochloa genotypes can inhibit ammonium oxidation in in vitro bioassay with Nitrosomonas and reduce net nitrification in soils, a phenomenon termed biological nitrification (BNI). However, net nitrification rates reflect the result of several N transformation processes that co-occur and together determine changes in NO3− concentrations in soils. Thus, to better understand the mechanisms underlying BNI, gross rates of nitrification, ammonification and inorganic N immobilization need to be assessed. In this study we used, for the first time, stable isotopes techniques to disentangle the different gross N transformation processes that determine net nitrification rates in soil of Urochloa genotypes differing in BNI. Intact soil cores were collected from two experimental sites in Colombia under different Urochloa genotypes, classified as low-BNI and high-BNI based on net nitrification rates determined in previous studies. Soil cores were labeled with (15NH4)2SO4 and K15NO3 to quantify gross N ammonification and nitrification, respectively and calculate the immobilization rates. Our results do not confirm lower gross nitrification rates under the high-BNI genotypes, despite reduced potential net nitrification rates and lower abundance of ammonia oxidising organisms, hence not supporting the widely accepted mechanism of BNI. Instead, the low potential nitrification rates could be explained by increased inorganic N immobilization under high-BNI genotypes, both in NH4+-N and NO3−-N form. The lack of differences might be explained by a strong N-limitation in our experiment, unlike previous BNI studies when large amounts of fertilizers were applied. Our results suggest that a combination of different mechanisms, particularly stimulation of N immobilization may be responsible for the BNI capacity observed as low NO3− soil content and reduced N losses.

Pasture in crop rotations influences microbial biodiversity and function reducing the potential for nitrogen loss from compost

Agroecosystems make up a significant portion of terrestrial ecosystems and receive a disproportionally high amount of terrestrial nitrogen inputs from fertilizer, leading to nitrogen loss and associated environmental problems. Integrated crop livestock systems, such as pasture-integrated crop rotations, may be more environmentally sustainable however the long-term effects of this management practice on soil microorganisms and nitrogen transformations are not well understood. To address this knowledge gap, samples were collected from a long-term experiment designed to assess the impacts of, and interaction between, compost application and pasture-integrated crop rotations. The compost-input and pasture-integrated rotation treatments increased soil organic matter by 41 % and 14 % respectively, carbon mineralization by 127 % and 146 %, and extracellular enzyme activity by 74 % and 35 %, suggesting enhanced heterotrophic microbial activity. Compost addition led to rapid ammonification, increased potential nitrification rates ∼3-fold, and enhanced nitrate concentration by ∼75%. Further, compost addition more than doubled the abundance of prokaryotic ammonia oxidizing organisms (AOO). These effects of compost on nitrogen cycling were greatly mitigated by the pasture-integration likely due to enhanced microbial decomposition activity associated with carbon inputs from perennial grasses. Specifically, pasture-integration mitigated increases in potential nitrification, AOO abundance, and soil nitrate concentrations. The rates of potential nitrification were correlated with the abundance of AOO, highlighting the connection between nitrogen cycling processes and microbial community composition. These patterns in nitrifier abundances, potential nitrification rates, and nitrate levels indicate that the long-term integration of pasture in crop rotations has the potential to reduce early-season nitrogen loss without reducing crop productivity. This work demonstrates how management practices that facilitate favorable interactions between microbial carbon and nitrogen cycling may enhance agroecosystem sustainability and reduce nitrogen pollution.

Storms and the Depletion of Ammonia in Jupiter: II. Explaining the Juno Observations

AbstractObservations of Jupiter's deep atmosphere by the Juno spacecraft have revealed several puzzling facts: The concentration of ammonia is variable down to pressures of tens of bars and is strongly dependent on latitude. While most latitudes exhibit a low abundance, the Equatorial Zone of Jupiter has an abundance of ammonia that is high and nearly uniform with depth. In parallel, the Equatorial Zone is peculiar for its absence of lightning, which is otherwise prevalent most everywhere else on the planet. We show that a model accounting for the presence of small‐scale convection and water storms originating in Jupiter's deep atmosphere accounts for the observations. Where strong thunderstorms are observed on the planet, we estimate that the formation of ammonia‐rich hail (“mushballs”) and subsequent downdrafts can deplete efficiency the upper atmosphere of its ammonia and transport it efficiently to the deeper levels. In the Equatorial Zone, the absence of thunderstorms shows that this process is not occurring, implying that small‐scale convection can maintain a near‐homogeneity of this region. A simple model satisfying mass and energy balance accounts for the main features of Juno's microwave radiometer observations and successfully reproduces the inverse correlation seen between ammonia abundance and the lightning rate as function of latitude. We predict that in regions where ammonia is depleted, water should also be depleted to great depths. The fact that condensates are not well mixed by convection until far deeper than their condensation level has consequences for our understanding of Jupiter's deep interior and of giant‐planet atmospheres in general.

The Range of Jupiter's Flow Structures That Fit the Juno Asymmetric Gravity Measurements

AbstractThe asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, J3, J5, J7, and J9, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud‐level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with J3 the most dominant at depths below 3,000 km, J5 the most restrictive overall, whereas J9 does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud‐level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth‐dependent flow profiles are still compatible with the gravity measurements.

Analyzing the effect of organic carbon on partial nitrification-anammox process based on metagenomics and quorum sensing.

The effects of adding organic carbon on the performance of different partial nitrification-anammox (PNA) process (the activated sludge process and biofilm process) were studied, especially nitrogen removal, functional microbial activity, and microbial community structure. The potential influences of quorum sensing (QS) on the nitrogen metabolism were also analyzed. The results showed that the addition of organic carbon in biofilm systems could reduce total nitrogen (TN) removal percentages, while in activated systems it could increase TN removal percentages. The TN removal percentages in SBBR-CN (the biofilm system with addition of organic carbon) and SBR-CN (the activated sludge system with addition of organic carbon) were 15% and 45%, respectively, and those in SBBR-N (the biofilm system without addition of organic carbon) and SBR-N (the activated sludge system without addition of organic carbon) were 75% and 21%, respectively. Batch experiments have proved that organic carbon inhibited the activities of nitrite-oxidizing bacteria (NOB) and anaerobic ammonia oxidation (anammox) bacteria, and organic carbon could promote the activity of denitrifying bacteria in activated sludge systems. Compared with activated sludge systems, biofilm systems could protect the activity of anammox bacteria. The relative abundances of ammonia oxidizing bacteria (AOB) and anammox bacteria were decreased, while the relative abundances of denitrifying bacteria (Thauera) were increased with the addition of organic carbon. The biofilm systems were more conducive to the growth of anammox bacteria. Metagenomics revealed that the same bacteria might be involved in different nitrogen metabolism, and nitrogen metabolism was achieved through the complex cooperation among functional bacteria. Besides, functional bacteria involving in the nitrogen metabolism had genes related to QS, indicating that QS might affect the nitrogen metabolism by regulating the functional bacteria activity. PRACTITIONER POINTS: PNA was achieved through SBBR and complete nitrification was achieved through SBR under the low ammonia nitrogen concentration condition. The effect of organic carbon on biofilm and activated sludge PNA process was different under the low ammonia nitrogen concentration condition. QS and QQ may affect the nitrogen removal performance by regulating the expression of nitrogen metabolism-related genes.

Nitrous oxide production from soybean and maize under the influence of weedicides and zero tillage conservation agriculture

Current experiment envisages evaluating N2O production from nitrification and denitrification under the influence of weedicides, cropping systems and conservation agriculture (CA). The weed control treatments were conventional hand weeding (no weedicide), pre emergence weedicide pendimethalin and post emergence weedicide imazethapyr for soybean, atrazine for maize. Experiment was laid out in randomized block design with three replicates. Soils were collected from different depths and incubated at different moisture holding capacity (MHC). N2O production from nitrification varied from 2.77 to 6.04 ng N2O g−1 soil d−1 and from denitrification varied from 0.05 to 1.34 ng N2O g−1 soil d−1. Potential nitrification rate (0.16–0.39 mM NO3 produced g−1 soil d−1) was higher than potential denitrification rate (0.45–0.93 mM NO3 reduced g−1 soil d−1). N2O production, nitrification, denitrification, and microbial gene abundance were higher in maize than soybean. Both N2O production and nitrification decreased (p < 0.05) with soil depth, while denitrification increased (p < 0.05) with soil depth. Abundance of eubacteria and ammonia oxidizing bacteria (AOB) were high (p < 0.01) at upper soil layer and declined with depth. Abundance of ammonia oxidizing archaea (AOA) increased (p < 0.05) with soil depth. Study concludes that intensive use of weedicides in CA may stimulate N2O production.

Information Content of JWST NIRSpec Transmission Spectra of Warm Neptunes

Abstract Warm Neptunes offer a rich opportunity for understanding exo-atmospheric chemistry. With the upcoming James Webb Space Telescope (JWST), there is a need to elucidate the balance between investments in telescope time versus scientific yield. We use the supervised machine-learning method of the random forest to perform an information content (IC) analysis on a 11-parameter model of transmission spectra from the various NIRSpec modes. The three bluest medium-resolution NIRSpec modes (0.7–1.27 μm, 0.97–1.84 μm, 1.66–3.07 μm) are insensitive to the presence of CO. The reddest medium-resolution mode (2.87–5.10 μm) is sensitive to all of the molecules assumed in our model: CO, CO2, CH4, C2H2, H2O, HCN, and NH3. It competes effectively with the three bluest modes on the information encoded on cloud abundance and particle size. It is also competitive with the low-resolution prism mode (0.6–5.3 μm) on the inference of every parameter except for the temperature and ammonia abundance. We recommend astronomers to use the reddest medium-resolution NIRSpec mode for studying the atmospheric chemistry of 800–1200 K warm Neptunes; its corresponding high-resolution counterpart offers diminishing returns. We compare our findings to previous JWST IC analyses that favor the blue orders and suggest that the reliance on chemical equilibrium could lead to biased outcomes if this assumption does not apply. A simple, pressure-independent diagnostic for identifying chemical disequilibrium is proposed based on measuring the abundances of H2O, CO, and CO2.

Effects of cadmium addition on net nitrogen mineralization processes in the urban constructed wetland soils of a Chinese delta.

Heavy metal pollution is a serious problem in wetland ecosystems, and the toxicity of heavy metals affects microorganisms, thus influencing the biogeochemical process of nitrogen (N). To investigate the effects of heavy metal cadmium (Cd) pollution on N mineralization in urban constructed wetland soils of the Pearl River Delta, a 40-day aerobic incubation experiment was conducted under three Cd addition treatments [no Cd addition (control), low Cd addition (LCA) and high Cd addition (HCA)]. The results showed that compared with the control, the LCA treatment enhanced the soil N mineralization rate (RM), while the HCA treatment inhibited RM, with theaverage RM values in the control treatment of 0.40mgkg-1day-1, LCA treatments (0.66mgkg-1day-1), and HCA treatments (0.21mgkg-1day-1). The average ammonification rate values in the LCA treatments (- 3.15 to 2.25mgkg-1day-1) were higher than those in the HCA treatments (- 2.39 to 0.74mgkg-1day-1) and the control treatment (- 0.68 to 0.90mgkg-1day-1) (P < 0.05). However, the nitrification values in the HCA treatments (- 0.37 to 3.36mgkg-1day-1) were higher than those in the LCA treatments (0.42-1.93mgkg-1day-1) and the control treatment (0.20-1.45mgkg-1day-1) (P < 0.05). The net N mineralization accumulation generally increased over the entire incubation time in different Cd addition treatments. The percentage of NH4+-N to total inorganic N showed a decrease, while an increase was observed for NO3--N over the incubation time. The urease activities were significantly inhibited in the LCA and HCA treatments and showed a "decreasing before increasing" trend. The abundance of ammonia oxidizing archaea (AOA) was higher in the two Cd addition treatments than the control treatment, and higher in the LCA treatments than inthe HCA treatment. AOA was the dominant microorganism in the ammonia oxidation process of N mineralization in constructed wetland soils. The findings of this work indicate that Cd addition has a profound effect on the balance of N mineralization and may further impact the plant productivity and water quality of constructed wetlands.