Nitrogen partitioning in greenhouse‐grown broccoli in response to varying NH+ 4:NO− 3 ratios

Abstract

Broccoli (Brassica oleracea var. italica) plants were grown in the greenhouse and supplied continuously with 18 mM N in the following NH⁺ ₄:NO^? ₃ ratios: 100:0, 75:25, 50:50, 25:75, 0:100. At commercial maturity, the plant characteristics and partitioning of nitrogen in xylem and phloem saps and in plant tissue were determined. Plants fed solely with NH⁺ ₄ were stunted, exhibited signs of marginal necrosis on the lower leaves, and accumulated NH⁺ ₄ in the foliage. The maximum yield and shortest harvest time, together with minimal NO^? ₃ and NH⁺ ₄ accumulation were found at a ratio of 75:25. Ammonium concentrations in xylem sap decreased linearly with decreasing NH⁺ ₄ portion in the nutrient solution, whereas the NO^? ₃ concentrations reached a maximum when NO^? ₃ constituted 50% of the N supply. The glutamate family dominated the amino acid composition of both xylem and phloem saps, but did not vary much with NH⁺ ₄:NO^? ₃ ratio. It is suggested that the NH⁺ ₄ concentration in xylem sap may be used to assess NH⁺ ₄ vs NO^? ₃ utilization by broccoli grown under field conditions.     

GROWTH AND NUTRITION OF YOUNG BEAN PLANTS UNDER HIGH ALKALINITY AS AFFECTED BY MIXTURES OF AMMONIUM,POTASSIUM, AND SODIUM

High concentrations of bicarbonate (HCO^? ₃) cause alkalinity of irrigation water and are associated with suppression in plant growth and micronutrient deficiencies, such as iron (Fe) and zinc (Zn). Because reports indicate that the deleterious effects of alkalinity may be counteracted partially by supplementary potassium (K⁺) or ammonium (NH₄ ⁺) an experiment was designed to evaluate the response of bean plants (Phaseolus vulgaris L.) grown in high alkalinity conditions to varying proportions of NH₄ ⁺, K⁺, or sodium (Na⁺) (as a potential substitute for K⁺). Plants established in a growth chamber were grown in hydroponics for 21 days in solutions containing 5 mM HCO^? ₃ and a total of 5 mM of a mixture of NH₄ ⁺, K⁺, and Na⁺. The proportions of NH₄ ⁺, K⁺, and Na⁺ were designed according to mixture experiment methodology. Total N in all the mixture treatments was maintained at 10 mM by using nitrate (NO^? ₃)-N, thus the NH₄ ⁺:NO^? ₃ ratio varied according to the proportion of NH₄ ⁺ in the mixtures. Alkalinity caused suppression in plant growth and chlorophyll concentration in the younger leaves, whereas excessive NH₄ ⁺ was associated with leaf scorching and decreased leaf expansion. High proportions of K⁺ alleviated alkalinity symptoms and produced higher shoot and root dry mass provided that NH₄ ⁺ was included in the mixture. However, a proportion of NH₄ ⁺ higher than 0.333 in the mixture (>1.66 mM NH₄ ⁺) induced toxicity. The highest shoot dry mass occurred if the NH₄ ⁺:NO^? ₃ ratio was 0.19:0.81 and the NH₄ ⁺:K⁺:Na⁺ proportion was 0.38:0.38:0.24 (1.9 mM NH₄ ⁺ + 1.9 mM K⁺ + 1.2 mM Na⁺). Thus, an improvement in plant growth is achieved when NH₄ ⁺, K⁺, and Na⁺ are blended together, in spite of the high alkalinity treatment imposed. Optimum NH₄ ⁺ was associated with a decrease in solution pH and an increase in shoot Fe and Zn concentration.     

Effects of Nitrogen Source on Growth and Development of Strawberry Plants

ABSTRACT

An experiment was conducted to study the effects of nitrate (NO₃ ^?) and ammonium (NH₄ ⁺) ratios in nutrient solutions on the growth and production of fruits, runners, and daughter plants of strawberry Fragaria x ananassa Duch., grown in a hydroponic system. Five treatments were applied, consisting of different proportions of NH₄ ⁺ and NO₃ ^? in the nutrient solution. The NH₄ ⁺:NO₃ ^? ratios were: T0 = 0:4, T1 = 1:3, T2 = 2:2, T3 = 3:1, and T4 = 4:0, at a constant nitrogen (N) concentration of 4 mol m^?3. Growth and morphogenesis were characterized by monitoring leaf-area increase, number of flowers and fruits per plant, and number of daughter plants of first and second generations. Nitrogen and carbon (C) content were measured at the end of the experiment in the organs of both mother and daughter plants. None of the variables related to the growth of the mother plant was affected by the treatments. However, the number of fruits increased with the proportion of NH₄ ⁺ in the nutrient solution. The number of daughter plants produced was affected only at high NH₄ ⁺ proportions, and their size (dry matter per daughter plant) and fertility (number of second-generation plants per first-generation plants) were reduced. The N or C content of the plants was not significantly affected by the treatments, but the C/N ratio in the crowns of mother plants was higher in treatments with 25% and 50% NH₄ ⁺ in the nutrient solution.     

Growth and nutrition of pansy as influenced by N‐form ratio and temperature

Abstract

Pansy (Viola xwittrockiana Gams.) producers often observe nutrient disorders among plants grown during warm periods (>18°C) of the growing season. These disorders typically are not seen when production temperatures are optimal (≥18°C) even though fertility regimes may remain the same. Our objectives were to assess the effects of temperature and nitrogen (N) fertility on growth and nutrition of pansy. Pansies cultivar ‘Crown White’ were grown until lateral branches had open flowers. Treatments consisted of two temperatures (12 and 22°C) and three NO₃ ^?:NH₄ ⁺ molar % ratios (100:0, 62:38, and 25:75) with a total concentration of 100 mg N L^?1. A modified Hoagland's solution was used with NO₃ ^?‐N supplied as Ca(NO₃)₂ and KNO₃ and with NH₄ ⁺‐N as (NH₄)₂SO₄. Cumulative nutrient absorption and foliar nutrient content were determined when plant lateral branches flowered. Root and shoot growth were limited when NH₄ ⁺ was present in solutions at high ambient air temperature (22°C), but not at low temperature (12°C). Individual absorption and accumulation of plant nutrients varied with N regimes and temperatures. Overall, pansies absorbed more total N, NH₄ ⁺, NO₃ ^?, calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P), zinc (Zn), and less iron (Fe) and manganese (Mn) at 12°C than at 22°C. In addition, absorption of NO₃ ^? by pansy was negligible if any NH₄ ⁺ was present in solutions at 22°C. Results suggest that pansy growers should adjust fertility programs according to production temperatures to avoid possible nutritional disorders and maximize plant growth. If maximum growth is to be obtained in warm temperatures, the use of NH₄ ⁺‐containing fertilizers should be reduced or eliminated. However, the choice of NO₃ ^?:NH₄ ⁺ ratio for nutrition may be less important under cool growing conditions.     

DOUGLAS-FIR SEEDLING RESPONSE TO A RANGE OF AMMONIUM: NITRATE RATIOS IN AEROPONIC CULTURE

The objective of the experiment was to identify the most favorable nitrogen (N) source ratio of ammonium (NH₄ ⁺) and nitrate (NO₃ ^?) for aeroponically-grown Douglas-fir when pH was maintained at pH 4.0. Seedlings were grown in controlled environments with solutions containing 0:100, 20:80, 40:60, 60:40, 80:20 or 100:0 NH₄ ⁺:NO₃ ^? ratios. Nutrient additions in the aeroponic culture units were controlled by solution conductivity set points. Seedling growth and nutrient allocation was observed for 45 days. Different NH₄ ⁺:NO₃ ^? ratios resulted in significant differences in the rate of N addition, growth, morphology, and nutrient allocation. Seedlings grown in solutions containing 60 or 80% NO₃ ^? were characterized by a combination of high growth and photosynthetic rates, high and stable internal plant N concentrations, and sufficient levels of other essential nutrients. High proportions of NH₄ ⁺ in solution resulted in low rates of N addition, stunted lateral root growth, and may have been toxic.     

Root Carbon Enrichment Alleviates Ammonium Toxicity in Cucumber Plants

ABSTRACT

The addition of carbonates to a nutrient solution to alleviate ammonium (NH₄ ⁺) toxicity in hydroponically-grown cucumber (Cucumis sativus L.) plants was investigated. Stable isotopes [nitrogen (¹⁵N) and carbon (¹³C)] were used to assess the uptake of nitrogen [NH₄ ⁺ or nitrate (NO₃ ^?)] as well as carbon [bicarbonate (HCO₃ ^?)/carbonate (CO₃ ^2?)] by the roots. Ammonium as the sole N source at 5 mM decreased plant fresh weights compared to NO₃ ^?. However, at lower concentrations of NH₄ ⁺ (25% of 5 mM total N), growth was increased compared to NO₃ ^? alone. Inorganic C enrichment [calcium carbonate (CaCO₃)] of the nutrient solution increased the fresh weight of NH₄ ⁺ grown plants with up to 150% relative to control plants receiving calcium hydroxide [Ca(OH)₂] for pH regulation. Root ¹⁵N enrichment was lower in ¹⁵NH₄ ⁺ supplied plants compared to ¹⁵NO₃ ^?, while the ¹³C enrichment in leaves was increased by NH₄ ⁺ nutrition compared to NO₃ ^? or NH₄NO_3. The enhanced C capture was associated with high PEPCase activity in the roots. It is concluded that inorganic carbon enrichment of the root medium may alleviate NH₄ ⁺ toxicity via increased synthesis of C skeletons and, accordingly, increased capacity for NH₄ ⁺ assimilation and N export to the shoots.     

Influence of Ammonium and Nitrate Nutrition on Plant Growth and Zinc Accumulation by Indian Mustard

ABSTRACT

The source of nitrogen (N) used in soil fertility practices affects plant growth, nutrient absorption, and the availability of nutrients. Consequently, the potential of plants to extract zinc (Zn) from soils may be increased by controlling the ratio of NH₄ ⁺ to NO₃ ^? to maximize growth and Zn accumulation. The objectives of this research were to determine the effects of Zn supply and different molar ratios of NH₄ ⁺ to NO₃ ^? on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.). In a factorial experiment with solution culture, Indian mustard (accession 182921) was supplied with two concentrations of Zn (0.05 and 4.0 mg L^?1) in combination with six N treatments with different molar percentage ratios of NH₄ ⁺ to NO₃ ^? (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for three weeks. Zinc supplied at 0.05 mg Zn L^?1 represented a common concentration of Zn in solution culture, whereas 4.0 mg Zn L^?1 was excessive for plant nutrition. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, which became severe if plants were supplied with 80% of N as NO₃ ^?. Supplying high proportions of NO₃ ^? in the nutrient medium stimulated Zn accumulation, whereas increasing proportions of NH₄ ⁺ (up to 50% of the total N) enhanced shoot growth. The pH of nutrient solutions generally decreased with increasing proportion of NH₄ ⁺ in solutions and with increased Zn supply. The Zn phytoextraction potential of Indian mustard was maximized, at about 15 mg Zn plant^?1, if plants received 10% of the total N as NH₄ ⁺ and 90% as NO₃ ^?.     

Tolerance of Lisianthus to High Ammonium Levels in Rockwool Culture

Nitrogen (N) by form of nutrition, ammonium (NH₄⁺) or nitrate (NO₃^?), affects metabolic and physiological processes of plants. In general, a high proportion of N in NH₄⁺ form results in poor growth. Nonetheless, a number of species exhibit optimum growth when high levels of NH₄⁺ are provided. In the present study, lisianthus [Eustoma grandiflorum (Raf.) Shinn] was grown in rockwool cultures and irrigated with nutrient solutions containing 15 mM N with varying proportions of NH₄⁺ and NO₃^?. The results showed that an increase in NH₄⁺-N form increased plant height, number of flowers and leaves, leaf area, and shoot, stem, and leaf dry weight. The proportion of NH₄⁺ also affected leaf concentration of phosphorus, potassium (K), calcium (Ca), and magnesium (Mg), although leaf N concentration was unaffected. Potassium leaf concentration was higher when a low proportion of NH₄⁺ was supplemented in the nutrient solution; however, plants exhibited a decrease in leaf K concentration and a decrease in leaf Ca as the proportion of NH₄⁺-N increased. Shoot dry weight was higher with low leaf K whereas high leaf Ca was associated with high shoot dry weight. Net photosynthesis rate was higher in plants irrigated with solutions containing 75% of total N in NH₄⁺ form than in those irrigated with solutions of 0 or 25%. The results suggest that lisianthus can tolerate high levels of NH₄⁺, probably associated with a higher assimilation of Ca.     

NITRATE/AMMONIUM RATIOS AFFECT RYEGRASS GROWTH AND NITROGEN ACCUMULATION IN A HYDROPONIC SYSTEM

Ryegrass has increasingly been used in constructed wetlands for treatment of eutrophic wastewater. To properly match plant species with the characteristics of wastewater being treated, it is important to know the performance of plant species under different nitrate/ammonium (NO₃ ^?/NH₄ ⁺) ratios. We investigated ryegrass (Lolium perenne L.) dry matter (DM) production and N accumulation under five NO₃ ^?/NH₄ ⁺ ratios (100/0, 75/25, 50/50, 25/75, 0/100) in a hydroponic system. The results showed that ryegrass total DM, shoot DM, root DM and nitrogen (N) accumulation were greater under NO₃ ^?/NH₄ ⁺ ratios of 50/50 and 75/25 than under other NO₃ ^?/NH₄ ⁺ ratios, indicating that ryegrass can be best used in constructed wetlands for treating wastewater with such NO₃ ^?/NH₄ ⁺ ratios to achieve high biomass production and efficient removal of N. On the other hand, for treating wastewater with either NO₃ ^? or NH₄ ⁺ dominate the inorganic N, other plant species that are more adapted to such conditions should be explored.     

PANSY FLORAL DEVELOPMENT AND NUTRIENT ABSORPTION AS INFLUENCED BY TEMPERATURE,NITROGEN FORM,AND STAGE OF PLANT DEVELOPMENT

Production temperatures can affect the marketability of pansies (Viola × wittrockiana Gams.) by influencing plant growth, the presence of nutrient disorders, and the rate of floral development. The choice of nitrogen (N) form in fertility can also influence pansy growth and nutrition, but the effect of fertility on pansy flowering is not clear. Whether or not temperature and N fertility work together to influence nutrient absorption at different stages of the pansy life cycle is unknown. Our objectives were to determine the influence of temperature and N form on pansy floral development, and to identify the peak nutrient demand periods at different temperatures and ratios of NO₃ ^? to NH₄ ⁺ in fertility. Pansies cv. ‘Crown White’ were grown in nutrient solution cultures until lateral branches had open flowers. Treatments consisted of two temperatures (12°C and 22°C) and three stages of floral development (five true leaf stage until visible bud, visible bud until first flower, first flower until flowering on lateral branches), and three NO₃ ^? :NH₄ ⁺ molar % ratios (100:0, 62:38, 25:75) with a total concentration of 100 mg N L^?1. A modified Hoagland's solution was used with NO₃ ^??N supplied as Ca(NO₃)₂ and KNO₃ and with NH₄ ⁺?N as (NH₄)₂SO₄. The effects of temperature and N form on the time required for development of different floral stages were assessed. In addition, the influence temperature and N form on nutrient absorption was determined for three pre‐determined stages of floral development to identify peak nutrient demand periods. The timing of flower bud development and first flower was not influenced by treatments. At 22°C, pansies flowered earlier on lateral branches than at 12°C, but these plants also suffered a loss in quality due to unfavorable growth characteristics and the development of nutritional disorders. Individual absorption of plant nutrients at different stages of development varied with temperature and N regime. Overall, pansies absorbed the greatest quantity of magnesium (Mg) before flower bud development, calcium (Ca) after flower bud development, and NH₄ ⁺, NO₃ ^? phosphorus (P), and potassium (K) after anthesis. In addition, pansies absorbed more NO₃ ^?, Ca, Mg, and P at 12°C than at 22°C. At times, the absorption of NO₃ ^? was dramatically decreased with increasing NH₄ ⁺ in solutions. Results suggest that nutrient absorption by pansy in different stages of development is influenced by production temperatures and the choice of N form in fertilization. Adjusting fertility programs according to peak demand periods and production temperatures will help prevent periodic nutrient disorders during the life cycle, and may reduce fertilization costs.     

Effect of N‐form on macronutrient and micronutrient concentration and uptake of creeping bentgrass 1

Abstract

Nitrogen‐form effect on nutrient uptake and the subsequent concentration of nutrients in turfgrass plant tissue has not been thoroughly investigated. This study evaluated the effects of clipping regime and N‐form on the tissue concentration of macronutrients and micronutrients and macronutrient uptake in ‘Penncross’ creeping bentgrass (Agrostis palustris Huds.). Turfgrass plugs were grown under greenhouse conditions in a modified Hoagland's solution with a combination of three nutrient solutions (100% NO₃ ^?, 100% NH₄ ⁺, and 50:50 ratio of NH₄ ⁺:NO₃ ^?) and two cutting regimes (cut and uncut). Concentrations of macronutrients and micronutrients were determined for shoot, root and verdure. Nutrient uptake was determined weekly. Uncut NO₃ ^?‐treated plants accumulated higher concentrations of K, Ca, Mg, B and Cu in the shoot tissue; P, K, Ca, Mg, B, Cu, Mn and Zn in the root tissue; and P, Ca, Mg, B, Fe and Mn in the verdure compared to uncut NN₄ ⁺‐treated plants. Nitrate uptake was greater with uncut NO₃ ^?‐treated plants than was NH₄ ⁺ absorption with uncut NH₄ ⁺‐treated plants. Plants grown with the uncut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with the uncut NO₃ ^? and 50:50 treatments adsorbed higher amounts of P, K, and Ca compared to the NH₄ ⁺ treatment. The cut NO₃ ^?‐treated plants accumulated higher concentrations of K in the shoot tissue; P, Ca, Mg, B, Cu, Fe and Mn in the root tissue; and B in the verdure than did the cut NH₄ ⁺‐treated plants. Cut NO₃ ^?‐treated plants adsorbed less NO₃ ^? than did cut NH₄ ⁺‐treated plants adsorbed NH₄ ⁺. The cut 50:50 treatment adsorbed more NH₄ ⁺ than NO₃ ^?. Plants grown with NO₃ ^? and 50:50 treatments, under both cutting regimes, resulted in higher concentrations of most macro‐ and micronutrients and greater nutrient uptake compared to the NH₄ ⁺‐treated plants.     

Effect of Nitrate/Ammonium Ratios on Growth,Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO₃^?)/ammonium (NH₄⁺) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH₄⁺ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO₃^? and NH₄⁺ compared to NO₃^? or NH₄⁺ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH₄⁺. The microelements concentrations were generally increased with more NH₄⁺ added. In addition, plants fed with higher NO₃^?/NH₄⁺ ratios resulted in more minerals accumulation.     

Fruit Yield of Tomato Cultivated on Media with Bicarbonate and Nitrate/Ammonium as the Nitrogen Source

ABSTRACT

This article presents the effects of nitrate/ammonium (NO₃ ^?/NH₄ ⁺), applied at different proportions to the root media with or without 5 mmol bicarbonate (HCO₃ ^?), on the yield and chemical composition of tomato fruit. Tomato plants were grown hydroponically (pH 6.9) in glasshouse conditions. The yield of fruit fresh matter from four clusters obtained from plants grown on the medium with NH₄ ⁺ was about 25% lower than from the plants grown on the medium containing NO₃ ^? as the nitrogen (N) source. Supplying NO₃ ^?/NH₄ ⁺ at a ratio of 4:1 increased the fruit yield by about 20% in comparison with the value recorded for NO₃ ^??plants. The enrichment of the medium with HCO₃ ^? stimulated the bearing, while the result depended on the ratio of NO₃ ^?/NH₄ ⁺. A combined treatment of HCO₃ ^? with NO₃ ^? or NH₄ ⁺ in the medium increased yields by about 28% and 11%, respectively, in comparison to plants cultivated without HCO₃ ^?. The application of NO₃ ^?/NH₄ ⁺ at ratios of 4:1 and 1:1 with HCO₃ ^? increased the respective yields by about 16% and 10% in comparison with plants grown without HCO₃ ^?. Modifications in the composition of the media affected the accumulation of organic solutions in the fruit. The NH₄ ⁺ nutrition effected a 20% decrease in the accumulation of reducing sugars in the fruit in comparison to the fruit of plants grown in media with NO₃ ^?. In the cultivation of plants in media with various NO₃ ^?/NH₄ ⁺ proportions the intermediate values of the reduced sugar concentrations were recorded in comparison with the values obtained for NO₃ ^??plants and NH₄ ⁺?plants. The enrichment of media with HCO₃ ^? increased the concentration of sugars in fruit from about 28% (for NO₃ ^??plants) to about 10% (for NH₄ ⁺?plants).

Malate and citrate are the main constituents of carboxylates in tomato fruit. The form of nitrogen applied to the medium did not significantly affect the concentration of carboxylates in fruit. Significant differences in carboxylate concentrations appeared in fruit grown on media enriched with HCO₃ ^? ions. In comparison with the cultivation without HCO₃ ^?, increases in the accumulation of carboxylates varied from about 22% to 30% depending on the form of the applied nitrogen. The concentration of amino acids in the fruit of plants grown with NH₄ ⁺ exceeded that in NO₃ ^??plants by about 55%. In the plants grown on media of modified NO₃ ^?/NH₄ ⁺ proportions, the concentration of amino acids in fruits were positively correlated with the level of NH₄ ⁺ in the medium. The enrichment of media with HCO₃ ^? stimulated a further increase in amino acid concentration in fruit by about 9% in NO₃ ^? plants and about 21% in NH₄ ⁺ plants compared with the respective control (without HCO₃ ^?).     

Effect of Ammonium: Nitrate Ratio on Yield,Calcium Concentration,and Photosynthesis Rate in Strawberry

The effect of ammonium:nitrate (NH₄:NO₃) ratio in nutrient solution on growth, photosynthesis (Pn), yield, and fruit quality attributes in hydroponically grown strawberry (Fragaria × ananassa Duch) cvs. ‘Camarosa’ and ‘Selva’ was evaluated. There were four nutrient solutions of differing NH₄:NO₃ ratios as follows: 0:100, 25:75, 50:50, and 75:25. Plants grown in solution with 75% NH₄ had lower leaf fresh and dry weights and leaf area than those with 25% NH₄ in both cultivars. High ratios of NH₄ and NO₃ in the solution always reduced the yield. The yield was increased by 38% and 84% in ‘Camarosa’ and ‘Selva,’ respectively, when the plants were grown in the 25NH₄:75NO₃ solution compared with plants grown in a higher NH₄ ratio solution. The increased yield at the 25 NH₄:75NO₃ ratio was the result of the increase in fruit size, i.e., length and fresh weight of fruits. Plants grown in the 25NH₄:75NO₃ solution had the highest rate of Pn, while those grown in 75NH₄:25NO₃ solution had the lowest Pn rates in both cultivars. Increasing the NH₄ ratio in the solution from 0 to 75% significantly reduced the calcium (Ca) concentration and postharvest life of the fruits in both cultivars. Both higher leaf area and Pn rate appeared to be the reason for the increased yield and plant growth in the 25:75 ratios of nitrogen (N). The results indicate the preference of strawberry plant growth toward a greater nitrate N form in a hydroponic solution. Therefore, a combination of two forms of N in an appropriate ratio (25NH₄:75NO₃) appears to be beneficial to plant growth, yield, and quality of strawberry fruits.     

Influence of the Modification of Nutritional Parameters in Aglaonema commutatum: K+, Ca2+, Mg2+ and Na+

Abstract

This trial was carried out to establish an appropriate nutrient solution for Aglaonema commutatum and to investigate the nutritional effects generated by modifications in the solution. Six treatments were tested: control (T₀; pH 6.5, E.C. 1.5 dS m^?1, 6 mmol L^?1 NO₃ ^?‐N, and 6 mmol L^?1 K⁺); high nitrogen (N) level (T₁; 9 mmol L^?1 6:3 NO₃ ^?–NH₄ ⁺); N form (T₂; 6 mmol L^?1 N‐NH₄ ⁺); high K⁺ level (T₃; 12 mmol L^?1 K⁺); high electrical conductivity (T₄; E.C. 4 dS m^?1, 25 mmol L^?1 NaCl), and basic pH (T₅; pH 8). At the end of the cultivation, leaf, shoot, and root dry weights and elemental concentrations were determined. Nutrient contents and total plant uptake were calculated from the dry weights and nutrient concentrations. Plant K⁺ uptake increased with application of K⁺ or basic nutrient solution. The uptake and transport of calcium (Ca) were enhanced by the use of NO₃ ^?‐N and inhibited by the presence of other cations in the medium (NH₄ ⁺, K⁺, Na⁺) and by basic pH. Magnesium (Mg) uptake increased with NO₃ ^?‐N application and with pH. Sodium (Na) uptake was the highest in the saline treatment (T₄), followed by the basic pH treatment. Sodium accumulation was detected in the roots (natrophobic plant), where the plant generated a physiological barrier to avoid damage. Dry weight did not differ significantly (p<0.05) among treatments except in the NaCl treatment. These results may help in the formulation of nutrient solutions that take into account the ionic composition of irrigation water and the physiological requirements of plants.     

Responses of Polygonatum odoratum seedlings in aeroponic culture to treatments of different ammonium: nitrate ratios

The objective was to determine the most favorable nitrogen (N) source ratio of ammonium (NH₄⁺) to nitrate (NO₃^?) for aeroponic culture of Chinese fragrant solomonseal Polygonatum odoratum (Mill.) Druce seedlings. Seedlings were cultured with solutions based on 50% Hoagland formula containing 0:100, 10:90, 20:80, and 30:70 NH₄⁺:NO₃^? ratios for 21 days. Activities of anti-oxidant enzymes and glutathione contents of leaves with treatments of 10:90 and 20:80 NH₄⁺:NO₃^? ratios were higher than that of all-nitrate treatment, and malondialdehyde (MDA) concentrations were lower than that of all-nitrate treatment. The maximum quantum yield ?P_o value was normal among all of the treatments, whereas the absorption energy ABS/CSm value with 20:80 NH₄⁺:NO₃^? treatment was highest and the heat dissipation DIo/CSm value with 20:80 NH₄⁺:NO₃^? treatment was lowest among all of the treatments. These results supported that moderate proportion of 20% NH₄⁺ in the solution provided optimal growth condition for (P) P. odoratum aeroponic culture.     

Effects of Nitrogen Levels and Nitrate/Ammonium Ratios on Oxalate Concentrations of Different Forms in Edible Parts of Spinach

Two hydroponic experiments were carried out to investigate the effects of nitrogen (N) levels and forms on the oxalate concentrations of different form in edible parts of spinach. Nitrogen was supplied at five levels (4, 8, 12, 16, 20 mM) in Experiment 1 and five ratios of nitrate (NO₃ ^?) to ammonium (NH₄ ⁺) (100/0, 75/25, 50/50, 25/75, 0/100) at a total N of 8 mM in Experiment 2. Biomass of spinach increased markedly from 4 mM to 8 mM N and reached the flat with further increase in N. The total oxalate and soluble oxalate in leaves and shoots (edible parts) increased significantly with increasing N levels from 4 to 12 mM, while the total oxalate and insoluble oxalate decreased markedly when N level was further increased from 12 to 20 mM. Oxalates of different forms in petioles increased first and then decreased and elevated again with increasing nitrogen levels. In the second experiment, decreasing NO₃ ^?/NH₄ ⁺ ratios markedly increased at first and then significantly decreased the biomass of spinach plants and the maximum biomass was recorded in the treatment of the NO₃ ^?/NH₄ ⁺ ratio of 50:50. The oxalate concentrations of different form in leaves and shoots were all decreased obviously as the ratio of NO₃ ^?/NH₄ ⁺ decreased from 100:0 to 0:100. Concentrations of total oxalate and soluble oxalate in petioles could be reduced by increasing ammonium proportion and were the lowest as the ratio of NO₃ ^?/NH₄ ⁺ was 50:50 and insoluble oxalate decreased as nitrate/ammonium ratio decreased. The concentrations of oxalate forms in leaves were all higher than those in petioles and soluble oxalate was predominant form of oxalates in both trials. It is evident that high biomass of spinach can be achieved and oxalate concentrations of different forms can be reduced by modulating N levels and NO₃ ^?/NH₄ ⁺ ratio, so this will benefit for human health especially for those people with a history of calcium oxalate kidney stones.     

Influence of Pre-Plant Micronutrient Mixes and Ammonium to Nitrate Ratios in Fertilizer Solution on Growth and Micronutrient Contents of Marigold in Plug Culture

ABSTRACT

The purpose of this work was to determine the effects of pre-plant micronutrient mixes and various ammonium/nitrate (NH₄ ⁺/NO₃ ^?) ratios in a fertilizer solution on growth and the nutrient uptake of French marigold ‘Orange Boy’ in a plug culture. Two kinds of granular glass frits containing six micronutrients were produced and incorporated into peatmoss+vermiculite (1:1, v/v) substrate at a rate of 0.3 g · L^{? 1}. The five NH₄ ⁺/NO₃ ^? ratios in fertilizer solution were 0/100, 25/75, 50/50, 75/25, and 100/0, each giving a total nitrogen (N) supply of 80, 100, and 120 mg · L^{? 1}in the root substrate during stages 2, 3, and 4, respectively. The plants produced a significantly higher fresh and dry matter yield at 35 days after sowing when grown in 25/75 N nutrition in micronutrient fertilizer 1 (MF1) and 50/50 in micronutrient fertilizer 2 (MF2) than in the other NH₄ ⁺/NO₃ ^? ratios tested. Treatments of the highest accumulation of iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), and boron (B) in plants were 25/75, 50/50, 50/50, 25/75 and 50/50 in MF1 and 50/50, 25/75, 50/50, 50/50, 50/50 in MF2, respectively. The trends in accumulations of Fe, Mn, Zn, Cu, and B in plants were quadratic (Q), linear (L) and Q, L and Q, L and Q, and Q, respectively, in MF1. Those in MF2 were Q, Q, Q, L and Q, and Q, respectively.     

铵硝比和磷素营养对菠菜生长、氮素吸收和相关酶活性的影响

通过水培试验研究了不同铵硝比的氮素营养和磷素营养对菠菜生长、氮素吸收及硝酸还原酶活性（NRA）和谷氨酰胺合成酶活性（GSA）的影响。结果表明：在供磷水平相同时，菠菜的生物量随着铵硝比的降低而降低，但铵硝比为25：75与0：100两个处理之间没有显著差异；在铵硝比相同时，随着营养液中磷含量的增加，菠菜的生物量随之增加。菠菜茎叶中硝酸盐的含量随着铵硝比和磷水平的降低而升高。不同铵硝比处理，菠菜含氮量没有明显差异，随着磷水平的提高，菠菜植株含氮量有升高的趋势，但各处理之间差异不显著；受到生物量显著差异的影响，菠菜植株中氮素累积量随着铵硝比的降低和磷素水平的增加而增加。在铵硝混合营养条件下，缺磷会显著抑制菠菜对铵态氮和硝态氮的吸收，且磷索缺乏对菠菜吸收硝态氮的抑制作用要大于对铵态氮吸收的抑制作用。铵硝比相同时，随着营养液中磷索供应量的增加，菠菜茎叶中NRA显著增加；但是营养液中铵硝比较高时，会显著抑制菠菜茎叶中NRA，而铵硝比较低时，则有利于提高菠菜的NRA。缺磷会严重抑制GSA；在磷素水平相同时，随着营养液中铵比例的增加，菠菜茎叶中GSA显著增加。为此，在一些硝酸盐含量较高的土壤上栽培蔬菜时，可以采取增施适量磷肥的方法，以降低叶菜的硝酸盐含量。     

Effects of different forms of nitrogen supply on the gas exchange of young pedunculate oaks (Quercus robur L.)

The effects of different forms and concentrations of N in the rooting medium on the CO₂/H₂O gas exchange of leaves of the pedunculate oak (Quercus robur L.) were investigated. Two-year-old seedlings were grown in nutrient solutions containing low (1.8 mM) or high (4.8 mM) concentrations of NH₄⁺, 3.6 mM NO₃^?, or both NH₄⁺ and NO₃^? (1.8 mM + 1.8 mM). In various sets of plants subjected to these N treatments, the following parameters were determined: biomasses of leaves and fine roots, leaf area-related net photosynthesis at light saturation (A) and leaf conductance (g), foliar concentrations of chlorophylls, N, Ca²⁺, Mg²⁺ and K⁺ and the ash alkalinity of the leaves (as a measure of the carboxylate content). In all treatments, the leaves were equally well supplied with nutrients. Oaks grown in high NH₄⁺ concentrations produced significantly smaller leaf and root biomasses. Compared to oaks cultivated with both N forms or with low NH₄⁺ concentration, oaks grown with high NH₄⁺ supply showed lower values of A and g, but no significant differences in ash alkalinity and leaf area-related chlorophyll concentrations. Oaks fed with NO₃^? as the only N form had an intermediate biomass production, but low values of A and g. The time courses of A in the different treatments closely followed the patterns of g. In all N treatments, the same linear relationship was found between A and g, indicating that, within a rather wide range, the variation in the form and amount of supplied N does not affect the instantaneous water use efficiency of young pedunculate oaks.