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1.
Comparative studies on the effect of nitrogen (N) form on iron (Fe) uptake and distribution in maize ( Zea mays L. cv Yellow 417) were carried out through three related experiments with different pretreatments. Experiment 1: plants were precultured in nutrient solution with 1.0×10 –4 M FeEDTA for 6 d and then exposed to NO 3–N or NH 4–N solution with 1.0×10 –4 M FeEDTA or without for 7 d. Experiment 2: plants were precultured with 59FeEDTA for 6 d and were then transferred to the solution with different N forms, and 0 and 1.0×10 –4 M FeEDTA for 8 d. Experiment 3: half of roots were supplied with 59FeEDTA for 5 d and then cut off, with further culturing in treatment concentrations for 7 d. In comparison to the NH 4-fed plants, young leaves of the NO 3-fed plants showed severe chlorosis under Fe deficiency. Nitrate supply caused Fe accumulation in roots, while NH 4–N supply resulted in a higher Fe concentration in young leaves and a lower Fe concentration in roots. HCl-extractable (active) Fe was a good indicator reflecting Fe nutrition status in maize plants. Compared with NO 3-fed plants, a higher proportion of 59Fe was observed in young leaves of the Fe-deficient plants fed with NH 4–N. Ammonium supply greatly improved 59Fe retranslocation from primary leaves and stem to young leaves. Under Fe deficiency, about 25% of Fe in primary leaves of the NH 4-fed plants was mobilized and retranslocated to young leaves. Exogenous Fe supply decreased the efficiency of such 59Fe retranslocation. The results suggest that Fe can be remobilized from old to young tissues in maize plants but the remobilization depends on the form of N supply as well as supply of exogenous Fe. 相似文献
2.
Nitrogen (N) limits plant productivity and its uptake and assimilation may be regulated by N source, N availability, and nitrate
reductase activity (NRA). Knowledge of how these factors interact to affect N uptake and assimilation processes in woody angiosperms
is limited. We fertilized 1-year-old, half-sib black walnut ( Juglans nigra L.) seedlings with ammonium (NH 4
+) [as (NH 4) 2SO 4], nitrate (NO 3
−) (as NaNO 3), or a mixed N source (NH 4NO 3) at 0, 800, or 1,600 mg N plant −1 season −1. Two months following final fertilization, growth, in vivo NRA, plant N status, and xylem exudate N composition were assessed.
Specific leaf NRA was higher in NO 3
−-fed and NH 4NO 3-fed plants compared to observed responses in NH 4
+-fed seedlings. Regardless of N source, N addition increased the proportion of amino acids (AA) in xylem exudate, inferring
greater NRA in roots, which suggests higher energy cost to plants. Root total NRA was 37% higher in NO 3
−-fed than in NH 4
+-fed plants. Exogenous NO 3
− was assimilated in roots or stored, so no difference was observed in NO 3
− levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over
NO 3
− or NH 4
+ alone, suggesting NH 4NO 3 is required to maximize productivity in black walnut. Our findings indicate that black walnut seedling responses to N source
and level contrast markedly with results noted for woody gymnosperms or herbaceous angiosperms. 相似文献
3.
In short-term water culture experiments with different 15N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH 4
+ at a higher rate than NO 3
–. Maximum NO 3
– uptake by the whole plant occurred at 120 mg L –1 NO 3
–-N, whereas NH 4
+ absorption was saturated at 240 mg L –1 NH 4
+-N. 15NH 4
+ accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO 3
– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH 4
+ (15–60 mg L –1 N) to nutrient solutions containing 120 mg L –1 N as 15N labeled nitrate reduced 15NO 3
– uptake. Maximum inhibition of 15NO 3
– uptake was about 55% at 2.14 m M NH 4
+ (30 mg L –1 NH 4
+-N) and it did not increase any further at higher NH 4
+ proportions.In a long-term experiment, the effects of concentration and source of added N (NO 3
– or NH 4
+) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH 4
+ versus NO 3
– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO 3
–-N:NH 4
+-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L –1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO 3
– or NH 4
+ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO 3
–-N/NH 4
+-N ratio. With increasing proportions of NH 4
+ in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH 4
+, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO 3
–-N:NH 4
+-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH 4
+ in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO 3
–:NH 4
+ ratio. 相似文献
4.
Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as NO 3− or NH 4+, the solutions being maintained at pH 5.5. In NO 3−-fed plants excess nutrient anion over cation uptake was equivalent to net OH − efflux, and the total charge from NO 3− and SO 42− reduction equated to the sum of organic anion accumulation plus net OH − efflux. In NH 4+-fed plants a large H + efflux was recorded in close agreement with excess cation over anion uptake. This H + efflux equated to the sum of net cation (NH 4+ minus SO 42−) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO 3− that is taken up and reduced in NO 3−-fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH 4+-fed plants absorbed NH 4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO 3−-fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake, assimilation, and accumulation data in terms of shoot/root pH regulation and cycling of nutrients. 相似文献
5.
In 1986 and 1987 surveys were conducted of 34 (1986) and 35 (1987) peanut ( Arachis hypogaea L.) fields in which the plants showed various degrees of chlorosis. In the areas concerned, plant appearance was classified according to a chlorotic index and corresponding soil samples were taken and analysed for CaCO 3, pH, NO 3–N and DTPA-extractable Fe in 1986 and for CaCO 3, NO 3–N and active lime in 1987.Regression analyses showed that CaCO 3, active lime and NO 3–N were positively correlated, while DTPA-extractable Fe was negatively correlated, with the chlorosis problem. The critical levels above which plants were chlorotic were 20 to 25% CaCO 3 and 10% active lime. Plants began to be chlorotic when DTPA-extractable Fe was below 2.5 mg·kg –1. The soil factors examined explained about 60% of the variability in plant chlorosis. 相似文献
6.
Summary The effects of concentration and source (NH 4, NO 3, and NO 3 plus NH 4) of added N on the rate of growth, final yield, and content and rate of intake of N, P, K, Ca, Mg and S by wheat seedlings were evaluated. Rate of growth in dilute liquid cultures differed among the N sources giving yields relative to those of the all-NO 3 system of 92 per cent for the all-NH 4 system, and of 154 per cent for the NO 3 plus NH 4 system. At low rates of NH 4 intake in the all-NH 4 systems growth rates were equal to or slightly better than those of plants supplied equivalent concentrations of NO 3. Rates of NH 4 intake exceeding 100 mole g –1 h –1 resulted in reduced growth rates and incipient NH 4 toxicity. Yields at 95 per cent of maximum resulted with steady-state N concentrations of 80 M in all NO 3 systems, 30 M NH 4 in all-NH 4 systems, and in combined source systems when 200 M NO 3 plus 30 M NH 4 were supplied. The rate of N intake and plant protein content, were maximal when both NO 3 and NH 4 were supplied. Increasing rates of NO 3 intake were associated with increases in the rates of Ca, Mg, and K intake; but with increasing rates of NH 4 absorption, intake of Ca and Mg decreased. The yield and growth rate enhancement observed from the addition of low concentrations of NH 4 to cultures supplying adequate NO 3 is suggested to result from the reduced energy requirement for utilization of NH 4, as compared to NO 3 in protein synthesis and from the increased photosynthetic capacity of the higher-protein NH 4-fed plants. In the all-NH 4 systems the maximum attainable growth rate was limited by NH 4 toxicity; whereas in the all-NO 3 systems the rate of NO 3 reduction was limiting.Contribution from the Department of Soils and Plant Nutrition, University of California, Davis, California 95616. 相似文献
8.
Sulphur fractionation and availability to plants are poorly understood in calcareous soils. Sixty-four calcareous soils containing varying amounts of CaCO 3 were collected from ten provinces in China and their S fractions determined. Organic S was the predominant fraction of S, accounting for on average 77% of the soil total S. The amounts of adsorbed sulphate were found to be negligible. 1 M HCl extracted substantially more sulphate than either 0.01 M CaCl 2 or 0.016 M KH 2PO 4, indicating the existence of water-insoluble but acid-soluble sulphate, probably in the form of sulphate co-precipitated with CaCO 3. The concentrations of water-insoluble sulphate correlated positively with the contents of CaCO 3 and accounted for 0.03–40.3% (mean 11.7%) of soil total S. To test the bioavailability of water-insoluble sulphate, a sulphate-CaCO 3 co-precipitate labelled with 35S was prepared and added to a calcareous soil in a pot experiment with either NH 4+ or NO 3– as the N source. In 29 days, wheat plants took up 10.6% and 3.0% of the 35S added to the soil in the NH 4+ and NO 3– treatments, respectively. At the end of the pot experiment, the decrease of water-insoluble, acid-soluble, sulphate was more apparent in the NH 4+ than in the NO 3– treatment. The results indicate that sulphate co-precipitated with CaCO 3 in calcareous soils may become partly available for plant uptake, depending on rhizosphere pH, if the field precipitate is similar to the laboratory prepared sample studied. 相似文献
9.
Summary Soybean plants were grown in nutrient culture solutions containing 150 ppm of N either as an equal concentration of NH 4
+ or NO 3
–, or all NO 3
–. At the R2 stage of growth for some plants, the N form was changed to either all NO 3
– or all NH 4
+, but at the same total N concentration as before. Highest seed yield was obtained with all NO 3
– over the entire growth period, the poorest when the N form was switched from an equal ratio of NH 4
+ and NO 3
– to all NH 4
+ at the R2 stage. Kjeldahl N concentrations in the plant leaves and seed were highest when NH 4
+ was part or all of the N source in the nutrient solution. These results may partially explain why the literature is inconsistent on the effect of added fertilizer N on soybean seed yield, and may pose a problem in using leaf Kjeldahl N concentration to determine plant N sufficiency. 相似文献
10.
Forest N fertilization is a common practice in areas of Sweden that are not affected by high levels of N deposition. The environmental consequences of high N input to closed forests are fairly well known, but the long-term effects following clear-felling are a lot less well known. Thus, residual effects on soil and planted seedlings of previous N additions at an experimental N gradient 11 years after clear-felling were studied at a naturally nutrient-poor forest site in central Sweden. The experimental N gradient had been established by three repeated applications (in 1967, 1974 and 1981) of six dosages of NH 4NO 3 with increments of 120 kg N ha –1. Thus, in total, the applied N dose ranged between 0 and 1800 kg N ha –1. The study examined extractable base cations and P, soil pH, total-N, total-C, net N-mineralization and potential nitrification in four soil horizons (the humus layer, and 0–5, 5–10 and 10–20 cm in the mineral soil). We also measured the survival and growth of planted Pinus sylvestris L. seedlings. The applied N had no effect on the amounts of extractable-P or base cations in the soil. The soil pH decreased with increasing N dose in the deeper soil horizons, while in the humus the pH showed a weak but statistically significant increase due to the N application. Both total-C and total-N increased as a result of the N application, while the C/N ratio decreased. In the humus layer and the uppermost mineral soil layer NH 4
+ was the major inorganic N source, in contrast to the lowest mineral soil horizon where NO 3
– dominated. For most of the studied horizons, there was a positive linear relationship between applied N dose and amount of inorganic N. Both net N-mineralization and potential nitrification showed increases with increasing N dose. As for the plants, no difference in survival or growth was found between the different N treatments. For doses generally applied in forest fertilization no significant differences in any of the studied properties were found. 相似文献
11.
The effect of phosphate (PO 4
+3) and pH in regulating nitrate (NO 3) and ammonia (NH 3
+) uptake by phytoplankton was investigated in two Oklahoma lakes using 15N tracers. Addition of PO 4
+3 above ambient concentrations had a negligible effect on the rate of uptake of NO 3
– or NH 3
+. Manipulation of pH of lake water had little effect on uptake of either NO 3
– or NH 3
+. A correlation analysis suggested that NO 3
– is not used by phytoplankton when NH 3
+ concentrations exceed about 210 µg NH 3
+-N(1) –1. 相似文献
12.
We compared growth kinetics of Prorocentrum donghaiense cultures on different nitrogen (N) compounds including nitrate (NO 3
−), ammonium (NH 4
+), urea, glutamic acid (glu), dialanine (diala) and cyanate. P. donghaiense exhibited standard Monod-type growth kinetics over a range of N concentraions (0.5–500 μmol N L −1 for NO 3
− and NH 4
+, 0.5–50 μmol N L −1 for urea, 0.5–100 μmol N L −1 for glu and cyanate, and 0.5–200 μmol N L −1 for diala) for all of the N compounds tested. Cultures grown on glu and urea had the highest maximum growth rates (μ m, 1.51±0.06 d −1 and 1.50±0.05 d −1, respectively). However, cultures grown on cyanate, NO 3
−, and NH 4
+ had lower half saturation constants (K μ, 0.28–0.51 μmol N L −1). N uptake kinetics were measured in NO 3
−-deplete and -replete batch cultures of P. donghaiense. In NO 3
−-deplete batch cultures, P. donghaiense exhibited Michaelis-Menten type uptake kinetics for NO 3
−, NH 4
+, urea and algal amino acids; uptake was saturated at or below 50 μmol N L −1. In NO 3
−-replete batch cultures, NH 4
+, urea, and algal amino acid uptake kinetics were similar to those measured in NO 3
−-deplete batch cultures. Together, our results demonstrate that P. donghaiense can grow well on a variety of N sources, and exhibits similar uptake kinetics under both nutrient replete and deplete conditions. This may be an important factor facilitating their growth during bloom initiation and development in N-enriched estuaries where many algae compete for bioavailable N and the nutrient environment changes as a result of algal growth. 相似文献
13.
Young bean plants ( Phaseolus vulgaris L. var Saxa) were fed with 3.5 or 10 millimolar N in either the form of NO 3− or NH 4+, after being grown on N-free nutrient solution for 8 days. The pH of the nutrient solutions was either 6 or 4. The cell sap pH and the extractable activities of phosphoenolpyruvate carboxylase and of pyruvate kinase from roots and primary leaves were measured over several days. The extractable activity of phosphoenolpyruvate carboxylase (based on soluble protein) from primary leaves increased with NO3− nutrition, whereas with NH4+ nutrition and on N-free nutrient solution the activity remained at a low level. Phosphoenopyruvate carboxylase activity from the roots of NH4+-fed plants at pH 4 was finally somewhat higher than from the roots of plants grown on NO3− at the same pH. There was no difference in activity from the root between the N treatments when pH in the nutrient solutions was 6. The extractable activity of pyruvate kinase from roots and primary leaves seemed not to be influenced by the N nutrition of the plants. The results are discussed in relation to the physiological function of both enzymes with special regard to the postulated functions of phosphoenolpyruvate carboxylase in C3 plants as an anaplerotic enzyme and as part of a cellular pH stat. 相似文献
14.
Phosphate-limited chemostat cultures were used to study cell growth and N assimilation in Anabaena flos-aquae under various N sources to determine the relative energetic costs associated with the assimilation of NH 3, NO 3−, or N 2. Expressed as a function of relative growth rate, steady state cellular P contents and PO 4 assimilation rates did not vary with N-source. However, N-source did alter the maximal PO 4-limited growth rate achieved by the cultures: the NO 3− and N 2 cultures attained only 97 and 80%, respectively, of the maximal growth rate of the NH 3 grown cells. Cellular biomass and C contents did not vary with growth rate, but changed with N source. The NO 3−-grown cells were the smallest (627 ± 34 micromoles C · 10 −9 cells), while NH 3-grown cells were largest (900 ± 44 micromoles C · 10 −9 cells) and N 2-fixing cells were intermediate (726 ± 48 micromoles C · 10 −9 cells) in size. In the NO 3−-and N 2-grown cultures, N content per cell was only 57 and 63%, respectively, of that in the NH 3-grown cells. Heterocysts were absent in NH 3-grown cultures but were present in both the N 2 and NO 3− cultures. In the NO 3−-grown cultures C 2H 2 reduction was detected only at high growth rates, where it was estimated to account for a maximum of 6% of the N assimilated. In the N 2-fixing cultures the acetylene:N 2 ratio varied from 3.4:1 at lower growth rates to 3.0:1 at growth rates approaching maximal. Compared with NH3, the assimilation of NO3− and N2 resulted either in a decrease in cellular C (NO3− and N2 cultures) or in a lower maximal growth rate (N2 culture only). The observed changes in cell C content were used to calculate the net cost (in electron pair equivalents) associated with growth on NO3− or N2 compared with NH3. 相似文献
15.
NH 4
+-N can have inhibitory effects on plant growth. However, the mechanisms of these inhibitory effects are still poorly understood. In this study, effects of different N forms and a combination of ammonium + 6-benzylaminopurine (6-BA, a synthetic cytokinin) on growth, transpiration, uptake and flow of water and potassium in 88-days-old tobacco ( Nicotiana tabacum L. K 326) plants were studied over a period of 12 days. Plants were supplied with equal amounts of N in different forms: NO 3
–, NH 4NO 3, NH 4
+ or NH 4
++6-BA (foliar spraying every 2 days after onset of the treatments). For determining flows and partitioning upper, middle and lower strata of three leaves each were analysed. During the 12 days study period, 50% replacement of NO 3
–-N by NH 4
+-N (NH 4NO 3) did not change growth, transpiration, uptake and flow of water and K + compared with the NO 3
–-N treatment. However, NH 4
+-N as the sole N-source caused: (i) a substantial decrease in dry weight gain to 42% and 46% of the NO 3
–-N and NH 4NO 3 treatments, respectively; (ii) a marked reduction in transpiration rate, due to reduced stomatal conductance, illustrated by more negative leaf carbon-isotope discrimination ( 13C) compared with the NO 3
– treatment, especially in upper leaves; (iii) a strong reduction both in total water uptake, and in the rate of water uptake by roots, likely due to a decrease in root hydraulic conductivity; (iv) a marked reduction of K + uptake to 10%. Under NH 4
+ nutrition the middle leaves accumulated 143%, and together with upper leaves 206% and the stem 227% of the K + currently taken up, indicating massive mobilisation of K + from lower leaves and even the roots. Phloem retranslocation of K + from the shoot and cycling through the root contributed 67% to the xylem transport of K +, and this was 2.2 times more than concurrent uptake. Foliar 6-BA application could not suppress or reverse the inhibitory effects on growth, transpiration, uptake and flow of water and ions (K +) caused by NH 4
+-N treatment, although positive effects by 6-BA application were observed, even when 6-BA (10 –8
M) was supplied in nutrient solution daily with watering. Possible roles of cytokinin to regulate growth and development of NH 4
+-fed plants are discussed. 相似文献
16.
为了解丛枝菌根真菌(AMF)和不同形态氮对杉木( Cunninghamia lanceolata)生长和养分吸收的影响,以1 a生杉木幼苗接种摩西球囊霉( Glomus mosseae)和添加不同形态氮(NH 4+-N和NO 3–-N),对其养分元素和生长状况的变化进行研究。结果表明,AMF显著提高了杉木的苗高和生物量,促进了杉木对N、P、K、Ca、Mg、Fe和Na的吸收,AMF对微量元素Fe、Na的促进作用总体上要强于大量元素K、Ca。与NO 3–-N相比,AMF显著提高了NH 4+-N处理杉木的生物量、总C和N、Ca、Mg、Mn含量,而且这种显著性在叶中普遍高于根和茎。接种AMF可以促进杉木幼苗的生长和对养分元素的吸收,且添加NH 4+-N处理的促进作用要强于NO 3–-N。 相似文献
17.
A nutrient solution experiment was conducted to determine the influence of N forms on growth, oxidative stress, and Cd and
N uptake in rice plants. The treatments were consisted of two Cd levels (0 and 1 μmol) and three N forms (NH 4) 2SO 4, NH 4NO 3 and Ca(NO 3) 2. The results indicated that without Cd addition in the culture solution, the N forms had no significant effect on all measured
parameters, including plant growth, photosynthetic traits, malondialdehyde (MDA) concentration, superoxide dismutase (SOD)
activity, and Cd and N concentration, while Cd addition in the medium resulted in significant differences in measured parameters
among the three forms of N fertilizers. The least inhibition of growth was noted in (NH 4) 2SO 4-fed plants, and the largest in Ca(NO 3) 2-fed plants, when plants were exposed to Cd stress. The highest photosynthetic rate and chlorophyll content was also recorded
in (NH 4) 2SO 4-fed plants. Addition of Cd caused a remarkable increase in SOD activity and MDA content in plants, and the extent of increase
varied with N form, with (NH 4) 2SO 4-fed plants being smallest. In comparison with the control plants, the N concentration in roots and shoots was not significantly
affected in (NH 4) 2SO 4-fed plants, but significant decrease in root N concentration was found for the NH 4NO 3 and Ca(NO 3) 2-fed plants under Cd stress. Moreover, the significant differences were also noted among the three N forms in both root and
shoot Cd concentrations, with (NH 4) 2SO 4-fed plants being the lowest. The results indicated that the toxic effect of Cd on rice varied with the form of N fertilizer. 相似文献
18.
A study was conducted to elucidate the effect of N form, either NH 4
+ or NO 3
–, on growth and solute composition of the salt-tolerant kallar grass [ Leptochloa fusca (L.) Kunth] grown under 10 m M or 100 m M NaCl in hydroponics. Shoot biomass was not affected by N form, whereas NH 4
+ compared to NO 3
– nutrition caused an almost 4-fold reduction in the root biomass at both salinity levels. Under NH 4
+ nutrition, salinity had no effect on the biomass yield, whereas under NO 3
– nutrition, increasing salinity from 10 m M to 100 m M caused 23% and 36% reduction in the root and shoot biomass, respectively. The reduced root growth under NH 4
+ nutrition was not attributable to impaired shoot to root C allocation since N form did not affect the overall root sugar concentration and the starch concentration was even higher under NH 4
+ compared to NO 3
– nutrition. The low NH 4
+ (2 m M) and generally higher amino-N concentrations in NH 4
+- compared to NO 3
–-fed plants indicated that the grass was able to effectively detoxify NH 4
+. Salinity had no effect on Ca 2+ and Mg 2+ levels, whereas their concentration in shoots was lower under NH 4
+ compared to NO 3
– nutrition (over 66% reduction in Ca 2+; over 20% reduction in Mg 2+), but without showing deficiency symptoms. Ammonium compared to NO 3
– nutrition did not inhibit K + uptake, and the K +-Na + selectivity either remained unaffected or it was higher under NH 4
+ than under NO 3
– nutrition. Results suggested that while NH 4
+
versus NO 3
– nutrition substantially reduced root growth, and also strongly modified anion concentrations and to a minor extent concentrations of divalent cations in shoots, it did not influence salt tolerance of kallar grass. 相似文献
19.
Although NH 4
+ has generally been accepted as the preferred N source for fertilising rice, some workers have concluded tha NO 3
- is as effective as NH 4
+. The present glasshouse study exmined the relative uptake of NH 4
+ and NO 3
- from solution and cultures containing 5–120 mg N/L supplied as NH 4NO 3 by a hybrid rice (India) and a conventional rice cultivar (Japonica). At all levels of N supply, the hybrid rice had higher leaf area and higher rates of uptake of total N than the conventional cultivar. Net photosynthesis rates were similar for both cultivars at the highest rates of N supply, but were lower at 5–40 mg N/L for the hybrid cultivar than for the conventional cultivar. At all levels of N supply, the conventional rice cultivar absorbed more NH 4
+ than NO 3
-. In contrast, the hybrid rice absorbed more NH 4
+ than NO 3
- at the low levels of N supply (5–40 mg N/L), but more NO 3
- than NH 4
+ at the high levels of at 80 and 120 mg N/L. It is concluded that the uptake of N by rice is under genetic control and also dependent on levels of N supply. Thus the appropriate form of N fertiliser for rice may depend on cultivar and rates of N supply. 相似文献
20.
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 NH 4–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 (NH 4
+ or NO 3
–) 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 CaOH 2, 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 NH 4–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 NH 4–N suppressed reproduction of T. basicola in soil and in root extract, while use of NO 3–N and depletion of NH 4–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 NH 4–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
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