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1.
Ammonium sulfate or urea were added as N-source to shredded straw of Miscanthus ogiformis ‘Giganteus’ and water was included as control. The combined materials were composted for seven months, and the resulting composts were tested as growth substrates for nursery container plants and compared with fertilized and unfertilized peat substrates. The pH was below recommended level for the compost substrate made with ammonium sulfate and for the unfertilized peat substrate throughout the experiment. Electrical conductivity and concentrations of most nutrients were low and decreased throughout the experiment for all growth substrates. Shrinking of the growth substrates after 4, 12 or 17 months was larger for compost substrates than for peat substrates. Bulk density increased in compost substrates and decreased in peat substrates, while the total loss of C was greater in compost substrates than in peat. Water retention was lower and air volume greater for compost substrate made with ammonium sulfate than for fertilized peat. Algae and mosses did not occur on Miscanthus compost growth substrates in contrast to peat substrates. The shoot length and dry matter of Hedera helix, produced after four and 12 months of growth, and five months following cut back, showed that plants can grow well in compost substrates made of Miscanthus straw and ammonium sulfate or urea. However, the compost substrates could not fully substitute for fertilized or unfertilized peat substrate with respect to dry matter production.  相似文献   

2.
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3.
The growth of Helianthus annuus L. calli and plants was reduced in the presence of Na2SO4 (10, 25, 50, and 100 mM). SO42— and Na concentrations increased in stressed calli and plants while NO3—, Cl—, P, K, and Mg decreased in stressed plants and Ca in shoots. Stressed calli showed decreases of NO3—, Ca, K, and Mg concentrations. Calli adapted to 50 mM Na2SO4 accumulated more K and Ca and less ammonium than stressed non‐adapted calli. Proline exhibited increases in stressed calli and plants that were accompanied by decreases of proline oxidase activities while pyrroline‐5‐carboxylate reductase (P5CR) and ornithine aminotransferase (OAT) activities increased. Adapted calli accumulated more proline and had higher P5CR and OAT activities than stressed non‐adapted calli. Glutamate concentration decreased with stress, together with a stimulation of cytosolic glutamine synthetase (GS1) and a decrease of plastidal GS (GS2) activity. These data strongly suggest that the increase of P5CR and GS1 activities are responsible for the decrease of glutamate concentration leading, together with the stimulation of OAT and the inhibition of the proline oxidation metabolism, to an increase of proline levels in Na2SO4‐stressed sunflower cells. These data also show that salt stress increases the release of endogenous ammonium and suggests that the increase of GS1 activity plays an important role in its elimination.  相似文献   

4.
Growth of vinca [Catharanthus roseus (L.) G. Don ‘Grape Cooler'] was compared under several cultural conditions. Conditions investigated included two types of media (a peat‐lite mix and a mix containing 25% pine bark) and five types of nutrient charges in the peat‐lite media (sulfated micros, chelated micros, sulfated or chelated micros with pH adjustment to 5.5, and no charge). Nitrogen (N) source effect on growth was also investigated. Plants were grown at five different ratios of nitrate‐N to ammonium‐N. Greatest growth as measured by shoot length and shoot dry weight occurred in the peat‐lite media at either the sulfated micro or chelated micros adjusted to pH 5.5 and at the highest ratios of nitrate‐N to ammonium‐N. Root dry weight and growth were negatively affected by high levels of ammonium‐N in the fertilizer solution.  相似文献   

5.
The mobility of nutrients in soils is well characterized, whereas little information is available for common horticultural substrates based on peat. Aim of the current study was to investigate the mobility and dynamics of phosphorus (P) as well as the parameters involved in P transport to plant roots in peat‐based substrates. A series of experiments was run to determine the impedance factor (f) and the buffer power (b). The impedance factor was determined for black peat and black peat mixed with 20% and 40% (v/v) of mineral component at volumetric water content (θ) of 40%, 50%, 60%, and 70% and at different diffusion time. Buffer power was calculated for black peat and black peat mixed with 20% (v/v) of seven different mineral components. Phosphorus was applied at rates of 0, 35, and 100 mg (L substrate–1), respectively. The impedance factor was not affected by addition of the mineral component to peat. However, f increased from 0.03 to 0.2, by increasing θ from 40% to 60%, indicating that water content has a significant effect on this parameter. Substrate‐solution P ranged from 0.3 to 27 and from 1 to 95 mg P (L solution)–1 for the P‐application rate of 35 and 100 mg P (L substrate)–1, respectively. Buffer power of the substrates ranged from 1 to 17.25 depending on the mineral component, and it was positively correlated with oxalate‐soluble Fe and Al in the substrate. The calculated effective diffusion coefficient for P in the substrate was in the range of 10–7 to 10–8 cm2 s–1. This high value could be attributed mostly to the low buffer power rather than to the high impedance factor.  相似文献   

6.
Two experiments were conducted to study the effect of grafting on nitrogen‐use efficiency (NUE) in mini‐watermelon plants. In the first study, mini‐watermelon plants (Citrullus lanatus [Thumb.] Matsum. and Nakai cv. Minirossa) either ungrafted or grafted onto Macis, Vita (Lagenaria siceraria [Mol.] Standl.), PS1313, and RP15 (Cucurbita maxima Duchesne × Cucurbita moschata Duchesne) rootstocks grown in hydroponics were compared in terms of shoot dry biomass, leaf area, root‐to‐shoot ratio, SPAD index, shoot N uptake, and nitrate reductase (NR) activity 40 d after transplantation in response to nitrate concentration in the nutrient solution (0.5, 2.5, 5, 10, 15, or 20 mM of NO$ _3^- $ ). In the second experiment, the suitability of a selected rootstock with high NUE (Vita) to improve crop performance and NUE of grafted mini‐watermelon plants was evaluated under field conditions. In the hydroponic experiment mini‐watermelon grafted onto Vita rootstock needed the lowest nitrate concentration (1.31 mM of NO3) in the nutrient solution to reach half maximum shoot dry weight. Total leaf area, SPAD index, and shoot N uptake increased in response to an increase of N concentration in the nutrient solution. At 2.5 mM NO$ _3^- $ , mini‐watermelon grafted on either Vita or RP15 had the highest NR activity whereas no significant difference was observed at 10 mM NO$ _3^- $ . The open‐field study indicated that increasing N‐fertilization rates from 0 to 100 kg ha–1 improved total and marketable yields of mini‐watermelon plants while decreasing NUE. When averaged over N levels, the marketable yield, NUE, N‐uptake efficiency, and N‐utilization efficiency were significantly higher by 39%, 38%, 21%, and 17%, respectively, in Minirossa grafted onto Vita compared to ungrafted Minirossa plants. Therefore, grafting mini‐watermelon plants onto selected rootstocks can be used as a quick and effective method for improving productivity and NUE.  相似文献   

7.
Growth, activity of antioxidant enzymes viz. glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX), and some metabolic processes related to ammonium metabolism were investigated in a salt‐tolerant Spatina alterniflora. In comparison to 0 mM–NaCl treatment, growth of S. alterniflora plant increased significantly at 200 mM NaCl, but was highly inhibited at 500 mM NaCl. Ammonium concentration in the leaves and roots increased 2.1–3.4 times when plants were treated with 500 mM NaCl. Under 200 mM NaCl, antioxidant‐enzyme activities increased, however, at 500 mM the antioxidant system was unable to compensate reactive oxygen species induced by NaCl. At this high level of salinity, ammonium production through nitrate reductase (NR) was inhibited, but no significant changes in the activities of glutamine synthetase (GS) or glutamate dehydrogenase (GDH) were found. We conclude that the accumulation of ammonium under high salt stress was not due to inhibition of the assimilatory activities of GS or GDH. Ammonia accumulation under high salinity may result from amino acid and protein catabolism activated by reactive oxygen species (ROS) and/or a lack of carbon skeletons to incorporate ammonium into organic molecules due to a decrease in photosynthetic activity in salt‐stressed plants.  相似文献   

8.
One of the requirements for the forest restoration of soils disturbed by the oil‐exploitation industry is that saplings be able to endure soil‐adverse conditions. In this study, saplings of 20 species susceptible to be used in reforestation programs were evaluated for their ability to grow on substrates derived from soils disturbed by petroleum extractions in the Ecuadorian Amazon. Seeds of each species were planted in germination trays. Once seedlings reached 5 cm in height they were transplanted to plastic bags with three treatment substrates: two derived from petroleum‐exploitation activity (soils from mud and drill cutting cells and from areas surrounding oil wells) and a control soil. Plant survival rate, stem height, and diameter were measured on a weekly basis until 14 weeks after transplantation, when we harvested the plants and also measured plant biomass and calculated the Dickson quality index for each species. Oil‐exploitation by‐product substrates impaired the performance of many saplings, with the substrate from mud and drill cutting cells being the one that most affected plant performance. Only saplings of five native species in the Amazon basin—Apeiba membranaceae, Cedrelinga cateniformis, Inga densiflora, Myroxylon balsamum, and Pouroma cecropiifolia—exhibited high or similar Dickson quality index values in all soil treatments and performed better than the rest. The use of these five species in remediation of soils disturbed by petroleum extraction in the Amazon basin could prove important because of their high potential to adapt to these disturbed sites. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

9.
The concentrations of polycyclic aromatic hydrocarbons (PAHs) were analyzed in samples of peat and of two plant species (Pinus sylvestris and Ledum palustre) overgrowing peat‐bogs in the north‐east of Poland. Peat samples were collected from different depths according to the stratigraphic profile of the peat bogs. The total concentrations of the 16 anthropogenic PAHs (15 from the US EPA list and benzo[e]pyrene) in all peat samples were between 70 and 439 ng g—1. The concentration for the same compounds in pine needles (Pinus sylvestris) and Dutch Myrthe leaves (Ledum palustre) varied between 194 and 1039 ng g—1. A noticeably high fluorene concentration in Dutch Myrthe leaves was found at some sites. In all peat samples 3‐ring compounds were predominant (55 to 319 ng g—1). There were less 4‐ring PAHs (15 to 110 ng g—1) and the least common PAHs were 5‐ring and 6‐ring compounds (0 to 81 ng g—1 for both groups). In some peat samples, the perylene concentration largely exceeds of the total concentration of all the other PAHs investigated. The high content of perylene in bottom layers could result from the processes of perylene sorption from water during peat‐bog formation or from biogenic formation of perylene.  相似文献   

10.
Mineral and organic fertilizers contain different forms and amounts of nitrogen (N), which can affect yield and product quality. The aim of this study was to determine appropriate amounts of N applied as nitrate (NO ), ammonium (NH ), and organic N (a mixture based on chicken manure) for optimal growth and quality of tomatoes. A pot experiment with sand as substrate was established in a greenhouse with six‐week‐old tomato plants (Lycopersicon esculentum Mill. cv. “Armada”). Nitrogen was applied in nutrient solutions at different NO : NH ratios combined with different chloride levels (NO ‐dominated, NO = NH at low Cl–, NO = NH at high Cl–, and NH ‐dominated, respectively) or as organic N at four N‐application rates (250, 500, 750, 1000 mg N plant–1 week–1). No significant differences in shoot biomass and yields of red tomatoes were observed between NO ‐ or NH ‐fed plants. Nitrogen rates above 750 mg N plant–1 week–1 did not significantly increase marketable fruit yield, but enhanced shoot‐biomass production. The NH ‐N‐dominated treatments (which also had high Cl– concentrations) showed increasing incidence of blossom‐end‐rot (BER)‐infected fruits. In the organic‐N treatments, shoot‐biomass production and yields were lower than in the inorganic‐N treatments, but fruit quality was good with few BER‐infected fruits. The results show that with a total N supply below 750 mg N plant–1 week–1, NH can be used as equivalent N source to NO , resulting in equivalent yields of marketable fruit under the conditions in this experiment.  相似文献   

11.
The use of compost with high salt concentration was evaluated, under commercial conditions, as a potential growing media constituent for vegetable transplant production. Two composts were prepared from sweet sorghum bagasse, pine bark, and either urea (compost A) or brewery sludge (compost B) as N source. Three vegetable species — broccoli (Brassica oleracea), tomato (Lycopersicum esculentum), and onion (Allium cepa) with different tolerance to salinity were used. Eleven substrates were formulated and tested: a control consisting of a moss peat-based commercial substrate; compost A; compost B; and, eight mixtures containing 33 or 67% by volume of each compost with either raw peat moss or commercial substrate as diluent. All the substrates prepared had suitable physical, physicochemical and chemical properties for use as growing media, except for the electrical conductivity (ranging from 3.20 to 13.21 dS m?1) which was above the reference levels for soilless cultivation. Broccoli was the least affected by substrate salinity whilst tomato was the most. Onion transplants had an intermediate response to saline conditions. Tomato seed germination was markedly reduced when compost A, with a higher salt concentration, was used at a rate higher than 67%. Media prepared with either of the composts, and mixed with either a commercial substrate or peat in a rate up to 67%, did not cause any detrimental effect on the growth and nutritional status of broccoli, tomato and onion transplants, despite the high initial salinity of the substrates. These composts appear to be acceptable substitutes for Sphagnum peat in seed sowing mixtures.  相似文献   

12.
Salt marshes are characterized by the occurrence of combined salinity and flooding stresses. The individual and combined effects of salinity and flooding on the establishment and activity of arbuscular mycorrhizal (AM) colonization in the salt marsh halophyte Aster tripolium L. by indigenous salt marsh AM fungi were evaluated. A. tripolium plants were cultivated in a mixture of sand and salt marsh soil under different salinity concentrations (5%, 50% or 100% artificial seawater) and water regimes (non-flooding, tidal flooding and continuous flooding). Plants were harvested after 3 and 8 weeks and their growth was negatively influenced by increased salinity and water level. Increased salinity level affected the establishment of AM colonization, AM fungal growth and activity (measured as succinate dehydrogenase activity) within roots, and extraradical mycelium growth. The influence of flooding on the establishment of colonization and on intra- and extraradical AM fungal growth was dependent on the water regime. Continuous flooding reduced colonization and AM fungal growth, whereas tidal flooding did not affect these parameters unless combined with intermediate salinity level (50% seawater) at the end of the experiment. The water regime did not influence AM active colonization. The ratio of root to soil AM fungal growth increased as the water level increased. The results of this study demonstrate that the establishment and activity of AM colonization in A. tripolium is more influenced by salinity than by flooding, and suggests that the functionality of salt marsh AM fungi is not affected by flooding.  相似文献   

13.
The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m–1 may have a deleterious effect on maize growth.  相似文献   

14.
Phosphorus (P) forms were sequentially extracted from peat derived soils (Eutric Histosols and Gleysols) at eight sites in Saxony‐Anhalt (Germany) to disclose general differences in P pools between mineral and organic soils and to investigate effects of peat humification and oxidation in conjunction with land use and soil management on the P status of soils. Overall 29 samples providing a wide variety of basic chemical properties were subjected to the Hedley fractionation. The Histosol topsoils contained more total P (Pt) (1345 ± 666 mg kg—1) than the Gleysol topsoils (648 ± 237 mg kg—1). The predominant extractable fractions were H2SO4‐P (36—63 % of Pt) in calcareous and NaOH‐Po (0—46 % of Pt) in non‐calcareous Histosols. These soils had large pools of residual P (13—93 % of Pt). Larger contents and proportions of Po and of labile P fractions generally distinguished organic from mineral soils. Regression analyses indicated that poorly crystalline pedogenic oxides and organic matter were binding partners for extractable and non‐extractable P. Intensive management that promotes peat humification and oxidation results in disproportional enrichments of labile P fractions (resin‐P, NaHCO3‐Pi, and NaHCO3‐Po). These changes in P chemistry must be considered for a sustainable management of landscapes with Histosols and associated peat derived soils.  相似文献   

15.
Abstract

An upland rice variety IAC‐47 was grown in a greenhouse to determine the effect of foliar nitrogen (N) supplementation during grain development on the activity of the N assimilation enzymes, nitrate reductase (NR) and glutamine synthetase (GS), on free amino‐N content and leaf soluble sugars, and on grain crude protein content. At 10 and 20 days after anthesis (DAA), the leaves were fertilized with a liquid fertilizer containing 32% N as 12.8% urea, 9.6% ammonium (NH4), and 9.6% nitrate (NO3) in increasing rates corresponding to 0,20+20, 40+40, and 60+60 kg N ha‐1. Leaves were collected twice (at 12 DAA and 14 DAA for GS activity, sugar and amino‐N content, and at 11 and 13 DAA for NRA) after each application of leaf N. The late foliar application of N increased significantly grain crude protein without a corresponding decrease in grain weight. The NR activity (NRA) increased after the foliar application of N. In the flag leaf, 60+60 kg N ha‐1 (21 DAA) resulted in higher NRA (20x over the control), while GS activity was smaller than the control. At 22 DAA there was an increase in GS activity in the flag leaf at 20+20 N level. However, the GS activity decreased as applied N levels increased. Also at the 20+20 level, there were increases in free amino‐N in the flag leaf and second leaf at the final harvest. Throughout the experiment, plants at the 60+60 N level had the lowest levels of soluble sugars. Increases in crude protein were highest at 40+40 N level (27.9%), followed by 60+60 (18.7%).  相似文献   

16.
A field method for the measurement of substrate‐induced soil respiration A novel method for in situ measurements of microbial soil activity using the CO2 efflux combined with kinetic analysis is proposed. The results are compared with two conventional, laboratory methods, (1) substrate‐induced respiration using a ’︁Sapromat’ and (2) dehydrogenase activity. Soil respiration was measured in situ after addition of aqueous solutions containing 0 to 6 g glucose kg—1 soil. The respiration data were analysed using kinetic models to describe the nutritional status of the soil bacteria employing few representative parameters. The two‐phase soil respiration response gave best fit results with the Hanes' or non‐parametric kinetic model with Michaelis‐Menten constants (Km) of 0.05—0.1 g glucose kg—1 soil. The maximum respiration rates (Vmax) were obtained above 1 g glucose. Substrate‐induced respiration rates of the novel in situ method were significantly correlated to results of the ’︁Sapromat’ measurements (r2 = 0.81***). The in situ method combined with kinetic analysis was suitable for the characterisation of microbial activity in soil; it showed respiration rates lower by 59% than measured in the laboratory with disturbed samples.  相似文献   

17.
This study aimed at investigating mechanisms of salt tolerance and ionic relations of chickpea (Cicer arietinum L.) cultivars with different nitrogen (N) sources. Two resistant genotypes, ILC‐205 and ILC‐1919, were subjected to four levels of salinity (0.5, 3.0, 6.0, and 9.0 dS m‐1). Nitrogen sources consisted of inoculation with two resistant Rhizobium strains, CP‐29 and CP‐32, mineral N additions, and no N application. Data was collected on root and shoot contents of sodium (Na+) chlorine, (Cl‐,) and potassium (K+), and shoot to root Na+ratio, as well as shoot K+ to Na+ ratio. Salinity affected shoot Na+ and Cl‐contents, but nodulating plants had higher shoot Na+ contents than plants supplied with mineral N. Shoot to root Na+ ratios were lower in the mineral N treatment than in nodulating treatments at 3.0 dS m‐1, indicating that root compartmentalization and shoot exclusion were only possible at low salinities. Potassium levels of nodulating plant shoots were lower than those of non‐nodulating plants only at low salinities. N‐source significantly affected shoot K+/Na+ ratio, with nodulating plants having lower ratios than non‐nodulating plants, indicating that rhizobial infection or nodule formation may lead to salt entry curtailing the selective ability of chickpea roots.  相似文献   

18.
Abstract

A field study evaluating the effects of gypsum and water management on the survival, yield, and protein content of selected species of marsh vegetation was conducted on an open area inundated by brackish water near Hackberry, Cameron Parish, Louisiana. The overall growth and yield response of four species of marsh vegetation: joint grass (Paspalum vaginatum SW.), marsh hay cordgrass (Spartina patens Muh L.), salt grass (Distichlis spicata L.), and American three square (Scirpus americanus Pers.) to gypsum addition (0 versus 7 Mg/ha) and water management (flooded versus non‐flooded plots) were statistically evaluated.

Soil drying was detrimental to the overall growth and yield of all marsh vegetation. There was zero plant survival in the non‐flooded plots except the marsh hay cordgrass with a survival rate of 32.8 %.

Plots receiving 7 Mg gypsum/ha had significantly higher dry matter production than the control. Gypsum application increased dry yield of joint grass (5.44 to 8.08 Mg/ha), marsh hay cordgrass (1.90 to 6.91 Mg/ha), salt grass (0.97 to 2.79 Mg/ha) and three‐square (1.55 to 2.84 Mg/ha) in flooded plots. The yield of marsh hay cordgrass, the only surviving species in the non‐flooded plots, produced a yield increase of 0.40 Mg/ha in response to gypsum. Significantly higher survival rates were observed in flooded plots treated with gypsum than in the non‐flooded plots receiving no gypsum. The mean survival rate for the gypsum‐ treated plots was 68.2%, as opposed to 21.9% for the untreated plots.  相似文献   

19.
The form of nitrogen (N) supply has a significant impact on rhizosphere chemistry and root growth responses of higher plants. The respective effects are also employed as management options to improve nutrient acquisition and to minimize nutrient losses in cropping systems. However, surprisingly little is known concerning the interactions with rhizosphere biota. In this study, we investigated the effects of selected bacterial and fungal inoculants with proven plant growth‐promoting and phosphate (P)‐solubilizing potential (plant growth‐promoting microorganisms, PGPM) in maize with nitrate or stabilized ammonium supply, on soils with limited P availability and sparingly soluble rock phosphate (Rock‐P) applied as P fertilizer. The combination of the bacterial inoculants Pseudomonas sp. DSMZ 13134 (Proradix) and Bacillus amyloliquefaciens FZB42 with ammonium sulphate fertilization, stabilized with the nitrification inhibitor 3,4‐dimethylpyrazole‐phosphate (DMPP), resulted in a superior shoot biomass production (79–111%) and shoot P accumulation (109–235%) as compared with nitrate supply. This effect could be partially attributed to (1) ammonium‐induced rhizosphere acidification via increased root extrusion of protons, (2) promotion of root hair elongation, and (3) increased shoot concentrations of hormonal growth regulators (indole‐3‐acetic acid, zeatin, gibberellic acid). The effects, induced by the microbial inoculants were mainly related to increased root length development (43–44%), associated with a 60% increase in auxin production potential. No inoculant effects were detected on root hair elongation or on chemical modifications of the rhizosphere involved in P solubilisation, such as rhizosphere acidification, release of carboxylates or secretory phosphohydrolases. However, the ammonium‐induced stimulation of root hair elongation increased preferential sites for root colonization by the selected inoculants, which may explain the increase in rhizosphere abundance of PGPMs, exemplarily recorded for the fungal inoculant Trichoderma harzianum OMG16 (210%). The presented data suggest a network of positive interactions between stabilized ammonium fertilization and plant growth‐promoting functions of various bacterial and fungal PGPM inoculants. This offers perspectives to increase the efficiency and the reproducibility of PGPM‐assisted fertilization strategies.  相似文献   

20.
Intraspecific differences in the activities of nitrate reductase (NR), glutamine synthetase (GS), NADH dependent glutamate synthase (NADH‐GOGAT), and glutamate dehydrogenase (GDH) under contrasting forms of nitrogen (N) supply were studied in tissues of three spinach (Spinacia oleracea L.) cultivars. The varieties (Viroflay, Butterflay, and Giant) were smooth, curly and semicurly leaved, respectively. The plants were grown in nutrient solutions containing NO3 as the sole source of N (100:0) and NO3 plus NH4 (80:20). Giant, the NH4 tolerance of which had been evaluated in growth and on the basis of nutrient uptake, had much higher GS and GDH activities in the roots and higher NR and NADH‐GOGAT levels in the leaves of plants grown on NO3 and NH4 than that grown on NO3 alone. On the level of N assimilating enzymes of Butterflay, mixed N nutrition caused an increase of GDH and NADH‐GOGAT in leaves and roots and at the same time a decrease of GS in the roots and NR in the leaves. An inverse relationship between GS and GDH activities was detected in the leaves and foots of Virofiay grown with both N sources. Finally, Viroflay gave the highest levels of GDH irrespective of the NO3:NH4 assayed, whereas the leaves of Giant were GDH deficient in comparison with the other cultivars. In addition, the GS activity approached zero in the roots of spinach cultivars characterized by hardly any NH4 tolerance, whereas in those of Giant it increased remarkably with the supply of NO3 plus NH4.  相似文献   

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