NH4 Nutrition Research Articles

NH4 -N/NO3- -N ratios on growth and NO3- -N remobilization in root vacuoles and cytoplasm of lettuce genotypes

Wang, B. and Shen, Q. R. 2011. NH4 -N/NO3- -N ratios on growth and NO3--N remobilization in root vacuoles and cytoplasm of lettuce genotypes. Can. J. Plant Sci. 91: 411-417. Aerobically growing crops generally prefer nitrate (NO3-) to ammonium (NH4 ), but partial replacement of NO3- by NH4 usually makes crops grow better. Five cultivars of lettuce (Lactuca sativa L.) frequently cultivated in southeast China, including Ny, Sx1, Rw, Nct and Nrnct, were hydroponically grown in four ratios of NH4-N:NO3-N: 0:100, 10:90, 25:75 and 50:50. Based on biomass of roots and shoots of plants, Sx1 was a mostly sensitive genotype, while Nrnct was a mostly insensitive genotype to partial NO3- replacement by NH4 among the five cultivars. Total root surface area, root length, SPAD readings and net photosynthesis rate of Sx1 and Nrnct were found to be highest at 25:75 of NH4-N:NO3-N. Sx1 had a greater improvement than Nrnct under moderate NH4 nutrition (NH4-N:NO3-N=25:75). The capacities of NO3- release and remobilization from vacuoles to cytoplasm of Sx1 were stronger than those of Nrnct. The results suggest that we can improve the utilization of nitrogen and decrease the NO3- content in lettuce through planting the appropriate lettuce cultivar in a proper NH4-N/NO3-N ratio.

Effect of Iron Seed Dressing and Form of Nitrogen-Supply on Growth and Micronutrient Concentration in Shoots of Sorghum Grown in a Calcareous Sand Culture

ABSTRACT Seeds of sorghum [Sorghum bicolor (L.) Moench cv ‘Wrangler’] dressed with three increasing concentrations of an iron ethylenediamine-di-O-hydroxphenylacetic acid (FeEDDHA) product up to 480 mg Fe kg− 1 seed as a sole source of iron supply as well as a treatment without any dressing were grown for 19 days after germination in sand culture buffered to pH 8 by calcium carbonate. Nitrogen was supplied either as ammonium (NH4)-N or nitrate (NO3)-N, the former being supplemented with nitrapyrin (N Serve) to prevent nitrification. Chlorosis of the younger leaves was evident in all treatments except at the two higher levels of NH4-supplied plants. Dry matter yields of the shoots were raised only relatively slightly by the increasing levels of Fe supply and at each level the NH4 form was superior to that of NO3 -N. At the end of the growth period the pH of the sand around the roots had fallen by about 0.5 of a unit for NH4–fed plants and increased by about 0.2 of a unit for NO3-fed plants. At each level of Fe supply, NH4 nutrition approximately doubled the micronutrient [Fe, zinc (Zn), copper (Cu), manganese (Mn)] shoot concentrations and uptakes as compared with NO3-nutrition. For the NO3 –fed plants, increasing rates of Fe seed dressing had little effect on shoot Fe concentrations or uptakes, the concentration values determined (about 40 μ g g− 1 dry wt.) being below the range of critical deficiency concentration. Similarly concentrations of Mn were also in the deficiency range in the seed dressed NO3-fed plants (11–12 μ g g− 1 dry wt) so that in the NO3 treatments chlorosis may have resulted from a lack of Mn as well as Fe. Dressing sorghum seeds with Fe chelates in conjunction with NH4 fertilization supplemented with an inhibitor to prevent nitrification would appear to be a worthwhile approach to ensure an initial source of Fe to the young developing plant in the avoidance of iron-induced chlorosis in the growth of sorghum on high pH calcareous soils.

Comparison between nitrate and ammonium nutrition in fennel, celery, and Swiss chard

To evaluate the chance to reduce leaf NO3 content and to increase capability to use NH4‐N even in the absence of NO3‐N in the nutrient solution, plants of two Apiaceae species, fennel (Foeniculum vulgare Miller var. azoricum Mill. Thell.) and celery (Apium graveolens L. var. dulce Mill. Pers.), and of one species of Chenopodiaceae, Swiss chard (Beta vulgaris L. var. vulgaris), were hydroponically grown in a growth chamber with three different NH4‐N: NO3‐N (NH4: NO3) ratios (100: 0,50: 50, and 0: 100), but with the same total N level (4 mM) for 14 days. Swiss chard growth was inhibited by NH4 nutrition and reached the highest values with the NH4: NO3 ratio 0: 100. For all the morphological and yield features analyzed, fennel and celery resulted to be quite unresponsive to nitrogen (N) chemical form. Water use efficiency increased in Swiss chard and decreased in fennel and celery with the increase of NO3‐N percentage in the nutrient solution. The dependency of N uptake rate on shoot increment per unit root was more conspicuous for Swiss chard than fennel and celery. All species took more NO3‐N than NH4‐N when N was administered in mixed form. In the best conditions of N nutrition, Swiss chard accumulated NO3 in leaves in high concentration (3,809 mg kg"1 fresh mass). On average, fennel and celery accumulated 564 mg NO3 kg−1 fresh mass with the ratio NH4: NO3100: 0 and showed that by using NH4 produce having very low NO3 content can be obtained. By increasing NO3‐N percentage in the nutrient solution; NO3 leaf content of fennel and celery increased remarkably (7,802 mg kg−1 fresh mass with the ratio N H4: NO3 0: 100).

Nitrate and ammonium nutrition in chicory and rocket salad plants

To evaluate chicory (Cichorium intybus L.) and rocket salad [Eruca vesicaria (L.) Cav.subsp. sativa (Mill.)] capability to use ammonium‐nitrogen (NH4‐N) even in the absence of nitrate‐nitrogen (NO3‐N) in the nutrient solution, and the chances they offer to reduce leaf NO3 content, cultivated rocket and two cultivars of chicory ('Frastagliata’, whose edible parts are leaves and stems, and ‘Clio’, a leaf hybrid) were hydroponically grown in a growth chamber. Three nutrient solutions with the same nitrogen (N) level (4 mM) but a different NH4‐N:NO3‐N (NH4:NO3) ratio (100:0, 50:50, and 0:100) were used. Rocket growth was inhibited by NH4 nutrition, while it reached the highest values with the NH4:NO3 ratio 50:50. Water and N‐use efficiencies increased in rocket with the increase of NO3‐N percentage in the nutrient solution. In the best conditions of N nutrition, however, rocket accumulated NO3 in leaves in a very high concentration (about 6,300 mg kg‐1 fresh mass). For all the morphological and yield features analyzed, chicory resulted to be quite unresponsive to N chemical forms, despite it took more NO3‐N than NH4‐N when N was administered in mixed form. By increasing NO3‐N percentage in the nutrient solution, NO3 leaf content increased (5,466 mg kg‐1 fresh mass with the ratio NH4:NO3 0:100). On average, both chicory cultivars accumulated 213 mg NO3 kg‐1 fresh mass with the ratio NH4:NO3 100:0 and, differently from rocket, they showed that by using NH4 produce can be obtained very low in NO3 content.

Root growth as a function of ammonium and nitrate in the root zone

ABSTRACTWe examined the effect of soil NH4+ and NO3− content upon the root systems of field‐grown tomatoes, and the influence of constant, low concentrations of NH4+ or NO3− upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH4+ or NO3−; they increased to a maximum in zones having 2μg‐N NO3− g−1 soil and 6 μg‐N NO3= g−1 soil, but decreased in zones having higher NH4+ or NO3− levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH4+ or NO3−, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO3−. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH4+ and NO3−.

POLYAMINE ACCUMULATION BY TOMATO PLANTS UNDER NUTRITIONAL STRESS

Polyamine accumulation is a response of plants to various environmental stresses. Polyamine accumulation was assessed in relation to ammonium accumulation and ethylene evolution in tomato (Lycopersicon esculentum Mill.) under nutritional stress. Nutritional stresses were imparted on plants grown in quartz sand culture under greenhouse conditions with NH4-based modified Hoagland's solution or with NO3-based solutions without P, K, Ca, or Mg. The plants receiving NH4 nutrition were grown with or without 10-5 M (aminooxy)acetic acid (AOA) or 10-5 M silver thiosulfate (STS). Plants on nutrient deficient solution were grown with or without the AOA. When plants appeared with toxic or deficient symptoms, the new fully expanded leaves were collected and extracted by 5% perchloric acid for polyamine analyzes by HPLC. Plants receiving NH4-based nutrition had high putrescine and low spermidine concentrations. High spermidine and low putrescine concentrations occurred in plants receiving complete NO3-based nutrition. For plants receiving NH4-based nutrition, application of AOA suppressed accumulation of putrescine but had no effect on spermidine, and STS had no effect on polyamine accumulation. For plants receiving NO3-based nutrition without P, K, Ca, or Mg, the application of AOA restricted accumulation of putrescine and spermidine. High putrescine concentration was accompanied by high ammonium accumulation, high ethylene evolution, and stressinduced symptoms, indicating an association between polyamine accumulation and other stress-related phenomena.

Growth of Actinorhizal Plants as Influenced by the Form of N with Special Reference to Myrica gale andAlnus incana

Growth of two actinorhizal species was studied in relation to the form of N supply in water culture. Non-nodulated bog myrtle (.Myrica gale) and grey alder (Alnus incana) were grown with NH4, NH4N03 or NO J (4 mol m-3 N). A nodulated series of bog myrtle was also cultivated in N-free medium. Relative growth rate (RGR), utilization rate of N, and shoot/root ratio were highest for the two species with the N completely supplied as NH4. In both species, nitrate was largely reduced in the roots and the presence of NOJ in combined-N supply always affected the RGR and N utilization rate negatively. Both N2 fixation and complete NO3 nutrition represented conditions of relative N-deficiency resulting in relatively low tissue-N concentrations and a greater allocation of dry mass to the roots. The physiological N status of nodulated M. gale plants was comparatively good, as indicated by a normal nodule weight ratio and a relatively high N2-fixing rate per unit nodule mass. However, whole-plant N2-fixing capacity remained relatively low in comparison with acquisition rates of N in combined-N plants. The anion charge from the nitrate reduction was largely directly excreted as an OH efflux. H + /N ratios generally agreed with the theory. In comparison with NH4 nutrition, carboxylate concentrations were higher in N2-fixing M. gale plants and the H+/N ratio in nodulated plants was less than unity below the value for ammonium plants as previously found for other actinorhizal species. Therefore, NH4 should be an energetically more attractive N source for actinorhizal plants than N2. The results agree with commonly accepted views on energetics of N uptake and assimilation in higher plants and support the concept of a basically similar physiological behaviour between non-legumes and legumes.

Nitrogen form effects on early corn root morphological and anatomical development

Abstract Enhanced NH4 nutrition causes thicker roots (higher g/m root length) than NO3 nutrition. This study examined the underlying anatomy of N‐form altered root morphology. Corn (B73xLH51) was cultured in complete nutrient solutions containing NO3‐ or NH4‐N. Plants were harvested four times between 13 and 20 days after germination. Root lengths were measured and photomicrographs taken of primary and nodal root cross‐sections. Plants grew better under the NH4 regime. This was probably due to controlling acidity in the pH 6.0 to 6.5 range using 2.0 mM MES. The primary root system was 16% thicker under NH4‐N. No difference due to N form in the cross‐sectional area of the primary axis base was detected, suggesting that NH4‐N caused thicker laterals. Cross sectional areas of the first tier nodal roots were 27%‐ and 2nd tier roots 10.5%‐ greater under NH4‐N. Changes in the stelar and cortical regions were proportional in 1st tier nodal roots, but the cortex accounted for most of the NH4‐induced thickening in...

Growth, Free Amino Acids, and Mineral Composition of Tomato Plants in Relation to Nitrogen Form and Growing Media

Abstract Tomato plants ‘Campbell 1327’ grown in peat with NH4 nutrition had no visible symptoms of NH4 toxicity, while severe symptoms of NH4 toxicity were displayed in solution or sand culture. Growth of plants was much better with NO3-N than NH4-N in sand, vermiculite, or solution culture; but in peat, growth of NH4-treated plants equalled or exceeded that of NO3-treated plants in sand, vermiculite, and peat. The total dry weight of NH4-treated plants grown in peat was 2, 2.5, and 3.4 times higher than plants grown in vermiculite, sand, and solution culture, respectively. Content of uncomplexed ASHS.109.3.406 in NH4-treated plants grown in peat was reduced markedly compared with other media. NH4-treated plants grown in sand, vermiculite, and solution culture, displaying NH4 toxicity symptoms, had a total amino acid:free NH4+ molar ratio < 2, compared to 6-8 with NO3. For NH4-treated plants grown in peat the ratio was similar to that of NO3-treated plants. Asparagine and glutamine in NH4-treated plants grown in peat were 3.5 and 11.3 times higher than with NO3-N, indicating a high efficiency in detoxification of NH4 through incorporation into these amino acids. The medium on which a plant is grown can have a marked influence on the plant response to N form.

Inhibitory Effects of Ammoniacal Nitrogen on Growth of Radish Plants. I. Characterization of Toxic Effects of NH4+ on Growth and its Alleviation by NO3−1

Abstract Growth of radish (Raphanus sativus L.) was inhibited by NH4 as the source of N at concentrations from 1 to 240 ppm N. Higher levels of free NH4 accumulated in the plants as a result of NH4 nutrition. Nitrate equivalent to 10% or more of the NH4 concentration alleviated the inhibitor effects of NH4 on growth and also decreased the NH4 content of the plants. Five cultivars of radish responded similarly. Ammonium was also harmful for growth of etiolated seedlings, but NO3 did not reverse the inhibitory effects of NH4.

Effects of Soil Water Regime and Nitrogen Form on Blossom-end Rot, Yield, Water Relations, and Elemental Composition of Tomato1

Abstract Decreasing soil water potential (minima of −0.3, −2.0 and −6.0 bars) reduced fruit number, set, and mean and total fruit weight of tomato (Lycopersicon esculentum Mill). Under the 2 wettest soil water regimes, NH4-N compared to NO3-N fertilization reduced total and mean fruit weights but increased fruit number whereas no differences in these variables were found between N-forms under the driest regime. Incidence and severity of blossom-end rot (BER) were increased by NH4 nutrition and by decreasing soil water potential (SWP). Decreasing SWP either had no effect or increased leaf Ca, Mg, and K concentrations but decreased fruit concentration of these ions. At any soil water regime, NH4 fertilization decreased leaf Ca and Mg concentration but generally increased leaf K and fruit Ca, Mg, and K concentrations. While BER incidence and severity did not appear to be related to fruit Ca, Mg, and K concentration, the disorder was associated with increased stylar to calyx fruit-half concentration ratios of these ions. Basal (pre-dawn) leaf xylem pressure potential (ψp) was unaffected by N nutrition but was greater (less negative) under the wettest regime. Compared to plants supplied with NO3-N whose minimal and mean light-saturation ψp values decreased with decreasing SWP, plants given NH4-N reached a constant ψp level regardless of soil water regime. Since leaf diffusive resistance (RL) values increased with decreasing SWP, but were unaffected by N form, the lower transpiration and transpiration rates under NH4-N might be explained by increased non-leaf resistances to water flux and/or by reduced soil-plant water potential gradients.

EFFECTS OF CYCOCEL AND NITROGEN FORM ON TOMATO WATER RELATIONS, ION COMPOSITION, AND YIELD

Fertilizing tomatoes (Lycopersicon esculentum Mill.) Missouri breeding line 76-1-60-8 with NH4-N, as compared to NO3-N sources, in pot culture with unequal anion species and concentration and constant substrate moisture supply increased leaf diffusive resistance and water stress; reduced total transpiration and transpiration rate, leaf area, and mean fruit weight; and increased fruit and leaf Ca concentration and fruit Mg, K, and P concentration. Cycocel applied both foliarly and as a substrate drench to plants under NH4 nutrition increased leaf diffusive resistance; and reduced water stress, total transpiration, plant height, and total and mean fruit weights. Cycocel treatment under both N forms, with the exception of reduced leaf Ca concentration, either had no effect or increased leaf and fruit ion concentration. Under NH4-N nutrition, Cycocel treatment gave a 54% increase in fruit Ca concentration.

施用窒素形態とそ菜の適応性

Twelve species of fruit vegetables were grown in solution culture in order to compare the growth and nitrogen assimilation between them, using NO3, NO3+NH4, NH4, NO3+NO2, and NO2 as nitrogen sources. The experiment consisted of 4 kinds of treatment conditions where 2 levels of nitrogen concn (2me/l designated as low-N and 12me/l as high-N) and 2 levels of solution pH (5 and 7) were combined. Plants were grown under different treatments for about 3 weeks.1. When plants were supplied with NO3, the growth of vegetables, in general, was better in high-N than in low-N regime, though kidney beans grew better in low-N than in high-N regime. In the NO3 treatment, solution pH exerted almost no effect on plant growth except for sweet corn which showed somewhat inhibited growth at pH 7.2. In general, fruit vegetables fertilized with NO3+NH4 grew well under any cultural conditions. Plant growth of the NO3+NH4 treatment was better than or almost equal to that of the NO3 treatment.3. Solution pH and nitrogen concn showed pronounced effects on growth of the plants cultured with NH4 as a nitrogen source, i.e., NH4 tended to reduce the plant growth markedly under high-N at pH 5, but not under low-N at pH 7. In comparison with NO3, the growth of kidney beans, tender soybeans, peas, tomatoes, and sweet peppers was inhibited with NH4, while the growth of sweet corn and strawberries was not. When plants were cultured with NH4, a relatively close relationship was observed between growth response and leaf NH4-N concn, i.e., the better the plant growth, the lower the NH4-N concn in leaves. In several fruit vegetables, growth responses of plants to NH4 seemed to have a relation with NH4-N/amide-N ratio or insoluble-N/total-N ratio of the leaves.4. In general, NH4 nutrition reduced leaf concn of K, Ca, and Mg as compared to NO3. Such reduction in concn of leaf basic elements was remarkable in sweet peppers, tomatoes, and watermelons, but only slight in sweet corn and strawberries.5. Growth responses of plants to NO3+NO2 and NO2 were severely affected by pH and nitrogen concn of nutrient solution, i.e., plant growth was inhibited more markedly at low pH and high N concn. However, the growth of some vegetables cultured under low-N of NO3+NO2 and under low-N of NO2 at pH 7 was comparable to that of NO3 plant. When cultured with solutions containing NO2, the growth of melones, eggplants, cucumbers, and sweet corn was relatively good, though the growth of kidney beans was markedly restricted. On the other hand, the growth of peas, tender soybeans, and tomatoes which were supplied with NO2 was good only under low-N at pH 7. Okra was the most sensitive to NO2 toxicity at pH 5, whereas at pH 7 this plant seemed to belong to a group of most NO2-tolerant vegetables. When plants were supplied with NO2, no significant interrelations were observed between growth responses and leaf concn of nitrogenous constituents and/or composition of inorganic elements in leaves.

Ammonium Tolerance of Tobacco Cultivars with Different Nicotine Contents1

Abstract Cultivars of Nicotiana tabacum, L. of high and low nicotine contents were grown in an unbuffered nutrient solution sand culture. All of the cultivars showed significant growth restriction on NH4-N and formed brown stem lesions. The appearance of the lesions was delayed in ‘Speight G-41’ and ‘Lizard Tail Orinoco’, cultivars known to have high nicotine contents. Nicotine contents were reduced under NH4 nutrition in ‘Speight G-41’ and ‘Lizard Tail Orinoco’ but not in ‘Va. 724’.

Corn Growth as Affected By Ammonium vs. Nitrate Absorbed From Soil1

AbstractThe effect of NH4 on corn (Zea mays L.) growth in a soil medium is of interest because of the possibility of significantly decreasing leaching and denitrification losses of applied N by preserving N in the NH4 form. The objective of this investigation was to determine growth and nutrient content of corn plants when the principal form of N was either NH4 or NO3.Corn, grown in the greenhouse in a soil medium, was allowed to absorb N as either NH4 or NO3. A chemical nitrification inhibitor and different sources of added N were used to manipulate the form of N available for absorption. The maximum amount of N absorbed as NO3 was estimated as the difference between the NO3 content of fallow and cropped pots at harvest. Plants grown with NH4 and a nitrification inhibitor were estimated to have absorbed at least 95% of their N as NH4. Other plants absorbed N almost solely as NO3. The effect of NH4 versus NO3 absorption on stover yield, percent N, Ca, Mg, K, and P in the plant was determined.Yield of corn plants was not negatively affected by form of N absorbed when the meq ratio of applied N:K was 2:1. Visual tissue damage and decreased yield were symptomatic of NH4 nutrition where the meq applied N:K ratio was 3.3, 4.0, 4.4, 6.6, and 8.0. Nutrient content of the plants reflected strong cation:cation and cation:anion interactions among N form absorbed and Ca, Mg, K, and P. Soil pH appeared to be affected less by form of N absorbed by the corn plants than by nitrification of applied NH4.

Response of Growth and Mineral Composition of Potato to Nitrate and Ammonium Nitrogen1

Abstract Fertilization of 2 cultivars of potato (Solanum tuberosum L.) grown in solution culture with NH4—N resulted in growth reduction, leaf roll, suppression of Ca and Mg uptake, and enhancement of P uptake compared with responses with NO3—N. Calcium and Mg decreased as time under NH4 nutrition increased. Solution pH had little affect on response to N form.

Comparative Reduction of Calcium and Magnesium Composition of Corn Tissue by NH4‐N and K Fertilization1

AbstractAmmonium‐N nutrition in nutrient culture has been shown to reduce Ca and Mg uptake to near‐deficient levels in many plants. The addition of K to soils also reduces Ca and Mg contents of plants. Since NH4‐N is often present during the seedling growth period of plants a study was set up on soils with high and low exchangeable Ca and Mg levels to determine the comparative effect of NH4‐N and rate of K on Ca and Mg absorption by corn (Zea mays L.) plants. Knowledge of these effects could be of benefit in formulating fertilizer programs in crop production where Ca and Mg content is a factor in forage or crop quality.A greenhouse study was conducted to compare the influence of N form and K levels on the absorption of Ca and Mg by corn plants grown in Princeton sand with 67 kg Mg/ha and Fincastle silt loam with 800 kg Mg/ha. The treatments used were 100 ppm N as NH4 or NO3, and 0, 50 and 100 ppm K in factorial design. Aerial portions of the plants were analysed for N, P, K, Ca, and Mg.Increasing levels of K in the soils under NO3 nutrition reduced the concentrations of Ca and Mg in the corn tissue. However, NH4‐N at the zero K rate reduced Ca and Mg concentrations in the corn tissue to less than that at the highest K rate with NO3‐N. K rate did not significantly change Ca or Mg uptake under NH4 nutrition on either soil. The exchangeable Mg level of the soil directly affected the Mg composition of the tissue with both NO3‐N and NH4‐N nutrition. The ammonium‐N source reduced Mg uptake by corn on the soil with exchangeable Mg of 67 kg/ha to a deficient level of less than 0.20% in this tissue, which is the critical Mg level of forage associated with incidence of hypomagnesemia in ruminant animals. Thus NH4‐N must be considered an important factor in its influence on cation concentration of tissue grown on low Mg soils during periods when NH4‐N is the predominant N source.

Effect of ammonium nutrition on uptake and metabolism of nitrate in wheat.

Wheat plants 1 month old grown in nitrate culture were exposed for 2 days to media containing 4 meq NO3 and 0-4 meq NH4/l. Where solutions contained both forms of N the uptake of NH4 exceeded that of NO3 even at the lowest NH4 level. NH4 metabolism predominated over NO3 assimilation and resulted in a higher free amino acid content, a lower carboxylate content and lower nitrate reductase activity in the tops than with NO3 alone. NH4 inhibited nitrate reductase activity whereas amino acids did not. The fall in activity of this enzyme in wheat tops caused by NH4 nutrition could not be related to the low level of tissue NH4 and it was suggested that changes in the redox situation in the cells might be involved. (Abstract retrieved from CAB Abstracts by CABI’s permission)

A comparison between ammonium and nitrate nutrition of young sugar-beet plants grown in nutrient solutions at constant acidity. 2. Effect of light and carbohydrate supply.

The effect of light and of glucose in the nutrient medium on the release of OH- or H+ and on ion accumulation by sugar beet plants grown with NO3 or NH4 nutrition was studied at a constant pH of 5.50. Decrease in OH- production rate in the dark was probably caused by retarded nitrate assimilation or carbohydrate shortage in the roots. Decrease in the rate of H+ production (NH4 uptake) in the dark was probably due to carbohydrate depletion. Both 24-h illumination and the addition of glucose increased H+ production during NH4 uptake and OH- production during NO3 uptake. 24 h darkness decreased the carboxylate pool on both N sources and it was tentatively concluded that light and darkness exert more influence on the carboxylate pool than N assimilation. Relationships between organic acid, carbohydrate and N metabolism, H+ or OH- production and inorganic composition were considered in detail. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Nutritional Factors Influencing the Mineral Content of Apple Leaves1

Abstract ‘York Imperial’ apple trees on EM 26 rootstock were grown in large, outdoor sand cultures for 3 years. All combinations of N at 2, 4, or 8 me/1 as all NO3 or as 3/4NH4 - 1/4 NO3; Ca at 1, 8 or 16 me/1; and B at 0.05 or 0.5 ppm were supplied in solution, with other nutrients in normal supply. Levels of N and Ca and their interactions affected growth under NO3 nutrition. Growth was greatly reduced under NH4 nutrition, but was little affected by levels of N and Ca. Leaf tissues were analysed for N, P, K, Ca, Mg, Al, B, Cu, Fe, Mn, and Zn. The average, 3-year over-all effect of NH4 nutrition was to increase leaf concentration of all elements except K, Al, and Mn. Source of N altered the main effects and interactions between levels of N and Ca. B had little effect on concentration of other elements in the leaves.