Effects Of Nitrogen Supply Research Articles

Effect of Nitrogen Supply on Carbon Dioxide–Induced Changes in Competition between Rice and Barnyardgrass (Echinochloa crus-galli)

As atmospheric carbon dioxide concentration ([CO2]) increases, it is anticipated that the competitive ability of C3 crops could be enhanced relative to C4 weeds in agricultural systems. However, given the different nitrogen use efficiencies of C3 and C4 plants, it is unclear whether any effect of increasing [CO2] on C3/C4 competition is nitrogen dependent. To determine the interaction of [CO2] and N availability on species growth and competitive outcomes, the growth of rice (C3 photosynthetic pathway) was examined in both monoculture and in competition with a common weed, barnyardgrass (C4 photosynthetic pathway) at two levels of N supply (0.357 and 1.071 mmol N L−1) and two levels of [CO2] (ambient and ambient + 200 µmol mol−1) under field conditions in eastern China. In monoculture, the biomass response of rice to elevated [CO2] depended on N supply, whereas the response of barnyardgrass to elevated [CO2] was less dependent on nitrogen. Consequently, when grown in mixture, the proportion of rice biomass increased relative to that of barnyardgrass under elevated [CO2] if the supply of nitrogen was adequate. However, if N was low, elevated [CO2] significantly reduced the proportion of leaf area and root biomass relative to barnyardgrass biomass. Although data from this experiment confirm that competitiveness of rice could be enhanced relative to C4 weeds in response to rising [CO2] in situ, the data also indicate that such a response could be contingent on the supply of nitrogen. This suggests that, for rice cropping systems where N is in limited supply, rising atmospheric CO2 could still exacerbate competitive losses, even from C4 weeds.

Sulfur‐Enhanced Defence: Effects of Sulfur Metabolism, Nitrogen Supply, and Pathogen Lifestyle

Evidence from field experiments indicates differential roles of sulfur and nitrogen supply for plant resistance against pathogens. Dissection of these observations in defined pathosystems and controlled nutritional conditions indicates an activation of plant sulfur metabolism in several incompatible and compatible interactions. Contents of cysteine and glutathione as markers of primary sulfate assimilation and stress response show increases in ARABIDOPSIS THALIANA upon infection, coinciding with the synthesis of sulfur-containing defence compounds. Similar increases of thiols were observed with necrotrophic, biotrophic, and hemibiotrophic pathogens. Sulfate supply was found to be neutral or beneficial for tolerance against fungal but neutral for bacterial pathogens under IN VITRO conditions. According to various reports and own observations the effects of nitrogen supply appeared to be neutral or harmful, depending on the pathogen. The activation of sulfur metabolism was a consequence of activation of gene expression as revealed by macroarray analysis of an A. THALIANA/ALTERNARIA BRASSICICOLA pathosystem. This activation appeared to be largely independent from sufficient or optimal sulfate supply and from the established sulfate deficiency response. The data suggest that plant-pathogen interactions and sulfur metabolism are linked by jasmonic acid as signal.

Comparing the photosynthetic activity of maize, winter wheat, potato and some significant weed

Special adaptations and policies will be necessary to take advantage of the opportunities and minimize the negative impacts of climate change on agriculture. Those farmers producing C4 crops, such as maize, sorghum and millet, will see very little benefit from higher C02, and at the same time their crops will face increased competition from C3 weeds. Many researchers studied the influencing factors of the photosynthesis system of the crops from different aspects. However, most of the literature reports on measurements made in the laboratories, field measurings are rare. Also there is little information available about the photosynthetic activity of the weeds. The aim of our work was to compare the photosynthetic activity of maize, winter wheat, the potato and some significant weed, on different light levels. The effects of increased light intensity were tested by Vidal et al. (1996) on soybean. Their results show, that in consequence of the tripling the light intensity from 400 pE m" V to 1200 pE m'V, the photosynthesis intensity was doubled. Sharma et al. (1998) studied the effect of UV-B radiation on net photosynthesis and chlorophyll fluorescence in wheat seedlings. They found that the UV-B radiation caused significant decrease in net photosynthesis, which was much greater than could be explained by limitation of stomatal conductance. Shangguan et al. (2000) investigated the nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange in winter wheat. The photosynthetic gas exchange parameters were remarkably improved by water and nitrogen supply. The effect of nitrogen nutrition on photosynthetic characteristics was not identical under different water status. In light acclimated pea leaves studied Park et al. (1996) the photosynthesis under three light intensity, 50 (low light), 250 (medium light), and 650 (high light) pmol photons m'V1. The results show that in the low light adapted leaves light -stress induced because of increasing the photon exposure. Under high light intensity the photoinactivation of PS II was greatly increased. Bindraban (1999) wrote that in his observations the photosynthesis in the lower leaves of wheat depended mainly on the light intensity. The effect of nitrogen supply was low. Photosynthesis and its tolerance to photoinhibition, high temperature and drought stress of flag leaves were investigated in wheat by Xinghong et al. (2006). Their results suggest that high resistance to photo-oxidative damage of the flag leaves be the physiological basis for the high yield.

Effects of nitrogen supply on photosynthetic and anatomical changes in current-year needles of Pinus koraiensis seedlings grown under two irradiances

We investigated the responses of photon-saturated photosynthesis rate (P sat) and its simultaneous acclimation of anatomy and nitrogen use patterns of current needles of Korean pine (Pinus koraiensis) seedlings grown under factorial combinations of two nitrogen levels and irradiances. Although N supply resulted in a significant increase of N content in needles under both irradiances, the increase of P sat tended to be suppressed only in shade (S). The significant increase of P sat in full sunlight (O) was associated with the increase of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and chlorophyll (Chl) contents. In contrast, small increase of Chl content and no increase of RuBPCO content were found in S (90 % cut of full irradiance), which would result in a small increase of P sat. This result suggests that extra N is stocked in needles under shade for the growth in next season. With N supply, a significant decrease of specific leaf area (SLA) was detected only in O. This decrease of SLA was due to the increase of density of needle. Furthermore, the increase of needle density was not due to the increased number and size of mesophyll cells, but the increased density of each mesophyll cell. Therefore, although SLA changed in O, the change did not involve anatomical adaptation to use increased N effectively, at least observable by light microscopy. Hence, even though the SLA would change, N deposition will improve the photosynthetic capacity of Korean pine seedlings, not through the development of needle anatomy but through improvement of the allocation of N in both irradiances.

Effects of Nitrogen Supply on the Sensitivity to O3 of Growth and Photosynthesis of Japanese Beech (Fagus crenata) Seedlings

To obtain basic information for evaluating critical levels of O3 under different nitrogen loads for protecting Japanese beech forests, two-year-old seedlings of Fagus crenata Blume were grown in potted andisol supplied with N as NH4NO3 solution at 0, 20 or 50 kg ha−1 year−1 and exposed to charcoal-filtered air or O3 at 1.0, 1.5 and 2.0 times the ambient concentration from 16 April to 22 September 2004. The O3 induced significant reductions in the whole-plant dry mass, net photosynthetic rate at 380 μmol mol−1 CO2 (A380), carboxylation efficiency (CE) and concentrations of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and total soluble protein (TSP) in the leaves. The concentrations of Rubisco and TSP were negatively correlated with the concentration of leaf acidic amino acid, suggesting that O3 enhanced the degradation of protein such as Rubisco. The N supply to the soil did not significantly change the whole-plant dry mass and A380, whereas it significantly increased the CE and concentrations of Rubisco and total amino acid. No significant interactive effects of O3 and N supply to the soil were detected on the growth, photosynthetic parameters and concentrations of protein and amino acid in the leaves. In conclusion, N supply to the soil at ≤50 kg ha−1 year−1 does not significantly change the sensitivity to O3 of growth and net photosynthesis of Fagus crenata seedlings.

Reciprocal Leaf and Root Expression ofAtAmt1.1and Root Architectural Changes in Response to Nitrogen Starvation

Nitrogen is an essential macronutrient for plant growth and survival. Here, the temporal and spatial sensing of nitrogen starvation is analyzed in Arabidopsis (Arabidopsis thaliana). The promoter for the high-affinity ammonium transporter, AtAmt1.1, is shown to be a valid indicator for nitrogen status in leaves and roots. An AtAmt1.1-Gal4 transgene using three 5x upstream activating sequence-driven reporters (luciferase, green fluorescent protein, and beta-glucuronidase) facilitated in vivo profiling at the whole-plant and cellular levels. The effects of nitrogen supply, light duration, light intensity, and carbon on the expression of the AtAmt1.1 gene in the roots and aerial tissues are reported. Under nitrogen starvation, high expression is observed in the roots and, under nitrogen-sufficient conditions, high expression is observed in the leaves. This reciprocal regulation of AtAmt1.1 was confirmed by quantitative reverse transcription-polymerase chain reaction, which was also used to quantitate expression of the five other Amt genes in Arabidopsis. Although some of these show tissue specificity (roots or leaves), none exhibit reciprocal regulation like the AtAmt1.1-encoded high-affinity transporter. This robust reciprocal expression suggests that Arabidopsis undergoes rapid resource reallocation in plants grown under different nitrogen supply regimens. Ultimately, nitrogen starvation-mediated reallocation results in root architectural restructuring. We describe the precise timing and cellular aspects of this nitrogen limitation response.

Effects of nitrogen supply on the photosynthetic traits in Pinus koraiensis seedlings grown under two light conditions

Effects of nitrogen supply on the photosynthetic traits in Pinus koraiensis seedlings grown under two light conditions

EFFECT OF NITRATE CONCENTRATION ON THE RELATIONSHIP BETWEEN PHOTOSYNTHETIC OXYGEN EVOLUTION AND ELECTRON TRANSPORT RATE IN ULVA RIGIDA (CHLOROPHYTA)1

The electron transport rate (ETR) versus gross photosynthesis (GPS) relationship varies as a function of species, temperature, irradiance, and inorganic carbon levels, but less is known about the effect of nitrogen supply on this relationship. The objective of this study was to evaluate the effect of nitrate concentration on the ETR versus GPS relationship in Ulva rigida C. Agardh from the Mediterranean Sea. Chlorophyll content and tissue absorptance increased 2‐fold as nitrate in the media increased from 0 to 50 μM. Whereas internal N content increases 3‐fold at 50 μM, internal C increased slightly. Oxygen evolution and ETR, evaluated as in vivo chl fluorescence using pulse amplitude modulated fluorometry, in general saturated at irradiances above 100 μmol photons·m−2·s−1. Both maximum ETR and GPS values increased as nitrate concentration increased. In general, the ETR versus GPS relationship showed a linear response to increasing nitrate with little variance of the data. This relationship, however, became more variable at high irradiances and high nitrate concentrations. The ETR/GPS ratio was close to the theoretical value of 4 at low nitrate concentrations, and the ratio decreased exponentially when nitrate concentration in the media increased. The variations of ETR/GPS under different inorganic nitrogen supply are discussed in terms of the effect of nitrate on the photosynthesis and respiration relationship.

Effects of nitrogen supply on wheat and on soil nitrate

Field experiments were conducted at two locations during two growing seasons in the Ebro Valley (Spain), to evaluate the effects of N fertilization on yield and quality of Mediterranean-type wheat in irrigated conditions. Seven N treatments and a control were investigated. The average grain yields ranged from 2117 to 5551 kg ha-1 depending on the year and location. Grain protein ranged from 14.25 to 16.9%, and other quality parameters such as the dough strength (W) also varied with year and location, confirming the suitability of Mediterranean-type wheat and the climate for the production of good bread-making quality wheat. However, grain yields are normally low and both yields and quality can be greatly affected by the variability of this type of climate, even under irrigation. Under these conditions, grain yield increases were mainly due to an increase in the number of grains per m2 without a reduction in the N content per spike, suggesting that N in the grain was not source-limited, possibly due to the lower grain yields and relatively high soil nitrate concentrations. In soils with lower initial soil NO-3N contents, better grain yields could be achieved by applying a N fertilizer rate of about 100 kg N ha-1, whereas in soils with high initial NO-3N contents, no N or a maximum rate of 50 kg N ha-1 is needed to obtain a good grain quality, showing the possibility of producing high-quality wheat with a low amount of N fertilizer and thus increasing the sustainability of the cropping system.

Ozone and increased nitrogen supply effects on the yield and nutritive quality of Trifolium subterraneum

Abstract The influence of ambient ozone (O3) concentrations and nitrogen (N) fertilization, singly and in combination, on the growth and nutritive quality of Trifolium subterraneum was assessed. This is an important O3-sensitive species of great pastoral value in Mediterranean areas. Plant material was enclosed in open-top chambers (OTCs). Three O3 levels were established: Filtered air with O3 concentrations below 15 ppb (CFA), non-filtered air with O3 concentrations in the range of ambient levels (NFA), and non-filtered air supplemented with 40 ppb O3 over ambient levels (NFA+). Similarly, three N levels were defined: 5, 15 and 30 kg ha−1. The increase in O3 exposure induced a reduction of the clover aerial green biomass and an increase of senescent biomass. Ozone effects were more adverse in the root system, inducing an impairment of the aerial/subterranean biomass ratio. Compared with the CFA treatment, nutritive quality of aerial biomass was 10 and 20% lower for NFA and NFA+ treatments, respectively, due to increased concentrations of acid detergent fiber, neutral detergent fiber and lignin. The latter effect appears to be related to senescence acceleration. The increment in N supplementation enhanced the increase of ADF concentrations in those plants simultaneously exposed to ambient and above-ambient O3 concentrations, and reduced the incremental rate of foliar senescence induced by the pollutant.

Effect of nitrogen supply on carbon and nitrogen partitioning after flowering in maize

AbstractLow nitrogen (N) supply may change assimilate partitioning between plant organs. We measured the effect of N supply on partitioning of recently assimilated 13C and recently absorbed 15N between generative and vegetative plant organs of two maize genotypes (Zea mays L.) 14 d after silking, i.e., during the lag phase of kernel growth. Furthermore, net partitioning of dry matter and N were assessed during grain filling. Plants were grown in a greenhouse in large containers. Our hypothesis was that N deficiency reduces grain set due to low partitioning of carbon (C) and N to the grains during the lag phase and reduces grain yield also because of excessive remobilization of N from the leaves during grain filling. During the lag phase, low N supply increased partitioning of recently assimilated photosynthates towards stem and roots at the expense of partitioning towards reproductive organs. However, despite of diminished sink strength of the reproductive organs for photosynthates, sugar concentrations in the grains of N‐deficient plants were increased, indicating that kernel set and potential kernel weight were not limited by low C supply at the end of the lag phase. In contrast to C, partitioning of recently absorbed N towards the reproductive organs was increased at low N supply at the expense of partitioning towards the roots. This indicates different mechanisms for the regulation of C and N distribution within the plant. During grain filling, biomass partitioning between plant organs was more affected by genotype than by rate of N supply. Nitrogen accumulation in the grains substantially exceeded total N uptake in the plant after flowering. Excess N accumulation in the grains was covered mainly by depletion of stem N at high N supply and by depletion of leaf N at low N supply. However, high concentrations of nonstructural carbohydrates in the stem at maturity indicated that grain yield of N‐deficient plants was not limited by low source strength of N‐depleted leaves.

The effect of nitrogen supply on specific yield and fruit quality of apple (Malus domestica Borkh.)

The aim of the present study was to determine the effect of nitrogen supply on yield and fruit quality of apple cultivars and to explore the relationships between canopy density and the different fruit quality parameters.
 The experiments were carried out at Kálmánháza, in Eastern Hungary in a private orchard in 2003-2004. The response of four apple cultivars ('Elstar', 'Gala Prince', 'Granny Smith', 'Idared') to different nitrogen dosages was studied. The assessed and calculated indices were: yield, fruit diameter, fruit height, shape index, fruit mass, firmness, dry matter content and colouration. The results indicated that nitrogen fertilization has a significant effect on the yield and fruit quality of apple cultivars. The calculated specific yield values were reduced by the application of nitrogen via the increase in the volume of the canopy. An opposit trend was observed for fruit diameter, fruit height and fruit weight, which increased with increasing nitrogen supply. The reduced shape index caused flattening of fruits.
 However, the improvement of fruit quality via increasing nitrogen dosage is only virtual, since these dosages increase the fruit size, but firmness, dry matter content and colouration are diminished, which decreases the value of the fruits on the market.
 The authors also studied the relationships between canopy density responsible for assimilation and light supply of the fruits and the different fruit quality parameters. The closest linear inversely proportional relationship was found in the case of colouration. There was a negative linear relationship between canopy density and firmness or dry matter content. The relationship between canopy density and fruit mass could be described by a quadratic polinomial function.

Effect of Nitrogen Supply on the Nitrogen Use Efficiency of an Annual Herb, Helianthus annuus L.

Abstract: Nitrogen use efficiency (NUE) is the product of nitrogen productivity (NP) and the mean residence time of nitrogen (MRT). Theory suggests that there should be a trade-off between both components, but direct experimental evidence is still scarce. To test this hypothesis, we analyzed the effect of varying nitrogen supply levels on NUE and its two components (NP, MRT) in Helianthus annuus L., an annual herb. The plants investigated were subjected to six nitrogen levels (0, 2, 4, 8, 16, and 32 g N/m2). Total plant production increased substantially with increasing nitrogen supply. Nitrogen uptake and loss also increased with nitrogen supply. Nitrogen influx (rin) and outflux (rout) were defined as the rates of nitrogen uptake and loss per unit aboveground nitrogen, respectively. Both rm and rout increased with increasing nitrogen supply. In addition, rm was far higher than rout. Consequently, the relative rate of nitrogen increment (rin-rout) also increased with nitrogen supply. There were marked differences between treatments with respect to parameters related to the stress resistance syndrome: nitrogen pool size, leaf nitrogen concentration, and net aboveground productivity increased with nitrogen supply. Plants at high nitrogen levels showed a higher NP (the growth rate per unit aboveground nitrogen) and a shorter MRT (the inverse of rout), whereas plants at low nitrogen levels displayed the reverse pattern. Shorter MRT for plants at high nitrogen levels was caused by the abscission of leaves that contained relatively large fractions of total plant nitrogen. We found a negative relationship between NP and MRT, the components of NUE, along the gradient of nitrogen availability, suggesting that there was a trade-off between NP and MRT. The NUE increased with increasing nitrogen availability, up to a certain level, and then decreased. These results offer support for the hypothesis that adaptation to infertile habitats involves a low nitrogen loss (long MRT in the plant) rather than a high NUE per se. The higher NUE at the plant level was a result, in part, of greater nitrogen resorption during senescence. We suggest that a long MRT (an index of nitrogen conservation) is a potentially successful strategy in nitrogen-poor environments. (Managing editor: Ya-Qin HAN)

Relationships Between Some Hordein Components and Quality Properties in Two Tunisian Barley Varieties as Influenced by Nitrogen Fertilisation

Two Tunisian barley varieties, Martin and Rihane, differing by their degrees of adaptation to the environmental conditions and grain yield potential, were grown under different levels of nitrogen (N) fertilisation. The effect of nitrogen supply on the hordein components (expressed in mg per albumen) was determined by Nu-PAGE electrophoresis system using the MOBS running buffer and densitometric analysis. Increasing nitrogen fertilisation increased the protein content by increasing the amount of C-hordeins. The sub-fraction BIII of high molecular weight B-hordeins appeared, in the present study, as the best criterion for distinguishing between the two barley varieties genetic adaptation, and its quantification could be recommended for the understanding of the quality properties of the barley response to different environmental conditions particularly nitrogen fertilisation which appears to be the main origin of differences in the protein aggregation mode of different B-hordein sulphur-rich sub-fractions.    

Effects of nutrient supply on the photosynthesis of maize hybrids

Light and nutrients are two essential factors that plants must have to grow and forming yield. The aim of our work is to add some information about the yield forming procedure of maize. Taking leaf gas exchange measurements not in a laboratory but in the field has great significance. We measured the assimilation parameters of maize hybrids in field trial on the nutrient supply. Lonhardne et al. (1996) investigated the photosynthetic potential in nutrient supply experiments. The photosynthetic potential depended on the nutrient levels. Bindraban (1999) wrote that in his observations the photosynthesis in the lower leaves of wheat depended mainly on the light intensity. The effect of nitrogen supply was low. Shangguan et al. (2000) agreed that the nitrogen and water supply has great affect on the photosynthetic gas exchange. The higher nitrogen supply lowered the water use efficiency of the plants and the net photosynthetic rate decreased. Janda et al. (1998) studied photosynthetic activity of maize plants under different environmental conditions. They estimated that there were no differences between net photosynthetic rate of genotypes in optimal temperature but in lower temperature there were differences. In the experiments in California Hirasawa et al. (1999) found that the leaves reach the maximum photosynthesis rate in the morning on droughty days in spite of that the soil was irrigated. Sharma et al. (1998) established that the UV-B light significantly decreased the net photosynthesis in the leaves of the wheat.

Effects of nitrogen supply on growth, contents of phenolic compounds and pathogen (scab) resistance of apple trees

The effect of long‐term N‐supply on growth, scab resistance and phenolic compounds in the leaves of two apple cultivars was studied. The different pools of phenylpropanoids (hydroxycinnamic acids, dihydrochalcones) and flavonoids (flavonols, catechins, procyanidins) were quanitfied by HPLC from non‐infected and inoculated leaves representing different ontogenetic stages. Scab incidence was also evaluated. Strictly following the carbon‐nutrient‐balance hypothesis, apple trees responded to high N‐supply with increased shoot growth and with a reduced accumulation of total phenolic compounds in their leaves. This was shown for the cultivar ‘Golden Delicious’, which is susceptible to the scab disease caused by Venturia inaequalis, and for the resistant cultivar ‘Rewena’. Whereas high N‐fertilization increased the susceptibility of ‘Golden Delicious’, it did not decrease the resistance of ‘Rewena’ despite of the pronounced reduction of phenolic concentrations. Thus, a simple C trade off between growth‐related metabolism and secondary metabolism cannot solely explain changes in defensive potential.

Effect of nitrogen supply on leaf appearance, leaf growth, leaf nitrogen economy and photosynthetic capacity in maize ( Zea mays L.)

Leaf area growth and nitrogen concentration per unit leaf area, N a (g m −2 N) are two options plants can use to adapt to nitrogen limitation. Previous work indicated that potato ( Solanum tuberosum L.) adapts the size of leaves to maintain N a and photosynthetic capacity per unit leaf area. This paper reports on the effect of N limitation on leaf area production and photosynthetic capacity in maize, a C4 cereal. Maize was grown in two experiments in pots in glasshouses with three (0.84–6.0 g N pot −1) and five rates (0.5–6.0 g pot −1) of N. Leaf tip and ligule appearance were monitored and final individual leaf area was determined. Changes with leaf age in leaf area, leaf N content and light-saturated photosynthetic capacity, P max, were measured on two leaves per plant in each experiment. The final area of the largest leaf and total plant leaf area differed by 16 and 29% from the lowest to highest N supply, but leaf appearance rate and the duration of leaf expansion were unaffected. The N concentration of expanding leaves (N a or %N in dry matter) differed by at least a factor 2 from the lowest to highest N supply. A hyperbolic function described the relation between P max and N a. The results confirm the ‘maize strategy’: leaf N content, photosynthetic capacity, and ultimately radiation use efficiency is more sensitive to nitrogen limitation than are leaf area expansion and light interception. The generality of the findings is discussed and it is suggested that at canopy level species showing the ‘potato strategy’ can be recognized from little effect of nitrogen supply on radiation use efficiency, while the reverse is true for species showing the ‘maize strategy’ for adaptation to N limitation.

Effect of Nitrogen Supply and Irradiance on Seedling Survival and Biomass in Two Evergreen, Ericaceous Species

Ericaceous species are important competitors in many northern conifer plantations. Nitrogen (N) fertilization of forests can reduce the cover of ericaceous species, but whether this is a direct effect of N or an indirect effect of increased shade from fertilized trees is debated. To address this question, the growth and photosynthetic characteristics of two evergreen ericaceous species were studied in response to N fertilization and irradiance in a controlled environment. Salal (Gaultheria shallon Pursch) seedlings were grown with 10, 100 or 250 mg l−1 N [+ phosphorus (P) and potassium (K)] under 0% or 60% shade. Evergreen huckleberry (Vaccinium ovatum Pursch) seedlings were grown with 10 or 250 mg l−1 N (+PK), and with 250 mg l−1 N+K only under 0 or 50% shade. Salal survival decreased with increasing N supply, but shoot biomass was greatest in the 100 mg l−1N treatment. Shade had no effect on salal survival, but shoot biomass was greater in shade. Survival of evergreen huckleberry grown in sun decreased with increasing N supply (+PK); however, survival of shaded plants was unaffected by N supply. Biomass of evergreen huckleberry shoots was greatest with 250 mg l−1 N (+PK) and was unaffected by irradiance. Shoot:root ratios increased with N supply and shade in both species. Rates of net photosynthesis in salal were unaffected by N treatment, and were higher in shaded plants. Chlorophyll concentrations in evergreen huckleberry increased with N supply, and were greatest in shade plants. It is suggested that fertilization of these ericaceous species with high levels of N reduces root growth which increases plant mortality under water stress. Shoot growth of plants surviving this stress is improved by fertilization.

Growth, nitrogen uptake, and metabolism in two semiarid shrubs grown at ambient and elevated atmospheric CO2 concentrations: effects of nitrogen supply and source

The effect of differences in nitrogen (N) availability and source on growth and nitrogen metabolism at different atmospheric CO(2) concentrations in Prosopis glandulosa and Prosopis flexuosa (native to semiarid regions of North and South America, respectively) was examined. Total biomass, allocation, N uptake, and metabolites (e.g., free NO(3)(-), soluble proteins, organic acids) were measured in seedlings grown in controlled environment chambers for 48 d at ambient (350 ppm) and elevated (650 ppm) CO(2) and fertilized with high (8.0 mmol/L) or low (0.8 mmol/L) N (N(level)), supplied at either 1 : 1 or 3 : 1 NO(3)(-) : NH(4)(+) ratios (N(source)). Responses to elevated CO(2) depended on both N(level) and N(source), with the largest effects evident at high N(level). A high NO(3)(-) : NH(4)(+) ratio stimulated growth responses to elevated CO(2) in both species when N was limiting and increased the responses of P. flexuosa at high N(level). Significant differences in N uptake and metabolites were found between species. Seedlings of both species are highly responsive to N availability and will benefit from increases in CO(2), provided that a high proportion of NO(3)- to NH(4)-N is present in the soil solution. This enhancement, in combination with responses that increase N acquisition and increases in water use efficiency typically found at elevated CO(2), may indicate that these semiarid species will be better able to cope with both nutrient and water deficits as CO(2) levels rise.

Effect of nitrogen supply on growth and photosynthesis of sunflower plants grown in the greenhouse

The effects of nitrogen availability on growth and photosynthesis were followed in plants of sunflower ( Helianthus annuus L., var. CATISSOL-01) grown in the greenhouse under natural photoperiod. The sunflower plants were grown in vermiculite under two contrasting nitrogen supply, with nitrogen supplied as ammonium nitrate. Higher nitrogen concentration resulted in higher shoot dry matter production per plant and the effect was apparent from 29 days after sowing (DAS). The difference in dry matter production was mainly attributed to the effect of nitrogen on leaf production and on individual leaf dry matter. The specific leaf weight (SLW) was not affected by the nitrogen supply. The photosynthetic CO 2 assimilation ( A) of the target leaves was remarkably improved by high nitrogen nutrition. However, irrespective of nitrogen supply, the decline in photosynthetic CO 2 assimilation occurred before the end of leaf growth. Although nitrogen did not change significantly stomatal conductance (gs), high-N grown plants had lower intercellular CO 2 concentration ( C i ) when compared with low-N grown plants. Transpiration rate ( E) was increased in high-N grown plants only at the beginning of leaf growth. However, this not resulted in lower intrinsic water use efficiency (WUE).