Soil-air exchange of nitric oxide: An overview of processes, environmental factors, and modeling studies

Terrestrial ecosystems with their main elements soil and plants may act, in principle, as both source and sink for atmospheric nitric oxide (NO). The net exchange between ecosystems and the atmosphere, however, is globally dominated by biogenic emissions of NO from soils. Consequently the soil–air exchange of NO is the focus of the following overview. Particular emphasis is placed on the major processes that are responsible for NO production in soils (nitrification, denitrification) and their regulation by environmental factors (nitrogen availability, soil water content, soil temperature, ambient NO concentration). It is shown that interactions of these factors are a major reason for the broad range that exists in published data on NO fluxes. This variability makes it difficult to predict the magnitude of NO fluxes on relevant spatial and temporal scales. To overcome the problem various generalization procedures for scaling up in space and time have been developed, and the potential and limitations of the different approaches is discussed.     

Soil microorganisms as controllers of atmospheric trace gases (H2, CO, CH4, OCS, N2O, and NO).

Production and consumption processes in soils contribute to the global cycles of many trace gases (CH4, CO, OCS, H2, N2O, and NO) that are relevant for atmospheric chemistry and climate. Soil microbial processes contribute substantially to the budgets of atmospheric trace gases. The flux of trace gases between soil and atmosphere is usually the result of simultaneously operating production and consumption processes in soil: The relevant processes are not yet proven with absolute certainty, but the following are likely for trace gas consumption: H2 oxidation by abiontic soil enzymes; CO cooxidation by the ammonium monooxygenase of nitrifying bacteria; CH4 oxidation by unknown methanotrophic bacteria that utilize CH4 for growth; OCS hydrolysis by bacteria containing carbonic anhydrase; N2O reduction to N2 by denitrifying bacteria; NO consumption by either reduction to N2O in denitrifiers or oxidation to nitrate in heterotrophic bacteria. Wetland soils, in contrast to upland soils are generally anoxic and thus support the production of trace gases (H2, CO, CH4, N2O, and NO) by anaerobic bacteria such as fermenters, methanogens, acetogens, sulfate reducers, and denitrifiers. Methane is the dominant gaseous product of anaerobic degradation of organic matter and is released into the atmosphere, whereas the other trace gases are only intermediates, which are mostly cycled within the anoxic habitat. A significant percentage of the produced methane is oxidized by methanotrophic bacteria at anoxic-oxic interfaces such as the soil surface and the root surface of aquatic plants that serve as conduits for O2 transport into and CH4 transport out of the wetland soils. The dominant production processes in upland soils are different from those in wetland soils and include H2 production by biological N2 fixation, CO production by chemical decomposition of soil organic matter, and NO and N2O production by nitrification and denitrification. The processes responsible for CH4 production in upland soils are completely unclear, as are the OCS production processes in general. A problem for future research is the attribution of trace gas metabolic processes not only to functional groups of microorganisms but also to particular taxa. Thus, it is completely unclear how important microbial diversity is for the control of trace gas flux at the ecosystem level. However, different microbial communities may be part of the reason for differences in trace gas metabolism, e.g., effects of nitrogen fertilizers on CH4 uptake by soil; decrease of CH4 production with decreasing temperature; or different rates and modes of NO and N2O production in different soils and under different conditions.     

Plant Functional Type Effects on Trace Gas Fluxes in the Shortgrass Steppe

Plant community structure is expected to regulate the microbial processes of nitrification and denitrification by controlling the availability of inorganic N substrates. Thus it could also be a factor in the concomitant release of NO and N2O from soils as a result of these processes. C3 and C4 plants differ in several attributes related to the cycling of nitrogen and were hypothesized to yield differences in trace gas exchange between soil and atmosphere. In this study we estimated fluxes of NO, N2O and CH4 from soils of shortgrass steppe communities dominated by either C3 plants, C4 plants or mixtures of the two types. We collected gas samples weekly from two sites, a sandy clay loam and a clay, throughout the growing seasons of 1995 and 1996. Plant functional type effects on gas fluxes at the clay site were not apparent, however we found several differences among plant communities on the sandy clay loam. CH4 uptake from atmosphere to soil was significantly greater on C4 plots than C3 plots in both years. NO fluxes were significantly greater from C4 plots than from C3 plots in 1995. NO fluxes from C3 and mixed plots were not significantly different between 1995 and 1996, however fluxes from C4 plots were significantly greater in 1995 compared to 1996. Results indicate that under certain environmental conditions, particularly when factors such as moisture and temperature are not limiting, plant community composition can play an important role in regulating trace gas exchange.     

陆地生态系统植物挥发性有机化合物的排放及其生态学功能研究进展

综述了国内外生物源挥发性有机化合物 (Biologicalvolatileorganiccompounds, BVOCs) 研究现状及未来的研究方向, 侧重介绍了陆地生态系统中植物排放BVOCs的种类、生物学功能及其对大气化学过程的影响。BVOCs按其化学结构以及在大气中的滞留时间可以分为 4类 :异戊二烯、单萜、其它活性BVOCs和其它次活性BVOCs。不同的植物类群排放不同的BVOCs种类并具有不同的排放特性, 环境条件对植物不同BVOCs的排放影响也不同。BVOCs作为有机物质被排放到体外, 从植物能量代谢的角度来讲要消耗一部分植物光合作用产物从而降低植物的生产力, 因此推测植物排放BVOCs具有一定的生理学或者生态学的功能。其中比较成熟的假说是抗热胁迫假说, 其次是抗氧化假说, 也有一些其它假说例如促氮同化假说等。但这些假说都还缺乏直接的有力证据, 有待更多的研究来支持。BVOCs被排放到大气中对大气化学过程的影响更是科学家关注的问题, BVOCs对大气的影响一方面是在大气对流层中促进臭氧 (O3 ) 的形成, 造成环境污染, 另一方面BVOCs通过对大气中的OH自由基和臭氧等氧化物浓度的调整而影响到大气中甲烷等温室气体的平衡, 对大气温室效应具有间接的贡献。我国在BVOCs的研究上也做了大量的工作, 包括分析鉴定了一些植物排放的BVOCs, 探讨了环境因子对植物BVOCs排放速率的影响, 从不同尺度估测了BVOCs的排放量等等。今后对BVOCs的研究将会集中在以下几个方面 :1) 进一步研究不同植物类群释放的BVOCs种类及其它们在大气中的理化性质 ;2 ) 继续探讨植物排放BVOCs的合成与代谢途径及其生物学功能 ;3) 研究BVOCs对大气化学过程的作用, 以及区域植被变化对BVOCs排放格局进而对区域乃至全球环境变化的影响 ;4 ) 加强对一些研究比较薄弱的生态系统例如在热带地区所进行的BVOCs研究工作 ;5 ) 进一步建立和完善BVOCs排放的理论模型, 以模拟不同陆地生态系统BVOCs排放的时空动态。     

Acidity and organic matter promote abiotic nitric oxide production in drying soils

Soils are an important source of NO, particularly in dry lands because of trade‐offs that develop between biotic and abiotic NO‐producing processes when soils dry out. Understanding how drier climates may offset the balance of these trade‐offs as soils transition toward more arid states is, therefore, critical to estimating global NO budgets, especially because drylands are expected to increase in size. We measured NO emission pulses after wetting soils from similar lithologies along an altitudinal gradient in the Sierra Nevada, CA, where mean annual precipitation varied from 670 to 1500 mm. Along the gradient, we measured field NO emissions, and used chloroform in the laboratory to reduce microbial activity and partition between biotic and abiotic NO‐producing processes (i.e., chemodenitrification). Field NO emission pulses were lowest in the acidic and SOM‐rich soils (4–72 ng NO‐N m^?2 s^?1), but were highest in the high‐elevation barren site (~560 ng NO‐N m^?2 s^?1). In the laboratory, NO emission pulses were up to 19× greater in chloroform‐treated soils than in the controls, and these abiotic pulses increased with elevation as pH decreased (6.2–4.4) and soil organic matter (SOM) increased (18–157 mg C g^?1). Drought can shift the balance between the biotic and abiotic processes that produce NO, favoring chemodenitrification during periods when biological processes become stressed. Acidic and SOM‐rich soils, which typically develop under mesic conditions, are most vulnerable to N loss via NO as interactions between pH, SOM, and drought stimulate chemodenitrification.     

A semi-empirical model of methane emission from flooded rice paddy soils

Reliable regional or global estimates of methane emissions from flooded rice paddy soils depend on an examination of methodologies by which the current high variability in the estimates might be reduced. One potential way to do this is the development of predictive models. With an understanding of the processes of methane production, oxidation and emission, a semi-empirical model, focused on the contributions of rice plants to the processes and also the influence of environmental factors, was developed to predict methane emission from flooded rice fields. A simplified version of the model was also derived to predict methane emission in a more practical manner. In this study, it was hypothesized that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane production in flooded rice soils are determined by the availability of methanogenic substrates and the influence of environmental factors. Rice growth and development control the fraction of methane emitted. The amount of methane transported from the soil to the atmosphere is determined by the rates of production and the emitted fraction. Model validation against observations from single rice growing seasons in Texas, USA demonstrated that the seasonal variation of methane emission is regulated by rice growth and development. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, including Italy, China, Indonesia, Philippines and the United States, suggests that methane emission can be predicted from rice net productivity, cultivar character, soil texture and temperature, and organic matter amendments.     

Microbial Processes of Heavy Metal Removal from Carbon‐Deficient Effluents in Constructed Wetlands

This paper reviews the main microbial processes involved when toxic metals are removed from wastewater in constructed wetlands. Microbial activity is thought to play a key role in the detoxification of these metals. The paper concentrates on the microbial processes which affect the mobility, the toxicity and bioavailability of metals, namely biosorption, metal sulfide precipitation by sulfate reducers, redox transformations, and methylation, as well as microbe‐plant interactions. These reactions result in either the precipitation and accumulation of metals in wetland soils, or their volatilization and emission into the atmosphere. The possibilities of optimizing the microbially mediated reactions for the development of wetland technology are discussed as a long‐term metal retention strategy.     

植物在CH4产生、氧化和排放中的作用

综合评述了植物对CH4产生、内源CH4氧化和CH4排放的影响．不同植物释放根系分泌物能力的不同是造成CH4产生量差异的主要原因。而植物不同生育期分泌分泌物能力的差异是造成季节性变化的关键．植物泌O2能力的高低和季节性变化通过影响内源CH4的氧化来改变CH4的排放数量．植物问通气组织数量和密度的差异及其随生育期的变化,通过影响对CH4的传输能力来改变CH4的排放量．因此,植物排放CH4的通量及其季节性变化规律是由植物根系分泌分泌物能力、分泌O2能力和传输CH4能力综合决定的．     

Volatile emissions from thawing permafrost soils are influenced by meltwater drainage conditions

Vast amounts of carbon are bound in both active layer and permafrost soils in the Arctic. As a consequence of climate warming, the depth of the active layer is increasing in size and permafrost soils are thawing. We hypothesize that pulses of biogenic volatile organic compounds are released from the near‐surface active layer during spring, and during late summer season from thawing permafrost, while the subsequent biogeochemical processes occurring in thawed soils also lead to emissions. Biogenic volatile organic compounds are reactive gases that have both negative and positive climate forcing impacts when introduced to the Arctic atmosphere, and the knowledge of their emission magnitude and pattern is necessary to construct reliable climate models. However, it is unclear how different ecosystems and environmental factors such as drainage conditions upon permafrost thaw affect the emission and compound composition. Here we show that incubations of frozen B horizon of the active layer and permafrost soils collected from a High Arctic heath and fen release a range of biogenic volatile organic compounds upon thaw and during subsequent incubation experiments at temperatures of 10°C and 20°C. Meltwater drainage in the fen soils increased emission rates nine times, while having no effect in the drier heath soils. Emissions generally increased with temperature, and emission profiles for the fen soils were dominated by benzenoids and alkanes, while benzenoids, ketones, and alcohols dominated in heath soils. Our results emphasize that future changes affecting the drainage conditions of the Arctic tundra will have a large influence on volatile emissions from thawing permafrost soils – particularly in wetland/fen areas.     

Selective inhibition of ammonium oxidation and nitrification-linked n(2)o formation by methyl fluoride and dimethyl ether

Methyl fluoride (CH(3)F) and dimethyl ether (DME) inhibited nitrification in washed-cell suspensions of Nitrosomonas europaea and in a variety of oxygenated soils and sediments. Headspace additions of CH(3)F (10% [vol/vol]) and DME (25% [vol/vol]) fully inhibited NO(2) and N(2)O production from NH(4) in incubations of N. europaea, while lower concentrations of these gases resulted in partial inhibition. Oxidation of hydroxylamine (NH(2)OH) by N. europaea and oxidation of NO(2) by a Nitrobacter sp. were unaffected by CH(3)F or DME. In nitrifying soils, CH(3)F and DME inhibited N(2)O production. In field experiments with surface flux chambers and intact cores, CH(3)F reduced the release of N(2)O from soils to the atmosphere by 20- to 30-fold. Inhibition by CH(3)F also resulted in decreased NO(3) + NO(2) levels and increased NH(4) levels in soils. CH(3)F did not affect patterns of dissimilatory nitrate reduction to ammonia in cell suspensions of a nitrate-respiring bacterium, nor did it affect N(2)O metabolism in denitrifying soils. CH(3)F and DME will be useful in discriminating N(2)O production via nitrification and denitrification when both processes occur and in decoupling these processes by blocking NO(2) and NO(3) production.     

Variation of nitric oxide emission potential in plants: a possible link to leaf N content and net photosynthetic activity

Aims Ecological systems, especially soils, have been recently recognized as an important source of atmospheric nitric oxide (NO). However, the study on the contribution of plants to atmospheric NO budget is significantly lagged. The specific objectives of this study are to reveal the phylogenetic variation in NO emission potential existing in various plant species and find out the possible leaf traits affecting NO emission potential.Methods We measured NO emission potential, leaf N and C content, C:N ratio, specific leaf area, net photosynthetic rate (P n) and estimated photosynthetic N use efficiency (PNUE) of 88 plant species. Further investigation of the relationships between NO emission potential and leaf traits were performed by simple linear regression analysis and pair-wise correlation coefficients analysis.Important findings Major results are as follows: (1) NO emission from plant species exhibited large variations, ranging from 0 to 41.7 nmol m ?2 h^-1, and the species frequency distributions of NO emission potential could be fitted to a log-normal curve. (2) Among 88 species, NO emission potential was the highest in Podocarpus macrophyllus, but lowest in Zanthoxylum nitidum and Vernicia montana. (3) NO emission potential has strong correlation to leaf N content, P n and PNUE. The variations in NO emission potential among diverse plant species may be closely related to leaf N level and net photosynthetic ability.     

Contributions of Autotrophic and Heterotrophic Nitrifiers to Soil NO and N(2)O Emissions

Soil emission of gaseous N oxides during nitrification of ammonium represents loss of an available plant nutrient and has an important impact on the chemistry of the atmosphere. We used selective inhibitors and a glucose amendment in a factorial design to determine the relative contributions of autotrophic ammonium oxidizers, autotrophic nitrite oxidizers, and heterotrophic nitrifiers to nitric oxide (NO) and nitrous oxide (N(2)O) emissions from aerobically incubated soil following the addition of 160 mg of N as ammonium sulfate kg. Without added C, peak NO emissions of 4 mug of N kg h were increased to 15 mug of N kg h by the addition of sodium chlorate, a nitrite oxidation inhibitor, but were reduced to 0.01 mug of N kg h in the presence of nitrapyrin [2-chloro-6-(trichloromethyl)-pyridine], an inhibitor of autotrophic ammonium oxidation. Carbon-amended soils had somewhat higher NO emission rates from these three treatments (6, 18, and 0.1 mug of N kg h after treatment with glucose, sodium chlorate, or nitrapyrin, respectively) until the glucose was exhausted but lower rates during the remainder of the incubation. Nitrous oxide emission levels exhibited trends similar to those observed for NO but were about 20 times lower. Periodic soil chemical analyses showed no increase in the nitrate concentration of soil treated with sodium chlorate until after the period of peak NO and N(2)O emissions; the nitrate concentration of soil treated with nitrapyrin remained unchanged throughout the incubation. These results suggest that chemoautotrophic ammonium-oxidizing bacteria are the predominant source of NO and N(2)O produced during nitrification in soil.     

长效碳酸氢铵对土壤硝化-反硝化过程和NO与N2O排放的影响

Compared with ammonium bicarbonate(AB), the effect of modified ammonium bicarbonate (MAB) on nitrification and denitrification processes and NO and N2O emissions in a clay soil (C soil) and a loam soil (L soil) was studied in laboratory (25 degrees C and 50% WFPS). The inhibition effect of DCD from MAB on nitrification was relatively small in C soil, but considerably great in L soil. Compared with AB, MAB extended 7 days and 33 days for retaining NH4+. During 15 days, the NO emission from C soil and L soil respectively accounted for 0.60% and 1.06% of applied N under AB application (100 micrograms N.g-1), which were as 30 and 12 times as the N2O emission from corresponding soils. After applying MAB, the emission of NO from C soil and L soil decreased by 67% and 95%, and the emission of N2O decreased by 64% and 95%, respectively. After 39 days of aerobic incubation, then anaerobically flooded incubation with nitrate addition (200 micrograms KNO3-N.g-1) for 7 days, the total loss of denitrification in MAB in L soil was 50% less, and N2O emission was 113% more than in AB in same soil.     

Mercury transport and fate in municipal solid waste landfills and its implications

Mercury (Hg) release and migration from municipal solid waste landfills has been an important issue to nearby ecosystems and human health. To completely understand the Hg biogeochemical cycle in landfills, this review presents the Hg emission processes via different pathways, related controlling mechanisms, and critical Hg transport and transformation processes involving the diffusion and advection of Hg, Hg volatilization, Hg adsorption and desorption, Hg redox reactions, and Hg methylation and demethylation. These critical physical, chemical, and biological processes result in the phase transfer of Hg and the distribution of different Hg species in landfill gas (LFG), leachates, and cover soils. In addition, key factors (e.g., LFG, meteorological conditions, cover soils, and vegetation) affecting Hg emission processes and their impacts are discussed here. This work provides a comprehensive picture of Hg behavior in landfills, and has positive implications for the development of a process-based model and the control of Hg emissions from landfills.

     

长效碳酸氢铵对土壤硝化-反硝化过程和NO与N2O排放的影响

室内实验(25℃和50%WFPS)比较研究了碳酸氢铵(普碳)和长效碳酸氢铵(长碳)对粘质土壤(粘土)和壤质土壤(壤土)硝化反硝化过程和NO与N₂O排放的影响.长碳中的DCD在粘土中的硝化抑制作用很弱,在壤土中显著,与普碳处理相比,NH₄⁺持续时间分别延长7d和33d.15d内,施普碳(100μgN·g^-1)情况下,粘土和壤土NO排放量分别占施N量的0.60%和1.06%,分别是相应土壤N₂O排放量的30和12倍.施长碳后,粘土和壤土NO排放量分别减少67%和95%,N₂O排放量分别减少64%和55%.有氧培养39d后,外加硝酸盐(200μgKNO₃-N·g^-1),接着淹水厌氧培养7d,壤土长碳处理较普碳处理反硝化总损失减少50%,但N₂O排放量增加113%.     

Production of NO, N2O and N2 by extracted soil bacteria, regulation by NO2(-) and O2 concentrations.

The oxygen control of denitrification and its emission of NO/N2O/N2 was investigated by incubation of Nycodenz-extracted soil bacteria in an incubation robot which monitors O2, NO, N2O and N2 concentrations (in He+O2 atmosphere). Two consecutive incubations were undertaken to determine (1) the regulation of denitrification by O2 and NO2(-) during respiratory O2 depletion and (2) the effects of re-exposure to O2 of cultures with fully expressed denitrification proteome. Early denitrification was only detected (as NO and N2O) at 相似文献   

一氧化氮对豆科植物结瘤及固氮的影响机制

豆科植物-根瘤菌共生过程受双方基因复杂且精细的调控, 能够产生特异的根瘤结构并可将大气中的惰性氮气(N₂)转化为可被植物直接利用的氨态氮。结瘤与固氮受多种因素影响, 其中, 一氧化氮(NO)作为一种自由基反应性气体信号分子, 可参与调节植物的许多生长发育过程, 如植物的呼吸、光形态建成、种子萌发、组织和器官发育、衰老以及响应各种生物及非生物胁迫。在豆科植物中, NO不仅影响寄主与菌共生关系的建立, 还参与调控根瘤菌对氮气的固定并提高植株氮素营养利用效率。该文主要从豆科植物及共生菌内NO的产生、降解及其对结瘤、共生固氮的影响和对环境胁迫的响应, 阐述了NO调控豆科植物共生体系中根瘤形成和共生固氮过程的作用机制, 展望了NO信号分子在豆科植物共生固氮体系中的研究前景。     

Community-specific pH response of denitrification: experiments with cells extracted from organic soils

Denitrifying prokaryotes are phylogenetically and functionally diverse. Little is known about the relationship between soil denitrifier community composition and functional traits. We extracted bacterial cells from three cultivated peat soils with contrasting native pH by density gradient centrifugation and investigated their kinetics of oxygen depletion and NO2 -, NO, N(2) O and N(2) accumulation during initially hypoxic batch incubations (0.5-1 μM O(2)) in minimal medium buffered at either pH 5.4 or 7.1 (2 mM glutamate, 2 mM NO3 -). The three communities differed strikingly in NO2 - accumulation and transient N(2) O accumulation at the two pH levels, whereas NO peak concentrations (24-53 nM) were similar across all communities and pH treatments. The results confirm that the communities represent different denitrification regulatory phenotypes, as indicated by previous denitrification bioassays with nonbuffered slurries of the same three soils. The composition of the extracted cells resembled that of the parent soils (PCR-TRFLP analyses of 16S rRNA genes, nirK, nirS and nosZ), which were found to differ profoundly in their genetic composition (Braker et al., ). Together, this suggests that direct pH response of denitrification depends on denitrifier community composition, with implications for the propensity of soils to emit N(2) O to the atmosphere.     

Nitric oxide emission from tobacco leaves and cell suspensions: rate limiting factors and evidence for the involvement of mitochondrial electron transport

Quantitative data on nitric oxide (NO) production by plants, and knowledge of participating reactions and rate limiting factors are still rare. We quantified NO emission from tobacco (Nicotiana tabacum) wild-type leaves, from nitrate reductase (NR)- or nitrite reductase (NiR)-deficient leaves, from WT- or from NR-deficient cell suspensions and from mitochondria purified from leaves or cells, by following NO emission through chemiluminescence detection. In all systems, NO emission was exclusively due to the reduction of nitrite to NO, and the nitrite concentration was an important rate limiting factor. Using inhibitors and purified mitochondria, mitochondrial electron transport was identified as a major source for reduction of nitrite to NO, in addition to NR. NiR and xanthine dehydrogenase appeared to be not involved. At equal respiratory activity, mitochondria from suspension cells had a much higher capacity to produce NO than leaf mitochondria. NO emission in vivo by NiR-mutant leaves (which was not nitrite limited) was proportional to photosynthesis (high in light +CO(2), low in light -CO(2), or in the dark). With most systems including mitochondrial preparations, NO emission was low in air (and darkness for leaves), but high under anoxia (nitrogen). In contrast, NO emission by purified NR was not much different in air and nitrogen. The low aerobic NO emission of darkened leaves and cell suspensions was not due to low cytosolic NADH, and appeared only partly affected by oxygen-dependent NO scavenging. The relative contribution of NR and mitochondria to nitrite-dependent NO production is estimated.     

Effects of elevated atmospheric CO2 concentrations on soil microorganisms

Effects of elevated CO(2) on soil microorganisms are known to be mediated by various interactions with plants, for which such effects are relatively poorly documented. In this review, we summarize and synthesize results from studies assessing impacts of elevated CO(2) on soil ecosystems, focusing primarily on plants and a variety the of microbial processes. The processes considered include changes in microbial biomass of C and N, microbial number, respiration rates, organic matter decomposition, soil enzyme activities, microbial community composition, and functional groups of bacteria mediating trace gas emission such as methane and nitrous oxide. Elevated CO(2) in atmosphere may enhance certain microbial processes such as CH(4) emission from wetlands due to enhanced carbon supply from plants. However, responses of extracellular enzyme activities and microbial community structure are still controversy, because interferences with other factors such as the types of plants, nutrient availabilitial in soil, soil types, analysis methods, and types of CO(2) fumigation systems are not fully understood.