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1.
The present study with young poplar trees aimed at characterizing the effect of O2 shortage in the soil on net uptake of NO3
- and NH4
+ and the spatial distribution of the N taken up. Moreover, we assessed biomass increment as well as N status of the trees affected by O2 deficiency. For this purpose, an experiment was conducted in which hydroponically grown young poplar trees were exposed to hypoxic and normoxic (control) conditions for 14 days. 15N-labelled NO3
- and NH4
+ were used to elucidate N uptake and distribution of currently absorbed N and N allocation rates in the plants. Whereas shoot biomass was not affected by soil O2 deficiency, it significantly reduced root biomass and, consequently, the root-to-shoot ratio. Uptake of NO3
- but not of NH4
+ by the roots of the trees was severely impaired by hypoxia. As a consequence of reduced N uptake, the N content of all poplar tissues was significantly diminished. Under normoxic control conditions, the spatial distribution of currently absorbed N and N allocation rates differed depending on the N source. Whereas NO3
- derived N was mainly transported to the younger parts of the shoot, particularly to the developing and young mature leaves, N derived from NH4
+ was preferentially allocated to older parts of the shoot, mainly to wood and bark. Soil O2 deficiency enhanced this differential allocation pattern. From these results we assume that NO3
- was assimilated in developing tissues and preferentially used to maintain growth and ensure plant survival under hypoxia, whereas NH4
+ based N was used for biosynthesis of storage proteins in bark and wood of the trees. Still, further studies are needed to understand the mechanistic basis as well as the eco-physiological advantages of such differential allocation patterns. 相似文献
2.
Nitrogen solutes in an Adirondack forested watershed: Importance of dissolved organic nitrogen 总被引:6,自引:2,他引:6
Michael R. McHale Myron J. Mitchell Jeffrey J. McDonnell Christopher P. Cirmo 《Biogeochemistry》2000,48(2):165-184
Nitrogen (N) dynamics were evaluated from 1 June 1995 through 31 May 1996 within the Arbutus Lake watershed in the Adirondack Mountains of New York State, USA. At the Arbutus Lake outlet dissolved organic nitrogen (DON), NO3
- and NH4
+ contributed 61%, 33%, and 6% respectively, to the total dissolved nitrogen (TDN) flux (259 mol ha-1 yr-1). At the lake inlet DON, NO3
-, and NH4
- constituted 36%, 61%, and 3% respectively, of TDN flux (349 mol ha-1 yr-1). Differences between the factors that control DON, NO3
+, and NH4
+ stream water concentrations were evaluated using two methods for estimating annual N flux at the lake inlet. Using biweekly sampling NO3
- and NH4
+ flux was 10 and 4 mol ha-1 yr-1 respectively, less than flux estimates using biweekly plus storm and snowmelt sampling. DON flux was 18 mol ha-1 yr-1 greater using only biweekly sampling. These differences are probably not of ecological significance relative to the total flux of N from the watershed (349 mol ha-1 yr-1). Dissolved organic N concentrations were positively related to discharge during both the dormant (R2 = 0.31; P < 0.01) and growing season (R2 = 0.09; P < 0.01). There was no significant relationship between NO3
- concentration and discharge during the dormant season, but a significant negative relationship was found during the growing season (R2 = 0.29; P < 0.01). Biotic controls in the growing season appeared to have had a larger impact on stream water NO3
- concentrations than on DON concentrations. Arbutus Lake had a major impact on stream water N concentrations of the four landscape positions sampled, suggesting the need to quantify within lake processes to interpret N solute losses and patterns in watershed-lake systems. 相似文献
3.
B. J. Atwell 《Plant and Soil》1992,139(2):247-251
Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO3
-, NH4
+ or NH4NO3 with a total nitrogen concentration of 2.8 M m-3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO3
-, NH4
+ or NH4NO3. However, when NO3
- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with 15NH4NO3 or NH4
15NO3 for 30 h, NH4
+ uptake was generally twice as fast as NO3
- uptake, even for plants grown in the presence of NO3
-. Low rates of NO3
- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO3
-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH4
+ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH4
+ was the sole nitrogen source. 相似文献
4.
马尾松属高氮需求树种,然而在苗木培育中马尾松对氮素,尤其是不同形态氮素的需求尚不明确.该文以马尾松组培苗为试验材料,采用基质培养方法,针对硝态氮、铵态氮两种氮素形态均分别设置了2、4、8、16 mmol·L-14个处理,以不添加氮素为对照,对苗木的高径生长、根构型参数(总根长、总表面积、总体积、平均直径和根尖数)以及生... 相似文献
5.
Growth, chemical composition, and nitrate reductase activity (NRA) of hydroponically cultured Rumex crispus, R. palustris, R. acetosa, and R. maritimus were studied in relation to form (NH4
+, NO3
-, or both) and level of N supply (4 mM N, and zero-N following a period of 4mM N). A distinct preference for either NH4
+ or NO3
- could not be established. All species were characterized by a very efficient uptake and utilization of N, irrespective of
N source, as evident from high concentrations of organic N in the tissues and concurrent excessive accumulations of free NO3
- and free NH4
+. Especially the accumulation of free NH4
+ was unusually large.
Generally, relative growth rate (RGR) was highest with a combination of NH4
+ and NO3
-. Compared to mixed N supply, RGR of NO3
-- and NH4
+-grown plants declined on average 3% and 9%, respectively. Lowest RGR with NH4
+ supply probably resulted from direct or indirect toxicity effects associated with high NH4
+ and/or low Ca2+ contents of tissues. NRA in NO3
- and NH4NO3 plants was very similar with maxima in the leaves of ca 40 μmol NO2
- g-1 DW h-1. ‘Basal’ NRA levels in shoot tissues of NH4
+ plants appeared relatively high with maxima in the leaves of ca 20 μmol NO2
- g-1 DW h-1. Carboxylate to organic N ratios, (C-A)/Norg, on a whole plant basis varied from 0.2 in NH4
+ plants to 0.9 in NO3
- plants.
After withdrawal of N, all accumulated NO3
- and NH4
+ was assimilated into organic N and the organic N redistributed on a large scale. NRA rapidly declined to similar low levels,
irrespective of previous N source. Shoot/root ratios of -N plants were 50–80% lower than those from +N plants. In comparison
with +N, RGR of -N plants did not decline to a large extent, decreasing by only 15% in -NH4
+ plants due to very high initial organic-N contents. N-deprived plants all exhibited an excess cation over anion uptake (net
proton efflux), and whole-plant (C-A)/Norg ratios increased to values around unity.
Possible difficulties in interpreting the (C-A)/Norg ratio and NRA of plants in their natural habitats are briefly discussed. 相似文献
6.
The carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) grown hydroponically at a constant pH on either 4 mM or 12 mM NO3
- or NH4
+ nutrition were investigated using either 14C or 15N techniques. Greater allocation of 14C to amino-N fractions occurred at the expense of allocation of 14C to carbohydrate fractions in NH4
+-compared to NO3
--fed plants. The [14C]carbohydrate:[14C]amino-N ratios were 1.5-fold and 2.0-fold greater in shoots and roots respectively of 12 mM NO3
--compared to 12 mM NH4
+-fed wheat. In both 4 mM and 12 mM N-fed maize the [14C]carbohydrate:[14C]amino-N ratios were approximately 1.7-fold and 2.0-fold greater in shoots and roots respectively of NO3
--compared to NH4
+-fed plants. Similar results were observed in roots of wheat and maize grown in split-root culture with one root-half in NO3
--and the other in NH4
+-containing nutrient media. Thus the allocation of carbon to the amino-N fractions occurred at the expense of carbohydrate fractions, particularly within the root. Allocation of 14N and 15N within separate sets of plants confirmed that NH4
--fed plants accumulated more amino-N compounds than NO3
--fed plants. Wheat roots supplied with 15NH4
+ for 8 h were found to accumulate 15NH4
+ (8.5 g 15N g-1 h-1) whereas in maize roots very little 15NH4
+ accumulated (1.5 g 15N g-1 h-1)It is proposed that the observed accumulation of 15NH4
+ in wheat roots in these experiments is the result of limited availability of carbon within the roots of the wheat plants for the detoxification of NH4
+, in contrast to the situation in maize. Higher photosynthetic capacity and lower shoot: root ratios of the C4 maize plants ensure greater carbon availability to the root than in the C3 wheat plants. These differences in carbon and nitrogen partitioning between NO3
--and NH4
+-fed wheat and maize could be responsible for different responses of wheat and maize root growth to NO3
- and NH4
+ nutrition. 相似文献
7.
The influence of nitrogen concentration and ammonium/nitrate ratio on N-uptake,mineral composition and yield of citrus 总被引:9,自引:0,他引:9
In short-term water culture experiments with different 15N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH4
+ at a higher rate than NO3
–. Maximum NO3
– uptake by the whole plant occurred at 120 mg L–1 NO3
–-N, whereas NH4
+ absorption was saturated at 240 mg L–1 NH4
+-N. 15NH4
+ accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO3
– was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH4
+ (15–60 mg L–1 N) to nutrient solutions containing 120 mg L–1 N as 15N labeled nitrate reduced 15NO3
– uptake. Maximum inhibition of 15NO3
– uptake was about 55% at 2.14 mM NH4
+ (30 mg L–1 NH4
+-N) and it did not increase any further at higher NH4
+ proportions.In a long-term experiment, the effects of concentration and source of added N (NO3
– or NH4
+) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH4
+ versus NO3
– nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO3
–-N:NH4
+-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 NO3
– or NH4
+ as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO3
–-N/NH4
+-N ratio. With increasing proportions of NH4
+ 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 NH4
+, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO3
–-N:NH4
+-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH4
+ 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 NO3
–:NH4
+ ratio. 相似文献
8.
Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings 总被引:4,自引:2,他引:4
The effect of NO2 fumigation on root N uptake and metabolism was investigated in 3-month-old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO2 to the plant N budget was measured during a 48 h fumigation with 100mm3m?3 NO2. Plants were pre-treated with various nutrient solutions containing NO2 and NH4+, NO3? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH4+ in the solution for 6d led to an increased capacity for NO3? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO3? uptake. In fumigated plants, NO2 uptake accounted for 20–40% of NO3? uptake. Root NO3? uptake in plants supplied with NH4+plus NO3? solutions was decreased by NO2 fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO2 and NH4+ and were fumigated or not with 100mm3m?3 NO2 for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and 15N labelling. Root NH4+ uptake was approximately three times higher than NO3? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO3? nor NH4+ accumulated in the shoot, showing that all the absorbed NO2 was assimilated. Root NO3? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO2-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed. 相似文献
9.
J. S. Bailey 《Plant and Soil》1992,143(1):19-31
Solution culture studies have shown that plant uptake of NH4
+ and NO3
- can be improved by increasing the concentration of Ca2+ in the root environment: the same may be true for grass grown in soil culture. An experiment was set up to see whether gypsum (CaSO4 2H2O) increased the rate at which perennial ryegrass absorbed 15NH4
+ and 15NO3
- from soil.The results demonstrated that gypsum increases the rates of uptake of both NH4
+ and NO3
- by perennial ryegrass. However because there was little potential for mineral-N loss from the experimental system, either by gaseous emission or by N immobilization, long term improvements in fertilizer efficiency were not observed. Nitrogen cycling from shoots to roots commenced once net uptake of N into plants had ceased. Labelled N transferred thus to roots underwent isotopic exchange with unlabelled soil N. It was suggested that this exchange of N might constitute an energy drain from the plant, if plant organic N was exchanged for soil inorganic N. The fact that the exchange occurred at all cast doubt on the suitability of the 15N-isotope dilution technique for assessing fertilizer efficiency in medium to long term experiments. There was evidence that the extra NO3
--N taken up by plants on the all-nitrate treatments as a result of gypsum application, was reduced in root tissue rather than in shoots, but to the detriment of subsequent root growth and N uptake. 相似文献
10.
Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH4+), nitrite (NO2?), and nitrate (NO3?) immobilization among soils developed under different tree species in the Catskill Mountains of New York State, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where 15N was added as NH4+, NO2?, or NO3? to live and mercury‐treated O horizon soils from three tree species (American beech, northern red oak, sugar maple), and 15N recoveries were determined in the SOM pool. Mercuric chloride was used to treat soils as this chemical inhibits microbial metabolism without significantly altering the chemistry of SOM. The recovery of 15N in SOM was almost always greater for NH4+ (mean 20%) and NO2? (47%) than for NO3? (10%). Ammonium immobilization occurred primarily by biotic processes, with mean recoveries in live soils increasing from 9% at 15 min to 53% after 28 days of incubation. The incorporation of NO2? into SOM occurred rapidly (<15 min) via abiotic processes. Abiotic immobilization of NO2? (mean recovery 58%) was significantly greater than abiotic immobilization of NH4+ (7%) or NO3? (7%). The incorporation of NO2? into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO3? dynamics among species. As over 30% of the 15NO2? label was recovered in SOM within 15 min in live soils, and the products of NO2? incorporation into SOM remained relatively stable throughout the 28‐day incubation, our results suggest that NO2? incorporation into SOM may be an important mechanism of N retention in forest soils. The importance of NO2? immobilization for N retention in field soils, however, will depend on the competition between incorporation into SOM and nitrification for transiently available NO2?. Further research is required to determine the importance of this process in field environments. 相似文献
11.
氮(N)是高山和极地生态系统重要的限制性生长因子。目前对冻土区植物N利用机制的研究主要集中于完全融化期,而冻融循环期植物N吸收策略仍存在不确定性。以高寒紫花针茅为研究对象,分别在冻结期(晚秋)和融化期(早春)采用同位素示踪技术,分析植物对(15NH4)2SO4和Na15NO3的吸收量与偏好动态变化。研究结果显示冻结期紫花针茅冠层生长已停滞,融化期冠层尚未返青,但根系和立枯均可以吸收同化15N,具备吸收养分的需求。融化期紫花针茅15N在标记21天后15N-NH+4和15N-NO-3的总回收率分别为4.44%和6.91%,而冻结期紫花针茅在15N标记21天后15N-NH+4和15... 相似文献
12.
13.
以5份不同种源的菘蓝为材料,采用田间小区试验,设置不施氮(CK)、硝态氮(NO3--N)、铵态氮(NH4+-N)、NH4+-N/NO3--N=75/25、NH4+-N/NO3--N=50/50、NH4+-N/NO3--N=25/75和酰胺态氮等7个处理,分析比较了不同种源植株的靛蓝、靛玉红和总生物碱含量、(R,S)-告依春及多糖含量等指标的差异,为菘蓝栽培生产中氮素的高效利用提供理论参考。结果表明:氮素处理有利于提高山西运城菘蓝和陕西商洛菘蓝叶内靛蓝含量,以及安徽亳州菘蓝和陕西商洛菘蓝叶内的总生物碱含量;NH4+-N/NO3--N=50/50处理对山西运城菘蓝,以及酰胺态氮处理对山西运城菘蓝和陕西商洛菘蓝叶内生物碱类成分的积累均有促进作用;与对照相比,氮素处理亦能有效地提高甘肃张掖菘蓝和陕西商洛菘蓝根内的(R,S)-告依春及安徽亳州菘蓝根内的多糖含量;安徽阜阳菘蓝(R,S)-告依春含量在任一氮处理下均远远高于其他种质菘蓝。研究表明,不同种源菘蓝对氮素处理的响应存在较大的差异,建议生产中综合考虑菘蓝的来源和需肥规律,采用经济有效的施氮组合,以提高其活性成分含量。 相似文献
14.
为探讨不同氮素水平的硝态氮与铵态氮对油麦菜(Lactuca sativa L.)生长及品质的影响,自主设计并制作了适合蔬菜水培的立体管道栽培系统,配制了NO3-:NH4+=10:0,NO3-:NH4+=7:1,NO3-:NH4+=7:3的营养液,通过模糊数学原理,采用层次分析法(AHP)确定品质的权重值,综合评价了不同氮素水平对油麦菜的栽培效果。结果表明,以NO3-:NH4+=7:3营养液的栽培效果最好,其次是NO3-:NH4+=7:1。当营养液的NO3-:NH4+=7:3时,油麦菜的产量最高,叶片叶绿素、可溶性糖、可溶性蛋白质含量最高,硝酸盐含量最少,其综合品质最好。层次分析法对油麦菜不同氮素水平营养液的栽培效果的综合评价有较好的适用性,有助于获得南方设施管道栽培油麦菜最佳的营养液配方。 相似文献
15.
Gert Arnold 《Plant and Soil》1992,142(1):41-51
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively.
The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern
as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause
soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers. 相似文献
16.
采用水培法,研究了旱柳苗在外源添加不同氮水平(贫氮、中氮、富氮、过氮)的铵态氮(NH+4-N)和硝态氮(NO-3-N)的生长、氮吸收、分配和生理响应。结果表明:一定范围氮浓度的增加能够促进旱柳苗的生长,但过量氮会抑制其生长,且NH+4-N的抑制作用大于NO-3-N;两种氮处理下,旱柳表现出对NH+4-N的吸收偏好,在同一氮水平时,旱柳各部位氮原子百分含量Atom%15N(AT%)、15N吸收量和来自氮源的N%(Ndff%)均为NH+4-N处理大于NO-3-N处理,且随着氮浓度的增加,差异增大,且在旱柳各部位的分布为根﹥茎﹥叶;2种氮素过量和不足均会对旱柳根和叶生理指标产生不同的影响,其中在过氮水平时,NH+4-N和NO-3-N处理下根系活力比对照减少了50.61%和增加了19.53%;在过氮水平时,NH+4-N处理柳树苗根总长、根表面积、根平均直径、根体积和侧根数分别对照下降了30.92%、29.48%、19.44%、27.01%和36.41%,NO-3-N处理柳树苗相应的根系形态指标分别对对照下降了1.66%、5.65%、1.49%、5.06%和25.72%。可见,高浓度NH+4-N对旱柳苗的胁迫影响大于NO-3-N,在应用于水体氮污染修复时可通过改变水体无机氮的比例,削弱其对旱柳的影响,从而提高旱柳对水体氮污染的修复效果。 相似文献
17.
Contemporary and pre-industrial global reactive nitrogen budgets 总被引:56,自引:6,他引:50
Elisabeth A. Holland Frank J. Dentener Bobby H. Braswell James M. Sulzman 《Biogeochemistry》1999,46(1-3):7-43
Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NOx, and a reduced nitrogen compound, NH3, have driven an increase in nitrogen deposition. We estimate global NOx and NH3 emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NOy and NHx deposition. Pre-industrial wet plus dry NOx and NHx deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NOy+NHx wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of preindustrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO
3
–
and NH
4
+
were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO
3
–
and NH
4
+
but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.Abbreviations EMEP
European Monitoring and Evaluation Program
- GEIA
Global Emissions Inventory Activity
- NADP/NTN
National Atmospheric Deposition Program/National Trends Network in the US
- NH
Northern Hemisphere
- NHx=NH3+NH
+
4
NOx=NO+NO2
NOy total odd nitrogen=NOx+HNO3+HONO+HO2NO2+NO3+radical (NO3
.)+Peroxyacetyl nitrates+N2O5+organic nitrates
- SH
Southern Hemisphere
- Gg
109 g
- Tg
1012 g 相似文献
18.
E. S. Jensen 《Plant and Soil》1991,133(1):83-92
Simultaneous determination of 15N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of 15N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated 15N analysis showed that the recovery of inorganic N in the NH3 trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO3
- and the NH4
+ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO3
- or NH4
+ alone, but can be used for combined diffusion of the two ions. 相似文献
19.
Although NH4
+ has generally been accepted as the preferred N source for fertilising rice, some workers have concluded tha NO3
- is as effective as NH4
+. The present glasshouse study exmined the relative uptake of NH4
+ and NO3
- from solution and cultures containing 5–120 mg N/L supplied as NH4NO3 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 NH4
+ than NO3
-. In contrast, the hybrid rice absorbed more NH4
+ than NO3
- at the low levels of N supply (5–40 mg N/L), but more NO3
- than NH4
+ 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.
Supplying both N forms (NH4
++NO3
−) to the maize (Zea mays L.) plant can optimize productivity by enhancing reproductive development. However, the physiological factors responsible
for this enhancement have not been elucidated, and may include the supply of cytokinin, a growth-regulating substance. Therefore,
field and gravel hydroponic studies were conducted to examine the effect of N form (NH4
++NO3
− versus predominantly NO3
−) and exogenous cytokinin treatment (six foliar applications of 22 μM 6-benzylaminopurine (BAP) during vegetative growth versus untreated) on productivity and yield of maize. For untreated plants,
NH4
++NO3
− nutrition increased grain yield by 11% and whole shoot N content by 6% compared with predominantly NO3
−. Cytokinin application to NO3
−-grown field plants increased grain yield to that of NH4
++NO3
−-grown plants, which was the result of enhanced dry matter partitioning to the grain and decreased kernel abortion. Likewise,
hydroponically grown maize supplied with NH4
++NO3
− doubled anthesis earshoot weight, and enhanced the partitioning of dry matter to the shoot. NH4
++NO3
− nutrition also increased earshoot N content by 200%, and whole shoot N accumulation by 25%. During vegetative growth, NH4
++NO3
− plants had higher concentrations of endogenous cytokinins zeatin and zeatin riboside in root tips than NO3
−-grown plants. Based on these data, we suggest that the enhanced earshoot and grain production of plants supplied with NH4
++NO3
− may be partly associated with an increased endogenous cytokinin supply. 相似文献