铵态氮/硝态氮对水稻铝吸收的影响及其机制研究

选用两个水稻品种武运粳7号（耐铝品种）和扬稻6号（铝敏感品种）作为实验材料,利用水培试验,通过长期和短期处理相结合的方式研究了NH4+-N和NO3--N对水稻Al吸收的影响及其作用机制。结果表明,与NH4+-N相比,NO3--N促进了水稻对Al的吸收。而且随着NO3--N浓度的提高,水稻根中Al含量显著增加,随着NH4+-N浓度的提高,水稻根中Al含量显著降低。这些结果表明NH4+-N和NO3--N对水稻Al吸收的影响具有浓度效应。当向Al溶液添加pH缓冲剂后,NH4+-N和NO3--N对根尖Al累积的影响变小,表明NH4+-N和NO3--N处理下溶液pH的变化可能是NH4+-N和NO3--N对水稻Al吸收影响不同的一个原因。     

CO2与NH4+/NO3-比互作对番茄幼苗培养介质pH、根系生长及根系活力的影响

为探讨CO2浓度升高能否减缓高浓度NH4+-N对番茄根系的毒害作用,本试验在营养液栽培条件下,以番茄为材料,在CO2生长箱中研究2个CO2浓度与5个不同NH4+/NO3-配比的交互作用对生长介质的pH、根系生长及根系活力的影响。结果表明,随着生育期的推进与CO2浓度的升高,pH变化幅度增大。两个CO2浓度均表现为全NO3--N含量营养液的pH呈上升趋势,其它处理营养液的pH均呈现出不同程度的下降趋势,下降的幅度随NH4+/NO3-比例的增加而增加;而且全NH4+-N引起pH值下降的程度大于全NO3--N引起pH增加的程度。CO2浓度升高增加了低NH4+/NO3-比例供应处理的蕃茄幼苗冠干重、根干重、根系活力、根系总吸收面积、活跃吸收面积。这些指标对CO2的响应随NH4+/NO3-比例的降低而加强,冠干重、根干重、根系活力、根系总吸收面积、活跃吸收面积增加分别高达65.8%、78.0%、18.9%、12.9%与18.9%。说明在CO2浓度升高条件下,番茄幼苗根生长潜力在全NO3--N处理中最大,但不能减弱全NH4+-N对番茄根系的毒害作用。     

铝胁迫下不同耐铝性小麦根际pH值变化及其与耐铝性的关系

Al3＋是植物铝毒害的主要形态,而其活性受环境pH值的影响,H＋-ATPase通过调节根的质子分泌改变根际pH值。为探讨铝胁迫下根际pH值变化与小麦耐铝性的关系,以小麦品种ET8（耐铝型）、ES8（铝敏感型）为试验材料,采用溶液培养的方法对铝胁迫下根际pH值及根尖H＋-ATPase活性变化进行了研究。结果表明,铝处理条件下,小麦根际pH值随培养时间的延长而升高;随培养液中铝浓度的增加,根际pH值上升幅度下降,相同铝浓度处理条件下ET8根际pH值显著高于ES8。根际pH值与根尖铝含量呈极显著负相关（R2=0.932 1）,与根相对伸长率呈极显著正相关（R2=0.858 5）,表明小麦通过提高根际pH值降低根尖铝含量,减轻铝毒害。根尖H＋-ATPase活性随铝处理浓度升高而显著降低,100 μmol·L-1Al处理24 h ET8和ES8根尖H＋-ATPase活性分别为各自无铝处理的69.8%和60.0%,根尖H＋-ATPase相对活性与根际pH值呈极显著负相关（R2=0.831 9）。温度显著影响根的伸长,低温处理（9 ℃）根际pH值显著高于常温处理（25 ℃）,而根尖铝含量却显著低于常温处理。表明小麦通过根尖H＋-ATPase提高根际pH值降低铝毒害。综上所述,铝胁迫下小麦可通过提高根际pH值减轻铝毒害,不同耐铝性小麦品种根际pH值的显著差异是耐铝性差异显著的     

不同氮效率茄子基因型及其杂种F1的氮素吸收特性

为阐明杂种一代在氮素吸收方面的优势,研究了不同氮效率茄子基因型及其杂种 F1的氮素吸收特性。试验以3个典型氮效率的茄子基因型及其F1代为材料,研究其在正常供氮和低氮胁迫条件下的根系体积、根系干重、氮素吸收总量、根系活力、硝酸还原酶活性及谷氨酰胺合成酶活性。结果表明,与高氮低效-低氮低效基因型L相比,氮高效基因型H1、H2的单株根系体积、根系干重、根系活力以及氮素吸收总量均较大; 且具有较高的硝酸还原酶与谷氨酰胺合成酶活性。三个杂交组合F1-1（L×H1）、F1-2（L×H2）和F1-3（H1×H2）的单株根系体积、根系干重、根系活力、硝酸还原酶活性、谷氨酰胺合成酶活性以及氮素吸收总量的中亲优势（Hm）和超亲优势（Hp）多为正向优势; 其中,组合F1-3杂种优势最为明显。利用杂种在氮素吸收方面的优势,对于改善植株体内的氮代谢水平进而提高氮效率具有重要意义。     

适量施氮增强盐胁迫下高羊茅生长和抗氧化能力

为土壤盐渍地区高羊茅(Festuca arundinacea)草坪的合理施肥,该研究用NaCl浓度为0,70,140mmol/L和不同NH4NO3水平(质量浓度为0.01,0.6,1.2g/L)对盆栽高羊茅植株进行交互处理,并测定处理后其生长量和抗氧化能力。结果表明,同一水平NH4NO3相比,NaCl胁迫下高羊茅鲜质量、干质量、含水率均低于无NaCl处理;而根系脱氢酶活性、硝酸还原酶(nitratereductase,NR)活性、超氧化物歧化酶(superoxidedismutase,SOD)同工酶活性NO3-含量、质膜透性和丙二醛(malonicdialdehyde,MDA)含量均强于或高于无NaCl处理;CAT(catalase,CAT)同工酶活性及蛋白表达量发生改变。同一浓度NaCl胁迫下,随NH4NO3水平增加,其鲜质量、干质量、含水率呈上升趋势;NO3-含量、质膜透性和MDA含量呈下降趋势;SOD同工酶增强;根系脱氢酶活性、NR活性、CAT同工酶活性和蛋白表达量增强幅度明显减弱。因此,与NH4NO30.01g/L相比,NH4NO30.6g/L改善了同浓度盐胁迫下高羊茅氮素营养、抗氧化能力和蛋白质表达量,增强了其耐盐性;而NH4NO31.2g/L能一定程度上改善其氮素营养,但根系主动吸收离子能力、清除H2O2能力和蛋白质表达量增强有限,引起根际环境NH4NO3积累,严重导致土壤次生盐渍化。该研究为盐渍土壤上的高羊茅草坪合理施用NH4NO3提供参考。     

水稻(Oryza sativa L.)铝毒害与耐性机制及铝毒害的缓解作用

铝 (Al) 毒是广泛存在于热带亚热带地区酸性土壤上的主要的生产力限制因子之一。水稻Al毒害主要发生在新开垦的旱地酸性土壤上。本文较详细地总结了: (1) 水稻发生Al毒的环境条件,水稻Al毒害的可见症状和Al毒害的部位;(2) 水稻耐Al指标,营养元素的吸收与分配对水稻耐受Al毒害的影响,以及Al胁迫下根系分泌物、根际pH的变化等对水稻耐Al的贡献,水稻耐Al基因的定位等;(3) 水稻Al毒害的缓解作用机理及可能的解决措施。最后对水稻Al毒害和水稻耐Al机制研究中存在问题进行了分析探讨,同时对今后的研究作了展望。     

不同水、氮条件对水稻苗生长及伤流液的影响

为探明不同水分供应和氮素形态对水稻根苗及伤流液的影响,设正常水分及50 g/L PEG模拟水分胁迫和3种不同质量比例的NH4+-N/NO3--N（9/1,5/5,1/9）氮素营养处理,测定了水稻幼苗生物量,根系形态指标,根系活力及根基伤流量。结果表明,正常水分条件下,NH4+-N促进水稻根系平均直径增大,有利于水稻地上部物质累积;NO3--N则使水稻根系总吸收面积增大,促进根系物质累积;NH4+-N/NO3--N为5/5处理的水稻活跃吸收面积最大,活跃吸收面积比亦最高。水分胁迫条件下,NH4+-N/NO3--N为5/5的处理更有利于水稻地上部分的生长,NO3--N有利于水稻鲜重和干重增加,促进根系平均直径增大,水稻的根系总吸收面积、活跃吸收面积均随NO3--N供应比例的增加呈上升趋势。正常水分条件下,水稻幼苗白天的耗水量随NH4+-N/ NO3--N比例降低呈下降趋势,水分胁迫条件降低了水稻对水分的吸收。水分胁迫显著降低各处理水稻伤流量,正常水分条件下,NH4+-N/NO3--N为5/5处理的水稻伤流量最大;水分胁迫后,9/1处理的水稻伤流量相对较多。     

酸性条件下氮素形态对西红柿根系释放羟基的影响

为研发酸化土壤的生物修复技术,本文用水培实验和电位滴定方法研究了酸性条件下氮素形态对西红柿根系释放羟基的影响,结果表明,在初始pH为4.0、NO3-/NH4+ 比为15:1、5:1、1:1和1:5的营养液中,由于西红柿对NO3--N的偏好吸收导致根系释放羟基,培养液pH升高。培养1周后4个NO3-/NH4+ 比培养液pH分别升高了1.60、1.15、0.57和0.29,与西红柿对NO3--N的吸收量和羟基释放量的大小一致。当西红柿生长在初始pH为5.0营养液中时,仅NO3-/NH4+ 比为15:1和5:1体系中西红柿根系释放羟基,导致培养液pH升高;在NO3-/NH4+ 比为1:1和1:5体系中西红柿根系释放质子,导致培养液pH降低。初始pH5.0条件下西红柿吸收的NO3--N低于初始pH4.0条件下的,其根系释放的羟基量也低于pH4.0体系中的。这些结果说明低pH条件有利于西红柿对NO3--N的吸收,西红柿根系也会释放更多的羟基。因此可以根据西红柿在强酸性条件下对NO3--N的偏好吸收和根系释放羟基的特点对酸化土壤进行生物修复。     

生境因子作用下NO_3~-/NH_4~+吸收及硝酸还原酶活性变化

土壤中的氮素因土壤类型和季节变化产生异质性。在长期的进化过程中,植物适应各自的氮营养生境,形成了对NO3-/NH4+吸收的分子机制。饱和高亲和传输系统(HATS)中,植物在不同的转录基因控制下吸收NO3-/NH4+,表现出对两种氮源的偏选性。这种偏选性主要取决于植物种的特性,但是NO3-/NH4+的吸收受光照、介质N强度、pH值、外源氨基酸和温度等生境因子的影响,同时植物的营养生境也因NO3-/NH4+的吸收被深刻改造。硝酸还原酶(NR)在氮同化过程中作用于NO3-还原阶段,其活性受各种生境因子的制约,影响植物对NO3-吸收利用。     

氮素形态及HCO3——对豌豆铁素营养的影响

在水培条件下研究了NO3-N ,NH4-N及添加HCO3-和HEPES对豌豆铁营养的影响。与NO3-N相比 ,供应NH4-N时豌豆根系铁还原力上升较早 ,铁还原酶活性显著较高 ,铁向地上部转移较多。供应NH4-N时培养Sparkle的营养液pH下降较快 ,而培养E107营养液 pH受氮源形态的影响较小。对根系质外体铁的利用 ,以NH4-N为氮源时 ,两种豌豆经过 15天后都全部利用 ;供应NO3-N的E107能全部利用 ,Sparkle也利用了约 3/4 ;以HCO3-缓冲时E107利用了约 3/4 ,而Sparkle则几乎不能利用。但是生长在HCO3-缓冲的营养液中的豌豆根系结构完好 ,转移到低pH环境中后铁还原力不仅没有降低 ,反而比对照有所提高。HCO3-和HEPES对豌豆铁营养的影响相似。表明HCO3-对豌豆铁营养的影响不是破坏了根系的结构和功能 ,而主要是通过提高根际 pH值 ,抑制了根系铁还原酶活性的作用 ,从而降低了对铁的吸收利用能力。氮素形态对豌豆铁营养的影响主要是通过影响质外体 pH起作用的。     

Effects of aluminum on nutrient solution pH and nitrate/ammonium uptake by triticale

Aluminum (Al) plant tolerance has been frequently associated with a pH increase in the rhizosphere. The changes in pH are dependent on plant genotypes and ionic composition and strength of nutrient solutions. This work was performed in order to study in triticale (Triticosecale Wittm.) the association of pH change with nitrogen (N) uptake and growth performance in acid conditions. Three‐day‐old seedlings were treated with Al (185 μM) in solutions having different proportion nitrate/ammonium (NO₃/NH₄), 15/1 and 8/1, but the same total N content. Along the period with Al treatment, several measurements have been made: pH, every day; NO₃ and NH₄ uptake from the solution as well as shoot and root biomass production every two days (five and seven days of plant age). The maximum growth inhibition (30%) of fresh weight was found in roots of plants in the 15/1 (NO/NH,) nutrient solution. The presence of a higher proportion of NH₄ (8/1 solution) had a protective effect on Al damage as shown by less growth inhibition and less reduction in NO₃ uptake. Changes in pH apparently were not relevant for the tolerance. The results suggest that NH₄ fertilization may be useful for alleviating Al toxicity in triticale.     

Nitrogen source and aluminum toxicity of two sorghum genotypes differing in aluminum susceptibility

After a 35 days growth on nutrient solutions with NO^‐ ₃ NH₄NO₃ and NH⁺ ₄ as nitrogen source (pH 4.2) dry matter yield of the sorghum genotype SC0283 was much less affected by Al (1.5 mg‐¹) than that of the genotype NB9040. With NO^‐ ₃ as the sole nitrogen source only growth of the NB9040 plants was significantly reduced. Since OH^‐ efflux, shoot Al content and concentrations of all major nutrients of both genotypes were almost equal, a higher sensitivity to Al may underlie the lower Al tolerance of the NB9040 genotype. In the presence of NH.‐N Al again lowered d.m. yield of the NB plants. With SCO283 significant Al effects on d.m. yield were observed only with NH₄NO₃. Aluminum drastically increased the amount of protons released per unit of root surface area, especially with the NB9040 line. This shift in proton flux density was partly the result of a decrease of the specific root surface area and partly due to enhanced excess of catlonic nutrients taken up. With NH₄NO₃‐fed plants the latter could almost completely be attributed to a changed N preference brought about by inhibited uptake of NO^‐ ₃ and a simultaneous enhanced NH, absorption. Although both proton efflux and NH⁺ ₄ preference of the NB plants were severely increased by Al, relative yields of this genotype were not lowered by NH⁺ _4. This can probably be explained by (1) the high NH, sensitivity of this cultivar through which Al effects can be masked and (2) the continuous adjustment of the solution pH through which rhizosphere conditions were prevented.     

Rhizosphere effects of maize hybrids and N forms on Cd bioavailability in a limed soil

Replacing new corn genotypes in agricultural practices requires adequate information on the reaction of the selected hybrids to Cd uptake in Cd-polluted soil and an understanding of interactions with N fertilizers. A 2 × 2 × 3 factorial pot experiment with limed soil (pH 8), two maize (Zea mays) hybrids (Pioneer cultivar yellow and Pioneer cultivar white), two N fertilization forms (NH₄ ⁺ and NO₃ ^?) and three Cd exposures (0, 2 and 5 mg kg^?1 soil) was conducted under greenhouse conditions. Shoot dry mass increased significantly with NH₄ ⁺ nutrition compared with NO₃ ^? nutrition in both maize hybrids, with greater negative influence of Cd application combined with NH₄ ⁺ nutrition. The yellow cultivar had significantly greater shoot dry mass and lower Cd uptake than the white cultivar. Both hybrids exhibited similar N uptake in shoots and roots, with the exception of yellow cultivar with NH₄ ⁺ nutrition without Cd application. NO₃ ^? nutrition always decreased Cd uptake in both cultivars compared with NH₄ ⁺ nutrition. The N balance (mean across cultivars and Cd supply) after harvest showed most N uptake with NH₄ ⁺ nutrition (63.4%) and N_min remains in the soil with NO₃ ^? nutrition (48.7%). Soil pH decreased more with NH₄ ⁺ (?0.95 pH units) than NO₃ ^? nutrition (?0.21).     

铵硝营养对水稻氮效率和矿质养分吸收的影响

NH_4~+和NO_3~–是对植物有效的两种主要无机氮源。水稻一般被认为是偏好NH_4~+的植物,但是在NO_3~–条件下,水稻也能良好地生长。大多数关于水稻铵硝营养的报道是在pH 6.0左右的水培条件下开展的,但是对于酸性条件下水稻铵硝营养研究很少。随着土壤酸化的加重及一些边际酸性土壤被用作水稻种植,研究酸性条件下水稻的铵硝营养具有重要意义。本文采用水培试验,在pH 5.0的条件下,通过添加和不添加pH缓冲剂MES(2-(N-吗啡啉)乙磺酸),研究了NH_4~+和NO_3~–对水稻生长、氮效率和矿质养分(N、P、K、Ca、Mg、Fe、Zn、Cu、Mn)吸收的影响。结果表明,在不添加MES的条件下,水稻地上部生长(株高、叶绿素含量、干重)在NH_4~+和NO_3~–之间没有显著差异,而添加MES后,NH_4~+处理的水稻地上部生长优于NO_3~–。不管是否添加MES,NO_3~–处理的水稻地下部生长(根长、根表面积和根物质量)优于NH_4~+。水稻含氮量和氮利用效率在不同NH_4~+和NO_3~–处理之间没有显著差异,但是NH_4~+处理的水稻氮吸收效率高于NO_3~–。与NO_3~–相比,NH_4~+增加了水稻地上部P和Fe含量,而降低了水稻地上部Ca、Mg、Zn、Cu和Mn含量,对K含量影响较小。上述结果表明,NH_4~+有利于改善水稻地上部生长,提高氮吸收效率、地上部P和Fe含量,而NO_3~–则有利于水稻发根,提高地上部Ca、Mg、Zn、Cu和Mn含量。     

Fertilizer ammonium : nitrate ratios determine phosphorus uptake by young maize plants

We investigated the interacting effects of inorganic nitrogen and the main inorganic phosphorus form in dairy manure (dicalcium phosphate, CaHPO₄) on growth, nutrient uptake, and rhizosphere pH of young maize plants. In a pot experiment, three levels of CaHPO₄ (0, 167, and 500 mg P pot^?1) were combined with nitrogen (637 mg N pot^?1) applied at five NH₄‐N : NO₃‐N ratios (0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0) and a nitrification inhibitor in a concentrated layer of a typical acid sandy soil from Denmark. ¹⁵N‐labeled NH₄‐N was applied to differentiate the role of nitrification and to partition nitrogen uptake derived from NH₄‐N. Among treatments including nitrogen, shoot biomass, rooting and phosphorus uptake were significantly higher at the five‐leaf stage when CaHPO₄ was applied with NH₄‐N : NO₃‐N ratios of 50 : 50 and 75 : 25. In these treatments, rhizosphere pH dropped significantly in direct proportion with NH₄‐N uptake. The fertilizers in the concentrated layer had a root‐inhibiting effect in treatments without phosphorus supply and in treatments with pure NO₃‐N or NH₄‐N supply. Increased nitrogen uptake as NH₄‐N instead of NO₃‐N reduced rhizosphere pH and enhanced acquisition of applied CaHPO₄ by young maize plants, which may have positive implications for the enhanced utilization of manure phosphorus.     

土壤-根系微区养分状况的研究 Ⅵ.不同形态肥料氮素在根际的迁移规律

本文研究了不同形态氮肥施用后,氮素在作物根际的分布规律,及其与作物种类、土壤水分条件的关系.在淹水条件下的水稻根际土壤中,(NH₄)₂SO₄和(NH₂)₂CO荨NH₄⁺-N肥,其亏缺率随离根面距离增加呈指数相关的减小.而旱作条件下的玉米、大麦、黑麦草等作物根际NH₄⁺-N肥料在离根面1-3毫米内存在相对累积,然后再出现亏缺梯度.试验证明,NH₄⁺-N在旱作根际的相对累积,部分来源于根系分泌物.然而,NO₃^--N肥即使在淋失量较大的情况下,无论在淹水水稻还是旱作根际土壤中均未测出亏缺,仅存在累积.     

Aluminum tolerance in maize: Minimizing pH changes in screening solutions 1

Preliminary screening of maize (Zea mays L.) genotypes for aluminum (Al) tolerance in nutrient solutions over a 12‐day growth period showed greater plant‐induced pH changes in solutions without Al than in solutions containing Al. Such pH changes may alter the specific effect of Al on relative root length (length in Al‐containing solution/length in 0 Al solution) commonly used as an index to rank genotypes with respect to Al tolerance. The objective of this study was to examine several screening methods for identifying Al‐tolerant maize genotypes, and to identify those procedures which resulted in minimal pH fluctuations during the course of screening. The following methods of controlling pH in nutrient solutions were compared: (i) 12‐day exposure to 0 or 5 mg Al/L in nutrient solutions (a) with or (b) without daily pH adjustment or (c) with different NO₃ ^‐/NH₄ ⁺ ratios, and (ii) 2‐day exposure to 0, 5, 10, 25 or 40 mg Al/L treatment solutions followed by a 3‐day recovery period in solutions with an initial pH at (a) 4.6 or (b) 4.0. In the 12‐day experiments, daily pH adjustment to 4.6 did not eliminate large pH fluctuations in the control (0 Al) solutions, and it substantially decreased the soluble Al concentration in the Al‐treatment solution. Varying the ratio of NO₃ ^‐ to NH₄ ⁺ did not eliminate large pH fluctuations. Exposing the seedlings for 2 days to Al solutions at pH 4.6 resulted in large pH differences between 0 Al and Al‐containing solutions and in precipitation of large amounts of Al. In contrast, the 2‐day procedure using solutions with an initial pH at 4.0 was more satisfactory in that the pH was maintained between 4.0 and 3.7 in all solutions, and Al precipitation was minimized. When the 2‐day method at pH 4.0 was used to screen the genotypes, PDMR3 had consistently higher relative root lengths in Al‐containing solutions than did Kalimpos, IPB Varl, UPCA Varl and Trinidad Grp1&2.     

两个品种水稻中硝酸盐吸收和利用率对氮素饥饿的响应特征

Ammonium（NH＋4） is the main nitrogen（N） form for rice crops, while NH＋4near the root surface can be oxidized to nitrate（NO-3）by NH＋4-oxidizing bacteria. Nitrate can be accumulated within rice tissues and reused when N supply is insufficient. We compared the remobilization of NO-3stored in the tissue and vacuolar between two rice（Oryza sativa L.） cultivars, Yangdao 6（YD6, indica）with a high N use efficiency（NUE） and Wuyujing 3（WYJ3, japonica） with a low NUE and measured the uptake of NO-3, expression of nitrate reductase（NR）, NO-3transporter genes（NRTs）, and NR activity after 4 d of N starvation following 7-d cultivation in a solution containing 2.86 mmol L-1NO-3. The results showed that both tissue NO-3concentration and vacuolar NO-3activity were higher in YD6 than WYJ3 under N starvation. YD6 showed a 2- to 3-fold higher expression of OsNRT2.1 in roots on the 1st and 4th day of N starvation and had significantly higher values of NO-3uptake（maximum uptake velocity, Vmax） than the cultivar WYJ3.Furthermore, YD6 had significantly higher leaf and root maximum NR activity（NRAmax） and actual NR activity（NRAact） as well as stronger root expression of the two NR genes after the 1st day of N starvation. There were no significant differences in NRAmax and NRAact between the two rice cultivars on the 4th day of N starvation. The results suggested that YD6 had stronger NRA under N starvation, which might result in better NO-3re-utilization from the vacuole, and higher capacity for NO-3uptake and use, potentially explaining the higher NUE of YD6 compared with WYJ3.     

Short-Term Physiological Responses of Mosses to Atmospheric Ammonium and Nitrate

Many bryophytes rely to a large extent on atmospheric deposition for their nutrient uptake.However, increasing levels of atmospheric ammonium NH ₄ ⁺ and nitrate NO ₃ ^- attract concern as to the possible harmful effects onbryophytes from these two nutrient sources. Changes in nitrate reductase (NR) activities, cation(Ca, K and Mg), total nitrogen (N) and organic acid concentrations were investigated for themosses, Racomitrium lanuginosum, Rytidiadelphus loreus and Philonotis fontana, in response to asingle field misting with 3 mol m^-3 NH ₄ ⁺ and NO ₃ ^- . Increases of 20% were recordedfor tissue N content, 48 hr after misting with N containing solutions. When labelled NH ₄ ⁺ or NO ₃ ^- were applied to R. Lanuginosum at 1, 3 and 6mol m^-3 concentrations, partitioning ofincorporated ¹⁵N between different tissueregions occured, with the highest N uptake in the upper stem and leaves. High concentrations ofapplied N resulted in reduced efficiency of N uptake. NH ₄ ⁺ applications caused declines in NR activities, organic acidsand cations, whereas, NO ₃ ^- treatments causedthe reverse response. Changes in cation contents, organic acids and NR activity reflect short-termregulation of N metabolism in the presence of defined N sources, as well as potential mechanismsof regulating cell pH homoeostasis. The consistency of physiological responses, especially NRactivities, over short-term pollution episodes, provides evidence for their use as indicators of both NH ₄ ⁺ and NO ₃ ^- pollution.