Cotton Growth and Physiological Responses to Boron Deficiency

Abstract

Boron (B) deficiency is common in some cotton (Gossypium hirsutum L.) growing regions of the world. A better understanding of changes in the growth and physiological characteristics of cotton plants during the development of B deficiency will help us to define field diagnosis techniques and improve B fertilizer management recommendation. An experiment was conducted in a controlled‐environment growth chamber to determine effects of B deficiency during early vegetative growth on leaf photosynthesis, plant dry matter accumulation, photosynthetic assimilate partitioning, and other physiological parameters. Boron deficiency considerably decreased leaf net photosynthetic rate, plant height, leaf area, fruiting sites, and dry matter accumulation during squaring and fruiting. Depressed photosynthesis and plant growth (especially fruits and roots) resulted in increased fruit abscission and changes in dry matter partitioning among plant tissues. The results help explain effects of B deficiency on suppression of cotton growth and yield and provide information for improving the diagnosis of B deficiency in cotton production.     

Grapevine Growth and Physiological Responses to Iron Deficiency

ABSTRACT

Iron (Fe) deficiency is one of the major abiotic stresses affecting fruit tree crops growing in calcareous soils in the Mediterranean region. A better understanding of changes in the growth and physiological characteristics of grapevine plants during the development of Fe deficiency will help to improve Fe fertilizer management recommendations. An experiment was conducted in field conditions to determine the effects of Fe deficiency during vegetative growth on leaf photosynthesis, dry matter accumulation, pigments, and other physiological parameters. Iron deficiency considerably decreased leaf net photosynthetic rate, leaf area, and dry matter accumulation. Depressed photosynthesis and plant growth resulted in increased fruit abscission and changes in dry matter among plant tissues. The results help explain the effects of Fe deficiency on suppression of grapevine growth and yield and provide information for improving the diagnosis of Fe deficiency in grapevine production.     

Physiological responses of irrigated wheat (Triticum aestivum L.) genotypes to water stress

The recent drought in South Africa has reduced the production of both dryland and irrigated wheat. This study evaluated physiological traits of irrigated wheat genotypes in response to water stress (WS) imposed at different growth stages. A 8?×?2?×?3 [(genotypes)?×?(water treatmets; stresses and non-stressed)?×?(growth stages; tillering, flowering and grain filling)] factorial experiment based on a randomised complete block design with three replicates was conducetd. In general, the rate of photosynthesis was unaffected by WS except for genotypes LM43 at tillering and LM98 at grain filling. Stomatal conductance (SC) and transpiration rate (Tr) followed the same treand except for genotype LM35 which reduced its SC and Tr significantly at grain filling. Instantaneous waster use efficiency (IWUE) of genotype LM35 and LM57 was unaffected (p?>?0.05) by WS at tillering but at flowering stage it was affected. However, at grain filling IWUE was affected (p?<?0.05) in genotypes LM35, ML57, LM79 and LM 98. The relative water content was unaffected at tillering except for LM35 and LM47 genotypes whereas at flowering LM57, ML79, LM83 and LM98 were affected. These results indicate some degree of drought tolerance of these genotypes at different growth stages.     

Soil and Plant Responses to the Application of Ascophyllum nodosum Extract to No-Till Wheat (Triticum aestivum L.)

A field trial consisting of four granule formulation doses and five liquid formulation sprays of a seaweed extract from Ascophyllum nodosum commercially known as Biovita, along with the recommended dose of nitrogen (N)–phosphorus (P)–potassium (K), was conducted during 2008 and 2009 in BHU, Varanasi, India, to evaluate its effect on wheat (var. HUW 468) under a no-tillage system. Among the granule doses, the 10 kg ha^?1 basal application and the two liquid sprays of 500 cm³ ha^?1 each at 25 and 50 days after sowing significantly improved the performance of wheat. On an average under these two treatments, the greatest grain and straw yields were observed were 3454.5, 3446.5 and 5187.5, 5220.0 kg ha^?1, respectively. The greatest protein content was found when further high doses of extract were applied. A faster decomposition of the paddy residue was also observed as indicated by an earlier decline in carbon (C)/N ratio of the soil in the treated plots.     

Foliar, Physiologial and Growth Responses of Four Maple Species Exposed to Ozone

In order to restore the forest ecosystem in the vicinity of an industrial park, Ulsan, southeastern Korea, which has been heavily acidified by air pollution, a preliminary experiment by applying tolerant plants selected through several procedures, and dolomite and sewage sludge as soil ameliorators was carried out. Furthermore, a restoration based on the results was executed and the effects were evaluated based on the creation of safe sites, where new species can establish: regeneration of the forest with species similar in composition to the natural vegetation of native forests that are distant from the industrial park; increase in species diversity. In a preliminary study, the necessity of soil amelioration was diagnosed. Quercus serrata, Alnus firma and Ligustrum japonicum, which represent for tree, subtree, and shrub layers of vegetation in this region, were used as sample plants. Dolomite, sludge, and a mixture of both materials were applied as soil ameliorators. Bare ground (BG), and two grasslands dominated by forbs (GF) and grass (GG), respectively were designated as experimental plots based on a vegetation map of the corresponding area. BG and GF plots, which have lower organic matter contents, increased the growth of sample plants in response to soil amelioration, whereas that with higher contents, GG plot, did not show this response. The result suggests that necessity of soil amelioration depends on site quality. The effects of soil amelioration depended also on the sample plants. This difference is due to an ecological property of A. firma, which can fix atmospheric nitrogen through a symbiotic relationship with actinomycetic fungi. This result implies that this alder could be used as a substitute for soil ameliorators in restoration plan of this area. The height and standing crop of undergrowth, which forms dense grass mat and thereby impedes establishment of new plants, decreased in the restored stands. Such a decrease in the height and biomass of undergrowth could be recognized as providing safe sites, in which the other plants can invade, by removing the dense carpet formed by Miscanthus sinensis. The results of stand ordination showed a progression of the former bare grounds to either M. sinensis (GG) or Pueraria thunbergiana (GF) stands, suggesting a natural recovery through succession toward the stands dominated by both plants. But the change was not progressed beyond the grassland stage. Active restoration practice, which was carried out by applying tolerant plants, however, led to a change toward species composition similar to the natural vegetation before devastation. Furthermore, restored stands reflected the restoration effect by showing higher diversity than the stands in the degraded state. These results showed that the restorative treatment carried out by introducing tolerant plants functioned toward increasing both biological integrity and ecological stability and thereby could meet the restoration goal.     

镉胁迫下小麦根系的生理生态变化

本文通过水培和砂培两种方法 ,研究了镉胁迫下小麦 (TriticumaestivmL .)根系的生理生态变化。通过研究镉对小麦根系生长发育状况 ,根系活力 ,根系对矿质元素的吸收 ,探讨镉胁迫下植物根系的生理生态效应。研究结果表明 :镉影响根系的长度、生物量、体积和根系活力。Cd2 + 在低浓度 (处理浓度低于 5mg/L)作用下 ,随处理浓度的升高 ,刺激小麦根系的长度、生物量、体积相应地升高 ;当处理浓度高于相应浓度时 ,根长度、生物量、体积相应随浓度升高而降低。镉胁迫下根系活力受到抑制。水培和砂培中 ,镉对根系的影响趋势一致 ,但是影响幅度有差异。砂培好于水培。镉影响小麦根对矿质元素的吸收 ,Ca、Cu、Fe、K、Mg、Mn、Na、Zn吸收情况不太一致。Ca、Cu、Fe、Mg、Mn、Na的吸收量随Cd2 + 浓度升高而增加 ,K、Zn的吸收量随Cd2 + 浓度升高而减少     

两种稗属牧草生长生理指标对光周期变化的响应

湖南稷子（Echinochloa frumentacea）和宁夏无芒稗（Echinochloa crusgalli）是改良盐碱土壤的优质稗属牧草。本研究通过设置昼/夜8h/16h（记为Ph8）、12h/12h（Ph12）和16h/8h（Ph16）3种不同的光周期处理,测定不同处理下两种稗属牧草的株高、叶宽、穗重、丙二醛（MDA）、可溶性蛋白、叶绿素含量、光合和叶绿素荧光参数等生长生理指标,以探究两种稗属牧草生长生理特性对光周期改变的响应规律,为优质牧草异地引种及高产栽培提供科学依据。结果表明：随着光照时间的延长,（1）湖南稷子和宁夏无芒稗的叶宽、穗鲜重、穗干重均呈“倒V”型变化趋势,而株高呈上升趋势,各处理下株高、穗鲜重和穗干重均表现为湖南稷子高于宁夏无芒稗。（2）两种稗属牧草的MDA含量呈现出“V”型变化过程。（3）可溶性蛋白含量呈“倒V”型变化过程。（4）两种稗属牧草的净光合速率、叶绿素含量、最大光化学效率（PII）及其潜在活性均呈现“倒V”型变化过程,在Ph12处理下达到最大值,且在三种光周期处理下,湖南稷子的净光合速率高于宁夏无芒稗。本研究表明,光照时长中等条件（12h）能够显著促进湖南稷子和宁夏无芒稗的叶绿素和可溶性蛋白合成,增强光合作用,提高产量,且对湖南稷子产量的促进作用高于宁夏无芒稗。     

Determination of Heavy-Metal Concentration with Chlorophyll Contents of Wheat (Triticum aestivum) Exposed to Municipal Sewage Sludge Doses

The present study was conducted to assess the suitability of sewage-sludge amendment in soil for Triticum aestivum (wheat) by evaluating the heavy-metal accumulation and physiological responses of plants grown at 10, 25, and 50% sewage sludge amendment rate. Sewage sludge amendment modified the physicochemical properties of soil, thus increasing the availability of heavy metals in soil and consequently greater accumulation in plant parts. The chlorophyll contents generally increased after the sewage sludge treatments. Heavy-metal accumulation in the soil after the treatments did not exceed the limits for land application of sewage sludge recommended by the U.S. Environmental Protection Agency. Recycling sewage sludge as fertilizer will generate economical profits. However, the use of sewage sludge amendment in the soil for growing wheat may not be a good option due to risk of contamination of some heavy metals.     

Growth,morphological and yield responses of irrigated wheat (Triticum aestivum L.) genotypes to water stress

Water shortages is a major constraint in wheat production in South Africa. It is important therefore to assist irrigated wheat farmers to identify water stress tolerant growth stages in irrigated wheat genotypes. This study evaluated new wheat genotypes for water stress at different growth stages. An 8 (genotypes) × 2 (water treatments) × 3 (growth stages) factorial experiment was laid out in a randomised complete block design with three replicates. The results indicated that plant height was not affected (p > .05) by water stress at tillering and grain filling. Water stress imposed at the tillering stage reduced the number of fertile tillers (p < .05) in susceptible genotypes while at the flowering and grain filling stages all genotypes were tolerant (p > .05). Aboveground biomass was only affected (p < .05) by water stress imposed at the tillering stage. Water stress reduced grain yield on the genotypes where stress was imposed at the tillering stage (p < .05); whereas when stress was imposed at flowering and grain filling the grain yield was not reduced (p > .05). This study provided evidence to suggest that most genotypes were tolerant to water stress at the flowering and grain filling stages.     

2种雀稗属牧草对低磷胁迫的生长、生理应激响应

为比较宽叶雀稗(Paspalum wettsteinii)和巴哈雀稗(Paspalum notatum)适应低磷胁迫的能力,揭示其对低磷胁迫的形态及生理响应机理,试验以石英砂为基质,定期浇灌200μmol·L-1(常磷)、20μmol·L-1、2 μmol· L-1的Hoagland营养液模拟低磷胁迫处理,分别在磷处理...     

Physiological and Growth Responses of Transplants of the Moss Pseudoscleropodium purum to Atmospheric Pollutants

Chlorine is the most commonly used chemical for water and wastewater disinfection worldwide, and it reacts with both ammonia and dissolved organic nitrogen. Using the salicylate spectrophotometric method, effects of glycine on the classic breakpoint chlorination are studied using glycine as a surrogate for dissolved organic nitrogen. The results show that the shape of the breakpoint chlorination curve with glycine was analogous to that of water without glycine. Increasing the glycine concentration moves the chlorination breakpoint curve to the right, demonstrating that more chlorine must be added to replace the chlorine consumed by glycine and yield the desired residual active chlorine concentration. At the peak of the chlorination breakpoint curve, both NH₂Cl and mono-chlorinated organic chloramine reach their maximum. The Cl₂/N ratio of the peak is linearly related to the glycine concentration, and our calculations indicate that the maximum of mono-chlorinated organic chloramine formation by glycine chlorination occurs at a stoichiometric ratio of 1:1; the same as that for chlorinating ammonia to NH₂Cl. The distribution of NH₂Cl and organic chloramines is controlled by [Gly]/[NH₃-N]. At the breakpoint, ammonia and glycine are completely oxidized by chlorine, which leads to chlorine depletion. The stoichiometric ratio for the complete oxidation of glycine was 3:1, larger than that for complete oxidation of ammonia (2:1). For the different stoichiometric ratio in reaction of oxidation of ammonia and glycine, the sum of ammonia and glycine cannot be used as a chlorine dosage control parameter. The chlorine control method involving ammonia and glycine for chlorine and chloramination process is established.     

Growth Responses,Metal Accumulation and Phytoremoval Capability in Amaranthus Plants Exposed to Nickel Under Hydroponics

Surfactant-enhanced solubilization and subsequent biodegradation of phenanthrene and pyrene from aqueous solutions by Arthrobacter strain Sphe3 was investigated. The results show that growth of Arthrobacter strain Sphe3 was increased upon increase in concentration of Tween 20 and Tween 80. Inhibition of bacterial growth was observed with increasing Triton X-100 concentrations, whereas sodium dodecyl sulfate (SDS) totally inhibited this bacterial growth. Phenanthrene and pyrene solubilization was enhanced in the presence of surfactants and found to be linearly proportional to their concentrations, above the critical micelle concentration (CMC). In addition, Tween 20 and Tween 80 enhanced the biodegradation of phenanthrene and pyrene. The high correlation coefficient (R ²) values obtained at all the concentrations studied, suggest that biodegradation kinetics of both phenanthrene and pyrene in the presence of Tween 20 and Tween 80 follow first-order kinetic equation model. Experimental results suggest that Tween 20 and Tween 80 may have great potential for applications in bioremediation of these polycyclic aromatic hydrocarbon (PAH) compounds using Arthrobacter strain Sphe3.     

Growth stage-based response of wheat (Triticum aestivum L.) to kinetin under water-deficit environment: pigments and gas exchange attributes

Plant growth regulator, kinetin, is known to modulate the key physiological processes under abiotic stresses in different crops. However, kinetin-mediated response at different growth stages of crop plants is lagging behind. Therefore, a field experiment was conducted to appraise the potential role of exogenously applied kinetin in alleviating the effects of water scarcity on wheat. Three levels of kinetin (0, 75, and 150 mg/L) were used either as seed treatment or foliar spray at the vegetative or the post-anthesis stage. Water deficit markedly reduced shoot fresh mass, plant chlorophyll level, flag leaf photosynthesis, stomatal conductance, and transpiration rate. Degradation of chlorophyll a was greater in plants subjected to post-anthesis water-deficit conditions. However, plants growing under continuous water-deficit conditions had significantly lower concentration of chlorophyll b than those treated with water scarcity at the post-anthesis stage or receiving normal irrigation. Inhibited photosynthesis of wheat in response to post-anthesis water-deficit conditions was largely due to non-stomatal factors. In contrast, stomatal factors were the main constraints for photosynthesis in plants growing under continuous scarcity of water. Plants subjected to continuous water starvation had markedly lower grain yield than those subjected to water-deficit conditions at post-anthesis stage. Application of kinetin before seed sowing or at the post-anthesis stage significantly reduced the negative effects of drought on flag leaf chlorophyll and stomatal conductance. Lower level of kinetin (75 mg/L) was found to be more effective in mitigating the inhibitory effects of water shortage on photosynthesis and growth, and improved grain yield under water scarcity.     

Toxic reactivity of wheat (Triticum aestivum) plants to herbicide isoproturon

The herbicide isoproturon is widely used for controlling weed/grass in agricultural practice. However, the side effect of isoproturon as contaminants on crops is unknown. In this study, we investigated isoproturon-induced oxidative stress in wheat ( Triticum aestivum). The plants were grown in soils with isoproturon at 0-20 mg/kg and showed negative biological responses. The growth of wheat seedlings with isoproturon was inhibited. Chlorophyll content significantly decreased at the low concentration of isoproturon (2 mg/kg), suggesting that chlorophyll was rather sensitive to isoproturon exposure. The level of thiobarbituric acid reactive substances (TBARS), an indicator of cellular peroxidation, showed an increase, indicating oxidative damage to plants. The isoproturon-induced oxidative stress resulted in a substantial change in activities of the majority of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). Activities of the antioxidant enzymes showed a general increase at low isoproturon concentrations and a decrease at high isoproturon concentrations. Activities of CAT in leaves showed progressive suppression under the isoproturon exposure. Analysis of nondenaturing polyacrylamide gel electrophoresis (PAGE) confirmed these results. We also tested the activity of glutathione S-transferase (GST) and observed the activity stimulated by isoproturon at 2-10 mg/kg.     

小麦黄绿近等基因系主要生理特性及叶绿体形态结构的比较

探索小麦(Triticum aestivum)叶绿素合成及叶绿体形成发育的遗传和生理机制对小麦高光效育种具有重要意义.为研究叶色变异形成的生理机制及其对叶绿体形成发育的影响,本研究以新创制的3个黄绿小麦近等基因系(near-isogenic lines,NILs)(黄化系1-20YY、黄绿系1-20YG和绿色系1-20GG)为材料,研究不同发育时期的叶片可溶性物质含量和抗氧化酶系统活力等性状,并对其叶绿体形态结构进行了比较分析.结果表明,叶色黄化对叶片可溶性糖含量和可溶性蛋白质含量的影响远大于其对游离脯氨酸含量的影响,除苗期黄化系1-20YY的可溶性糖含量和可溶性蛋白质含量显著低于黄绿系1-20YG和绿色系1-20GG(P＜0.05),各发育期黄绿系1-20YG的可溶性糖含量和可溶性蛋白质含量与绿色系1-20GG的差异不显著.同时,叶色黄化对叶片抗氧化酶系统的活性有一定的影响,其中对过氧化物酶(peroxidase,POD)活性的影响大于其对超氧化物歧化酶(superoxide dismutase,SOD)和过氧化氢酶(hydrogen peroxidase,CAT)活性的影响.从3个NILs的叶绿体形态结构比较分析结果可以看出,黄化系1-20YY叶绿体多呈不规则状且分布趋向叶肉细胞中央,其基质类囊体和基粒类囊体不发达且联结不紧密,与绿色系1-20GG叶绿体形态结构差异明显;而黄绿系1-20YG叶绿体形态与绿色系1-20GG有差异,多呈近球形,但其超微结构与1-20GG系基本一致,基质类囊体和基粒类囊体较发达且联结较为紧密.研究结果为进一步探讨叶色黄化的生物学机制提供了基础资料.     

燕麦对盐碱胁迫的生理响应

通过分析渗透调节物质脯氨酸和可溶性糖含量的变化,利用洗叶技术分析燕麦叶片洗脱物的离子组成,以及对气孔周围结晶的X—ray分析,并利用扫描电子显微镜观察燕麦叶片的表面结构,研究了燕麦对盐碱胁迫的生理响应。结果表明,在盐碱胁迫下,燕麦叶片中脯氨酸和可溶性糖含量增加;经过混合盐处理后,叶片洗脱物主要由Clˉ、Na^＋、K^＋、HCO3ˉ、Mg^2＋和Ca^2＋等离子组成,不含CO3^2-和SO4^2-,其中Clˉ、Na^＋、K^＋含量极显著高于对照,HCO3ˉ、Mg^2＋含量显著高于对照,Ca^2＋含量与对照差异不显著;通过扫描电镜观察叶片表面,发现气孔周围分布着盐结晶,表明燕麦通过气孔排盐适应盐碱胁迫。     

Performance of wheat (Triticum aestivum) to incorporation of organic manure and bioinoculants

A field experiment was conducted to evaluate the effect of integrated use of farmyard manure and bio-inoculants on wheat productivity for two years in succession. Increasing levels of farmyard manure (FYM) up to 15 t ha^?1 significantly (p ≤ 0.05) improved the dry matter accumulation, effective tillers per m row length, and grain weight per spike in both the years. Application of 15 t ha^?1 FYM caused significant increase in spikelets per spike and grains per spike over control and 5 t ha^?1 during two consecutive years. Inoculation with MSX-9 strain of Azotobacter chroococcum produced significantly higher dry matter accumulation to 25.63, 13.33, 7.78 and 23.66, 8.35, 5.50% over uninoculation, Azospirillum brasilense (SP-7) and Azospirillum lipoferum (A-5) at harvest during 1999–2000 and 2000–2001, respectively. Incorporation of 15 t ha^?1 FYM significantly (p ≤ 0.05) enhanced grain and straw yield to 62.45 and 38.05%; 56.66 and 36.28%; 59.42 and 37.52% over control in 1999–2000, 2000–2001 and pooled analysis, respectively. The grain and straw yield of wheat significantly (p ≤ 0.05) enhanced to 26.51, 10.10, 7.54 and 14.45, 5.77, 3.16% through A. chroococcum (MSX-9), A. brasilense (SP-7) and A. lipoferum (A-5) over uninoculation.     

Differential Responses of Jatropha Species on Growth and Physiological Parameters to Salinity Stress at Seedling Plant Stage

The effect of salinity on Jatropha curcas (J. curcas), native to nonsaline humid areas, and Jatropha cinerea (J. cinerea), native to saline dry areas, was compared to assess the potential of cultivating J. curcas for biodiesel production in saline soils that are not suitable for food production. Growth parameters, water relations, chlorophyll content, and stomatal conductance of both species under salinity were measured. Dry weight of both species decreased with increasing concentrations of salt; however, both species can grow at salinities up to ?100 mM sodium chloride (NaCl). Decline of stomatal conductance was one of the main factors causing reduction in growth of Jatropha spp. Growth of J. curcas was inhibited more than that of J. cinerea by decline in growth parameters and chlorophyll content, but J. curcas shows sufficient hardiness to be cultivated in moderately saline soils with more favorable water relations.     

Effects of Salinity and Pistachio Waste Application on Growth and Physiological Responses of Pistachio Seedlings

Low organic matter and high salinity are widespread throughout all pistachio (Pistacia vera L.) growing areas of Iran. The objective of this study was conducted to investigate effect of pistachio waste (PW), salinity, and their interaction on growth and chemical composition of pistachio seedlings. The experiment was carried out based on factorial and completely randomized design (CRD) with four replications. The treatments contained salinity in three levels [0, 1000, and 2000 mg sodium chloride (NaCl) kg^?1 soil] and PW in three levels (0, 3, and 6%). The results indicated that salinity application decreased leaf, stem, and root dry weights; leaf area; and length of stem, while this effect diminished with 3% PW application. Application of PW at the rate of 6% significantly reduced these parameters and accelerated effect of salinity levels. Leaf, stem, and root potassium (K) and phosphorus (P) concentrations were decreased by salinity application, while leaf, stem, and root sodium (Na) concentrations was increased. However, PW application increased these nutrient concentrations in the leaves, stem, and root, but significantly diminished the effect of salinity. The results showed that proline accumulation and reducing sugar content in the leaves were increased by salinity, PW, and their combination application. The results suggest that application of PW, especially at rate of 3%, can reduce some adverse effects of salinity on growth and chemical composition of pistachio seedlings.     

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.