化学转化法测定水体中硝酸盐的氮氧同位素比值

采用化学转化法可同时测定各种水体样品中硝酸盐的氮、氧同位素比值。在弱碱性环境中,镀铜镉粒将硝酸盐还原为亚硝酸盐,然后在弱酸性缓冲体系中叠氮酸根将亚硝酸盐转化为氧化亚氮。通过带有预浓缩装置的同位素比值质谱计测定氧化亚氮的氮、氧同位素比值,并用公式将其换算为硝酸盐的氮、氧同位素比值。通过国际标准样品和实验室标准样品的多次检测证实化学转化法具有适用范围广、灵敏度高、操作简便、准确的特点,其转化过程仅需两步,且需样量仅为4.5μg NO3--N。δ15N和δ18O的测量精度分别为0.31‰和0.55‰,测定值与参考值的差异均小于1σ,测量的精确度和准确度均可满足样品分析的需求。     

Oxygen exchange between nitrogen oxides and H2O can occur during nitrifier pathways

Interpretation of the oxygen isotopic signature of soil-derived N₂O may be flawed when it is based on reaction stoichiometry and fractionation alone. In fact, oxygen (O) exchange between H₂O and intermediates of N₂O production pathways may largely determine this O isotopic signature. Although in our previous work we conclusively proved the occurrence of O exchange during N₂O production by denitrification of NO₃⁻, its occurrence in N₂O production pathways by nitrifiers remains unclear. The aim of this study was to examine the likeliness of O exchange during various stages of N₂O production in soil via nitrification, nitrifier denitrification and denitrification. We evaluated a set of scenarios on the presence of such exchange using data from a series of ¹⁸O and ¹⁵N tracing experiments. The measured actual O incorporation from H₂O into N₂O (AOI) was compared with the theoretical maximum O incorporation (MOI) from various scenarios that differed in their assumptions on the presence of O exchange. We found that scenarios where O exchange was assumed to occur exclusively during denitrification could not explain the observed AOI, as it exceeded the MOI for 9 out of 10 soils. This demonstrates that additional O exchange must have occurred in N₂O production through nitrifier pathways. It remains to be determined in which steps of these pathways O exchange can take place. We conclude that O exchange is likely to be mediated by ammonia oxidizers during NO₂⁻ reduction (nitrifier denitrification), and that it could possibly occur during NO₂⁻ oxidation to NO₃⁻ by nitrite oxidizers as well.     

Tracing sources of soil nitrate using the dual isotopic composition of nitrate in 2 M KCl-extracts

Soils comprise a critical interface between the atmosphere, lithosphere, hydrosphere and biosphere, and play a major role in the cycling of nitrogen (N), an element crucial to plant growth. Isotope techniques constitute a powerful tool to study the origin and fate of N compounds (e.g. NO₃⁻) within the environment including soils. The objective of our study was to test the usefulness of the isotope composition of soil NO₃⁻ extracted with 2 M KCl (soil NO₃) as a tool to investigate the origin and fate of NO₃⁻ in the environment. Specifically issues related to repeat extractions, crop type, length of fertilization, and soil depth were addressed. Soils from four contrasting agricultural management regimes were sampled. Within the relatively confined study area (4 ha), the isotopic compositions of soil NO₃ differed markedly due to management treatments (up to 6 and 17‰ for δ¹⁵N and δ¹⁸O, respectively), but were repeatable among replicate plots (±1‰). Differences in both δ¹⁵N and δ¹⁸O values were observed between legume and non-legume treatments, as well as fertilized versus non-fertilized treatments, which were larger than the variability observed between replicate plots. Differences in the isotopic composition of extractable soil nitrate were not limited to the surface layer, but also occurred within deeper soil layers. This study indicates that the analysis of the natural abundance stable isotope composition of soil NO₃ may provide a promising additional tool for tracing the origin and fate of NO₃⁻ in the soil zone.     

施用铵态氮对森林土壤硝态氮和铵态氮的影响

对取自武夷山的红壤、黄壤、黄壤性草甸土分别在对照(CK,N 0 mg/kg)、低氮(LN,N 50 mg/kg)、高氮(HN,N 100 mg/kg)3种氮(N)水平处理下开展培养实验,研究施加NH4+-N对森林土壤N转化的短期影响.结果表明,添加NH4+-N可显著(p＜0.05)降低土壤NO3--N含量4.5％～25.7％,但LN与HN处理差异不显著,NO3--N降低可能与NO3--N反硝化和异氧还原有关;然而,黄壤性草甸土NO3--N没有降低.与培养前比较,在第56天红壤NO3--N含量显著增加5倍左右;桐木关黄壤增加40％左右,而黄冈山25 km黄壤仅在CK处理下增加16％,但是黄壤性草甸土显著降低;结果显示LN与HN处理土壤NO3--N含量变化幅度小于CK.与CK相比,LN和HN处理红壤NH4+-N分别显著(p＜0.05)升高24.1％ ～ 96.5％和68.7％～114.1％,且随培养进行没有累积,可能与微生物固N有关;桐木关NH4+-N分别升高17.6％ ～ 39.6％和37.6％～95.8％ (p＜0.05),LN处理黄冈山25 km黄壤NH4+-N只有第7天升高17.8％ (p＜0.05),HN处理第7、14、28、42天显著升高17.5％～48.6％(p＜0.05).LN处理黄壤性草甸土的NH4+-N在前3周显著降低11.6％～28.5％ (p＜0.01); HN处理在第7天和14天分别降低10.8％(p＜0.01)和7.5％,但是在第28～56天显著增加17.6％～20.4％(p=0.002).随着培养进行,CK处理红壤NH4+-N逐渐降低,桐木关黄壤、黄冈山25 km黄壤和黄壤性草甸土升高;LN和HN处理黄壤和黄壤性草甸土NH4+-N逐渐升高.可见,不同海拔土壤类型对NH4+-N添加响应存在差异.     

基于稳定同位素和贝叶斯模型的引黄灌区地下水硝酸盐污染源解析

地下水硝酸盐（NO₃^-）污染已经成为全球严重的水环境问题之一,由于饮用水中高含量NO₃^-会转化成亚硝酸盐而增加各种疾病和癌症风险,其来源的确定对于NO₃^-污染的预防和控制非常重要。本文以黄河下游第二大灌区——潘庄灌区为例,首次采用NO₃^-的氮氧稳定同位素结合贝叶斯模型追溯地下水NO₃^-的来源并量化各种来源的贡献比例。结果表明,地下水NO₃^-含量分布在0.1~197.0 mg·L^-1,平均值为34.2 mg·L^-1。与《生活饮用水卫生标准》中规定的地下水NO₃^-最大含量[20 mg（N）·L^-1,相当于NO₃^-含量90 mg·L^-1]相比,有10%的样品NO₃^-含量超标。井深<30 m、30~60 m和>60 m的地下水NO₃^-平均含量分别为25.9 mg·L^-1、39.7 mg·L^-1和20.1 mg·L^-1。空间上,宁津县、武城县、平原县和禹城市有大片区域地下水NO₃^-含量较高。地下水NO₃^-的δ¹⁵N组成范围为0.72‰~23.93‰,平均值为11.62‰;δ¹⁸O组成范围为0.49‰~22.50‰,平均值为8.46‰。同位素结果表明粪便和污水、农业化肥是地下水中NO₃^-的主要污染来源。这反映了人类活动是引起地下水NO₃^-污染的主要原因。贝叶斯模型结果显示,粪便和污水对潘庄灌区地下水中NO₃^-平均贡献率高达56.2%,化肥的平均贡献率为19.3%,大气降水和土壤的平均贡献率分别为6.2%和12.3%。由于污水、粪便和化肥是地下水中NO₃^-的主要来源,为保护和改善研究区地下水水质,建议加强污水管道建设,强化畜禽粪便的管理以及提高化肥利用效率。     

Nitrifier denitrification as a distinct and significant source of nitrous oxide from soil

Soils are the major source of the greenhouse gas nitrous oxide (N₂O) to our atmosphere. A thorough understanding of terrestrial N₂O production is therefore essential. N₂O can be produced by nitrifiers, denitrifiers, and by nitrifiers paradoxically denitrifying. The latter pathway, though well-known in pure culture, has only recently been demonstrated in soils. Moreover, nitrifier denitrification appeared to be much less important than classical nitrate-driven denitrification. Here we studied a poor sandy soil, and show that when moisture conditions are sub-optimal for denitrification, nitrifier denitrification can be a major contributor to N₂O emission from this soil. We conclude that the relative importance of classical and nitrifier denitrification in N₂O emitted from soil is a function of the soil moisture content, and likely of other environmental conditions as well. Accordingly, we suggest that nitrifier denitrification should be routinely considered as a major source of N₂O from soil.     

Precipitation but not soil texture alters effectiveness of dicyandiamide to decrease nitrate leaching from dairy cow urine

This experiment compared the effectiveness of the nitrification inhibitor dicyandiamide (DCD) in decreasing NO₃‐N leaching from dairy cow urine (1000 kg N/ha equivalent). DCD was applied to perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) on three soil types (silt loam, sandy loam and clay) and under two precipitation regimes using intact soil monolith zero tension lysimeters (50 cm diameter by 65 cm deep). Over the two experiment years, annual precipitation (rainfall plus supplemented irrigation) covered the range 1103 to 2351 mm. Soil type affected the forms of N that leached after urine application. Most urea was lost from the clay soil in the first drainage collections after application. Ammonium‐N leached from the sandy soil. Apart from one soil type (sandy loam) giving a nil response to DCD in 1 yr, there was no strong evidence that soil type changed DCD effectiveness (the amount of NO₃‐N retained, expressed as a percentage of the NO₃‐N leached from untreated urine). Where DCD decreased leaching, effectiveness ranged between 6 and 57% with a mean value of 34 ± 5%. Drainage depth explained 50% of the variation in DCD effectiveness (P < 0.05) and indicated a 7% decrease per 100 mm extra drainage. Extra pasture growth and N uptake were strongly related to the amount of N saved by DCD application. We conclude that there may be scope to use rainfall/drainage as an estimate of likely DCD effectiveness at a site, but further work is required to test this across a wider range of circumstances.     

Automated method for determining nitrate and nitrite in water and soil extracts

Abstract

This paper describes an AutoAnalyzer method for measuring nitrate plus nitrite in thirteen commonly used soil extraction solutions. The AutoAnalyzer is normally equipped with a column containing cadmium chips. In this study the column is replaced with a cadmium‐silver wire inserted in plastic tubing which has several advantages. There is no compaction of cadmium chips, it eliminates the need to debubble the sample stream before it enters the reductor, the dead volume is decreased, and it eliminates the copper sulfate treatment process except for one given the first time the wire is used. The method is also excellent for measuring nitrate plus nitrite in rain water.     

北方区域尺度地下水-包气带硝酸盐分布与变化特征

我国农业生产过程造成的地下水硝酸盐污染问题备受关注,作为硝态氮累积和存储的重要场所和硝酸盐淋失进入地下水的主要通道,包气带土壤中硝酸盐存储分布特征与地下水硝酸盐污染密切相关。本文以北方典型黑土、潮土和褐土区农田为研究对象,建立了北方地下水硝酸盐监测网（东北、华北、西北）,通过对不同区域地下水的采样和测定,比较了地下水硝酸盐污染的区域差异,结合历史数据对地下水硝酸盐时空变化进行了分析。进一步选择华北平原作为厚包气带的代表区域,实地取样分析了包气带硝态氮累积存储和分布特征。结果表明：东北黑土区地下水硝酸盐超标率最高,达39.6%;其次为华北潮土区,超标率为19.3%;西北褐土区的地下水硝态氮超标率最低,为14.9%。随时间推移,华北平原区域尺度浅层地下水硝酸盐超标率有增长趋势,2016—2018年403个采样点地下水超标率为18.9%,高于1998年的11.8%。华北平原区域厚包气带硝酸盐存贮总量可达1854万t,粮食种植对区域包气带硝酸盐累积存储的平均贡献率为78.3%;包气带0~6 m是华北平原区硝酸盐存储的主要土层,这部分存储的硝态氮对地下水构成了潜在的威胁。     

Identifying resource competition in maize-based soil conservation systems using 13C and 15N isotopic discrimination

Soil conservation measures such as establishing grass barriers or cover crops effectively control erosion but also provoke competition, which reduces yields of companion crops. We used ¹³C and ¹⁵N natural abundance profiles to identify the causes of competition of soil conservation measures on a field with 59% slope in Northwest Vietnam three years after establishment. Treatments were maize under farmer’s practice (T1, control), maize with Guinea grass barriers (T2), maize under minimum tillage (MT) with Pinto peanuts as cover crop (T3), and maize under MT and relay cropped with Adzuki beans (T4). A pretest using data from zero-N plots revealed that abundance of water and limited nitrogen availability induced low grain N concentrations, enriched leaf δ¹³C, and reduced maize grain yield. Similar low N leaf concentrations and elevated δ¹³C values were observed in maize growing close to frequently pruned grass barriers under positive water balance conditions, indicating that yield decline in these rows can be attributed mainly to N competition. Enriched δ¹⁵N values of maize from rows next to barriers indicated reliance on soil N rather than on ¹⁵N-depleted fertiliser N. Vigorous cover crop growth under MT resulted in maize yield decline due to N competition while relay-cropped legumes did not trigger inter-species competition having a similar maize yield, leaf N concentration, δ¹³C, and δ¹⁵N as the control.     

地下水位波动对不同施氮量农田土壤硝态氮运移影响

明确地下水位波动对农田土壤剖面和地下水NO_3~--N运移的影响,可为减少土壤氮素淋失、降低地下水硝酸盐污染风险提供依据。本研究采用大型土柱温室种植甘蓝,研究2种水位波动(水位不变、水位每隔10 d波动20 cm)和3种施氮量[0 kg(N)·hm~(-2)、225 kg(N)·hm~(-2)、450 kg(N)·hm~(-2)]对土壤含水量、土壤溶液NO_3~--N浓度、地下水NO_3~--N浓度和作物产量的影响。结果表明,水位波动和施氮肥对NO_3~--N运移的影响与土壤剖面深度有关。0～20cm包气带土壤NO_3~--N含量受施氮量影响,过量施氮肥[450kg(N)·hm~(-2)]导致该剖面NO_3~--N累积。20～60cm水位波动带土壤NO_3~--N含量受施氮量和水位波动的共同作用:施氮量增加提高NO_3~--N含量;水位波动降低剖面土壤NO_3~--N含量,水位上升和下降均促进土壤NO_3~--N随着水流运动向下层迁移;剖面土壤硝态氮含量高,增加NO_3~--N进入地下水的风险。60～80 cm淹水区剖面土壤NO_3~--N含量较低。作物产量受水位波动影响不显著。在地下水位埋深较浅的农业区进行氮素污染防控时,不可忽视水位波动对NO_3~--N运移的影响。     

耕层土层交换对土壤氮素关键转化过程和玉米氮素利用的影响

翻耕会使耕层土壤发生显著位置交换。耕层土壤位置交换会通过影响土壤物理、化学和生物性状,改变氮素转化过程。本文研究了土层交换对黄淮海平原南端砂姜黑土硝化、反硝化过程和玉米生长及氮素利用的影响,为该区域选择合理的耕作方式、减少氮素损失及提高氮素利用效率提供理论依据。试验在人工气候室条件下,以土壤(0～35 cm)田间原位分层作为常规土层处理(CK),以原位0～10 cm和10～20 cm土层交换后作为土层交换处理(SE),并用20μm的尼龙网区分非根际和根际土壤。于玉米小喇叭口期利用荧光定量PCR技术测定土壤氨氧化微生物和反硝化菌群丰度,并结合非根际和根际土壤的硝化潜势、土壤呼吸、反硝化能力、反硝化潜势、土壤理化性质和玉米总氮含量及根系形态的测定,探讨土层交换对土壤氮素转化和玉米生长及氮素利用的影响。结果显示,SE处理的玉米植株氮吸收量比CK处理显著降低8.9%(P0.05)。土层交换显著影响根际而不是非根际土壤的硝化潜势,使其显著降低13.5%(P0.05);并使非根际和根际土壤的反硝化能力分别提高36.6%(P0.05)和8.4%(P0.05)。土层交换使非根际和根际土壤的可溶性有机碳含量分别提高11.7%(P0.05)和5.2%。相关分析显示硝化潜势与氨氧化细菌(AOB)丰度呈显著正相关(r=0.91**),与氨氧化古菌(AOA)丰度无显著相关关系;反硝化能力与土壤可溶性有机碳和呼吸速率呈显著正相关(r=0.89**和0.93**),与nirK、nirS拷贝数无显著相关性;玉米植株氮吸收量与根际土壤的硝化潜势、根表面积×AOB拷贝数都呈显著正相关(r=0.83*和0.86*),而与反硝化能力呈显著负相关(r=?0.88**)。以上结果表明砂姜黑土土壤硝化速率的降低和反硝化速率的增强,是土层交换后玉米氮素利用效率低的重要原因。AOB是硝化速率的主要驱动微生物。土层交换后土壤可溶性有机碳是反硝化能力的关键主导因子。在翻耕条件下,有效调节土壤可溶性有机碳含量是提高作物氮肥利用效率的关键。     

土壤磷酸盐氧同位素分析方法和应用研究进展

在一定温度下磷酸盐和周边水体氧的同位素分馏仅受生物活动控制,因此磷酸盐氧同位素成为生态系统中磷源和磷循环研究的良好示踪剂。介绍了磷酸盐氧同位素研究应用的理论基础和近几年来针对土壤富含有机质,氧元素来源多样的特点发展起来的土壤磷酸盐氧同位素的分析和纯化方法,综述了磷酸盐氧同位素在土壤磷源示踪和磷循环应用研究中的初步进展,并提出目前研究存在的局限和对未来工作的展望。     

A proposed use of ion exchange resins to measure nitrogen mineralization and nitrification in intact soil cores

Abstract

A procedure is proposed for measuring nitrogen mineralization and nitrification in intact soil cores. The method relies on ion exchange resins to trap ammonium and nitrate entering and leaving cores of soil otherwise open at the top and bottom. Changes in soil concentrations plus an accounting of ions trapped by the lower resin after field incubations, indicate rates of nitrogen reactions. Using this technique, we estimated net ammonification rates from 0–36 mg N/kg/mo and nitrification rates from 0–16 mg N/kg/mo for the surface of a sandy, low nutrient soil under pine cultivation in north Florida; higher rates occurred after urea fertilization. The procedure has potential advantages over others, but must be more fully evaluated under a variety of conditions.     

Phosphate interference in the Devarda's alloy reduction method for nitrate

Abstract

Phosphate interfered markedly with a Devarda's alloy distillation method for the determination of nitrate. Only 9% of added nitrate was recovered by this method when 200 mg P was present. This interference can be overcome by the addition of calcium ions, to precipitate the phosphate, and an extended distillation time.     

Ammonium determination in soil extracts by the salicylate method

Abstract

An ammonium determination, based on formation of a substituted indophenol with sodiumsalicylate as phenolic reagent, has been reexamined. An increase of 70% in absorbancy compared with existing salicylate methods in soil science, and an increase in reproducibility compared with pre‐existing equivalent methods in other disciplines were obtained. The method can be applied satisfactorily for ammonium in 2M KCl soil extracts and soil and plant digests. The use of salicylate in place of phenol is advised for safety reasons.     

保护地菜田土壤硝酸盐积累及其调控措施的研究进展

本文概述了近年来国内外有关保护地菜田土壤硝酸盐积累方面的研究结果 ,就土壤硝酸盐积累的影响因素、调控措施做了较为详尽的评介     

蒸发与降水入渗过程中不同水体氢氧同位素变化规律

为了研究土壤水蒸发与降水入渗非饱和带过程中不同水体氢氧同位素的变化规律,该文选用2种不同性质的土壤-砂土和黄土,设计了土壤水蒸发和降水入渗室内试验。结果表明:对于砂土,土壤水蒸发过程中剩余水体氢氧同位素分馏遵从瑞利模式;对于黄土,随着蒸发时间的延长,剩余土壤水氢氧同位素值越来越远离瑞利分馏关系线;在降水入渗非饱和带的初期,相对于风干砂土,风干的黄土颗粒对土柱出流水的氢氧同位素值产生了影响,并且出流水的氢氧同位素亦受到土壤原水同位素值的影响,只有入渗的降水达到了一定数量,土柱出流水才能与降水的同位素值相同。该研究可为运用氢氧同位素研究降水能否通过非饱和带补给地下水提供数据分析的依据。     

氮肥用量对旱地冬小麦产量及夏闲期土壤硝态氮变化的影响

在陕西渭北旱塬,利用长期定位试验研究了长期不同氮肥用量（0、80、160、240、320 kg hm-2）对旱地冬小麦产量形成,氮素利用,土壤硝态氮残留、夏闲期淋溶和矿化的影响。结果表明：随用量增加,施氮提高旱地小麦产量的效应下降,而土壤硝态氮残留迅速增加。作物生长当季的硝态氮残留主要分布在0～60 cm土层,施氮超过160 kg hm-2时,达56.8～211.7 kg hm-2,来源于当季施用氮肥的残留占64%～90%。夏闲期土壤硝态氮发生淋失的土层深度和硝态氮淋失量均与施氮量呈显著的抛物线关系（r = 0.988 9和0.994 0）,施氮量超过160 kg hm-2时,每增加100 kg hm-2的氮肥投入,硝态氮淋失深度和淋失量增加量分别高于27 cm和80.4 kg hm-2。平均每10 mm的夏闲期降水可使离开原土层发生淋溶的硝态氮向下移动2～4 mm。施氮量对硝态氮淋失的深度没有显著影响。夏闲期土壤氮素矿化量、来源于当季施入土壤肥料氮被生物固定后的再矿化量分别为51.8～160.9 kg hm-2和31.6～109.2 kg hm-2。基于本研究,建议渭北旱塬冬小麦施氮量控制在146～163 kg hm-2,以保证旱地小麦高产,防止过量肥料氮残留,减少淋溶风险。     

甘蔗集约化种植区施肥显著增加入河硝态氮污染:基于氮氧同位素的流域示踪

[目的]过量施用肥料会导致土壤养分过剩,在降雨径流冲刷下极易流失进入河湖水体,引起地表水体污染.本研究旨在阐明农区施肥与入河硝态氮污染的关系,为有效防控农业面源污染提供科学依据.[方法]选择广西集约化蔗区客兰水库水源区的那辣流域,应用双稳定同位素(δ15N-NO3–、δ18O-NO3–)示踪技术,确定流域内3个子流域(...