Effects of leaf age,nitrogen nutrition and photon flux density on the distribution of nitrogen among leaves of a vine (Ipomoea tricolor Cav.) grown horizontally to avoid mutual shading of leaves

Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the distribution of nitrogen among leaves were investigated in a vine, Ipomoea tricolor Cav., which had been grown horizontally so as to avoid mutual shading of leaves. The nitrogen content was highest in newly developed young leaves and decreased with age of leaves in plants grown at low nitrate concentrations and with all leaves exposed to full sunlight. Thus, a distinct gradient of leaf nitrogen content was formed along the gradient of leaf age. However, no gradient of leaf nitrogen content was formed in plants grown at a high nitrate concentration. Effects of PFD on the distribution of nitrogen were examined by shading leaves in a manner that simulated changes in the light gradient of an erect herbaceous canopy (i.e., where old leaves were placed under increasingly darker conditions with growth of the canopy). This canopy-type shading steepened the gradient of leaf nitrogen content in plants grown at a low nitrogen supply, and created a gradient in plants grown at high concentrations of nitrate. The steeper the gradient of PFD, the larger the gradient of leaf nitrogen that was formed. When the gradient of shading was inverted, that is, younger leaves were subjected to increasingly heavier shade, while keeping the oldest leaves exposed to full sunlight, an inverted gradient of leaf nitrogen content was formed at high nitrate concentrations. The gradient of leaf nitrogen content generated either by advance of leaf age at low nitrogen availability, or by canopy-type shading, was comparable to those reported for the canopies of erect herbaceous plants. It is concluded that both leaf age and PFD have potential to cause the non-uniform distribution of leaf nitrogen. It is also shown that the contribution of leaf age increases with the decrease in nitrogen nutrition level.     

Oxalate Accumulation as Regulated by Nitrogen Forms and Its Relationship to Photosynthesis in Rice (Oryza sativa L.)

Four-leaf rice seedlings (Oryza sativa L.), which had been cultivated in Kimura B complete nutrient solution, were treated with two nitrogen forms by replacing the nitrogen element in the complete solution with sole nitrate or ammonium (2.86 mmol/L). Nitrate-N nutrition tended to increase oxalate content in all parts of the plant, including the leaves, stems, roots, and root exudates, whereas ammonium had the opposite effect. Consequently, marked differences in oxalate content were observed between the two treatments throughout the time tested (0--12 d), with maximal differences of approximately 12-fold at 6 d after treatment. Photosynthetic/respiratory parameters were examined over time simultaneously with changes in oxalate content. Net photosynthetic rate, chlorophyll fluorescence parameters (i.e. maximal photochemical efficiency (Fv/Fm) and photochemical quantum yields of photosystem (PS)Ⅱ (φ PSⅡ)), and respiratory rate were not significantly different between plants treated with the two nitrogen forms, although ammonium-fed plants had apparently higher leaf chlorophyll content than nitrate-fed plants. Leaf glucose content was altered little, but the content of fructose, sucrose, and total soluble sugar was significantly higher in the leaves of ammonium-fed plants than nitrate-fed plants, The results indicate that nitrate/ammonium may serve as efficient regulators of oxalate accumulation owing to regulation of metabolism in rice leaves rather than oxalate downward transfer and root excretion, and that photosynthetic metabolism is not directly correlated with the regulation of oxalate accumulation in rice plants.     

Oxalate Accumulation as Regulated by Nitrogen Forms and Its Relationship to Photosynthesis in Rice （Oryza sativa L.）

Four-leaf rice seedlings (Oryza sativa L.), which had been cultivated in Kimura B complete nutrient solution, were treated with two nitrogen forms by replacing the nitrogen element in the complete solution with sole nitrate or ammonium (2.86 mmol/L). Nitrate-N nutrition tended to increase oxalate content in all parts of the plant, including the leaves, stems, roots, and root exudates, whereas ammonium had the opposite effect. Consequently, marked differences in oxalate content were observed between the two treatments throughout the time tested (0-12 d), with maximal differences of approximately 12-fold at 6d after treatment. Photosynthetic/respiratory parameters were examined over time simultaneously with changes in oxalate content. Net photosynthetic rate, chlorophyll fluorescence parameters (i.e. maximal photochemical efficiency (Fv/Fm) and photochemical quantum yields of photosystem (PS)II (ΦPSⅡ)), and respiratory rate were not significantly different between plants treated with the two nitrogen forms, although ammonium-fed plants had apparently higher leaf chlorophyll content than nitrate-fed plants. Leaf glucose content was altered little, but the content of fructose, sucrose, and total soluble sugar was significantly higher in the leaves of ammonium-fed plants than nitrate-fed plants. The results indicate that nitrate/ammonium may serve as efficient regulators of oxalate accumulation owing to regulation of metabolism in rice leaves rather than oxalate downward transfer and root excretion, and that photosynthetic metabolism is not directly correlated with the regulation of oxalate accumulation in rice plants.     

Role of carboxylate in the nitrogen metabolism of plants from different natural habitats

The carboxylate and organic nitrogen content was studied in plants from 5 different habitats in Austria in order to determine both the form of nitrogen utilized by the plants and the preferential site of nitrate reduction within the plant, if nitrate is the predominant nitrogen form and is reduced mainly in the shoots, the ratio between carboxylate and organic nitrogen should be about 1. Ratios less then 1 would indicate either participation of root reduction, transport of carboxylate from shoots to roots or ammonium/ammonia nutrition.
In the plants investigated, the lowest ratios were found in a bog, where ammonium is usually the predominant nitrogen form. Species from a xerophytic and a nutrient-rich habitat, as well as from a carr, showed higher organic nitrogen values. Highest contents of carboxylate and organic nitrogen were found in halophytes from the area around the take Neusiedlersee. As additional bicarbonate uptake is known to occur at these sites, accumulation of carboxylate here may not he related to nitrate reduction alone.
The relationship between the carboxylate/organic nitrogen ratio and N indicator values revealed the same pattern of differences in the plant species, indicating that the determination of these values could give information of ecophysiological characteristics of, and differences between, plant species from various habitats.     

Does the Response of Perennial Ryegrass to Elevated CO2 Concentration Depend on the Form of the Supplied Nitrogen?

To test whether different nitrogen form (nitrate or ammonium) in substrate can alter the response to elevated partial pressure of CO₂ (pCO₂) plants of perennial ryegrass (Lolium perenne cv. Bastion) were grown from seeds in growth chambers under pCO₂ of either 35 Pa (ambient, CA) or 70 Pa (elevated, CE) in a hydroponic system (with nutrient and pH control) for 24 d. Nitrogen was supplied as ammonium, nitrate or an equimolar mixture of both N forms. Under CE plants grew faster than their counterparts under CA during the first 14 d but after 23 d of cultivation stimulation disappeared. Despite the strong positive effect of mixed forms of N on plant growth, the beneficial effect of CE was similar to that in the other two N treatments. However, the almost alike final growth response to CE had different underlying mechanisms in different N treatments. Plants supplied with nitrate as a sole source of nitrogen had lower leaf mass ratio but much higher specific leaf area compared to plants supplied with ammonium. The decrease in the content of leaf organic N (per unit of structural dry mass) under CE was found only in leaves of plants supplied with ammonium on day 14. Nevertheless, the available form of N evidently contributes to changes of leaf N content under CE. The high levels of N and non-structural saccharides in plants supplied with ammonium at CE suggest that the CO₂ response of these plants was controlled by factors other than amount of available carbon and nitrogen.     

Some effects of nitrate abundance and starvation on metabolism and accumulation of nitrogen in barley (Hordeum vulgare L. cv Sonja)

Nitrate and nitrite reductases were both induced by adding three concentrations of nitrate to the nutrient supply of nitrate-starved barley seedlings. Enzyme induction was not proportional to the amount of nitrate introduced. Glutamine synthetase also increased above a high endogenous activity but the increase did not differ significantly between any of the three nitrate treatments. Nitrate accumulated rapidly in leaves of plants given 4.0 mM or 0.5 mM nitrate but not with 0.1 mM nitrate. In all treatments, amino acids in leaves increased for 2 d, chiefly attributable to glutamine, then declined. Transferring plants from the three nitrate treatments to nitrate-free nutrient produced an immediate decline in nitrate reductase but nitrite reductase continued to increase for 2 d, before declining. Glutamine-synthetase activity was not affected by withdrawal of nitrate, nor did nitrate withdrawal retard plant growth during the 9-d period of the experiment. The disparity between accumulated nitrate and nitrate-reducing capacity and the rapid decrease in leaf nitrate when nutrient nitrate supply was removed, indicated the presence of a nitrate-storage pool that could be called upon to maintain amino-acid production in times of nitrogen starvation.Abbreviations GS glutamine synthetase - NR nitrate reductase - NiR nitrite reductase     

Interaction of sulfur and nitrogen nutrition in tobacco (Nicotiana tabacum) plants: significance of nitrogen source and root nitrate reductase

Abstract: The significance of root nitrate reductase for sulfur assimilation was studied in tobacco (Nicotiana tabacum) plants. For this purpose, uptake, assimilation, and long-distance transport of sulfur were compared between wild-type tobacco and transformants lacking root nitrate reductase, cultivated either with nitrate or with ammonium nitrate. A recently developed empirical model of plant internal nitrogen cycling was adapted to sulfur and applied to characterise whole plant sulfur relations in wild-type tobacco and the transformant. Both transformation and nitrogen nutrition strongly affected sulfur pools and sulfur fluxes. Transformation decreased the rate of sulfate uptake in nitrate-grown plants and root sulfate and total sulfur contents in root biomass, irrespective of N nutrition. Nevertheless, glutathione levels were enhanced in the roots of transformed plants. This may be a consequence of enhanced APR activity in the leaves that also resulted in enhanced organic sulfur content in the leaves of the tranformants. The lack of nitrate reductase in the roots in the transformants caused regulatory changes in sulfur metabolism that resembled those observed under nitrogen deficiency. Nitrate nutrition reduced total sulfur content and all the major fractions analysed in the leaves, but not in the roots, compared to ammonium nitrate supply. The enhanced organic sulfur and glutathione levels in ammonium nitrate-fed plants corresponded well to elevated APR activity. But foliar sulfate contents also increased due to decreased re-allocation of sulfate into the phloem of ammonium nitrate-fed plants. Further studies will elucidate whether this decrease is achieved by downregulation of a specific sulfate transporter in vascular tissues.     

Growth pattern and carbon allocation to volatile leaf terpenes under nitrogen-limiting conditions in Heterotheca subaxillaris (Asteraceae)

Summary Rosettes of Heterotheca subaxillaris were grown at four levels of nitrate. Individual leaf volatile mono- and sesquiterpene content, leaf nitrogen content, and root and shoot dry weight were measured on individual leaves every two weeks for 18 weeks. Rosettes with the highest nitrate availability had 2.2-fold greater leaf nitrogen levels compared to plants with the lowest availability. As nitrate availability became increasingly limited, carbon allocation to both volatile leaf terpenes and root growht increased. Leaf mono- and sesquiterpene content was greatest in the young leaves of individuals growing at the lowest nitrate availability conditions. Higher levels of carbon-based herbivore-deterring chemicals in nitrate-limited plants may increase net productivity through retention of nitrogen that would otherwise be lost to herbivory.     

The response ofPlantago lanceolata L. andP. major L. spp.major to nitrate depletion

To study aspects of the ecology of grassland species, in a comparative experiment, plants ofP. lanceolata andP. major were grown in pots in a greenhouse, and subjected to a gradual nitrate depletion for several weeks. Control plants were weekly supplied with nitrate. Growth, leaf appearance and disappearance, concentrations of cations and inorganic anions, soluble and insoluble reduced nitrogen concentrations,in vivo nitrate reductase activity (NRA) and the concentration of non-structural carbohydrates in several parts of the plants were followed. Depletion of nitrate caused a reduction of shoot growth, both in biomass and number of leaves. Withering of leaves increased. Accumulation of root dry matter was little (P. lanceolata), or not (P. major) affected. The concentration of reduced nitrogen in all tissues also decreased, both that of the soluble and that of the insoluble fraction. As a result, nitrogen use efficiency (NUE, g dry matter produced per mmol N incorporated) increased by nitrate depletion. NRA was higher in the roots than in the leaves, and decreased with increasing nitrate depletion. In control plants, nitrate became also limiting. This resulted in decreasing nitrate concentrations in leaves and roots. In the leaves, the decrease in nitrate concentration was preceded by a decrease in NRA. The decrease of the nitrate concentration was parallelled by an increase in the concentration of soluble sugar. No major differences in the response towards nitrate depletion were observed between the two species. Grassland Species Research Group, publication no. 129     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 2. The Partitioning of Dry Matter, Nitrogen and Nitrate

Potatoes (Solanum tuberosum L.) were planted in pots in a temperature-controlledglasshouse The treatments consisted of three levels of nitrogensupply, ie 25, 8 and 16 g N per pot (treatments called N1, N2and N3) The accumulation rates of dry matter and nitrogen showedan upper limit of response to nitrogen supply, N3 plants continuedto accumulate dry matter and N at a constant rate for a longerperiod of time than N2 and N1 plants The uptake of nitrogenslowed earlier in time than the rate of dry matter accumulationin all treatments. The proportion of the dry matter in tubersof mature plants was not affected by nitrogen treatment, butthe start of tuber bulking was delayed in the N3 plants Thefinal proportion of total plant nitrogen in the tubers was similarfor all treatments The concentration of nitrogen in the drymatter of mature plants increased with the level of N supplyMaximum haulm weight increased with the level of N supply Apicallateral branches of the first and second order made up largerproportions of the total haulm dry weight and total leaf areaas more nitrogen was supplied. Yet, the distribution of drymatter over stems and leaves was not different between nitrogentreatments Stems were the most responsive to N treatment interms of N concentrations In each of the component organs (stems, leaves, tubers) theconcentration of nitrogen declined with time Fairly strong associationswere observed between the concentrations of N in component organs.The concentration of nitrate in leaves usually increased initiallywith leaf age, peaked and declined. A substantial part of thedifferences between treatments in the concentrations of N inleaf dry matter were attributable to differences in nitrateconcentration Nitrate in stems and tubers fell virtually belowthe limit of detection at total nitrogen concentrations of lessthan 1%, but increased in proportion to total N above that threshold,especially in stems Potato, Solanum tuberosum L, dry matter production, dry matter distribution, nitrogen nutrition, nitrogen distribution, nitrogen concentration     

Decomposition of leaves of huisache (Acacia tortuoso) and mesquite (Prosopis spp) in soil of the central highlands of Mexico

In the central highlands of Mexico, mesquite (Prosopis spp) and huisache (Acacia tortuoso), N₂ fixing trees or shrubs, dominate the vegetation and are used in an alley cropping system to prevent erosion and restore soil fertility. We investigated how much the leaves of both trees contribute to dynamics of carbon (C) and nitrogen (N) in soil by adding leaves of both species to soil sampled under the canopy of mesquite and huisache, outside their canopy and from fields cultivated with maize at three different sites and monitoring microbial biomass C, production of carbon dioxide (CO₂), and dynamics of inorganic N (ammonium and nitrate) in an aerobic incubation. The soluble fraction and N content of the mesquite leaves were larger than in the huisache leaves, but lignin and polyphenol content were lower. Evolution of CO₂ increased 2.7-times when mesquite and 2.4-times when huisache leaves were added to soil. During all stages of decomposition and in all treatments, C mineralization of leaves from mesquite was greater than from huisache leaves. Mesquite leaves induced an increase in mineral N of 25.6 mg N kg^–1 soil after 56 days and those of huisache 9.8 mg N kg^–1. Twenty-six percent of N from mesquite leaves and 11% of huisache was mineralized, if no priming effect was considered. Nitrogen release from the leaves was greater when the soil organic matter content was lower. It was found that soil under the canopy of mesquite and huisache effectively accumulated organic material, micro-organisms and valuable nutrients. In an alley cropping system huisache might be a better choice than mesquite as huisache grows faster than mesquite and sheds its leaves twice a year while mesquite only once, although the amount of N mineralized was larger from mesquite leaves than from those of huisache.     

The use of different soil nitrogen sources by young Norway spruce plants

 Three-year-old Norway spruce trees were planted into a low-nitrogen mineral forest soil and supplied either with two different levels of mineral nitrogen (NH₄NO₃) or with a slow-release form of organic nitrogen (keratin). Supply of mineral nitrogen increased the concentrations of ammonium and nitrate in the soil solution and in CaCl₂-extracts of the rhizosphere and bulk soil. In the soil solution, in all treatments nitrate concentrations were higher than ammonium concentrations, while in the soil extracts ammonium concentrations were often higher than nitrate concentrations. After 7 months of growth, ¹⁵N labelled ammonium or nitrate was added to the soil. Plants were harvested 2 weeks later. Keratin supply to the soil did not affect growth and nitrogen accumulation of the trees. In contrast, supply of mineral nitrogen increased shoot growth and increased the ratio of above-ground to below-ground growth. The proportion of needle biomass to total above-ground biomass was not increased by mineral N supply. The atom-% ¹⁵N was higher in younger needles than in older needles, and in younger needles higher in plants supplied with ¹⁵N-nitrate than in plants supplied with ¹⁵N-ammonium. The present data show that young Norway spruce plants take up nitrate even under conditions of high plant internal N levels. Received: 1 April 1998 / Accepted: 9 October 1998     

The effect of nitrogen fertilization and rust fungus infection, singly and combined, on the leaf chemical composition of Rumex obtusifolius

1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusifolius growing in a range of nutrient conditions and also on plants infected with the foliar fungus Uromyces rumicis . In a controlled environment, we investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations, with or without infection, on leaf nutritional quality.
2. Increasing nitrate fertilization increased leaf oxalate, total nitrogen and nitrate concentrations and water content, and decreased total non-structural carbohydrate (NSC) concentrations. Increasing ammonium fertilization increased leaf nitrogen concentration and water content, decreased nitrate and NSC concentrations, and had no effect on oxalate concentrations.
3. Infection produced a mainly additive effect to fertilization, increasing NSC and oxalate, and decreasing nitrate and nitrogen concentration in whole plants fed nitrate, and increasing nitrate and NSC in whole plants fed ammonium.
4. Young leaves on infected plants remained uninfected and had greater nitrogen and NSC concentrations, and lower oxalate and nitrate concentrations, than infected leaves on the same plant.
5. These results are discussed in relation to changes in C:N and NSC:organic nitrogen ratios, the effect of nitrate and oxalate, and the known feeding and oviposition preferences of the beetle. The results suggest that there is an optimum nitrogen fertilization level for G. viridula development.     

氮素营养对苗期菘蓝叶中硝酸还原酶活性与矿质元素吸收的影响

采用正交试验设计,研究铵态氮、硝态氮和酰胺态氮3种氮素形态及其不同浓度配比对苗期菘蓝的单株干重、叶内的硝酸还原酶活性及矿质元素吸收的影响。结果显示:(1)影响苗期菘蓝单株干重的氮素形态依次为酰胺态氮>铵态氮>硝态氮。(2)不同氮素形态对叶片硝酸还原酶活性影响有差异,铵态氮影响最大,其次是硝态氮和酰胺态氮。(3)不同形态氮素配合施用后均能促进P、K、Ca、Mg、Cd、Mn、Cr、Sr 8种元素的吸收,但不利于Ni和Fe的吸收;元素吸收受铵态氮影响最大的矿质元素有K、Ba、Se、Ni、B、Si、Fe 7种元素,受硝态氮影响最大的元素有P、Cd、Ti、Al、Cu 5种元素,受酰胺态氮影响最大的元素有Na、Ca、Mg、Zn、Mo、Mn、Cr、Sr 8种元素。研究表明,不同形态氮素对苗期菘蓝吸收矿质元素的影响存在很大的差异,应注重酰胺态氮与无机的铵态氮、硝态氮的配合施用;适宜氮素形态及其配比能提高叶中硝酸还原酶的活性并促进矿质元素的吸收,从而有效地促进菘蓝的生长。     

Oxalate accumulation and regulation is independent of glycolate oxidase in rice leaves

Cellular oxalate, widely distributed in many plants, is implicated to play important roles in various functions and is also known to affect food qualities adversely in fruits and vegetables. How oxalate is regulated in plants is currently not well understood. Glycolate oxidase (GLO) has long been considered as an important player in oxalate accumulation in plants. To gain further insight into the biochemical and molecular mechanisms, the possible roles of GLO in the process were studied. Drastically different levels of oxalate could be achieved by treating rice with various nitrogen forms (nitrate versus ammonium). While nitrate stimulated oxalate accumulation, ammonium reduced its level. Such treatments resulted in similar pattern changes for some other related organic acids, such as glycolate, oxaloacetate, and malate. By feeding plants with exogenous glycolate it was possible almost completely to restore the ammonium-decreased oxalate level. Under the two treatments few differences were observed for GLO mRNA levels, protein levels, and in vitro activities. Both K(m) for glycolate/glyoxylate and K(i) for oxalate remained almost the same for GLO purified from either nitrate- or ammonium-fed leaves. A further in vivo study, with transgenic plants carrying an estradiol-inducible GLO antisense gene, showed that, while the estradiol-induced antisense expression remarkably reduced both GLO protein levels and activities, oxalate levels were not significantly altered in the estradiol-treated transgenic plants. Taken together, it is suggested that oxalate accumulation and regulation is independent of GLO in rice leaves.     

The effects of nutrients and secondary compounds of Coffea arabica on the behavior and development of Coccus viridis

Phytochemicals may modify the food quality, reduce a plant's palatability to insects, or defend against pests. This work aimed to study 1) relationships between the nitrogen and potassium levels given to plants in nutritive solutions and the foliar phytochemical concentrations, 2) the effect of nutrients and secondary compounds of Coffea arabica on the behavior of Coccus viridis, and 3) tolerance of C. arabica to losses. Deficient, normal, and excessive nitrogen and potassium fertilization treatments were used. Each treatment had two plants (one infested and one noninfested plant). The contents of phytochemicals in the infested plants' leaves and their dry matter of roots, stems, and leaves as well as the total contents in noninfested plants, were determined. The adults and nymphs of C. viridis were counted for 60 d in all treatments. It was verified that elevated nitrogen and potassium levels in the nutritional solutions led to increased of nymphs and adults of C. viridis to the coffee plants over time. Potassium and nitrogen had both direct and indirect effects on C. viridis. The direct effect was because of the increase of the nitrogen content in the leaves. The indirect effect instead was because of reductions in the caffeine and chlorogenic acid contents in the leaves. This is the first study to show relationship nutrient levels of coffee phytochemicals in response to herbivory by scale insects. Caffeine and chlorogenic acid applied on coffee leaves stimulated the locomotory activity of the green scale, thus reducing their feeding compared with untreated leaves. The elevation of caffeine and chlorogenic acid levels in coffee leaves affect this generalist insect by stimulating the locomotion of crawlers.     

An Analysis of the Response of Young Barley Seedlings to Time of Application of Nitrogen

The reasons for the sensitivity of young barley seedlings totime of application of nitrogen have been examined. It is shownthat the transfer of nitrogenous reserves from endosperm toembryo which begins at about 36 h from planting proceeds ata faster relative rate than that of dry matter as a whole. Inconsequence embryo and endosperm nitrogen contents become temporarilysimilar some 24–36 h earlier than is the case for dryweights. Addition of nitrate on day 2 does not affect ratesof transfer of endosperm reserves but leads to a significantlyhigher nitrogen content in the embryo of treated plants, particularlyin the shoots. This additional nitrogen is present as nitrateup to around day 5 when reduction of accumulated nitrate commencesin the first leaf in significant amounts. For plants up to 14 days old delay in application of nitrateleads to a lowering of total nitrogen level which is proportionalto the delay in treatment. This is so for all parts of the plantexcept the first leaf for which the evidence indicates thatlevels of total and organic nitrogen and of accumulated nitrateare much lower when treatment is made late. It is argued thatnitrate accumulation by the leaf becomes progressively lessas it reaches full expansion, but irrespective of time of nitrateapplication about 95 per cent of the additional nitrogen presentin the leaf is in organic form Significant increases in organic nitrogen are found from day6 for plants supplied with nitrate up to day 4; for plants suppliedon day 6, or day 8nitrateand nitrate reductase activity in leafextracts are found within 6 h of treatment. Peak levels of nitratereductase activity are found for all treatments around days8–10 when the first leaf is fully expanded and when photosyntheticactivity is maximal. However, late supply of nitrate leads toa lower level of enzyme activity. Nitrate reduction in the rootsystem is undetectably low, and it is concluded that a substantialamount of carbon translocated from leaf to roots is in the formof nitrogenous compounds. The effects of time of application are also found when ammoniumnitrogen is substituted for nitrate indicating that the responseis independent of effects on the nitrate reducing system inthe leaf. Some inhibition of growth, particularly of the roots,is found due to ammonium toxicity. Why plants supplied early with nitrate show superior growthand enhanced photosynthetic activity in the first leaves isexplained in terms of treatment alleviating the restrictiveeffects of declining endosperm reserves. This is only possibleif nitrogen is supplied while the first leaf is expanding andable to accumulateand utilise the available nitrogen. Late supplyis associated with failure to use the nitrogen provided leadingto a lower protein level in the leaf; this can be correlatedwith the smaller size of leaf and the lower rates of carbonfixation occurring there.     

The effects of organic and inorganic fertilizer applications to Miscanthus×giganteus,Arundo donax and Phalaris arundinacea,when grown as energy crops in Wales,UK

Two pot trials and one field trial were established to investigate the effects of organic and inorganic fertilizer applications to energy crops grown in mid‐Wales. Chicken litter and sewage cake applied at a high level in excess of MAFF recommendations produced an increased yield response in Miscanthus and Arundo plants. Miscanthus plants exhibited an increased growth response to all fertilizers applied in its second year. Fertilizer applications in accordance with MAFF recommendations produced no significant differences in yields for Miscanthus or Arundo potted plants. In the field there was an increased yield response of Miscanthus to inorganic nitrogen applications compared with organic manures, but not with control plots. Analysis of the Miscanthus plant material at harvest showed significant differences in the nitrogen, potassium and copper content between treatments. No mineral content differences were shown for Miscanthus rhizome material or Arundo plant material. The Phalaris plants did not exhibit significant differences in growth or yield parameters, but their plant matter showed differences in nitrogen, phosphorus, potassium, calcium, sulphur and boron content between treatments.     

Nutrient uptake by tupelo gum and bald cypress from saturated or unsaturated soil

Summary Seedlings of tupelo gum (Nyssa aquatica L.) and bald cypress (Taxodium distichum L. Rich.) were grown in pots containing a sphagnum moss-peat soil mix. Plants approximately 20 to 25 cm tall were subjected to three moisture treatments, saturated-aerated, saturated, and unsaturated soil; and three nitrogen fertilization treatments, control (no N added), urea (a reduced N source), and nitrate (an oxidized N source).Data include dry weights (g/culture) of leaves, stems, and roots; concentrations (percentage of dry weight) and contents (mg/culture) of N, P, K, Ca, and Mg in leaves, stems, and roots. Total dry weight was greater for plants grown in saturated-aerated soil than in either saturated or unsaturated soil. Differences in nutrient absorption and distribution between the plants and among the water treatments were principally the result of growth differences produced by the water treatments. Element contents and often the concentrations of P, K, Ca, or Mg were highest in both species when grown on the saturated-aerated soil and lowest when grown on unsaturated soil. The low levels of N in plants grown on saturated soils were probably the result of denitrification, as shown by the greater content of N in plants grown on soil fertilized with urea as opposed to nitrate. Thus, urea would appear to be a better N source than nitrate for fertilization in swamp forests. Growth of, and nutrient uptake by cypress was restricted less than that of tupelo when the plants were grown on saturated as compared to saturated-aerated soil. Thus, cypress appeared more tolerant than tupelo to the anaerobic root environment found in saturated soil.     

不同种源花榈木苗期生长及生理特性比较

为了解不同种源花榈木在贵阳的生长特性和差异,该文通过对10个种源地花榈木进行育苗试验,测定其两年生实生苗的苗高、地径、生物量、叶片光合参数、光合色素、硝酸还原酶活性、硝态氮含量和根系活力,并进行差异性分析。结果表明:(1)10个种源花榈木净光合速率、气孔导度、胞间CO₂浓度、蒸腾速率和水分利用效率差异显著(P<0.05),表明不同种源花榈木光合特性及光能利用效率具有较大差异,浙江杭州和浙江永康花榈木是具有较高光合生长潜力的种源。(2)种源间的叶绿素含量、硝酸还原酶、硝态氮、根系活力存在显著差异,福建建瓯种源的叶绿素a、叶绿素b含量和叶绿素总量最高,能够将光合原初反应过程中积蓄的光能进行高效地传递,促进碳的同化; 贵州花溪种源硝酸还原酶活性最大,硝态氮含量最高,对氮元素的利用能力较强,能够促进植物蛋白质、氨基酸和叶绿素等的合成; 贵州望谟种源根系活力最大,吸收养分的能力强。(3)各种源间苗高、地径和生物量的分配存在显著差异,浙江杭州种源的植株枝叶繁茂、根系发达,生长表现好,安徽黄山种源的植株矮小,生长表现较差; 浙江杭州种源将生物量更多分配在根和叶,提高其根系吸收养分和叶片获取光能的能力,安徽黄山种源总体生物量积累最少,长势最差。(4)通过主成分分析法对各种源的花榈木适应性进行综合评价,结果显示浙江杭州种源>贵州黎平种源>浙江永康种源>贵州望谟种源>福建建瓯种源>贵州凯里种源>贵州石阡种源>贵州花溪种源>贵州平塘种源>安徽黄山种源。综上结果表明,浙江杭州、贵州黎平和浙江永康种源花榈木对贵阳地区立地环境具有较强的适应能力和生长潜力。