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1.
Ammonium sulphate is a major component of the air pollutants deposited on forests in the Netherlands. Different amounts of NH4 + were added to Douglas-fir seedlings grown in tall containers of sand, to study the influence of high concentrations of NH4 + in the soil on the development of fine roots and the effects of nitrogen uptake on rhizosphere pH. At the end of this eight-month experiment part of the ammonium appeared to have nitrified into nitrate. High doses of ammonium negatively affected root length and root length per unit of dry matter (specific root length). Although Douglas fir shows a preferential ammonium uptake in nutrient solutions the increases in the pH of the rhizosphere in this experiment indicate that nitrogen was mostly taken up as nitrate. When the ammonium concentration in the soil is low, it cannot be taken up readily because of its low mobility in soil. Shoot growth was stimulated by high availability of nitrogen. The possible effects of high doses of ammonium on long-term forest vitality are discussed.  相似文献   

2.
Excessive use of nitrogen (N) fertilizer has increased ammonium (NH4+) accumulation in many paddy soils to levels that reduce rice vegetative biomass and yield. Based on studies of NH4+ toxicity in rice (Oryza sativa, Nanjing 44) seedlings cultured in agar medium, we found that NH4+ concentrations above 0.75 mM inhibited the growth of rice and caused NH4+ accumulation in both shoots and roots. Use of excessive NH4+ also induced rhizosphere acidification and inhibited the absorption of K, Ca, Mg, Fe and Zn in rice seedlings. Under excessive NH4+ conditions, exogenous γ‐aminobutyric acid (GABA) treatment limited NH4+ accumulation in rice seedlings, reduced NH4+ toxicity symptoms and promoted plant growth. GABA addition also reduced rhizosphere acidification and alleviated the inhibition of Ca, Mg, Fe and Zn absorption caused by excessive NH4+. Furthermore, we found that the activity of glutamine synthetase/NADH‐glutamate synthase (GS; EC 6.3.1.2/NADH‐GOGAT; EC1.4.1.14) in root increased gradually as the NH4+ concentration increased. However, when the concentration of NH4+ is more than 3 mM, GABA treatment inhibited NH4+‐induced increases in GS/NADH‐GOGAT activity. The inhibition of ammonium assimilation may restore the elongation of seminal rice roots repressed by high NH4+. These results suggest that mitigation of ammonium accumulation and assimilation is essential for GABA‐dependent alleviation of ammonium toxicity in rice seedlings.  相似文献   

3.
Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability. Rice is the most Al-resistant species among small grain cereal crops and prefers NH4 + as its major inorganic nitrogen source. This study investigates the effects of NH4 + and NO3 ? on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH4 + preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH4 + and NO3 ? supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH4 +-preferring than Yangdao6. NH4 + alleviated Al toxicity in two cultivars compared with NO3 ?. Both NH4 +-Al supply and pretreatment with NH4 + reduced Al accumulation in roots and root tips compared with NO3 ?. NH4 + decreased but NO3 ? increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO3 ? concentration enhanced Al accumulation in root tips but increasing the NH4 + concentration had the opposite effect. These results show NH4 + alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO3 ?, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH4 +, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated with the preferred utilization of NH4 + is suggested.  相似文献   

4.
Root hair development is orchestrated by nutritional factors and plant hormones. We investigated the action of ammonium (NH4+) and its interactions with methyl jasmonate (MeJA) and ethylene in Arabidopsis root hair growth. The formation of root hair branches was dramatically stimulated in media containing 1.25 to 20 mM NH4+ at pH values of 4.0 to 6.5. The NH4+-treated root hairs showed a very short tip growth stage and swells on the sides that indicated the emergence of branches. MeJA (0.08 to 10 μM) worked in synergism with NH4+ to enhance hair branching. In contrast, ethylene had an antagonistic effect; the stimulation of hair branching by NH4+ was suppressed by the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and was diminished in ethylene-overproducing mutant eto1-1 seedlings. Moreover, the application of Ag+, an ethylene inhibitor, reduced the ACC-induced inhibition of NH4+-stimulated hair branching and restored NH4+-stimulated hair branching in eto1-1 seedlings. Thus, the actions of jasmonate and ethylene appear to be dependent on nutritional conditions such as available nitrogen.  相似文献   

5.
Root growth in higher plants is sensitive to excess ammonium (NH4+). Our study shows that contact of NH4+ with the primary root tip is both necessary and sufficient to the development of arrested root growth under NH4+ nutrition in Arabidopsis. We show that cell elongation and not cell division is the principal target in the NH4+ inhibition of primary root growth. Mutant and expression analyses using DR5:GUS revealed that the growth inhibition is furthermore independent of auxin and ethylene signalling. NH4+ fluxes along the primary root, measured using the Scanning Ion‐selective Electrode Technique, revealed a significant stimulation of NH4+ efflux at the elongation zone following treatment with elevated NH4+, coincident with the inhibition of root elongation. Stimulation of NH4+ efflux and inhibition of cell expansion were significantly more pronounced in the NH4+‐hypersensitive mutant vtc1‐1, deficient in the enzyme GDP‐mannose pyrophosphorylase (GMPase). We conclude that both restricted transmembrane NH4+ fluxes and proper functioning of GMPase in roots are critical to minimizing the severity of the NH4+ toxicity response in Arabidopsis.  相似文献   

6.

Aims

Rice is known as an ammonium (NH4 +)-tolerant species. Nevertheless, rice can suffer NH4 + toxicity, and excessive use of nitrogen (N) fertilizer has raised NH4 + in many paddy soils to levels that reduce vegetative biomass and yield. Examining whether thresholds of NH4 + toxicity in rice are related to nitrogen-use efficiency (NUE) is the aim of this study.

Methods

A high-NUE (Wuyunjing 23, W23) and a low-NUE (Guidan 4, GD) rice cultivar were cultivated hydroponically, and growth, root morphology, total N and NH4 + concentration, root oxygen consumption, and transmembrane NH4 + fluxes in the root meristem and elongation zones were determined.

Results

We show that W23 possesses greater capacity to resist NH4 + toxicity, while GD is more susceptible. We furthermore show that tissue NH4 + accumulation and futile NH4 + cycling across the root-cell plasma membrane, previously linked to inhibited plant development under elevated NH4 +, are more pronounced in GD. NH4 + efflux in the root elongation zone, measured by SIET, was nearly sevenfold greater in GD than in W23, and this was coupled to strongly stimulated root respiration. In both cultivars, root growth was affected more severely by high NH4 + than shoot growth. High NH4 + mainly inhibited the development of total root length and root area, while the formation of lateral roots was unaffected.

Conclusions

It is concluded that the larger degree of seedling growth inhibition in low- vs. high-NUE rice genotypes is associated with significantly enhanced NH4 + cycling and tissue accumulation in the elongation zone of the root.  相似文献   

7.
Deposition of ammonium (NH4+) from the atmosphere is a substantial environmental problem. While toxicity resulting from root exposure to NH4+ is well studied, little is known about how shoot‐supplied ammonium (SSA) affects root growth. In this study, we show that SSA significantly affects lateral root (LR) development. We show that SSA inhibits lateral root primordium (LRP) emergence, but not LRP initiation, resulting in significantly impaired LR number. We show that the inhibition is independent of abscisic acid (ABA) signalling and sucrose uptake in shoots but relates to the auxin response in roots. Expression analyses of an auxin‐responsive reporter, DR5:GUS, and direct assays of auxin transport demonstrated that SSA inhibits root acropetal (rootward) auxin transport while not affecting basipetal (shootward) transport or auxin sensitivity of root cells. Mutant analyses indicated that the auxin influx carrier AUX1, but not the auxin efflux carriers PIN‐FORMED (PIN)1 or PIN2, is required for this inhibition of LRP emergence and the observed auxin response. We found that AUX1 expression was modulated by SSA in vascular tissues rather than LR cap cells in roots. Taken together, our results suggest that SSA inhibits LRP emergence in Arabidopsis by interfering with AUX1‐dependent auxin transport from shoot to root.  相似文献   

8.
Ruan  Jianyun  Zhang  Fusuo  Wong  Ming H. 《Plant and Soil》2000,223(1-2):65-73
The effects of nitrogen form and phosphorus source on the growth, nutrient uptake and rhizosphere soil property of tea (Camellia sinensis L.) were investigated in a pot experiment. The experiment was performed with a compartmental cropping device, which enables the collection of rhizosphere soil at defined distances from the root of tea plant. Nitrogen was supplied as nitrate or ammonium in combination with soluble phosphorus as Ca(H2PO4)2 or insoluble P as rock phosphate. The leaf dry matter production of tea was significantly greater in the treatments with NH4 + than NO3 -, whereas dry matter production of root and stem was not significantly affected. Addition of phosphorus as either source did not influence the dry matter production. The concentrations of K in root, Mg and Ca in both the shoot and root supplied with NO3 - were significantly higher than in NH4 + and influence of P sources was minor. On the contrary, Al and Mn concentrations were significantly larger in NH4 --fed plants which could be attributed to remarkably increased availability of Al and Mn caused by acidification of the rhizosphere soil (the first 1-mm soil section from the root surface) with NH4–N nutrition. The concentration of N in shoot was also significantly higher in NH4- than in NO3-fed plants, indicating higher use efficiency of NH4–N. Whatever the phosphate source, rhizosphere pH declined in ammonium compared to in nitrate treatment. The pH decrease was much larger when no P or soluble P were applied and reached 0.85–1.30 units which extended to 3–5 mm away from the root surface. Exchangeable acidity, content of exchangeable Al and Mn were also considerably higher in the rhizosphere soils of NH4 + fed tea plants. Significant amounts of P dissolved from rock phosphate accumulated in rhizosphere of NH4 +, not NO3 -, suggesting that the dissolution of rock phosphate was induced by the proton excreted by tea root fed with ammonium. With soluble P addition, shoot and root P concentrations were greater in NH4 + than in NO3 - treatment and it appeared that this difference could not be sufficiently explained by the available P content in soil which was only slightly higher in NH4 + treatment. With rock phosphate addition, the shoot and root P concentrations were hardly affected by nitrogen form, although the available P content was much higher and accumulated in the rhizosphere soil supplied with ammonium. The reason for this was discussed with regard to the inter-relationship of Al with P uptake. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.
Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH4 or NO3 at 10 mmol m?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO3. The specific absorption rate (SAR) of NH+4 was greater at all temperatures than SAR-NO3. In plants grown with NH+, 3–5% of the total N was recovered as NH+4, whereas in those grown with NO?3 the unassimilated NO?3 rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH+4 lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO?3-grown plants. Plants grown with NH+4 had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO?3 grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH+4 or NO?3. The additional residual N (protein) in NH+4 grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.  相似文献   

10.
Nitrate reductase activity (NRA) was found in primary roots, but not in foliage of red spruce (Picea rubens Sarg.) seedlings. Nitrate induced NRA:NH4+ did not induce and slightly depressed NRA in older seedlings. Induction required 8 hours and, once induced, NRA decreased slowly in the absence of exogenous NO3. Seedlings were grown in perlite with a complete nutrient solution containing NH4+ to limit NR induction. Established seedlings were stressed with nutrient solutions at pH 3, 4, or 5 supplemented with Cl salts of Al, Cd, Pb, or Zn each at two concentrations. NRA in primary root tips was measured at 2, 14, 28, and 42 days. NRA induction was greatest at pH 3, and remained high during the period of study. NRA induction at pH 4 was lower. Metal ions suppressed NRA at pH 3 and 5, but enhanced NRA at pH 4. It is concluded that acidity and soluble metals in the root environment of red spruce are unlikely to be important factors in nitrogen transformations in red spruce roots.  相似文献   

11.
Abstract Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH4+, NO3? and K+ were frequently monitored and adjusted to set values. In a pre-experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C. When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature-dependent, steady value (phase 2). The fresh: freeze-dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1). In both growth phases and at all temperatures, plants absorbed more NH4+ than NO4+, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH4+. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH4+. Specific absorption rates for NH4+, NOx?, K+ and H2PO4? showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2. The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes.  相似文献   

12.
Harrison  Una J.  Shew  H. D. 《Plant and Soil》2001,228(2):147-155
Black root rot of tobacco, caused by Thielaviopsis basicola, is generally severe at soil pH values >5.6 and suppressed under more acidic conditions (pH < 5.2). Soil acidifying fertilizers containing NH4–N are generally recommended for burley tobacco production in North Carolina, but the effects of N form and application rate on development of black root rot and on the population dynamics of T. basicola have not been determined. Greenhouse and laboratory studies were conducted to evaluate the effects of N form (NH4 + or NO3 ) and rate on pathogen and disease parameters at several initial soil pH levels. A moderately-conducive field soil, initial pH 4.7, was adjusted to a pH of 5.5 or 6.5 by the addition of CaOH2, then amended with the desired nitrogen form and rate. Pathogen populations were determined over time. In addition, spore production in extracts of roots from plants grown in the various nitrogen and pH treatments was determined. Finally, because tobacco responds to acidic soil conditions and exposure to NH4–N by accumulating high concentrations of the polyamine putrescine, the toxicity of putrescine on vegetative growth and reproduction of T. basicola was investigated. Low soil pH and high levels of NH4–N suppressed reproduction of T. basicola in soil and in root extract, while use of NO3–N and depletion of NH4–N resulted in rapid increases in populations of T. basicola. At 20 mM, putrescine inhibited hyphal growth by 60% and aleuriospore production by 98%. Fertilizers that reduced soil pH also reduced reproduction by T. basicola, and thus have potential for management of black root rot by suppressing populations of T. basicola over multiple years of crop production. The suppression of T. basicola and black root rot observed with NH4–N amendments may partially be due to development of an inhibitory environment in the root and not solely to changes in rhizosphere pH.  相似文献   

13.
Cd-tolerant and Cd-sensitive rice cultivars were used to study the role of NH4 + accumulation in Cd-induced toxicity. NH4 + accumulation seems to be involved in regulating the toxicity of rice seedlings caused by CdCl2. This conclusion was based on the observations that (a) on treatment with CdCl2, NH4 + content increased rapidly in the leaves of the Cd-sensitive cultivar (cv. Taichung Native 1, TN1) but not in the Cd-tolerant cultivar (cv. Tainumg 67, TNG67), (b) pretreatment with abscisic acid (ABA) enhanced Cd tolerance and reduced Cd-induced NH4 + accumulation in TN1 seedlings, (c) exogenous application of the ABA biosynthesis inhibitor, fluridone, decreased Cd tolerance and increased NH4 + content in leaves of TNG67, (d) exogenous application of phosphinothricin, an inhibitor of glutamine synthetase (GS), which resulted in NH4 + accumulation in the leaves, also induced toxicity similar to Cd in TN1 seedlings. Evidence is presented to show that Cd-induced NH4 + accumulation in TN1 leaves is attributable to a decrease in GS activity. Since Cd-treated TN1 leaves had higher glutamine and glutamate contents than control leaves, it is unlikely that glutamine (or glutamate) depletion is the mechanism which regulates Cd-induced toxicity.  相似文献   

14.
R. H. Teyker 《Plant and Soil》1992,144(2):289-295
Growth of maize seedlings can be improved by enhanced ammonium nutrition, but placing fertilizer anhydrous ammonia close to seedlings introduces the risk of ammonia toxicity. In this study, growth and root elongation response to rates of closely placed NH4OH bands were investigated in two contrasting maize hybrids. Seven rates of NH4OH, ranging from 0 to 200 mg N kg-1 soil were injected into the center of each pot. A single rate of Ca(NO3)2-N was included to compare hybrids for N form preference at a moderate N rate. Three seedlings per pot were planted 5.7 cm from the injection point.Hybrid B73×LH51 produced a quadratic response in shoot growth to NH4OH rates, whereas LH74×LH123 exhibited a significant linear decline in response to NH4OH rate. Root length density sampled from the fertlized zone declined linearly in response to NH4OH rate while a slight increase in root length density in unfertilized zones was observed at intermediate NH4OH rates. Hybrids did not differ in root length density in either zone.The hybrid with greater tolerance of NH4OH rates (B73×LH51) also showed a preference in shoot growth for NH4-over NO3-N at 66.7 mg N kg-1 compared to LH74×LH123. On average across hybrids, nitrate concentrations of xylem exudate collected from detopped plants were 14.5 mmol g-1 for Ca(NO3)2 treatments and 1.5 mmol g-1 for NH4OH treatments, indicating that contrasting N-form nutrition resulted from fertilizer treatments. Malate concentrations were higher in the NH4OH treatment indicating that this organic acid anion may substitute for the negative charge of nitrate during enhanced ammonium nutrition in maize.The results suggest that potentially useful genetic variation exists in maize for N form preference and for tolerance to increasing ammonical-N rates.  相似文献   

15.
  • Ammonium gluconate (AG) provides both an organic carbon source and a nitrogen source, which can positively improve soil fertility and delay soil degradation.
  • We investigated the underlying mechanisms of both NH4+‐ and C6H11O7?‐mediated resistance to high salt concentrations in maize (Zea mays L.), and how they relate to antioxidant cellular machinery, root system architecture, root activity and lignin content in roots.
  • Seedlings treated with AG maintained lower Na+ content, higher chlorophyll content, higher CAT and POD activity, compared with those without AG and ammonium carbonate (AC). The total size of the root system, primary root length and number of lateral roots detected on the primary root treated with AG decreased compared with those not treated with AG at the same NaCl concentration. However, average root diameter and root activity when treated with AG were significantly higher than roots without AG at the same NaCl concentration. Furthermore, total size of the root system, primary root length and number of lateral roots detected on primary rootsof seedlings treated with AG were higher than those treated with AC at the same NaCl concentration.
  • These results suggested that AG may be a good organic fertiliser under salt stress by decreasing Na+ content and increasing chlorophyll content, activity of antioxidant enzymes, root diameter and root activity in maize seedlings.
  相似文献   

16.
The effects of metabolic and protein synthesis inhibitors on NH4 + uptake by Pisum arvense plants at low (0.05 mM) and high (1 mM) external ammonium concentration were studied. In short-time experiments cycloheximide decreased the ammonium uptake rate at low level of NH4 + and increased the absorption of NH4 + from uptake medium containing high ammonium concentration. Arsenate and azide supplied into uptake solutions at low ammonium concentration strongly decreased or completely suppressed the NH4 + uptake rate, respectively. When the experiments were carried out at high level of ammonium only azide decreased the uptake rate of NH4 + and arsenate stimulated this process. Dinitrophenol very strongly repressed the uptake rate of NH4 + at both ammonium concentrations. After removing dinitrophenol from both solutions, neither at low nor high external ammonium level the recovery of NH4 + uptake rate was achieved within 150 min or 3 h, respectively. The recovery of NH4 + uptake rate after removing azide was observed within 90 min and 3 h at low and high ammonium concentrations, respectively. The regulation of NH4 + uptake by some inhibitors at low external ammonium level was investigated using plasma membrane vesicles isolated from roots by two-phase partitioning. Orthovanadate completely suppressed the uptake of NH4 + by vesicles and quinacrine decreased the NH4 + uptake which 55 suggests that ammonium uptake depends on activities of plasma membrane-bound enzymes. On the other hand, it was found that dinitrophenol completely reduced the NH4 + uptake by vesicles. The various effects of inhibitors on ammonium uptake dependent on external ammonium concentration suggest the action of different ammonium transport systems in Pisum arvense roots. The ammonium transport into root cells at low NH4 + level requires energy and synthesis of protein in the cytoplasm. The research was supported by grant of KBN No. 6PO4C 068 08  相似文献   

17.
The experiment was set up to examine the influence of different nitrogen forms: (NH4)2SO4, Ca(NO3)2 or NH4NO3 on growth response, root induced pH changes in the rhizosphere, root-borne acid phosphatase activity in strawberry plants cv. Senga Sengana. The plants grown on sandy mineral soil were fertilized with 3 forms of nitrogen, in concentrations of 46 mg N·kg−1 soil. The plants were grown in rhizoboxes with removable plexiglass lids. To ensure the root growth along the plexiglass lids, the rhizoboxes were placed at an angle of about 50° with the lid on the lower side. In case of ammonium supply, the nitrification inhibitor DIDIN was added (10 mg·kg−1 of moist soil) to prevent conversion of ammonium into nitrate. The growth response (roots and shoots) of strawberry plants were determined after 11 weeks of treatment with different N forms. The best development of the root system and shoots (root and shoot dry weight and root length) was obtained, when ammonium nitrate was supplied. It is suggested therefore, that NH4NO3 stimulates vegetative growth of strawberry plants cv. Senga Sengana. However, there were no statistical differences in a leaf and flower number of the plants grown under different forms of N-fertilization. Determination of rhizosphere pH, and acid phosphatase activity were executed using non-destructive techniques, which enabled weekly measurement of chemical changes in the rhizosphere. The results revealed that the form of nitrogen supplied had a predominant effect on chemical changes in the rhizosphere of strawberry plants. The highest pH values (average pH 6.8) were measured in the rhizosphere of individual plants supplied with Ca(NO3)2. Whereas the lowest pH values (average pH 5.8) were detected in the presence of (NH4)2SO4. The curve of rhizosphere pH measured along individual roots of the plants treated with Ca(NO3)2 represents the highest pH values whereas the curve of rhizosphere pH under (NH4)2SO4 treatment had the lowest pH values. The highest activity of acid phosphatase were observed in the rhizosphere of strawberry plants grown in the presence of (NH4)2SO4, at pH 5.8.  相似文献   

18.
In order to investigate the effects of homogeneous and localized supply of different nitrogen forms (nitrate, NO3 ? vs ammonium, NH4 +) on the growth of tomato seedlings, root morphology and six cytokinin (CTK) fractions in xylem sap were analyzed. Whole roots were supplied with different ratios of NO3 ? to NH4 + (100:0, as 100-0NA; 75:25, as 75-25NA; 50:50, as 50-50NA) under homogeneous supply. In split-root experiments, three treatments were compared: a sole NO3 ? supply (N|N), a spatially separated supply of NO3 ? and NH4 + (N|A), and a spatially separated supply of NO3 ? and a mixture of NO3 ? and NH4 + nutrition at a ratio of 75:25 (N|AN). All concentrations of total N were set at 5 mM. The results showed that (1) homogeneous 75% NO3 ? plus 25% NH4 + supply to the whole root zone led to maximum shoot and root dry matter (DM), root surface area (RS) and root volume (RV). The spatially separated supply of NO3 ? and NH4 + (N|A) resulted in a contrasting effect on root morphology: in comparison to N|N, root DM in the NO3 ?-containing pot was increased by 50% whereas it was depressed by 50% in the NH4 +-containing pot. The 75% NO3 ? plus 25% NH4 + supply in the split-root experiment led to no significant effects either on shoot DM and root DM, or on RS and RV when compared to N|N. (2) The presence of NH4 + in the external medium led to a significantly reduced total xylem-CTK concentration, and a close negative correlation was found between xylem NH4 + and total CTK concentration irrespective of culture mode. A relatively high level of zeatin riboside (ZR) was maintained both in 75-25NA and N|A treatments. It was concluded that, in addition to the percentage of NH4 + to NO3 ? in the nutrient solution, whether NH4 + was supplied to the whole root system or to only part of the root system was also an important factor affecting plant growth. The fact that the 75-25NA and N|A treatments resulted in optimal growth of tomato seedlings might be attributed to the higher ZR concentration in xylem.  相似文献   

19.
Douglas fir seedlings were grown for two to three months in sand and soil cultures in a greenhouse to examine their growth response to nitrogen (N) source at different levels of pH and iron (Fe) supply. In the first two experiments nutrient solutions of known pH were automatically applied to the top of the sand cultures and allowed to run to waste from the bottom. Under these conditions seedlings made most growth on nitrate (NO3–N) under acid (pH4) conditions, but most growth on ammonium (NH4–N) under neutral (pH7) conditions. Calcium carbonate (CaCO3) was used to create a range of pH conditions (from 4.0 to 7.2) in a peat and sand artificial soil. Over the pH range 4 to 6 NH4–N or NO3+NH4–N produced larger seedlings than NO3–N alone, but above pH6 growth on all N sources was depressed. Chemical analysis showed that seedling Ca concentration had increased and Fe concentration had decreased with increase in CaCO3 application. Both Ca and Fe concentrations were higher in seedlings receiving NO3–N than in those receiving NH4 or NO3+NH4.In sub-irrigated sand cultures, Doughlas fir seedlings receiving NO3–N were shown to respond to additions of Fe chelate, but seedlings receiving NH4–N responded little to Fe chelate. At pH5 seedlings receiving NO3–N did not grow as big as seedlings receiving NH4–N in the absence of Fe chelate, but addition of Fe chelate resulted in NO3-fed seedlings growing larger than NH4-fed seedlings. The relationship between seedling Fe concentration and N nutrition is discussed.The relatively larger root dry weight and surface area of seedlings grown on NO3–N, as compared to NH4–N, in sand culture, was noted.  相似文献   

20.
以野生型拟南芥(WT)及其生长素和乙烯不敏感型突变体(aux1-7、axr1-3、etr1-1和etr1-3)为实验材料,采用固体培养法研究了高浓度硝酸铵对根毛发育的影响,以揭示其调控根毛发育的机制。结果表明:(1)随着外源硝酸铵浓度的逐渐增加,拟南芥根毛伸长受阻,产生大量的分叉根毛。(2)高浓度硝酸铵条件下,外源活性氧或活性氧产生抑制剂二苯基氯化碘(DPI)的添加能抑制高浓度硝酸铵诱导的分叉根毛产生。(3)高浓度硝酸铵条件下,外源生长素或乙烯合成前体物质1-氨基-环丙烷-1-羧酸(ACC)处理能恢复根毛的正常生长,解除高浓度硝酸铵诱导根毛分叉现象。(4)高浓度硝酸铵条件下,外源生长素处理乙烯不敏感型突变体或ACC处理生长素不敏感型突变体均能抑制突变体分叉根毛的形成。研究表明,活性氧、生长素和乙烯都参与了高浓度硝酸铵对根毛发育的过程调控;在硝酸铵诱导的根毛分叉中生长素和乙烯存在相互作用,在缺乏生长素信号通路时,乙烯能够发挥补充作用抑制分叉根毛的产生;在缺乏乙烯信号通路时,生长素也可以弥补缺失乙烯的作用抑制根毛的分叉,但是需要更高浓度的生长素才能充分抑制分叉根毛的产生。  相似文献   

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