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1.
Detlev Helmig Brian Seok Mark W. Williams Jacques Hueber Robert SanfordJr. 《Biogeochemistry》2009,95(1):115-130
The effect of snow cover on surface-atmosphere exchanges of nitrogen oxides (nitrogen oxide (NO) + nitrogen dioxide (NO2); note, here ‘NO2’ is used as surrogate for a series of oxidized nitrogen gases that were detected by the used monitor in this analysis mode)
was investigated at the high elevation, subalpine (3,340 m asl) Soddie site, at Niwot Ridge, Colorado. Vertical (NO + NO2) concentration gradient measurements in interstitial air in the deep (up to ~2.5 m) snowpack were conducted with an automated
sampling and analysis system that allowed for continuous observations throughout the snow-covered season. These measurements
revealed sustained, highly elevated (NO + NO2) mixing ratios inside the snow. Nitrogen oxide concentrations were highest at the bottom of the snowpack, reaching levels
of up to 15 ppbv during mid-winter. Decreasing mixing ratios with increasing distance from the soil–snow interface were indicative
of an upwards flux of NO from the soil through the snowpack, and out of the snow into the atmosphere, and imply that biogeochemical
processes in the subnival soil are the predominant NO source. Nitrogen dioxide reached maximum levels of ~3 ppbv in the upper
layers of the snowpack, i.e., ~20–40 cm below the surface. This behavior suggests that a significant fraction of NO is converted
to NO2 during its diffusive transport through the snowpack. Ozone showed the opposite behavior, with rapidly declining levels below
the snow surface. The mirroring of vertical profiles of ozone and the NO2/(NO + NO2) ratio suggest that titration of ozone by NO in the snowpack contributes to the ozone reaction in the snow and to the ozone
surface deposition flux. However, this surface efflux of (NO + NO2) can only account for a minor fraction of ozone deposition flux over snow that has been reported at other mid-latitude sites.
Neither (NO + NO2) nor ozone levels in the interstitial air showed a clear dependence on incident solar irradiance, much in contrast to observations
in polar snow. Comparisons with findings from polar snow studies reveal a much different (NO + NO2) and ozone snow chemistry in this alpine environment. Snowpack concentration gradients and diffusion theory were applied
to estimate an average, wintertime (NO + NO2) flux of 0.005–0.008 nmol m−2 s−1, which is of similar magnitude as reported (NO + NO2) fluxes from polar snow. While fluxes are similar, there is strong evidence that processes controlling (NO + NO2) fluxes in these environments are very different, as subnivial soil at Niwot Ridge appears to be the main source of the (NO + NO2) efflux, whereas in polar snow (NO + NO2) has been found to be primarily produced from photochemical de-nitrification of snow nitrate. 相似文献
2.
Michael A. Nicodemus K. Francis Salifu Douglass F. Jacobs 《Trees - Structure and Function》2008,22(5):685-695
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 (NH4
+) [as (NH4)2SO4], nitrate (NO3
−) (as NaNO3), or a mixed N source (NH4NO3) 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 NO3
−-fed and NH4NO3-fed plants compared to observed responses in NH4
+-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 NO3
−-fed than in NH4
+-fed plants. Exogenous NO3
− was assimilated in roots or stored, so no difference was observed in NO3
− levels transported in xylem. Black walnut seedling growth and physiology were generally favored by the mixed N source over
NO3
− or NH4
+ alone, suggesting NH4NO3 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.
As part of the Kushiro Wetland Restoration Project, we evaluated the effect of the tree-cutting (February 2003) on soil water
chemistry for 3 years in an alder (Alnus japonica) shrubland on the peat soil in the Kushiro Wetland, the largest wetland in Japan. The alder stand was divided into two types;
low stature and high stature stands, mean heights being 1.5 and 2.6 m, respectively. The treatment plot with tree cutting
and the reference plot measuring 25 m × 25 m each were established in both stands, and a soil incubation experiment was also
conducted by trenching the root zone of wetland vegetation in the treatment plots in both stands in the summer of 2004. The
tree cutting did not substantially increase the concentrations of ammonium ion (NH4
+) and nitrate ion (NO3
−) in the soil water, although a gradual and slight increase of NO3
− concentration was found after the tree-cutting only in the high stature stand (<10 μmol/l). This increase in the NO3
− concentration in the high stature stand was probably due to the rhizosphere oxidation of wetland herbaceous vegetation, and
was accompanied by the increase of Ca2+ concentration. The soil incubation experiment showed no significant change of the nitrogen concentration, suggesting that
inorganic nitrogen was immobilized and NO3
− was denitrified intensively in this wetland peat soil. The results of this study suggested that this wetland ecosystem had
a high potential to stabilize the soil water chemistry. 相似文献
4.
Xi-Hua Cui Hosakatte Niranjana Murthy Chun-Hua Wu Kee-Yoeup Paek 《In vitro cellular & developmental biology. Plant》2010,46(5):437-444
The present study investigated the effect of nitrogen source (NH4+; NO3−) at different concentrations on the accumulation of biomass and secondary metabolites in adventitious root cultures of Hypericum perforatum L. Cultures were initiated in shake flasks by using half-strength Murashige and Skoog (MS) medium with B5 vitamins, 1.0 mg l−1 indole-3-butyric acid, 0.1 mg l−1 kinetin, 3% (w/v) sucrose, and different ratios of ammonium and nitrate (0:30, 5:25, 10:20, 15:15, 20:10, 25:5, and 30:0 mM, using NH4Cl and KNO3). The cultures were maintained in darkness. The medium supplemented with 5:25 (mM) NH4+/NO3− resulted in the optimum accumulation of biomass and total phenols and flavonoids. The antioxidant potential of a methanolic
extract, measured as the 1, 1-diphenyl-2-picrylhydrazyl and 2, 2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) radical
scavenging activities, of H. perforatum adventitious roots showed that antioxidant activity was high from root extracts that were grown on higher concentrations
of NO3− nitrogen (15, 20, and 25 mM). Further, assessment of hydrogen peroxide (H2O2) and malondialdehyde content of the root extracts revealed that cultures supplemented with higher levels of NO3− nitrogen (15–30 mM) were under oxidative stress, which boosted the levels of secondary metabolites in the adventitious roots.
These results suggest that optimal adventitious root biomass could be achieved with the supplementation of cultures with 5:25
ratios of MS nitrogen sources. 相似文献
5.
The nitrogen isotope composition (δ15N) of plants has potential to provide time‐integrated information on nitrogen uptake, assimilation and allocation. Here, we take advantage of existing T‐DNA and γ‐ray mutant lines of Arabidopsis thaliana to modify whole‐plant and organ‐level nitrogen isotope composition. Nitrate reductase 2 (nia2), nitrate reductase 1 (nia1) and nitrate transporter (nrt2) mutant lines and the Col‐0 wild type were grown hydroponically under steady‐state NO3– conditions at either 100 or 1000 μM NO3– for 35 days. There were no significant effects on whole‐plant discrimination and growth in the assimilatory mutants (nia2 and nia1). Pronounced root vs leaf differences in δ15N, however, indicated that nia2 had an increased proportion of nitrogen assimilation of NO3– in leaves while nia1 had an increased proportion of assimilation in roots. These observations are consistent with reported ratios of nia1 and nia2 gene expression levels in leaves and roots. Greater whole‐plant discrimination in nrt2 indicated an increase in efflux of unassimilated NO3– back to the rooting medium. This phenotype was associated with an overall reduction in NO3– uptake, assimilation and decreased partitioning of NO3– assimilation to the leaves, presumably because of decreased symplastic intercellular movement of NO3– in the root. Although the results were more varied than expected, they are interpretable within the context of expected mechanisms of whole‐plant and organ‐level nitrogen isotope discrimination that indicate variation in nitrogen fluxes, assimilation and allocation between lines. 相似文献
6.
Ammann M.; Stalder M.; Suter M.; Brunold C.; Baltensperger U.; Jost D. T.; Trler A.; Gggeler H.W. 《Journal of experimental botany》1995,46(11):1685-1691
For the first time, spruce shoots (Picea abies [L.] Karst.)were fumigated in vivo with 13N-labelled NO2 with the aim ofelucidating the mechanism of NO2 trapping in the apoplastof the substomatal cavity. Uptake by the needles could be monitoredon-line, and a quantitative analysis of the activity recordsdelivered a deposition velocity in agreement with the commondry deposition estimates and ruled out rapid export processes.A fast extraction procedure was applied which revealed thatNO2 did not produce any detectable traces of nitrite. In needlesin which the enzymes of nitrate reduction were not induced byprior fumigation with NO2, incorporation of NO2 was partiallyinhibited as compared to the fully induced shoots which tookup and assimilated NO2 as expected from a constant influx. Theonly labelled inorganic species found in the extracts was nitrate(60%), whereas the rest of the label (40%) was assimilated organicnitrogen.A quantitative analysis of the data shows that thereaction of NO2 in the apoplast yields at least three timesmore nitrate than nitrite, so that the existing models aboutthe apoplastic trapping reaction, disproportionation or antioxidantscavenging, which both postulate substantial production of nitrite,have to be reconsidered. Key words: 13N, nitrogen dioxide, spruce, air pollutants, deposition 相似文献
7.
Chaetoceros muelleri (Lemn.) was cultured with nitrite (NO2−) or nitrate (NO3−) as the sole nitrogen source and aerated with air or with CO2-enriched air. Cells of C. muelleri excreted into the medium nitrite produced by reduction of nitrate when grown with 100 μM NaNO3 as nitrogen source. Accordingly, NO2− concentration reached 10.4 μM after 95 h at the low CO2 condition (aerated with air); while the maximum NO2− concentration was only around 2.0 μM at the high CO2 condition (aerated with 5% CO2 in air), furthermore, after 30 h it decreased to no more than 1.0 μM. NO2− was almost assimilated in 80 h when C. muelleri was cultured at the high CO2 condition with 100 μM NaNO2 as sole nitrogen source. At the high CO2 condition, after 3 h the activity of nitrite reductase was as much as 50% higher than that at the low CO2 condition. It was indicated that enriched CO2 concentration could inhibit nitrite excretion and enhance nitrite assimilation by cells. Therefore, aeration with enriched
CO2 might be an effective way to control nitrite content in aquaculture systems. 相似文献
8.
The occurrence of nitrogen isotope discrimination with absorption and assimilation of nitrate (NO3–) and ammonium (NH4+) was investigated using two genotypes of barley, Hordeum vulgare L. cv. Steptoe and Az12 : Az70, the latter of which lacks the characterized nitrate reductase isozymes. Plants were grown under two situations: a closed system with limited nitrogen or an open system with unlimited nitrogen, to elucidate the conditions and processes that influence discrimination. There was no discrimination observed for Az12 : Az70 when supplied with limited nitrogen. Discrimination was observed for Steptoe seedlings at high external NO3– concentrations, but not with low NO3– when assimilation is probably rapid and complete. The same pattern was observed for Steptoe when NH4+ was supplied; indicating that for both nitrogen forms discrimination is dependent upon the presence of the assimilatory enzyme and the external concentration. The implications of this study are that both internal (assimilatory enzyme distribution) and external (source concentration) factors may have a larger impact on tissue δ 15N than the form of nitrogen utilized. This suggests that tissue δ 15N may not always be a reliable indicator of a plant's integrated nitrogen nutrition. 相似文献
9.
葡萄糖、根浸出液对丛枝菌根真菌吸收不同外源氮产生精氨酸的影响 总被引:1,自引:0,他引:1
以大葱(Allium fistulosum)为宿主植物, 接种丛枝菌根(Arbuscular mycorrhizal, AM)真菌Glomus intraradices, 采用三室隔离盆栽培养系统, 在菌丝室施加浓度为4 mmol/L的不同形态外源氮、1%葡萄糖及根浸出液, 通过测定根外菌丝(Extraradical mycelium, ERM)和菌根中精氨酸的含量, 探究葡萄糖、根浸出液对AM真菌吸收不同形式外源氮产生精氨酸的影响。结果表明, 不同外源氮对ERM中精氨酸含量的影响为尿素>Gln>NH4NO3>Arg/Gly>NH4Cl>KNO3, 对菌根中精氨酸含量的影响为Arg>Gln>尿素>NH4NO3>Gly>NH4Cl>KNO3; 施加葡萄糖和根浸出液在不同程度上提高ERM干重和菌丝室孢子数量, 但使ERM和菌根中的精氨酸含量降低。说明AM真菌吸收同化不同外源氮产生精氨酸的能力不同, 葡萄糖和根浸出液降低AM真菌吸收同化外源氮产精氨酸的能力。 相似文献
10.
Relationship between growth,nitrogen fixation and assimilation in a legume (Medicago sativa L.) 总被引:1,自引:0,他引:1
Summary Symbiotic N2 fixation, NO
3
−
assimilation and protein accumulation in the shoots were measured simultaneously in alfalfa (Medicago sativa L.) grown in the field or in pots, in order to study how the balance between the two modes of nitrogen nutrition could be
influenced by agronomic factors, such as harvest, mineral nitrogen supply and drought stress.
During periods of rapid growth, fixation and assimilation may function simultaneously; they are antagonistic at the beginning
and at the end of the growth cycle, when the nitrogen requirement of the plant is lower. When nitrogen nutrition does not
limit growth, mineral nitrogen supply favours assimilation at the expense of fixation, but does not modify the amount of nitrogen
accumulated, which is adjusted to the growth capacity of the plant.
After cutting, nitrate assimilation compensated for the decrease in fixation and supplied the plant with the nitrogen required
by the regrowth, the proliferation of which determined the fixation recovery.
Drought stress decreased N2 fixation much more than NO
3
−
assimilation. The latter made growth recovery possible when water supply conditions became normal again.
These results suggested the existence of an optimum level of nitrate assimilation, which differed depending on the age of
the plants and allowed both maximum growth and fixing activity. 相似文献
11.
Renata Matraszek 《Acta Physiologiae Plantarum》2008,30(3):361-370
The author studied the effect of different nickel concentrations (0, 0.4, 40 and 80 μM Ni) on the nitrate reductase (NR) activity
of New Zealand spinach (Tetragonia expansa Murr.) and lettuce (Lactuca sativa L. cv. Justyna) plants supplied with different nitrogen forms (NO3
−–N, NH4
+–N, NH4NO3). A low concentration of Ni (0.4 μM) did not cause statistically significant changes of the nitrate reductase activity in
lettuce plants supplied with nitrate nitrogen (NO3
−–N) or mixed (NH4NO3) nitrogen form, but in New Zealand spinach leaves the enzyme activity decreased and increased, respectively. The introduction
of 0.4 μM Ni in the medium containing ammonium ions as a sole source of nitrogen resulted in significantly increased NR activity
in lettuce roots, and did not cause statistically significant changes of the enzyme activity in New Zealand spinach plants.
At a high nickel level (Ni 40 or 80 μM), a significant decrease in the NR activity was observed in New Zealand spinach plants
treated with nitrate or mixed nitrogen form, but it was much more marked in leaves than in roots. An exception was lack of
significant changes of the enzyme activity in spinach leaves when plants were treated with 40 μM Ni and supplied with mixed
nitrogen form, which resulted in the stronger reduction of the enzyme activity in roots than in leaves. The statistically
significant drop in the NR activity was recorded in the aboveground parts of nickel-stressed lettuce plants supplied with
NO3
−–N or NH4NO3. At the same time, there were no statistically significant changes recorded in lettuce roots, except for the drop of the
enzyme activity in the roots of NO3
−-fed plants grown in the nutrient solution containing 80 μM Ni. An addition of high nickel doses to the nutrient solution
contained ammonium nitrogen (NH4
+–N) did not affect the NR activity in New Zealand spinach plants and caused a high increase of this enzyme in lettuce organs,
especially in roots. It should be stressed that, independently of nickel dose in New Zealand spinach plants supplied with
ammonium form, NR activity in roots was dramatically higher than that in leaves. Moreover, in New Zealand spinach plants treated
with NH4
+–N the enzyme activity in roots was even higher than in those supplied with NO3
−–N. 相似文献
12.
Nitrosomonas eutropha, an obligately lithoautotrophic bacterium, was able to nitrify and denitrify simultaneously under anoxic conditions when
gaseous nitrogen dioxide (NO2) was supplemented to the atmosphere. In the presence of gaseous NO2, ammonia was oxidized, nitrite and nitric oxide (NO) were formed, and hydroxylamine occurred as an intermediate. Between
40 and 60% of the produced nitrite was denitrified to dinitrogen (N2). Nitrous oxide (N2O) was shown to be an intermediate of denitrification. Under an N2 atmosphere supplemented with 25 ppm NO2 and 300 ppm CO2, the amount of cell protein increased by 0.87 mg protein per mmol ammonia oxidized, and the cell number of N. eutropha increased by 5.8 × 109 cells per mmol ammonia oxidized. In addition, the ATP and NADH content increased by 4.3 μmol ATP (g protein)–1 and 6.3 μmol NADH (g protein)–1 and was about the same in both anaerobically and aerobically grown cells. Without NO2, the ATP content decreased by 0.7 μmol (g protein)–1, and the NADH content decreased by 1.2 μmol (g protein)–1. NO was shown to inhibit anaerobic ammonia oxidation.
Received: 9 October 1996 / Accepted: 5 December 1996 相似文献
13.
Sampling spatial and temporal variation in soil nitrogen availability 总被引:18,自引:0,他引:18
There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part,
this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe
the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in
space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+
4) and nitrate (NO−
3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in
time, we also measured soil NH+
4 and NO−
3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil
nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+
4 and NO−
3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+
4 and NO−
3 concentrations decreased with the age of the dune. Soil NO−
3 concentration showed strong spatial structure, but soil NH+
4 concentration was not spatially structured. Plant-available NH+
4 and NO−
3 showed relatively little spatial structure: only NO−
3 availability in the second sampling period had significant patch structure. Spatial maps of NH+
4 and NO−
3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different
points in time. NO−
3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO−
3 concentrations, providing some evidence that patches of plant-available NO−
3 may reappear at the same spatial locations at irregular points in time.
Received: 20 February 1998 / Accepted: 23 November 1998 相似文献
14.
Mitochondrial Respiration Can Support NO(3) and NO(2) Reduction during Photosynthesis : Interactions between Photosynthesis, Respiration, and N Assimilation in the N-Limited Green Alga Selenastrum minutum 总被引:5,自引:5,他引:0
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Mass spectrometric analysis shows that assimilation of inorganic nitrogen (NH4+, NO2−, NO3−) by N-limited cells of Selenastrum minutum (Naeg.) Collins results in a stimulation of tricarboxylic acid cycle (TCA cycle) CO2 release in both the light and dark. In a previous study we have shown that TCA cycle reductant generated during NH4+ assimilation is oxidized via the cytochrome electron transport chain, resulting in an increase in respiratory O2 consumption during photosynthesis (HG Weger, DG Birch, IR Elrifi, DH Turpin [1988] Plant Physiol 86: 688-692). NO3− and NO2− assimilation resulted in a larger stimulation of TCA cycle CO2 release than did NH4+, but a much smaller stimulation of mitochondrial O2 consumption. NH4+ assimilation was the same in the light and dark and insensitive to DCMU, but was 82% inhibited by anaerobiosis in both the light and dark. NO3− and NO2− assimilation rates were maximal in the light, but assimilation could proceed at substantial rates in the light in the presence of DCMU and in the dark. Unlike NH4+, NO3− and NO2− assimilation were relatively insensitive to anaerobiosis. These results indicated that operation of the mitochondrial electron transport chain was not required to maintain TCA cycle activity during NO3− and NO2− assimilation, suggesting an alternative sink for TCA cycle generated reductant. Evaluation of changes in gross O2 consumption during NO3− and NO2− assimilation suggest that TCA cycle reductant was exported to the chloroplast during photosynthesis and used to support NO3− and NO2− reduction. 相似文献
15.
Wetlands are often highly effective nitrogen (N) sinks. In the Lake Waco Wetland (LWW), near Waco, Texas, USA, nitrate (NO3−) concentrations are reduced by more than 90% in the first 500 m downstream of the inflow, creating a distinct gradient in
NO3− concentration along the flow path of water. The relative importance of sediment denitrification (DNF), dissimilatory NO3− reduction to ammonium (DNRA), and N2 fixation were examined along the NO3− concentration gradient in the LWW. “Potential DNF” (hereafter potDNF) was observed in all months and ranged from 54 to 278 μmol N m−2 h−1. “Potential DNRA” (hereafter potDNRA) was observed only in summer months and ranged from 1.3 to 33 μmol N m−2 h−1. Net N2 flux ranged from 184 (net denitrification) to −270 (net N2 fixation) μmol N m−2 h−1. Nitrogen fixation was variable, ranging from 0 to 426 μmol N m−2 h−1, but high rates ranked among the highest reported for aquatic sediments. On average, summer potDNRA comprised only 5% (±2%
SE) of total NO3− loss through dissimilatory pathways, but was as high as 36% at one site where potDNF was consistently low. Potential DNRA
was higher in sediments with higher sediment oxygen demand (r
2 = 0.84), and was related to NO3− concentration in overlying water in one summer (r
2 = 0.81). Sediments were a NO3− sink and accounted for 50% of wetland NO3− removal (r
2 = 0.90). Sediments were an NH4+ source, but the wetland was often a net NH4+ sink. Although DNRA rates in freshwater wetlands may rival those observed in estuarine systems, the importance of DNRA in
freshwater sediments appears to be minor relative to DNF. Furthermore, sediment N2 fixation can be extremely high when NO3− in overlying water is consistently low. The data suggest that newly fixed N can support sustained N transformation processes
such as DNF and DNRA when surface water inorganic N supply rates are low. 相似文献
16.
M. Vuletić V. Hadži-Tašković Šukalović K. Marković J. Dragišić Maksimović 《Biologia Plantarum》2010,54(3):530-534
The activities of antioxidative enzymes and contents of proline and total phenolics were assayed in roots of two maize (Zea mays L.) genotypes grown in a medium containing nitrate (NO3
−) or both nitrogen forms, nitrate and ammonium (NH4
+/NO3
−). An increase in the activities of class III peroxidases (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), ascorbate
oxidase (AO) and proline content, and decrease in phenolic content were observed in NH4
+/NO3
− in comparison with NO3
− grown plants. When polyethylene glycol (PEG) was added to both nitrogen treatments, the content of total phenolics and proline
was increased, especially in NH4
+/NO3
− treatment. The PEG treatment decreased enzyme activities in NH4
+/NO3
− grown plants, but in NO3
− grown plants activities of POD and SOD were increased, opposite to decreased APX and AO. Isoelectric focusing demonstrated
increased activities of acidic POD isoforms in PEG treated NO3
− grown plants, and lower activities of both, acidic and basic isoforms in NH4
+/NO3
−grown plants. 相似文献
17.
Cramer M.D.; Schierholt A.; Wang Y.Z.; Lips S.H. 《Journal of experimental botany》1995,46(10):1569-1577
In hydroponically grown Lycopersicon esculentum (L.) Mill. cv.F144 the site of NO3 reduction and assimilation withinthe plant was shifted from the shoot to the root by salinity.Uptake of NO3 from the root solution was strongly inhibitedby salinization. Consequently, NO3 concentrations inthe leaf, stem and root tissues as well as the nitrate reductaseactivities of the leaves were lower in salinized than in controlplants. Lower NO3, but higher reduced-N, concentrationswere observed in the xylem sap as a result of the enhanced participationof the root in NO3 reduction in salinized plants. Lowerstem K+ concentrations and leaf malate concentrations were foundin salinized compared to control plants which indicates reducedfunctioning of the K+shuttle in the salinized plants. Incorporation of inorganic carbon by the root was determinedby supplying a pulse of NaH14CO3 followed by extraction andseparation of the labelled products on ion exchange resins.The rate of H14CO3 incorporation was c. 2-fold higherin control than in salinized plants. In salinized plants theproducts of H14CO3 incorporation within the roots werediverted into amino acids, while the control plants divertedrelatively more 14C into organic acids. Products of inorganiccarbon incorporation in the roots of salinized plants providean anaplerotic source of carbon for assimilation of reducedNO3 into amino acids, while in control plants the productswere predominantly organic acids as part of mechanisms to maintainionic balance in the cells and in the xylem sap. Key words: Tomato, nitrate, PEPc, respiration, salinity 相似文献
18.
We studied the effect of water exchange on the depletion (or accumulation) of bacterioplankton, dissolved organic matter and inorganic nutrients in small open framework cavities (50–70 l) at 15 m depth on the coral reef along Curaçao, Netherlands Antilles. The bacterioplankton removal rate in cavities increased with increasing water exchange rates up to a threshold of 0.0045 s−1, reaching values of 50–100 mg C m−2 total interior cavity surface area (CSA) per day. Beyond the threshold, bacterioplankton removal dropped. The cryptic community is apparently adapted to the average water exchange in these cavities (0.0041 s−1). Dissolved inorganic nitrogen (DIN), nitrate + nitrite (NO
x
) in particular, accumulated in cavity water and the accumulation decreased with increasing water exchange. Net NO
x
effluxes exceeded net DIN effluxes from cavities (average efflux rate of 1.9 mmol NO
x
vs. 0.8 mmol DIN m−2 interior CSA per day). The difference is ascribed to net ammonium losses (NH4) in cavities at reef concentrations >0.025 μM NH4, possibly due to enhanced nitrification. Dissolved inorganic phosphate accumulated in cavities, but was not related to water exchange. The cryptic biota in cavities depend on water exchange for optimization of consumption of bacterioplankton and removal of inorganic nitrogen. Coral cavities are an evident sink of bacterioplankton and a source of NO
x and PO
4
3−
. 相似文献
19.
Rees A.P.; Owens N.J.P.; Heath M.R.; Plummer D.H.; Bellerby R.S. 《Journal of plankton research》1995,17(6):1307-1324
Carbon (C) fixation and nitrogen (N) assimilation rates havebeen estimated from 14C and 15N techniques for a 12 month periodin a Scottish sea loch. The maximum rate of nitrogen assimilated(29.92 mmol N m2 day1) was in April at the mostseaward station; similar high rates were experienced duringMay at the other stations. Carbon fixation rates were maximal(4884047 mg C m2day1) at the time of highphytoplankton biomass (maximum 8.3 mg m3 chlorophylla) during May, whilst nitrate concentrations remained >0.7µ.mol l1. C:N assimilation ratios suggest nitrogenlimitation only during the peak of the spring bloom, althoughat times nitrogen (nitrate and ammonium) concentration fellto 0.2 µmol l1 in the following months. The verticalstability of the water column, influenced by tidal and riverineflushing, varied along the axis of the loch, resulting in markeddifferences between sampling stations. Although ammonium waspreferentially assimilated by phytoplankton, >50% of productionwas supported by nitrate uptake and only during the summer monthswas the assimilation of ammonium quantitatively important. 相似文献
20.
Measurements of CO2 and O2 gas exchange and chlorophyll a fluorescence were used to test the hypothesis that elevated atmospheric CO2 inhibits nitrate (NO3 – ) photo‐assimilation in the C4 plant, maize (Zea mays L.). The assimilatory quotient (AQ), the ratio of net CO2 assimilation to net O2 evolution, decreases as NO3 – photo‐assimilation increases so that the difference in AQ between the ammonium‐ and nitrate‐fed plants (ΔAQ) provided an in planta estimate of NO3 – photo‐assimilation. In fully expanded maize leaves, NO3 – photo‐assimilation was detectable only under high light and was not affected by CO2 treatments. Furthermore, CO2 assimilation and O2 evolution were higher under NO3 – than ammonia (NH4+) regardless of CO2 levels. In conclusion, NO3 – photo‐assimilation in maize primarily occurred at high light when reducing equivalents were presumably not limiting. Nitrate photo‐assimilation enhanced C4 photosynthesis, and in contrast to C3 plants, elevated CO2 did not inhibit foliar NO3– photo‐assimilation. 相似文献