Modes of action of nitrification inhibitors

 In recent years, substantial progress has been made towards understanding the modes of action for the specific inhibition of autotrophic NH₃ oxidation. This has included demonstrating that NH₃ monooxygenase (AMO) has a broad substrate range for catalytic oxidation, and the inhibitory effects of many compounds are due to competition for the active site. Other compounds, such as acetylenes, are oxidized by the normal catalytic cycle of AMO to highly reactive products which covalently bind the enzyme causing irreversible inhibition. Substantial evidence has shown the important role of Cu in the activity of AMO, and indicated that a large class of compounds containing thiono-S inhibit AMO activity by binding with Cu within the active site. Heterocyclic N compounds form another important class of nitrification inhibitors with little known about their mode of action, although evidence suggests that their inhibitory influence is closely related to the presence of ring N. Received: 21 July 1998     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

Microbial ethylene production and inhibition of methanotrophic activity in a deciduous forest soil

Production of C₂H₄, but not of CH₄, was observed in anoxically incubated soil samples (cambisol on loamy sand) from a deciduous forest. Ethylene production was prevented by autoclaving, indicating its microbial origin. Ethylene production gradually decreased from 4 to 12 cm soil depth and was not affected by moisture or addition of methionine, a possible precursor of C₂H₄. Oxidation of atmospheric CH₄ in soil samples was inhibited by C₂H₄. Ethylene concentrations of 3, 6 and 10 μl l⁻¹ decreased CH₄ uptake by 21, 63 and 98%, respectively. Methionine and methanethiol, a possible product of methionine degradation, also inhibited CH₄ oxidation. Under oxic conditions, C₂H₄ was consumed in the soil samples. Ethylene oxidation kinetics exhibited two apparent K_m values of 40 μl l⁻¹ and 12,600 μl l⁻¹ suggesting the presence of two different types of C₂H₄-oxidizing microorganisms. Methanotrophic bacteria were most probably not responsible for C₂H₄ oxidation, since the maximum of C₂H₄ oxidation activity was localized in soil layers (2-8 cm depth) above those (8-10 cm depth) of CH₄ oxidation activity. Our observations suggest that C₂H₄ production in the upper soil layers inhibits CH₄ oxidation, thus being one reason for the localization of methanotrophic activity in deeper soil layers.     

Short-term kinetic response of enhanced methane oxidation in landfill cover soils to environmental factors

 This paper aims at a better understanding of methane oxidation under conditions that are representative of landfill cover soils. The kinetics of methane oxidation were studied in landfill cover soils that had been exposed to high methane mixing ratios. This was done in batch experiments, under various environmental conditions. V _max increased exponentially with temperature in the range 5–35  °C, with a Q ₁₀ value of 2.8. K _m increased approximately linearly in this range from 1.2 μM to 7 μM. Consequently, the influence of temperature on methane consumption was more pronounced at high concentrations than at low concentrations. The inhibition by ammonium of methane consumption was much stronger after 6–7 months of exposure to high methane mixing ratios than after 5–7 weeks of exposure, indicating that there was a shift of dominating methanotrophic species in soils after long exposure times. Additions of nitrifying sludge or compost to soils initially inhibited methane oxidation, followed by a stimulation after a few days. Received: 19 May 2000     

围垦对崇明东滩湿地全程氨氧化微生物的影响

全程氨氧化细菌(complete ammonia oxidizers,Comammox)的发现根本改变了学术界对硝化过程的认识,但其地理分异规律及对氮转化过程的贡献仍不清楚。本研究选择长江口崇明东滩不同围垦年限(0、27、51、86 a)稻田表层耕作土壤,采用好氧培养试验测定土壤硝化潜力;通过标靶功能基因amo A实时荧光定量硝化微生物的数量变异特征,包括全程氨氧化细菌(Comammox)、氨氧化细菌(ammonia-oxidizing bacteria,AOB)和氨氧化古菌(ammonia-oxidizing archaea,AOA)。结果表明,与围垦0 a的自然滩涂湿地相比,围垦27、51、86 a的水稻土净硝化速率从N 2.24 mg/(kg·d)分别增加至N 19.3、11.6和11.4 mg/(kg·d),增幅高达5.1倍～8.7倍。AOA的丰度与围垦年限显著正相关。自然滩涂湿地中AOA和AOB的数量分别为0.34×10⁷ copies/g和1.14×10⁷ copies/g,围垦86 a后增幅最高可达27.9倍。自然滩涂湿地中Co...     

土壤甲烷单加氧酶活性测定的研究

以垃圾生物覆盖土、垃圾填埋场覆盖土、菜地土为材料,研究了土壤甲烷单加氧酶(Methane monooxygenase,MMO)活性的测定条件。结果表明:0.04 g kg-1 NaN3含量可抑制土壤生物活性,可作为土壤MMO活性测定时的对照;最适的底物丙烯浓度可为0.5%;培养时间对土壤MMO活性测定影响不大,但从测定的误差和可靠性考虑,可选用5 d作为土壤MMO活性测定的培养时间。统计分析表明:采用该方法测定的土壤MMO活性与其甲烷氧化潜力有很好的线性关系。     

4种畜禽粪便厌氧发酵产甲烷特性研究

本文采用玻璃厌氧发酵罐研究了猪粪、牛粪、鸡粪和鸭粪在室温下发酵20 d过程中产甲烷气量及其受物料特性影响的规律, 为动物废弃物的资源化利用提供指导。研究表明, 在同等条件下猪粪、牛粪、鸡粪和鸭粪经过20 d的厌氧发酵后, 总产气量从大到小排序为牛粪>鸭粪>猪粪>鸡粪, 分别为2 649 mL、2 515 mL、1 964 mL、1 278 mL; 与总产气量排序相似, 上述粪便厌氧发酵总固体物质降解产气率分别为47.60 mL·g^-1、45.23 mL·g^-1、37.27 mL·g^-1和33.49 mL·g^-1。猪粪在厌氧发酵过程中易发生酸化, 第10 d发酵液 pH降到5.62, 从而导致产气量下降; 鸡粪在厌氧发酵过程中铵态氮含量过高, 发酵液铵态氮含量在前5 d就快速增长, 第15 d达到最大值3 604 mg·L^-1, 从而抑制产气。可见, 源于物料自身的pH和铵态氮含量变化是影响畜禽粪便发酵液厌氧产气的重要因素。     

农田土壤硝化微生物的生态学研究进展

硝化作用是农田生态系统的重要过程。传统硝化作用是指微生物将氨氧化成亚硝酸盐再氧化为硝酸盐的两步反应,氨氧化过程是硝化过程的第一步也是限速步骤。该过程是由编码氨单加氧酶基因（amoA）的氨氧化细菌（AOB）和氨氧化古菌（AOA）催化完成。 2015年底,可以进行一步硝化的完全氨氧化菌（comammox）的发现颠覆了人们对硝化过程近百年的认知,并引发众多对comammox生理代谢、分布特征和相对贡献的深入思考。本文重点阐述农田土壤硝化微生物的生态学研究进展,通过比较AOB、AOA和comammox的发现、系统发育以及对环境因子的响应等方面的差异,对农田土壤硝化微生物相关研究成果进行概括和总结,以期深入了解农田土壤中氮素转化机制,为农田尺度氮素养分管理、面源污染防控及温室气体减排提供理论依据。     

Water-soluble Al inhibits methane oxidation at atmospheric concentration levels in Japanese forest soil

The effect of aluminium on methane oxidation was examined from incubation experiments involving the addition of several concentrations of Al solution (0.1, 0.2, 0.5, 1, 3 and 5 mM) to two soil samples that possessed different CH₄ oxidation potential. Atmospheric CH₄ oxidation activity was inhibited by the addition of as little as 0.1 mM Al solution (approximately 0.5 μg of Al per gram dry weight soil) to a forest soil that contained low water-soluble Al and possessed a high CH₄ oxidation potential. Our results indicate that Al inhibition of CH₄ oxidation activity is concentration-dependant after a certain time and the inhibition increases gradually over time until at least 96 h have elapsed. We also found that relatively small amounts of Al additions, such as 10-20 μg per gram dry weight of soil, halved the CH₄ oxidation rate compared to the control, regardless of the original CH₄ oxidation potential of the soil. Since the Al concentrations used in our experiment are often observed in forest soils, we can assume that Al acts as an important inhibitor of CH₄ oxidation in forest soils under natural conditions. The sharp falls and a continuous decrease in CH₄ oxidation rate in other forest samples with the addition of deionized water implies that the water-soluble Al contained in soils contributes to the inhibition of CH₄ oxidation rate. This result suggests that precipitation causes a relatively prolonged inhibition of CH₄ oxidation in soils containing a high concentration of water-soluble Al.     

Oxidation of methane in the rhizosphere of rice plants

Oxidation of CH₄ in the rhizosphere of rice plants was quantified using (1) methyl fluoride, a specific inhibitor of CH₄ oxidation, and (2) measuring changes in plant-mediated CH₄ emission after incubation under air, N₂, or 40% O₂. No significant rhizospheric CH₄ oxidation was observed from rice plants in the ripening stage. CH₄ emission from rice plants 1 week before panicle initiation increased by 40% if CH₄ oxidation in the rhizosphere was blocked. The growth stage of the rice plant is an important factor determining the rhizospheric CH₄ oxidation. Fluctuation of rhizospheric CH₄ oxidation during the growing season may help to explain the observed seasonal CH₄ emission patterns in field studies. Measurements from four rice varieties showed that one variety, Pokkali, had higher rhizospheric CH₄ oxidation. This was probably because Pokkali was in an earlier growth stage than the other three varieties. Both in the early and in the late growth stages, incubation under N₂ caused a much stronger CH₄ flux than inhibition of CH₄ oxidation alone. Apparently, N₂ incubation not only blocked CH₄ oxidation but also stimulated methanogenesis in the rhizosphere. Incubation under a higher O₂ atmosphere (40% O₂) than ambient air decreased the CH₄ flux, suggesting that increasing the oxidation of the rice rhizosphere may help in reducing CH₄ fluxes from rice agriculture. The O₂ pressure in the rhizosphere is an important factor that reduces the plant-mediated CH₄ flux. However, inhibition of methanogenesis in the rhizosphere may contribute more to CH₄ flux reduction than rhizospheric CH₄ oxidation.     

A positive relationship between the abundance of ammonia oxidizing archaea and natural abundance δ15N of ecosystems

We present a significant relationship between the natural abundance isotopic composition of ecosystem pools and the abundance of a microbial gene. Natural abundance ¹⁵N of soils and soil DNA were analysed and compared with archaeal ammonia oxidizer abundance along an elevation gradient in northern Arizona and along a substrate age gradient in Hawai'i. There was a significant positive correlation between the abundance of archaeal amoA genes and natural abundance δ¹⁵N of total soil or DNA suggesting that ammonia oxidizing archaea play an important role in ecosystem N release.     

温度对不同生态系统土壤甲烷氧化过程和甲烷氧化细菌的影响

温室气体的大量人为排放导致了近百年来的全球气候变化。甲烷是重要的温室气体,随着全球气温升高,甲烷排放量会随之增加,进一步加剧了全球温室效应。土壤是甲烷重要的源和汇,土壤中的甲烷氧化细菌在平衡甲烷的释放过程中发挥着关键作用。探究温度变化对土壤甲烷氧化能力的影响成为近年来的研究热点。本文综述了温度对土壤甲烷氧化过程以及甲烷氧化细菌的影响,分析了在不同温度下,各生态系统中的土壤甲烷氧化及甲烷氧化细菌响应特点和规律,比较了不同生态系统中土壤发生甲烷氧化的温度范围以及甲烷氧化菌株的生长温度范围。综述结果表明,不同生态系统能够发生甲烷氧化的温度范围不同;在能发生甲烷氧化的温度范围内,甲烷氧化速率随温度升高而增加;培养温度与土壤原位温度越相近时,甲烷氧化响应较为灵敏。与温度对甲烷氧化过程的影响类似,甲烷氧化细菌的丰度也随着温度升高而增加,并与增温幅度、优势甲烷氧化细菌的原位生长温度密切相关。土壤中的II型甲烷氧化细菌对温度较敏感,随着温度升高,II型甲烷氧化细菌丰度增加,因此,温度会通过影响甲烷氧化细菌的丰度和群落结构,从而影响甲烷氧化过程。但温度是否仅通过调控优势菌种更替来改变土壤甲烷氧化能力目前还尚未定论,未来需要进一步探究。本文讨论了土壤甲烷氧化过程对温度的响应及其微生物机制,可为全面解析全球变暖下的土壤甲烷氧化过程的变化提供参考。     

Effect of potassium phosphate fertilization on production and emission of methane and its C-stable isotope composition in rice microcosms

Rice fields are an important source for atmospheric CH₄, but the effects of fertilization are not well known. We studied the turnover of CH₄ in rice soil microcosms without and with addition of potassium phosphate. Height and tiller number of rice plants were higher in the fertilized than in the unfertilized microcosms. Emission rates of CH₄ were also higher, but porewater concentrations of CH₄ were lower. The δ¹³C values of the emitted CH₄ and of the CH₄ in the porewater were both 2-6% higher in the fertilized microcosms than in the control. Potassium phosphate did not affect rate and isotopic signature of CH₄ production in anoxic soil slurries. On the other hand, roots retrieved from fertilized microcosms at the end of incubation exhibited slightly higher CH₄ production rates and slightly higher CH₄-δ¹³C values compared to roots from unfertilized plants. Addition of potassium phosphate to excised rice roots generally inhibited CH₄ production and resulted in increasingly lower δ¹³C values of the produced CH₄. Fractionation of ¹³C during plant ventilation (i.e. δ¹³C in pore water CH₄ versus CH₄ emitted) was larger in the fertilized microcosms than in the control. Besides plant ventilation, this difference may also have been caused by CH₄ oxidation in the rhizosphere. However, calculation from the isotopic data showed that less than 27% of the produced CH₄ was oxidized. Collectively, our results indicate that potassium phosphate fertilization stimulated CH₄ emission by enhancing root methanogenesis, plant ventilation and/or CH₄ oxidation, resulting in residence times of CH₄ in the porewater in the order of hours.     

稻田甲烷氧化研究方法进展

土壤厌氧培养、添加CH4氧化抑制剂和稳定性C同位素方法是3种主要的稻田CH4氧化研究方法。采用土壤厌氧培养方法估算的CH4氧化率偏高,其大部分研究结果中CH4氧化率均>50%,高于其他方法的研究结果。添加CH4氧化抑制剂不仅会抑制CH4的氧化,同时也会减少或促进CH4的生成,这与添加的CH4氧化抑制剂的浓度有关。稳定性C同位素方法可在自然条件下测定CH4氧化率,无破坏性、灵敏度高,但计算CH4氧化率输入的δinitial、δfinal和α值还需要进一步研究。     

Dimethyl sulphoxide (DMSO) and dimethyl sulphide (DMS) as inhibitors of methane oxidation in forest soil

Dimethyl sulphoxide (DMSO) at 14 mM inhibits CH₄ oxidation in forest soil, but the inhibition mechanism is unknown. When soil slurries are incubated in gas tight flasks, there is a lag of about 45 h before DMSO inhibits CH₄ oxidation. We tried to determine if some metabolic compound derived from DMSO, as a result of microbial activity, is responsible for the inhibition. Dimethyl sulphide (DMS) accumulated in the sealed flasks up to 5-83 μl l⁻¹ in the headspace during a 2-week period. DMS at 1 μl l⁻¹ in the headspace (0.64 μM in soil-water slurry) had a negligible effect on CH₄ oxidation but 50 μl l⁻¹ DMS (32 μM) inhibited CH₄ oxidation completely. However, the inhibition by DMSO was already evident after 45 h, when DMS concentrations were generally non-inhibiting (0.1-0.7 μl l⁻¹). DMSO was also shown to inhibit CH₄ oxidation when the DMS produced was continuously removed. Results suggest that the production of DMS from DMSO makes a minor contribution to the inhibition of CH₄ oxidation by DMSO with incubation times relevant in CH₄ oxidation studies.