湖泊微生物反硝化过程及速率研究进展

湖泊中微生物介导的反硝化过程对于区域乃至全球的气候环境变化有着深远的影响。因此,研究湖泊微生物反硝化过程及速率有助于我们深刻理解湖泊氮元素生物地球化学循环规律,全面认识湖泊生境对全球氮循环的贡献。本文综述了湖泊生境中反硝化过程(包括典型的反硝化过程及与其他物质循环耦合的反硝化过程,如与有机氮耦合的共反硝化作用、与碳循环耦合的硝酸盐/亚硝酸盐依赖型厌氧甲烷氧化、与铁循环耦合的硝酸盐依赖型铁氧化、与硫循环耦合的硝酸盐还原硫氧化)的速率、驱动微生物及其影响因素。最后对湖泊反硝化过程研究现状和未来发展方向提出总结与展望。     

湖泊氮素氧化及脱氮过程研究进展

自然界中氮的生物地球化学循环主要由微生物驱动,由固氮作用、硝化作用、反硝化作用和氨化作用来完成。过去数十年间,随着异养硝化、厌氧氨氧化和古菌氨氧化作用的发现,人们对环境中氮素循环认识逐步深入,提出了多种脱氮途径新假说。对湖泊生态系统中氮素的输入、输出及其在水体、沉积物和水土界面的迁移转化过程进行了概括,对湖泊生态系统中反硝化和厌氧氨氧化脱氮机理及脱氮效率的最新研究进展进行了探讨,并对以后的氮素循环研究进行了展望。     

亚硝酸盐氧化细菌的生态位以及对海洋环境变化的响应机制

硝酸盐是海洋微生物可利用氮的主要形式,也是限制表层海洋生物生产力的主要营养物质,海洋中的硝酸盐主要由氨和亚硝酸盐的氧化产生。探索亚硝酸盐氧化细菌在海洋生态系统中的生态位以及对环境变化的响应机制,对认识微生物参与的氮循环具有十分重要的意义。本文综述了海洋亚硝酸盐氧化细菌的研究进程及其主要种类,并总结了其主要的生理生态学特征,指出微生物在海洋生态系统变迁中所衍生出的适应对策。基于当前的研究现状,展望亚硝酸盐氧化细菌未来的研究方向,以期更好地了解海洋中亚硝酸盐的氧化过程,为进一步认识氮在生物地球化学中的循环奠定基础。     

土壤氮素转化的关键微生物过程及机制

微生物是驱动土壤元素生物地球化学循环的引擎.氮循环是土壤生态系统元素循环的核心之一,其四个主要过程,即生物固氮作用、氨化作用、硝化作用、反硝化作用,均由微生物所驱动.近10年来,随着免培养的分子生态学技术和高通量测序技术等的发展,在硝化微生物多样性及其作用机理、厌氧氨氧化过程和机理等研究方面取得了突破性进展.本文重点阐述了我国有关土壤硝化微生物方面的研究进展,在此基础上,简要介绍了反硝化微生物和厌氧氨氧化及硝酸盐异化还原成铵作用的研究进展,并对今后的研究工作提出了展望.今后土壤氮素转化微生物生态学的研究,应瞄准国际微生生态学发展的前沿,加强新技术新方法的应用,结合我国农业可持续发展、资源环境保护和全球变化研究的重大需求,重点开展以下几方面的工作:(1)开展大尺度上土壤硝化作用及氨氧化微生物分布的时空演变特征及驱动因子的研究;(2)加强氮素转化关键微生物过程与机理的研究,并与相关过程的通量(如氨挥发、N2O释放)和反应速率(如矿化速率、硝化速率)关联起来;(3)在特定生态系统中系统研究各个氮转化过程的耦合关系,构建相关氮素转化和氮素平衡模型,为定向调控土壤氮素转化过程,提高氮素利用效率并减少其负面效应提供科学依据.     

陆地和淡水生态系统新型微生物氮循环研究进展

氮生物地球化学循环是地球物质循环的重要枢纽,是决定陆地生态系统生产力水平、水资源安全、温室气体生成排放的关键过程。氮循环是由微生物介导的一系列复杂过程,不同形态、价态氮化合物的转化分别由相应的功能微生物驱动完成。随着厌氧氨氧化、完全氨氧化等新型氮转化过程的相继报道和发现更新了人们对氮循环的认识。本文综述了陆地和淡水生态系统中厌氧氨氧化(anammox)、硝酸盐异化还原为铵(DNRA)、完全氨氧化(comammox)等新型氮循环过程的发生机制、热区分布及环境效应,并总结了这三种氮循环的相互关系。     

氮循环浅析

1　氮循环自然界中的氮素物质以 3种形式存在 ,即 :有机态氮 :据估计 ,地球上蕴藏的有机态氮至少有 2 0 0～ 2 50亿 t;无机态氮 :铵盐、硝酸盐 ,约为有机态氮总量的 1% ;分子态氮 :空气中大约 79%是氮气 ,整个大气层中的含氮量是极其巨大的。其中含量特别多的有机态氮和分子态氮 ,植物都不能直接利用。但是在自然界 ,通过微生物及人类的生产活动 ,以上 3种氮素物质可以相互转化。所谓氮循环就是指氮气、无机氮化合物、有机氮化合物在自然界中相互转化过程的总称 ,包括氨化作用、硝化作用、反硝化作用、固氮作用以及有机氮化合物的合成等。氮…     

硝化作用研究的新发现:单步硝化作用与全程氨氧化微生物

硝化作用是氨被微生物氧化为硝酸盐的过程,分别由氨氧化微生物(AOB和AOA)和亚硝酸盐氧化细菌(NOB)主导完成.一个世纪以来,我们把这个分步硝化过程当成唯一的硝化途径来学习和研究.虽然根据动力学理论推测,环境中应该存在单步硝化作用,即由一种微生物单独完成整个硝化过程,将NH₃氧化为NO₃^-,但一直没有研究能直接证明该种微生物的存在.直到2015年底,3个科研团队分别在不同环境中发现了3种不同的经过纯培养的细菌(Candidatus Nitrospira nitrosa、Candidatus Nitrospira nitrificans和Candidatus Nitrospira inopinata)和一种未经过纯培养的细菌(类Nitrospira),它们都具备单独将氨氧化为硝酸盐的能力,这些微生物被定义为全程氨氧化微生物(Comammox).单步硝化作用和全程氨氧化微生物的发现终结了传承百年的理论,并引发了众多关于全球氮素循环的重要科学问题,如这些微生物在环境中的生态位点及其在硝化作用中的相对贡献等.本文就单步硝化作用及全程氨氧化微生物的发现作了简要概述.     

硝酸盐型厌氧铁氧化菌的种类、分布和特性

硝酸盐型厌氧铁氧化(NAFO)是指微生物在厌氧条件下利用硝酸盐或亚硝酸盐作为电子受体,将低价铁(二价铁或零价铁)氧化为高价铁(三价铁)的过程。具有NAFO代谢能力的微生物称为硝酸盐型厌氧铁氧化菌(NAFOM)。NAFO是微生物领域的重大发现,也是环境领域开发新型脱氮技术和地学领域研究铁、氮循环的理论依据。整理文献报道的NAFOM资料,分析NAFOM系统发育性状,探讨典型NAFOM的生态分布及其营养、代谢特性,以期为NAFOM菌种资源的开发、地球铁素和氮素循环的研究、NAFO过程的优化提供借鉴。     

病毒辅助代谢基因的研究进展

病毒通过影响微生物的营养循环、生物多样性和遗传信息传递等,在全球海洋的生物地球化学循环中发挥关键作用。病毒还可以控制微生物的群落组成、关键代谢过程等,这些依赖于病毒基因组上的辅助代谢基因(auxiliary metabolic genes,AMGs)。AMGs在病毒感染宿主的过程中表达并参与调控宿主的代谢过程。病毒基因组中的AMGs包括中央碳代谢、氮代谢、磷和硫循环、核苷酸代谢以及与氧化应激反应相关的基因。AMGs有利于子代病毒更高效地组装和释放,对于病毒种群的繁衍具有重要意义,同时对病毒-宿主相互作用机制的研究产生重要影响。本文针对病毒辅助代谢基因的起源、类别及其重要的生态作用进行简要综述,以期为进一步阐明病毒在不同生态系统中的功能提供依据。     

微生物硫循环网络的研究进展

硫元素是所有生物的基本组成成分,是生物体必需的营养元素之一。硫氧化还原微生物的数量多、分布广、代谢途径多样化,硫化合物之间的平衡依赖于微生物代谢网络中的各种硫转化反应与代谢过程。此外,硫循环与碳、氮循环紧密相关,对地球生态循环起到了至关重要的作用。本文综述了近期微生物硫循环网络的研究进展,包括所涉及的主要微生物、硫循环的生物化学途径、硫循环的环境意义和工业应用潜能等,深入了解自然和人工生态系统中存在的硫循环过程,可为控制工农业生产中硫元素的增减与利用提供理论基础与应用方案。     

The nitrogen status of Austrian forest ecosystems as influenced by atmospheric deposition,biomass harvesting and lateral organomass exchange

Measurements of the deposition rates of atmospheric trace constituents to forest ecosystems in Austria have shown that the deposition of plant utilizable nitrogen compounds is in the range from 12 kg N to more than 30 kg N ha^-1 a^-1. Locally, even higher deposition rates are encountered as a consequence of point sources or special deposition mechanisms such as fog interception, hoar frost formation, and accumulation in snow drifts. In order to place these values into perspective, they are compared with the nitrogen demand of past and present forest land use and with natural processes of nitrogen depletion and accumulation in forest ecosystems. During wind erosion of forest litter, woody material with a wide C/N-ratio remains on the windward side of ridges, while nutrient-rich material with a narrow C/N-ratio is deposited on the leeward side. As a result, total nitrogen storage in the forest soil as well as overall C/N-ratios change dramatically along a transect over a ridge, thus indicating a strong influence of litter C/N ratio on nitrogen retention in the forest soil. A study of nitrogen stores in the soil of beech ecosystems of the same yield class in the Vienna Woods showed a significant correlation of total N-content with base saturation. These results suggest that nitrogen storage capacity of forest soils may be managed by liming and tree species selection. As knowledge is still meagre, a special study on factors which determine nitrogen storage in forest soils is proposed within the FERN-programme.     

Nitrogen yields from undisturbed watersheds in the Americas

Yields of total fixed nitrogen and nitrogen fractions are summarized for thirty-one watersheds in which anthropogenic disturbance of the nitrogen cycle, either through land use or atmospheric deposition, is negligible or slight. These yields are taken as representative of background conditions over a broad range of watershed areas, elevations, and vegetation types. The data set focuses on watersheds of the American tropics, but also includes information on the Gambia River (Africa) and some small watersheds in the Sierra Nevada of California. For the tropical watersheds, total nitrogen yield averages 5.1 kg ha^–1 y^–1. On average, 30% of the total is particulate and 70% is dissolved. Of the dissolved fraction, an average of 50% is organic and 50% is inorganic, of which 20% is ammonium and 80% is nitrate. Yields are substantially lower than previously estimated for background conditions. Yields of all nitrogen fractions are strongly related to runoff, which also explains a large percentage of variance in yield of total nitrogen (r²=0.85). For total nitrogen and nitrogen fractions, yield increases at about two-thirds the rate of runoff; concentration decreases as runoff increases. There is a secondary but significant positive relationship between elevation and yield of DIN. Ratios DON/TDN and PN/TN both are related to watershed area rather than runoff; DON/TDN decreases and PN/TN increases toward higher stream orders. The analysis suggests for tropical watersheds the existence of mechanisms promoting strong homeostasis in the yield of N and its fractions for a given moisture regime, as well as predictable downstream change in proportionate representation N fractions. Yields and concentrations for small tropical watersheds are much larger than for the few temperate ones with which comparisons are possible.     

Nitrogen outputs from fecal and urine deposition of small mammals: implications for nitrogen cycling

The contribution of small mammals to nitrogen cycling could have repercussions for the producer community in the maintaining or perhaps magnifying of nitrogen availability. Our objective was to model nitrogen outputs (deposition of feces and urine) of small mammals in an old-field ecosystem and estimate the amount of fecal and urinary nitrogen deposited annually. To address this objective, we used models from laboratory studies and combined these with data from field studies to estimate dietary nitrogen and monthly and annual nitrogen outputs from fecal and urine deposition of five rodent species. The models accounted for monthly fluctuations in density and biomass of small-mammal populations. We estimated that the minimal amount of nitrogen deposited by rodents was 1.0 (0.9–1.1) and 2.7 (2.6–2.9) kg Nha⁻¹ year⁻¹ from feces and urine, respectively, for a total contribution of 3.7 (3.5–4.0) kg Nha⁻¹ year⁻¹. Hispid cotton rats (Sigmodon hispidus) accounted for >75% of the total nitrogen output by small mammals. Our estimates of annual fecal and urinary nitrogen deposited by rodents were comparable to nitrogen deposits by larger herbivores and other nitrogen fluxes in grassland ecosystems and should be considered when assessing the potential effects of herbivory on terrestrial nitrogen cycles.     

Yield of nitrogen from minimally disturbed watersheds of the United States

Watersheds of the US Geological Survey's Hydrologic Benchmark Network program were used in estimating annual yield of total nitrogen and nitrogen fractions (ammonium, nitrate, dissolved organic N, particulate N) in relation to amount of runoff, elevation, and watershed area. Only watersheds minimally disturbed with respect to the nitrogen cycle were used in the analysis (mostly natural vegetation cover, no point sources of N, atmospheric deposition of inorganic N < 10 kg ha^–1 y^–1). Statistical analysis of the yields of total nitrogen and nitrogen fractions showed that elevation and watershed area bear no significant relationship to nitrogen yield for these watersheds. The yields of total nitrogen and nitrogen fractions are, however, strongly related to runoff (r ² = 0.91 for total N). Annual yield increases as runoff increases, but at a rate lower than runoff; annual discharge-weighted mean concentrations decline as annual runoff increases. Yields of total nitrogen and most nitrogen fractions bear a relationship to runoff that is nearly indistinguishable from a relationship that was documented previously for minimally disturbed watersheds of the American tropics. Overall, the results suggest strong interlatitudinal convergence of yields and percent fractionation for nitrogen in relation to runoff.     

The impact of humans on the nitrogen cycle,with focus on temperate arable agriculture

The 6 billion people alive today consume about 25 million tonnes of protein nitrogen each year, a requirement that could well increase to 40–45 million tonnes by 2050. Most of them ultimately depend on the Haber-Bosch process to fix the atmospheric N₂ needed to grow at least part of their protein and, over the earth as a whole, this dependency is likely to increase. Humans now fix some 160 million tonnes of nitrogen per year, of which 98 are fixed industrially by the Haber-Bosch process (83 for use as agricultural fertilizer, 15 for industry), 22 during combustion and the rest is fixed during the cultivation of leguminous crops and fodders. These 160 million tonnes have markedly increased the burden of combined nitrogen entering rivers, lakes and shallow seas, as well as increasing the input of NH₃, N₂O, NO and NO₂ to the atmosphere. Nitrogen fertilizers give large economic gains in modern farming systems and under favourable conditions can be used very efficiently. Losses of nitrogen occur from all systems of agriculture, with organic manures being particularly difficult to use efficiently. Although nitrate leaching has received much attention as an economic loss, a cause of eutrophication and a health hazard, gaseous emissions may eventually prove to be the most serious environmentally. Scientists working on the use and fate of nitrogen fertilizers must be careful, clear headed and vigilant in looking for unexpected side effects.     

Time course of N2 fixation in common bean (Phaseolus vulgaris L.)

Field and greenhouse experiments were conducted to assess the nitrogen fixation rates of four cultivars of common bean (Phaseolus vulgaris L.) at different growth stages. The ¹⁵N isotope dilution technique was used to quantify biological nitrogen fixation. In the greenhouse, cultivars M4403 and Kallmet accumulated 301 and 189 mg N plant^–1, respectively, up to 63 days after planting (DAP) of which 57 and 43% was derived from atmosphere. Under field conditions, cultivars Bayocel and Flor de Mayo RMC accumulated in 77 DAP, 147 and 135 kg N ha^–1, respectively, of which approximately one-half was derived from the atmosphere. The rates of N₂ fixation determined at different growth stages increased as the plants developed, and reached a maximum during the reproductive stage both under field and greenhouse conditions. Differences in translocation of N were observed between the cultivars tested, particularly under field conditions. Thus, the fixed N harvest index was 93 and 60 for cultivars Flor de Mayo and Bayocel, respectively. In early stages of growth, the total content of ureides in the plants correlated with the N fixation rates. The findings reported in the present paper can be used to build a strategy for enhancing biological N₂ fixation in common bean.     

嫁接与施氮对甜瓜产量和氮素吸收、利用的影响

通过裂区设计田间试验,主区为2种栽培方式(嫁接栽培和自根栽培),副区为4个施氮水平(0、120、240、360 kg N·hm^-2),研究了栽培方式和施氮量对甜瓜产量和品质、氮素运移和分配,以及氮素利用率的影响.结果表明: 嫁接栽培的甜瓜商品瓜产量较自根甜瓜提高了7.3%,可溶性固形物含量降低了0.16%～3.28%;生长前期嫁接栽培甜瓜氮素累积量较自根栽培低,结果后嫁接栽培氮素累积量显著升高,收获时植株氮素累积量较自根栽培增加了5.2%,果实中的氮素累积量提高了10.3%;嫁接栽培植株氮素向果实的转移量较自根栽培提高了20.9%,嫁接栽培果实中的氮素分配率在80%以上,自根栽培的分配率在80%以下;在同一施氮水平下,嫁接栽培的甜瓜氮素吸收利用率较自根栽培提高了1.3%～4.2%,氮素农学效率提高了2.73～5.56 kg·kg^-1,氮素生理利用率提高了7.39～16.18 kg·kg^-1;从商品瓜产量、氮素吸收量和氮素利用率综合考虑,施氮量240 kg·hm^-2为本区域嫁接甜瓜较适宜的氮素用量.     

Nitrogen inputs to a marine embayment: the importance of groundwater

We examined the importance of nitrogen inputs from groundwater and runoff in a small coastal marine cove on Cape Cod, MA, USA. We evaluated groundwater inputs by three different methods: a water budget, assuming discharge equals recharge; direct measurements of discharge using bell jars; and a budget of water and salt at the mouth of the Cove over several tidal cycles. The lowest estimates were obtained by using a water budget and the highest estimates were obtained using a budget of water and salt at the Cove mouth. Overall there was more than a five fold difference in the freshwater inputs calculated by using these methods. Nitrogen in groundwater appears to be largely derived from on site septic systems. Average nitrate concentrations were highest in the region where building density was greatest. Nitrate in groundwater appeared to behave conservatively in sandy sediments where groundwater flow rates were high (> 11/m²/h), indicating that denitrification was not substantially reducing external nitrogen loading to the Cove. Nitrogen inputs from groundwater were approximately 300 mmol-N/m³/y of Cove water. Road runoff contributed an additional 60 mmol/m³/y. Total nitrogen inputs from groundwater and road runoff to this cove were similar in magnitude to river dominated estuaries in urbanized areas in the United States.     

Available soil nitrogen in relation to fractions of soil nitrogen and other soil properties

The available N of 27 soils from England and Wales was assessed from the amounts of N taken up over a 6-month period by perennial ryegrass grown in pots under uniform environmental conditions. Relationships between availability and the distribution of soil N amongst various fractions were then examined using multiple regression. The relationship: available soil N (mg kg^–1 dry soil)=(N_min×0.672)+(N_inc×0.840)+(N_mom×0.227)–5.12 was found to account for 91% of the variance in available soil N, where N_min=mineral N, N_inc=N mineralized on incubation and N_mom=N in macro-organic matter. The N mineralized on incubation appeared to be derived largely from sources other than the macro-organic matter because these two fractions were poorly correlated. When availability was expressed in terms of available organic N as % of soil organic N (N_ao) the closest relationship with other soil characteristics was: N_ao=[N_inc×(1.395–0.0347×CN_mom]+[N_mom×0.1416], where CN_mom=CN ratio of the macro-organic matter. This relationship accounted for 81% of the variance in the availability of the soil organic N.The conclusion that the macro-organic matter may contribute substantially to the available N was confirmed by a subsidiary experiment in which the macro-organic fraction was separated from about 20 kg of a grassland soil. The uptake of N by ryegrass was then assessed on two subsamples of this soil, one without the macro-organic matter and the other with this fraction returned: uptake was appreciably increased by the macro-organic matter.     

The cycling of organic nitrogen through the atmosphere

Atmospheric organic nitrogen (ON) appears to be a ubiquitous but poorly understood component of the atmospheric nitrogen deposition flux. Here, we focus on the ON components that dominate deposition and do not consider reactive atmospheric gases containing ON such as peroxyacyl nitrates that are important in atmospheric nitrogen transport, but are probably not particularly important in deposition. We first review the approaches to the analysis and characterization of atmospheric ON. We then briefly summarize the available data on the concentrations of ON in both aerosols and rainwater from around the world, and the limited information available on its chemical characterization. This evidence clearly shows that atmospheric aerosol and rainwater ON is a complex mixture of material from multiple sources. This synthesis of available information is then used to try and identify some of the important sources of this material, in particular, if it is of predominantly natural or anthropogenic origin. Finally, we suggest that the flux of ON is about 25 per cent of the total nitrogen deposition flux.