渗透胁迫和离子毒害对转Bt基因棉幼苗生长及离子分布的影响

研究了渗透和盐胁迫处理对转Bt基因抗虫棉(Gossypium hirsutum) 99B种子的萌发和幼苗生长的影响,以及幼苗不同器官离子吸收和分配的差异。结果表明:渗透和盐胁迫均对转Bt基因抗虫棉幼苗的生长有抑制作用,其中PEG的抑制作用最强,而3种盐的抑制程度以CaCl₂>NaCl>Na₂SO₄,且在Na⁺含量相同时,Cl^-的毒害大于SO₄^2-。渗透胁迫下使根、茎和叶中的Na⁺和Cl^-含量提高,K⁺、Ca²⁺、SO₄^2-含量和K⁺/Na⁺、Ca²⁺/Na⁺和SO₄^2-/Cl^-比值降低,且地上部的变化幅度大于地下部的,其中以PEG的影响最为显著,其次是CaCl₂,Na₂SO₄处理最弱。这些说明,转Bt基因抗虫棉99B的耐盐性较弱。     

北亚热带3种典型森林群落对降水中氮、磷、硫的截留及分配特征

森林群落在净化空气、截留沉降污染物、改善地表水质等方面具有重要作用。本研究以北亚热带地区3种典型森林群落（毛竹林、杉木林、青冈阔叶林）为研究对象,通过分析沉降污染物（NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-）在大气降水、林内穿透雨、树干茎流、枯透水和地表径流中的浓度和通量变化特征,探讨不同森林群落对氮、磷、硫的截留净化作用和分配特征。结果表明,该区域大气降水中NH₄⁺-N、NO₃^--N、NO₂^--N、TP和SO₄^2-年均浓度分别为1.06、0.61、0.04、0.07、1.84 mg/L,其年均pH为5.88;各森林群落林冠层能够调升降雨的pH且全年稳定,对TP和NH₄⁺-N均有吸附作用,截留率分别为79.09%-84.68%和30.88%-69.36%;而枯落物层则是林下氮、磷、硫的主要释放源,对NH₄⁺-N、NO₃^--N、TP和SO₄^2-均具有淋溶作用;此外,由地表径流（输出）与大气降水（输入）的对比分析可知,各林地对沉降污染物中氮、磷、硫的截留率均超过98%;3种森林群落对沉降污染物中氮、磷、硫的截留能力依次为：青冈阔叶林 > 毛竹林 > 杉木林,阔叶林对沉降污染物的净化能力要高于毛竹林及针叶的杉木林。     

不同耐盐植物根际土壤盐分的动态变化

以甘肃秦王川引大灌区盐渍化土壤为研究背景,用盆栽根袋法对4种耐盐植物根际和非根际土壤pH和盐分离子的动态变化进行了分析比较。结果表明:4种待测植物随着培养时间的延长土壤pH和EC值呈降低趋势。新疆大叶(Medicago Sativa L.cv.Xinjiangdaye)、向日葵(Helianthus annuus)和霸王(Zygophyllum xanthoxylum)生长90 d后根际土壤pH明显低于非根际,而裸麦(Hordeum vulgare var. vulgare)根际较非根际pH差异不大。霸王和新疆大叶根际土壤EC值较非根际高,而裸麦和向日葵的根际与非根际差异不大。4种供试植物根际K⁺均出现亏缺,Ca²⁺、Na⁺、Mg²⁺、SO^2-₄和Cl^-在新疆大叶、霸王和向日葵3种植物根际均出现富集,对于裸麦:Ca²⁺、Mg²⁺和SO^2-₄ 3种离子在植物根际富集,而Cl^-和Na⁺在根际亏缺。随着待测植物培养时间的增加Na⁺/K⁺、Na⁺/Ca²⁺和Na⁺/Mg²⁺ 这3个比值呈降低趋势,说明Na⁺相对于K⁺、Ca²⁺和Mg²⁺的含量降低,生物措施对Na⁺的移除效果较显著。     

黄河口湿地柽柳灌丛土壤盐渍化特征

为探究黄河三角洲湿地柽柳灌丛下土壤的盐渍化特征，在黄河三角洲国家级自然保护区(37°35''-12''N，118°33''-119°20''E)黄河入海口附近，根据长势基本一致的原则分别在碱蓬群落、柽柳群落和芦苇群落各选3株柽柳，采集柽柳灌丛下土壤样品，分析土壤盐分和盐碱化参数的空间分布以及距基茎不同距离处研究对象(土壤总盐(TS)、电导率(EC)、pH、交换性钠百分率(ESP))和环境因子(Na⁺、K⁺、Ca²⁺、Mg²⁺、Cl^-、HCO₃^-、SO^2-₄)之间的关系。结果表明：(1)研究区土壤为弱碱化盐土，离子含量由高到低依次为Cl^->Na⁺>SO^2-₄ >Ca²⁺>Mg²⁺>HCO^-₃>K⁺。除pH在土壤表层数值最低外，表层土壤TS、EC、ESP和盐分离子大于深层土壤，显示表聚性。(2)土壤盐分和盐碱化参数空间分布总体为：在柽柳基茎周围形成"盐谷"、"碱谷"效应， Na⁺、Mg²⁺、Cl^-表现为"盐谷"，K⁺ 、SO^2-₄ 、Ca²⁺ 表现为"盐岛"。(3)在整个土壤剖面中，与TS、EC相关性最强的阴阳离子为Mg²⁺、Cl^-，从灌丛中心到灌丛间裸地Ca²⁺、SO^2-₄与TS、EC的相关性逐渐减弱，Mg²⁺、Cl^-与TS、EC的相关性逐渐增强。Ca²⁺和SO^2-₄与pH表现为较强的负相关性；与ESP相关性最强的阴离子为HCO^-₃，与之相关性最强的阳离子为Na⁺和K⁺，并且Na⁺和K⁺与ESP的相关性表现出从灌丛中心向外逐渐增强。(4)土壤盐渍化主要受控于Na⁺，从灌丛下到灌丛间裸地Cl^-对盐渍化程度的影响逐渐增加，SO^2-₄的影响逐渐降低。     

氮素形态对杉木幼苗侧根生长和叶片光合特性的影响

以3月龄的杉木实生苗为试验材料,分析了不同氮素形态——硝态氮(NO₃^- N)、铵态氮(NH4⁺ N)和硝酸铵(NH₄NO₃)(氮素浓度均为3 mmol·L^-1)对杉木幼苗侧根生长、叶片光合气体交换参数和叶绿素荧光参数的影响,以揭示杉木幼苗对不同形态氮的偏好性,以及不同形态氮肥下杉木幼苗侧根生长和光合生理的响应特征,为杉木苗期氮肥管理提供理论依据。结果显示：(1)不同氮素形态对杉木幼苗地上部和侧根生物量具有显著影响,其中NH₄⁺ N处理下幼苗地上部和侧根生物量最大,NO₃^- N处理次之,而NH₄NO₃处理最小。(2)NH₄⁺ N和NO₃^- N处理下杉木幼苗总根长、根系总表面积和根系总体积均显著高于NH₄NO₃处理(P＜0.05),且NH₄⁺ N处理又显著高于NO₃^- N处理,但不同氮形态处理间侧根数量差异不显著。(3)NH₄⁺ N处理下杉木幼苗叶片净光合速率、气孔导度和蒸腾速率明显高于NO₃^- N和NH₄NO₃处理,但NO₃^- N和NH₄NO₃处理之间无明显差异。(4)NH₄⁺ N处理下杉木叶片初始荧光强度低于NO₃^- N处理,而最大荧光强度、可变荧光强度和PSⅡ潜在活性却高于全硝氮和硝铵氮处理。上述结果表明,NH₄⁺ N处理不仅有利于杉木幼苗侧根生长发育,且其叶片具有较强的光合能力,较高的PSⅡ中心稳定性、光化学活性以及电子传递效率,从而更有利于植株生长。因此,从根系生长和光合特性来看,杉木幼苗对铵态氮具有偏好性。     

盐氮处理下盐地碱蓬种子成熟过程中的离子积累和种子萌发特性

研究了盐氮处理条件下盐地碱蓬种子成熟过程中的离子积累以及种子萌发特性,以理解盐地碱蓬在种子发育及萌发过程中对高盐低氮生境的适应性。结果表明,种子成熟过程中,不同浓度盐氮处理下(0.5和5 mmol/L NO₃^--N;1和500 mmol/L NaCl),与果皮和果枝相比, 胚中Na⁺、K⁺、Cl^- 和NO₃^-离子含量几乎没有变化。所有盐氮处理下Na⁺ 和Cl^-都是果皮和果枝中高于胚中,尤其是在高盐处理下。高盐处理下,K⁺ 和NO₃^-含量呈现相反的趋势。高氮时无论高盐还是低盐,果皮中NO₃^-离子含量高于胚中,而果枝中NO₃^-离子含量低于胚中。而低氮时果皮及果枝中NO₃^-离子含量均显著低于胚中。与高氮环境下收获的种子相比,低氮环境下收获的种子萌发率,萌发指数,活力指数都要明显高。上述结果说明,盐地碱蓬种子成熟过程中存在完善的离子调控机制,保护胚免受Na⁺ 和Cl^-等有害离子的伤害并且促进K⁺ 和NO₃^-等营养离子的积累。低NO₃^--N下收获的种子对外界的NO₃^-含量比较敏感,施以较高浓度的NO₃^-能够促进种子萌发,提高萌发指数和活力指数,可能与盐地碱蓬长期适应高盐低氮生境有关。     

苏干湖湿地土壤全盐含量特征及其与地下水的关联

地下水是内陆盐沼湿地生态水文过程及演变的关键因素,地下水位埋深和水质特征交互作用影响水盐运移过程和表层土壤盐渍化程度。根据2018年8月土壤盐分与地下水特征的监测数据,运用经典统计学、皮尔逊相关性和主成分分析等方法对苏干湖湿地（93°47''53″-94°04''26″E,38°50''07″-38°56''27″N）不同水位下表层0-10 cm土壤全盐含量、地下水水质特征及其间的关系进行定量分析。结果表明：（1）研究区0-10 cm土壤全盐含量的均值为204.41 g/kg,随地下水埋深的增加,土壤全盐含量的均值、变化幅度和变异系数呈先增加后降低的趋势。（2）地下水埋深介于0.17-6 m,pH在7.06-9.56范围,阳离子以Na⁺为主,阴离子以SO₄^2-和Cl^-为主,离子浓度变异系数从强到弱依次为Na⁺ > Mg²⁺ > Ca²⁺ > Cl^- > SO₄^2- > HCO₃^- > K⁺ > CO₃^2-。（3）关联分析表明,在水埋深<1 m、1-2 m的区域表层全盐含量与地下水埋深呈正相关,地下水埋深介于2-3 m和>3 m的区域两者间呈负相关;土壤全盐含量与地下水水质离子Na⁺、Mg²⁺、SO₄^2-、Cl^-间呈极显著正相关,与K⁺、CO₃^2-、HCO₃^-间的相关系数较低且不显著。内陆盐沼湿地表层土壤全盐含量与地下水埋深、地下水水质特征的关联分析,体现了内陆盐沼湿地土壤水盐运移过程的复杂性。     

重庆市近郊大气无机氮、硫沉降特征及其来源分析

以重庆市近郊中梁山槽谷为研究区,利用气象站和沉降仪获取2017年5月-2018年4月的大气无机氮、硫沉降数据和降水δ¹⁵N-NO₃^-、δ¹⁸O-NO₃^-和δ³⁴S-SO₄^2-、δ¹⁸O-SO₄^2-数据,通过离子浓度比值、同位素值和气团后向轨迹探讨了研究区大气中氮、硫沉降变化特征及其来源。结果表明：（1）大气DIN总沉降量为19.99 kg/hm²,干、湿沉降量分别占11%和89%;大气S总沉降量为32.62 kg/hm²,干、湿沉降量分别占13%和87%。大气氮、硫湿沉降量与降水量均呈正相关（n=12,P < 0.01）,氮、硫干湿沉降量具有明显的季节差异。（2）降水NH₄⁺-N/NO₃^--N比值介于0.45-2.2之间,雨季（5-10月）NH₄⁺-N/NO₃^--N>1,旱季（11-次年4月）NH₄⁺-N/NO₃^--N<1,表明雨季氮主要来源于农业源,旱季来源于工业和交通源;降水NO₃^-/SO₄^2-比值介于0.1-1.25之间,平均值为0.63,表明硫来源以固定污染源（燃煤）为主。（3）大气降水δ¹⁵N-NO₃^-、δ¹⁸O-NO₃^-值分别为-3.8‰-3.9‰（平均值为0.4‰±2.6‰）和58.7‰-98.7‰（平均值为76.1‰±14.3‰）,夏季偏负,冬季偏正;降水δ³⁴S-SO₄^2-和δ¹⁸O-SO₄^2-变化范围分别为1.3‰-3.2‰（平均值为2.3‰±1‰）和5.3‰-8.5‰（平均值为7.1‰±1.6‰）,大气降水中NO₃^-和SO₄^2-主要来源于当地的化石燃料燃烧,同时受到周边污染物的远距离传输影响。（4）气团后向轨迹表明影响研究区氮、硫干湿沉降来源的主要因素是东亚季风,北东-南西走向的川东平行岭谷大地貌格局加剧了季风的影响。     

Seasonal and spatial patterns of S,Ca, and N dynamics of a Northern Hardwood forest ecosystem

Seasonal dynamics of S, Ca and N were examined at the Huntington Forest, a northern hardwood ecosystem in the central Adirondacks of New York for a period of 34 months (1985–1988). Solute concentrations and fluxes in bulk precipitation, throughfall (TF) and leachates from the forest floor, E horizon and B horizon were quantified. Both above and below-ground elemental fluxes mediated by vegetation (e.g. uptake, litter inputs, and fine roots production) were also determined. The roles of abiotic and biotic processes were ascertained based on both changes in solute concentrations through the strata of the ecosystem as well as differences between dormant and growing seasons. Concentrations of SO₄ ²⁻, NO₃ ⁻, NH₄ ⁺ and Ca²⁺ were greater in TF than precipitation. Forest floor leachates had greater concentrations of SO₄ ²⁻, NO₃ ⁻ + NH₄ ⁺ and Ca²⁺ (9, 6 and 77 μeq L⁻¹, respectively) than TF. There were differences in concentrations of ions in leachates from the forest floor between the dormant and growing seasons presumably due to vegetation uptake and microbial immobilization. Concentrations and fluxes of NO₃ ⁻ and NH; were greatest in early spring followed by a rapid decline which coincided with a demand for N by vegetation in late spring. Vegetation uptake (44.7 kg N ha⁻¹ yr⁻¹ ) could account for the low leaching rates of N0₃ ⁻. Within the mineral soil, changes with soil depth and the absence of seasonal patterns suggest that cation exchange (Ca⁺) or anion sorption (SO₄ ²⁻) are primarily responsible for regulating solute concentrations. The increase in SO₄ ²⁻ concentration after leachates passed through the mineral soil may be attributed to desorption of sulfate that was adsorbed during an earlier period when SO₄ ²⁻ concentrations would have been greater due to elevated S inputs.     

厌氧氨氧化菌特性及其在生物脱氮中的应用*

在无分子氧环境中,同时存在NH₄⁺和NO₂^-时,NH₄⁺作为反硝化的无机电子供体,NO₂^-作为电子受体,生成氮气,这一过程称为厌氧氨氧化。目前已经发现了3种厌氧氨氧化菌(Brocadia anamm oxidans,Kuenenia stuttgartiensis,Scalindua sorokinii);对厌氧氨氧化     

Chemical Characteristics of Water-Soluble Ions in Particulate Matter in Three Metropolitan Areas in the North China Plain

PM_2.5 and PM₁₀ samples were collected simultaneously in each season in Beijing, Tianjin and Shijiazhuang to identify the characteristics of water-soluble ion compositions in the North China Plain. The water-soluble ions displayed significant seasonal variation. The dominant ions were NO₃ ⁻, SO₄ ²⁻, NH₄ ⁺ and Cl⁻, accounting for more than 90% and 86% to the mass of total water-soluble ions in PM_2.5 and PM₁₀, respectively. The anion/cation ratio indicated that the ion acidity of each city varied both between sites and seasonally. Over 50% of the ion species were enriched in small particles ≤1 µm in diameter. The [NO₃ ⁻]/[SO₄ ²⁻] ratio indicated that vehicles accounted for the majority of the particulate pollution in Beijing. Shijiazhuang, a city highly reliant on coal combustion, had a higher SO₄ ²⁻ concentration.     

Simultaneous Study of NH+ 4, Na+, Mg2+, Ca2+, NO2- 3, SO2- 4, (NO- 2), H{2in}PO- 4 and CI- Uptake by Intact Winter Wheat Seedlings in a Single Depletion ExperimentPO- 4 and CI- Uptake by Intact Winter Wheat Seedlings in a Single Depletion Experiment

Simultaneous uptake of NH⁺ ₄, Na⁺, Mg²⁺, Ca²⁺, NO^- ₃, SO^2- ₄, (NO^- ₂), H²PO^- ₄ and C1^- ions by N-limited winter wheat seedlings(Triticum aestivum L., cv. Regina) in a single depletion experiment was investigated. Individual ion species in uptake solution samples were determined using capillary isotachophoresis. The operating systems used are described in detail. Processing of obtained concentration data allow to construct time curves of individual ions concentration in uptake solution, time curves of accumulative uptake, and curves for uptake rate versus time and uptake rate versus external concentration. From these curves there is possible to reveal a more complex picture of behaviour of individual ions during uptake process as well as to assess interactions among them. Attention was paid to the points of intersection of time curves of NO^- ₃ and NH⁺ ₄ uptake rates. These points characterized by equal uptake rates may be considered as limits for preference of given ion species under given experimental conditions.     

Atmospheric deposition, mass balances, and processes regulating streamwater solute concentrations in mixed-conifer catchments of the Sierra Nevada, California

Solute concentrations in atmospheric deposition and stream water were measuredfrom 1984 through 1993 to determine the fate and mobility of solutes in twogauged mixed-conifer catchments (Tharp's and Log creeks) located in theSierra Nevada, California. The two catchments contain mature forest standsdominated by Abies concolor (white fir), Sequoiadendron giganteum (giantsequoia), Abies magnifica (red fir) and Pinus lambertiana (sugar pine).Ammonium, Cl^-, Ca²⁺ and NO^- ₃were highest in concentration of the solutes measured in wet deposition;bulk deposition was highest in SO^{2- 4}, NH⁺ ₄,Cl^- and H⁺. Net retention ofH⁺, NO₃ ^-, NH₄ ⁺,SO₄ ^2- and Cl^- occurred in both catchments.Discharge was dominated by spring snowmelt with the largest export yieldsfor acid neutralizing capacity (ANC), SiO₂, andCa²⁺. Export yields of H⁺,NO₃ ^-, NH₄ ⁺ and PO₄ ^3-were relatively small (0.5 kg ha^-1 y^-1).Discharge-concentration relationships for ANC, SiO₂,Na⁺, K⁺, Ca²⁺ andMg²⁺ were inverse and their concentrations in stream waterwere primarily influenced by discharge and annual differences in the relativecontributions of snowmelt and groundwater. The mobility of these solutes iscontrolled by the rates of mineral weathering and ion exchange. The positiverelationship of SO₄ ^2- concentration with increasingdischarge suggests that atmospherically deposited SO₄ ^2-is temporarily stored and that its release is controlled by the extent of soilwater flushing.     

杨树人工林生态系统降水再分配及主要离子特征

大气降水是森林生态系统养分输入的主要途径之一,对养分的生物地球化学循环有着重要的意义。对13年生杨树人工林林外雨、树干流、林内雨和地表径流等水文过程中的养分特征进行了调查分析,旨在了解该生态系统的养分输入与输出规律,为杨树人工林可持续经营提供依据。结果表明,从2013年11月至2014年10月,杨树人工林生态系统林外雨量为1154.1 mm,树干流量仅占大气降水量的2.3%,15.4%的大气降水被杨树人工林的冠层截留;林内雨、树干流与大气降水量(林外雨)的动态变化规律相似。各类降水年加权平均pH值表现为林内雨林外雨树干流;各类降水的离子浓度动态变化规律基本一致,即在降水量较小的11月至次年1月份,各阴阳离子的浓度普遍较高,在降水量较大的2—9月份,阴阳离子浓度普遍较低。SO_4~(2-)-S和Ca~(2+)分别是各类降水中的主要阴离子和阳离子;整体上,树干流的离子浓度林内雨大气降水;林内雨是养分输入的主要形式,通过林内雨输入林地较多的养分离子是Ca~(2+)和K~+,分别为70.83 kg hm~(-2)a~(-1)和63.31 kg hm~(-2)a~(-1);地表径流和土壤渗漏是养分输出的主要形式,输出林地较多的离子是Cl~-和Ca~(2+),分别为196.47 kg hm~(-2)a~(-1)和123.09 kg hm~(-2)a~(-1),其次为SO_4~(2-)-S、Mg~(2+)、Na~+、K~+;NH_4~+-N和NO_3~--N的输出量不足输出离子总量的1%。所以,从水文过程看,杨树人工林生态系统无机氮(NH_4~+-N和NO_3~--N)和K~+表现为净积累,净积累量分别为10.9 kg hm~(-2)a~(-1)和56.4 kg hm~(-2)a~(-1),其他离子表现为净损失,其中Cl~-的净损失量达179.8 kg hm~(-2)a~(-1)左右,其他离子损失量50 kg hm~(-2)a~(-1)。     

黑河天涝池流域典型林分生态水文化学特征

采集了黑河天涝池流域典型林分林外雨、穿透雨、树干径流和枯透水,并检测水体pH值和12种离子(K~+、Ca~(2+)、Na~+、Mg~(2+)、NH_4~+、Cu~(2+)、Zn~(2+)、Pb~(2+)、Cd~(2+)、Cl~-、SO_4~(2-)、NO_3~3)的质量浓度。结果表明:天涝池流域大气降水pH均值为7.74,呈碱性,降水中离子绝对质量浓度较低,最高的是NO_3~-,质量浓度为1.1111 mg/L,最低的为Na~+,质量浓度为0.0108 mg/L;两种林分冠层有降低降雨pH值的作用,青海云杉林冠层对NH_4~+有升高作用,祁连圆柏林冠层对NH_4~+有降低作用,两种林冠层对NO_3~-和Cu~(2+)质量浓度有降低作用,对其它离子质量浓度均表现为升高作用;两种林分树干径流有提高穿透雨pH值的作用,与穿透雨相比,两种林分树干径流中阴离子均有升高,圆柏树干径流中所有阳离子质量浓度均有下降,云杉树干径流中Ca~(2+)、K~+、Mg~(2+)和Na~+减少,NH_4~+和Cu~(2+)增加;典型林分枯透水有提升穿透雨pH值的作用,与穿透雨相比,两种林分枯透水中阴离子质量浓度均有升高,云杉枯透水各阳离子均有降低,圆柏枯透水中Ca~(2+)、K~+和Mg~(2+)质量浓度升高,NH_4~+、Na~+和Cu~(2+)质量浓度下降;在采集的所有样本中,Pb~(2+)和Cd~(2+)均未检出,而Zn~(2+)仅在云杉树干径流中检出。     

模拟酸沉降对鼎湖山季风常绿阔叶林地表径流水化学特征的影响

通过模拟酸沉降实验,研究了旱季期间(10-3月份)鼎湖山季风常绿阔叶林在4种不同pH模拟酸雨处理(对照、pH 4.0、pH 3.5、pH 3.0)下地表径流水化学输出特征.结果显示:(1)地表径流pH随酸处理强度增强呈“U”型变化模式,酸沉降对地表径流pH的影响不显著(P＞0.05),表明模拟酸沉降尚未引起地表水的酸化.(2)地表径流中NO3-、SO24-浓度随酸处理强度增强略有增加;HCO3-浓度的变化模式与地表径流pH类似.酸根离子浓度与地表径流pH相关性分析表明,SO24-、HCO3-有助于提高地表水抗酸化能力而NO3-则有助于促进地表水酸化.(3)地表径流中盐基离子对酸沉降的响应不尽相同.pH 3.0处理显著提高地表径流中Ca2+、Na+浓度;Mg2+浓度具有随酸处理梯度增强而增加的趋势;K+受模拟酸度的影响小.表明强酸(pH3.0)处理将导致土壤Na+、Ca2+、Mg2+盐基离子流失.(4)酸沉降具有诱发土壤可溶性有机碳(DOC)流失的倾向,增加地表水受有机污染的风险.     

Plant induced alteration in the rhizosphere and the utilisation of soil heterogeneity

Plant-soil interactions result in a special rhizosphere soil chemistry, differing from that of the bulk soil found only a few mm from the root. The aim of this study was to investigate adaptation mechanisms of herbs growing in acid soils through studying their rhizosphere chemistry in a greenhouse experiment and in a field study. Ten herbs were grown in acid soil (pH 4.2 in the soil solution) in the greenhouse. The concentrations of NO₃ ^-, SO₄ ^2-, phosphates, Ca²⁺, Mg²⁺, Mn²⁺, K⁺, Na⁺, NH₄ ⁺ and pH were analysed in soil solutions obtained by centrifugation. The general pattern found was a depletion of nutrients in the rhizosphere compared with their concentrations in the bulk soil. The pH increase (up to 0.7 units) in the rhizosphere soil appeared to be caused by plant uptake of NO₃ ^- (r²=0.88). The ion concentrations in the soil solution of the rhizosphere were dependent on plant species and biomass increase. Although species with a larger biomass and higher growth rates showed a higher degree of ion depletion (except for Na⁺, SO₄ ^2-) in the rhizosphere, there were also species specific responses. A field study of five herbs at five oak forest sites in Southern Sweden (Scania) was also carried out. In addition to the soil solution concentrations, the loss on ignition (LOI) and the concentrations of 0.1 M BaCl₂ extractable K⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Al ions were measured. The amount of soil solution Al was determined as free ionic (quickly reacting) Al. For all species and sites, the LOI and the concentrations of exchangeable cations were higher in the rhizosphere than in the bulk soil, apparently due to the roots preferably growing at organic-rich microsites. The concentrations of the ions as measured in the centrifuged soil solution, were either higher in the rhizosphere than in the bulk soil or were the same in both, except for NO₃ ^- and quickly reacting Al. The lower concentrations of quickly reacting Al in the rhizosphere, compared with the bulk soil could indicate the uptake of Al by the plant or the exudation of complexing substances. The pH differences were only small and mostly non-significant. Plant-soil interactions and the ability of plants to utilise heterogeneity of the soil appear to be more important for plant growth in acid soils than recognised heretofore. Rhizosphere studies provide an important means of understanding plant strategies in acid soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of some ammonium salts on nitrate reductase level,onin vivo nitrate reduction and on nitrate content in excisedpisum sativum roots

The effect of some ammonium salts on nitrate reductase (NR) level, onin vivo nitrate reduction and on nitrate content was followed in the presence of nitrate in the medium, under changing experimental conditions, in excisedPisum sativum roots, and their effect was compared with that of KNO₃, Ca(NO₃)₂ and NaNO₃ at 15 mM NO₃ ^- concentration, i.e. at a concentration which considerably exceeded the level of saturation with nitrate with respect to nitrate reductase. The effect of ammonium salts on NR level is indirect and changes from a positive one to a strongly negative one which is dependent on the time of action of the salt, on the presence of other cations, on pH of the solution of the ammonium salt and on the nature of the anion of the ammonium salt. A positive effect on the enzyme level can be observed in the presence of other cations than NH₄ ⁺ at suitable concentrations of those ammonium salts, the solutions of which have their pH values in the acid region (i.e. NH₄H₂PO₄, (NH₄)₂SO₄ and NH₄NO₃). However their positive effect is independent of the presence of NH₄ ⁺ ions, and it is obviously the result of an increased concentration of H⁺ ions. A clear-cut negative effect on NR level can be observed after 24 h in one-salt NH₄NO₃ solution where NH₄ ⁺ is not balanced with other cations and thus certainly can adversely influence many metabolic processes, and in the solutions containing neutral (pH 6.2) and dibasic ammonium phosphates in which dissolved undissociated ammonia [(NH₃). (H₂O) which can also affect many metabolic processes incl. proteosynthesis] probably has a toxic influence. Thein vivo nitrate reduction is always depressed in excised pea roots in the presence of ammonium salts in the medium, regardless of the level of nitrate reductase. Under the described conditions, no relationship could be established between the enzyme level and the so-called metabolic NO₃ ^- pool (i.e. NO₂ ^- production under anaerobic conditions), nor between NR level and the total nitrate content in the roots. One-salt solutions of NaNO₃, Ca(NO₃)₂ and KNO₃ exert different effects on the level of nitrate reductase and on the content of NO₃ ^- in the roots, but the in vivo NO₃ ^- reduction shows the same trend as NR level in the roots influenced by these salts. Cl^- ions, supplied in NH₄C1, depress both NR level and NO₃ ^- content in the roots at higher concentrations, but they do not significantly affect the in vivo nitrate reduction in comparison with other ammonium salts. These results indicate that NR level,in vivo nitrate reduction, and nitrate uptake can be regulated in pea roots independently of each other.