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1.
The relative influence of the photoperiod and of periodic ammonium pulses in entraining the cell division cycle in nitrogen-limited cyclostat cultures differs dramatically in Hymenomonas carterae Braarud and Fagerl, Amphidinium carteri Hulburt and Thalassiosira weissflogii Grun. We examined how each species processes an NH4+ pulse at various times during the cell cycle and the L/D cycle. Rates of NH4+ uptake and changes in cellular concentrations of NH4+, free amino acids, and protein were examined after the addition of an NH4+ pulse. Depletion of NH4+ from the medium occurred earlier when the pulse was given at the beginning of the light period than at the beginning of the dark period in H. carterae and A. carteri. Depletion took longer in the T. weissflogii cultures and the kinetics were similar during both stages of the photocycle in this species. Similarly, the temporal phasing and maximum pool sizes varied with timing of the NH4+ pulse in H. carterae and A. carteri but complete assimilation was relatively rapid. More persistent pools of NH4+ and free amino acids accumulated in T. weissflogii, and the patterns of assimilation varied little as a function of the timing of the pulse with respect to the photocycle. Although nitrogen metabolism occurred rapidly in nitrogen-limited H. carterae and A. carteri, the entrainment of the cell division cycle by the photoperiod resulted in a large degree of uncoupling between completion of nitrogen assimilation and cell division. It is hypothesized that the strong entrainment of the cell division cycle of T. weissflogii by NH4+ pulses results from a relatively slow rate of nitrogen metabolism. 相似文献
2.
Cellular pH estimated from cell extract pH, and the ion compositions of major inorganic ions (Na+, NH4+, K+, Mg2+, Ca2+, Cl?, Br?, NO3?, S042‐) were studied by ion chromatography in 15 species of 4 orders (Cladophorales, Codiales, Siphonocladales and Ulvales) of Ulvophyceae and 49 species of 8 orders (Bangiales, Ceramiales, Corallinales, Cryptonemiales, Gelidiales, Gigartinales, Nemaliales and Rhodymeniales) of Rhodophyceae. Among the Rhodophyceae, relatively low intracellular pH (approximately 2.0 within cells) and high concentration of S042‐ was demonstrated in Plocamium telfairiae(Harvey) Harvey. Furthermore, five species of Hypnea Lamouroux were shown to contain high concentrations of S042‐ balanced by relatively high concentrations of Na+. Among the Ulvophyceae, Codium cylindricum Holmes and Ulva pertusa Kjellman contained high concentrations of S042‐ balanced by relatively high concentrations of Mg2+. 相似文献
3.
Alpine meadows of high ecological value could be severely endangered by anthropogenic N enrichment, modifying the relationships between species and the environment. While a constraint exerted by N availability on alpine plant development has been demonstrated by some fertilization experiments, in others no effect was observed. Basically, the problem is that mineral N absorption has not been characterized in alpine plants. In growth chamber experiments, we investigated the component fluxes of 15NO3? and 15NH4+ uptake in a tussock grass (Festuca nigrescens) very common and representative of the dominant plant growth form in European alpine meadows. Rates of influx supported data already published for low elevation herbaceous species. These rates were up to ten times higher for NH4+ than for NO3? but rates of net uptake were similar for both ions demonstrating the occurrence of elevated NH4+ efflux (80% of primary influx). An increase in external N in the range of field-relevant concentrations did not substantially enhance net uptake. Thus, the alpine plant which is assumed to be adapted to relatively high soil NH4+ responded like an NH4+-sensitive species: as if it was unable to use the incoming nitrogen. It is suggested that the ability of this typical alpine grass to respond to increasing N availability due to global changes is limited. 相似文献
4.
The uptake of nitrate, nitrite and ammonium by Codium fragile subsp. tomentosoides (van Goor) Silva was measured at different combinations of temperature (6–30 C) and irradiance (0–140 μEin.m-2. s-1). Uptake of all three forms of N was greater at 12–24 C than at 6 and 30 C. Although uptake was stimulated by light, saturation occurred at relatively low irradiance (7–28 μEin m-2 s-1, depending on the N source and temperature). The Michaelis-Menten uptake constants (Vmax K)varied with temperature. Vmax was greatest at intermediate temperatures and K was lowest at lower temperatures. The Vmaxfor NH4+ was higher and the K, for NH4+was lower than those for NO3-- and NO2--. Codium was capable of simultaneously taking up all three forms of inorganic N although the presence of NH4+ reduced the uptake of both NO3-- and NO2--. The results of this study indicate that part of the ecological success of Codium in a N-limited environment may be due to its N uptake capabilities. 相似文献
5.
Many plants develop toxicity symptoms and have reduced growth rates when supplied with ammonium (NH4+) as the only source of inorganic nitrogen. In the present study, the growth, morphology, NH4+ uptake kinetics and mineral concentrations in the tissues of the free-floating aquatic plant Salvinia natans (water fern) supplied exclusively with NH4+–N at concentrations of 0.25–15 mM were investigated. S. natans grew well, with relative growth rates of c. 0.25 g g?1 d?1 at external NH4+ concentrations up to 5 mM, but at higher levels growth was suppressed and the plants had small leaves and short roots with stunted growth. The high-affinity transport system (HATS) that mediate NH4+ uptake at dilute NH4+ levels was downregulated at high NH4+ concentrations with lower velocities of maximum uptake (Vmax) and higher half-saturation constants (K1/2). High NH4+ levels also barely affected the concentrations of mineral cations and anions in the plant tissue. It is concluded that S. natans can be characterized as NH4+-tolerant in line with a number of other species of wetland plants as growth was unaffected at NH4+ concentrations as high as 5 mM and as symptoms of toxicity at higher concentrations were relatively mild. Depolarization of the plasma membrane to the equilibrium potential for NH4+ at high external concentrations may be a mechanism used by the plant to avoid excessive futile transmembrane cycling. S. natans is tolerant to the high NH4+ levels that prevail in domestic and agricultural wastewaters, and the inherent high growth rate and the ease of biomass harvesting make S. natans a primary candidate for use in constructed wetland systems for the treatment of various types of nitrogen-rich wastewaters. 相似文献
6.
Changes in the size of intracellular nitrogen pools and the potential feedback by these pools on maximum N uptake (NH4+ and NO3?) rates were determined for Chaetomorpha linum (Müller) Kützing grown sequentially under nutrient-saturating and nutrient-limiting conditions. The size of individual pools in N-sufficient algae could be ranked as residual organic N (RON) comprised mainly of amino acids and amino compounds > protein N > NO3? > NH4+ > chlorophyll N. When the external N supply was removed, growth rates remained high and individual N pools were depleted at exponential rates that reflected both dilution of existing pools by the addition of new biomass from growth and movement between the pools. Calculated fluxes between the tissue N pools showed that the protein pool increased throughout the N depletion period and thus did not serve a storage function. RON was the largest storage reserve; nitrate was the second largest, but more temporary, storage pool that was depleted within 10 days. Upon N resupply, the RON pool increased 3 × faster than either the inorganic or protein pools, suggesting that protein synthesis was the rate-limiting step in N assimilation and caused a buildup of intermediate storage compounds. Maximum uptake rates for both NH4+ and NO3? varied inversely with macroalgal N status and appeared to be controlled by changes in small intracellular N pools. Uptake of NO3? showed an initial lag phase, but the initial uptake of NH4+ was enhanced and was present only when the intracellular NH4+ pool was depleted in the absence of an external N supply. A strong negative correlation between the RON pool size and maximum assimilation uptake rates for both NH4+ and NO3? suggested a feedback control on assimilation uptake by the buildup and depletion of organic compounds. Enhanced uptake and the accumulation of N as simple organic compounds or nitrate both provide a temporary mechanism to buffer against the asynchrony of N supply and demand in C. linum. 相似文献
7.
As one of the main species causing “green tides”, Ulva prolifera always inhabits in estuarine areas with changes in salinity and nutrients. Reduced salinity may affect directly or indirectly the processes of uptake and assimilation of nitrate, in which the nitrate reductase (NR) activity play the crucial roles. In this experiment, we investigated the different effects of enriched nitrogen and phosphate on NR activity of Ulva prolifera at salinity 30, 15, and 5 psu. The results showed that when salinity being lowered NR activity decreased under no enrichment (CT) or PO4 3? enrichment condition. NO3 ? or combination with PO4 3? could significantly enhance NR activity at three salinities, among which the highest value occurred at 15 psu. Enrichment of NH4 + significantly decreased NR activity at 30 and 15 psu, but not at 5 psu. The results suggested NR of Ulva prolifera could be triggered by NO3 ?, especially at middle salinity, and keep low when exposed under hyposaline or NH4 + enrichment for long term to rapidly respond to pulse of NO3 ? in estuarine areas. 相似文献
8.
Variation in growth rate,carbon assimilation,and photosynthetic efficiency in response to nitrogen source and concentration in phytoplankton isolated from upper San Francisco Bay
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Gry Mine Berg Sara Driscoll Kendra Hayashi Melissa Ross Raphael Kudela 《Journal of phycology》2017,53(3):664-679
Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH4+), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (Fv/Fm) was a sensitive indicator of NH4+ toxicity, manifested by a suppression of Fv/Fm in a dose‐dependent manner. Two chlorophytes were the least sensitive to NH4+ inhibition, at concentrations of >3,000 μmoles NH4+ · L?1, followed by two estuarine diatoms that were sensitive at concentrations >1,000 μmoles NH4+ · L?1, followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 μmoles NH4+ · L?1. At non‐inhibiting concentrations of NH4+, the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO3?), whereas the other grew significantly faster on NH4+. All four diatoms tested grew faster on NH4+ compared with NO3?. We showed that in cases where growth rates were faster on NH4+ than they were on NO3?, the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH4+ dominates the total N pool and they will also not have a growth advantage when NO3? is dominant, as long as N concentrations are sufficient. 相似文献
9.
The effects of inorganic nutrient (ammonium [NH4 + ] and nitrate [NO3 − ]) and amino acid (glutamate [glu] and glutamine [gln]) additions on rates of N2 fixation, N uptake, glutamine synthetase (GS) activity, and concentrations of intracellular pools of gln and glu were examined in natural and cultured populations of Trichodesmium. Additions of 1 μM glu, gln, NO3 − , or NH4 + did not affect short-term rates of N2 fixation. This may be an important factor that allows for continued N2 fixation in oligotrophic areas where recycling processes are active. N2 fixation rates decreased when nutrients were supplied at higher concentrations (e.g. 10 μM). Uptake of combined N (NH4 + , NO3 − , and amino acids) by Trichodesmium was stimulated by increased concentrations. For NO3 − , proportional increases in NO3 − uptake and decreases in N2 fixation were observed when additions were made to cultures before the onset of the light period. GS activity did not change much in response to the addition of NH4 + , NO3 − , glu, or gln. GS is necessary for N metabolism, and the bulk of this enzyme pool may be conserved. Intracellular pools of glu and gln varied in response to 10 μM additions of NH4 + , glu, or gln. Cells incubated with NH4 + became depleted in intracellular glu and enriched with intracellular gln. The increase in the gln/glu ratio corresponded to a decrease in the rate of N2 fixation. Although the gln/glu ratio decreased in cells exposed to the amino acids, there was only a corresponding decrease in N2 fixation after the gln addition. The results presented here suggest that combined N concentrations on the order of 1 μM do not affect rates of N2 fixation and metabolism, although higher concentrations (e.g. 10 μM) can. Moreover, these effects are exerted through products of NH4 + assimilation rather than exogenous N, as has been suggested for other species. These results may help explain how cultures of Trichodesmium are able to simultaneously fix N2 and take up NH4 + and how natural populations continue to fix N2 once combined N concentrations increase within a bloom. 相似文献
10.
Non-linear time courses of ammonium (NH4+) depletion from the medium and internal accumulation of soluble nitrogen (N) in macroalgae imply that the rate-limiting step for ammonium uptake changes over time. We tested this hypothesis by measuring the time course of N accumulation in N-limited Ulva rigida C. Agardh. Total uptake was measured as removal of NH4+ from medium. Rates for the component processes (transport of NH4+ across the membrane = Rv assimilation of tissure NH4+ into soluble N compounds = Ra, assimilation of tissue NH4+ into soluble N compounds = Ra and incorporation of soluble N compounds into macromolecules = R1) were determined by measuring the rate of labelling of the major tissue N pools after the addition of 15N-ammonium. The results indicate that nitrogen-specific rates (mass N taken up / mass N present / unit time) are ranked in the order of Rt < Ra < R1 Absolute uptake rates (μmol N. mg dry wt?1. h?1) showed a different relationship. Membrane transport appears to be inhibited when NH4+ accumulates in the tissue. Maximum uptake rates occur when assimilation of NH4+ into soluble N compounds begins. Assimilation of NH4+ into soluble N compounds was initially faster than incorporation of soluble N compounds into macromolecules. Implications of rate limitations caused by differences in maximal rates and maximal pool sizes are discussed. 相似文献
11.
Optimization of ammonium acquisition and metabolism by potassium in rice (Oryza sativa L. cv. IR-72)
KONSTANTINE D. BALKOS DEV T. BRITTO & HERBERT J. KRONZUCKER 《Plant, cell & environment》2010,33(1):23-34
We present the first characterization of K+ optimization of N uptake and metabolism in an NH4+‐tolerant species, tropical lowland rice (cv. IR‐72). 13N radiotracing showed that increased K+ supply reduces futile NH4+ cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux. Pharmacological testing showed that low‐affinity NH4+ influx may be mediated by both K+ and non‐selective cation channels. Suppression of NH4+ influx by K+ occurred within minutes of increasing K+ supply. Increased K+ reduced free [NH4+] in roots and shoots by 50–75%. Plant biomass was maximized on 10 mm NH4+ and 5 mm K+, with growth 160% higher than 10 mm NO3‐‐grown plants, and 220% higher than plants grown at 10 mm NH4+ and 0.1 mm K+. Unlike in NH4+‐sensitive barley, growth optimization was not attributed to a reduced energy cost of futile NH4+ cycling at the plasma membrane. Activities of the key enzymes glutamine synthetase and phosphoenolpyruvate carboxylase (PEPC) were strongly stimulated by elevated K+, mirroring plant growth and protein content. Improved plant performance through optimization of K+ and NH4+ is likely to be of substantial agronomic significance in the world's foremost crop species. 相似文献
12.
Ammonium and nitrate uptake rates in the macroalgae Ulva fenestrata (Postels and Ruprecht) (Chlorophyta) and Gracilaria pacifica (Abbott) (Rhodophyta) were determined by 15N accumulation in algal tissue and by disappearance of nutrient from the medium in long‐term (4–13 days) incubations. Nitrogen‐rich algae (total nitrogen> 4% dry weight [dw]) were used to detect isotope dilution by release of inorganic unlabeled N from algal thalli. Uptake of NH4 + was similar for the two macroalgae, and the highest rates were observed on the first day of incubation (45 μmol N·g dw ? 1·h ? 1 in U. fenestrata and 32 μmol N·g dw ? 1·h ? 1 in G. pacifica). A significant isotope dilution (from 10 to 7.9 atom % enrichment) occurred in U. fenestrata cultures during the first day, corresponding to a NH4 + release rate of 11 μmol N·g dw ? 1·h ? 1. Little isotope dilution occurred in the other algal cultures. Concurrently to net NH4 + uptake, we observed a transient free amino acid (FAA) release on the first day in both macroalgal cultures. The uptake rates estimated by NH4 + disappearance and 15N incorporation in algal tissue compare well (82% agreement, defined as the percentage ratio of the lower to the higher rate) at high NH4 + concentrations, provided that isotope dilution is taken into account. On average, 96% of added 15NH4 + was recovered from the medium and algal tissue at the end of the incubation. Negligible uptake of NO3 ? was observed during the first 2–3 days in both macroalgae. The lag of uptake may have resulted from the need for either some N deprivation (use of NO3 ? pools) or physiological/metabolic changes required before the uptake of NO3 ? . During the subsequent days, NO3 ? uptake rates were similar for the two macroalgae but much lower than NH4 + uptake rates (1.97–3.19 μmol N·g dw ? 1·h ? 1). Very little isotope dilution and FAA release were observed. The agreement between rates calculated with the two different methods averaged 91% in U. fenestrata and 95% in G. pacifica. Recovery of added 15NO3 ? was virtually complete (99%). These tracer incubations show that isotope dilution can be significant in NH4 + uptake experiments conducted with N‐rich macroalgae and that determination of 15N atom % enrichment of the dissolved NH4 + is recommended to avoid poor isotope recovery and underestimation of uptake rates. 相似文献
13.
Alpine plants show species-level differences in the uptake of organic and inorganic nitrogen 总被引:7,自引:1,他引:6
As an estimate of species-level differences in the capacity to take up different forms of N, we measured plant uptake of 15N-NH4
+, 15N-NO3
– and 15N, [1]-13C glycine within a set of herbaceous species collected from three alpine community types. Plants grown from cuttings in the greenhouse showed similar growth responses to the three forms of N but varied in the capacity to take up NH4
+, NO3
– and glycine. Glycine uptake ranged from approximately 42% to greater than 100% of NH4
+ uptake; however, four out of nine species showed significantly greater uptake of either NH4
+ or NO3
– than of glycine. Relative concentrations of exchangeable N at the sites of plant collection did not correspond with patterns of N uptake among species; instead, species from the same community varied widely in the capacity to take up NH4
+, NO3
–, and glycine, suggesting the potential for differentiation among species in resource (N) use. 相似文献
14.
Nitrogen uptake rates of Ulva curvata (Kütz.) de Toni (Ulvales) and Codium decorticatum (Woodw.) Howe (Caulerpales) grown under several N addition regimes were determined by perturbation and continuous mode techniques, and as N demand, by the product of growth rate and tissue N. Uptake rates are reported as the slope of rate vs. concentration curves in each case. N uptake rates of U. curvata were inversely correlated with tissue N and affected only slightly by temperature. There was no correlation of N uptake rate with tissue N in C. decorticatum. N uptake rates of C. decorticatum were affected by temperature but to a lesser degree than were growth rates. Neither N addition per se nor light affected N uptake capacity of either species. The proximal mechanism for seaweeds accumulation of N at low light and temperatures may be that N uptake is less limited by light and temperature than is growth. This in turn may partially compensate for the effects of reduced light and temperature on growth by increasing pigment and enzyme levels. Perturbation uptake rates were higher than continuous mode or N demand rates in Ulva but not in Codium. N uptake rates of Ulva were higher than those of Codium, but N storage capacities were lower. These two observations suggest that Ulva experiences a fundamentally more variable N supply than does Codium. This is consistent with the clarification of Ulva as an ephemeral form and of Codium as persistent. A seaweed's functional form therefore appears to influence the spectrum of resource variability available to it as well as its ability to persist in the environment. 相似文献
15.
The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH4NO3 and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, 15N-labelled NH4+ or NH4++ NO3? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO3? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO3? uptake restarting 1 or 2 days earlier than NH4+ uptake, even when NH4+ was the only form of N supply. LD timothy plants supplied solely with NH4+ were slowest to resume uptake of mineral N. Supplying NO3? in addition to NH4+ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation. 相似文献
16.
O. K. ATKIN 《Plant, cell & environment》1996,19(6):695-704
The Arctic is often assumed to be an NH4+-dominated ecosystem. This review assesses the validity of this assumption. It also addresses the question of whether Arctic plant growth is limited by the ability to use the forms of nitrogen that are available. The review demonstrates that several sources of soil nitrogen are available to Arctic plants, including soluble organic nitrogen (e.g. glycine, aspartic acid and glutamic acid), NH4+ and NO?3. In mesic Arctic soils, soluble organic nitrogen is potentially more important than either NH+4 or NO?3. Many Arctic species are capable of taking up soluble organic nitrogen (either directly and/or in association with ectomycorrhizae), with the greatest potential for soluble organic nitrogen uptake being exhibited by deciduous species. The ability to take up soluble organic nitrogen may enable some Arctic plants to avoid nitrogen limitations imposed by the slow rate of organic matter decomposition. NO?3 is also present in many Arctic soils, especially calcareous soils and soils near flowing water, animal burrows and bird cliffs. Arctic species characteristic of mesic and xeric habitats are capable of taking up and assimilating NO?3. Even when present in lower concentrations in soils than NH+4, NO?3 is still an important source of nitrogen for some Arctic plants. Arctic-plants therefore have a variety of nitrogen sources available to them, and are capable of using those nitrogen sources. Taken together, these findings demonstrate that the Arctic is not an NH+4dominated ecosystem. Symbiotic fixation of atmospheric N2 does not appear to be an important source of nitrogen for Arctic plants. The reliance of Arctic plants on internal recycling of nitrogen substantially reduces their dependence on soil nitrogen uptake (this is particularly the case for slow-growing evergreens). Despite the high level of internal nitrogen recycling, Arctic plant growth remains limited by the low levels of available soil nitrogen. However, Arctic plant growth is not limited by an inability to utilize any of the available forms of nitrogen. The potential effects of climatic warming on nitrogen availability and use are discussed. The question of whether the Arctic ecosystem is uniquely different from temperate nitrogen-deficient ecosystems is also assessed. 相似文献
17.
Lenka Vojtíšková Edita Munzarová Olga Votrubová Hana Čížková Helena Lipavská 《Hydrobiologia》2006,563(1):73-85
Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using
water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6
mM) and/or forms of N (NH4+ versus NO 3–) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH4+–N nutrition described in our previous study [Vojtíšková et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure
NH4+–N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH4+–N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates
(TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and
negatively affected by high N availability (P = 0.001), as well as by NH4+–N nutrition (P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch
in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to
33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high
content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue
differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%,
Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH4+ received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was
not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH4+ nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in
favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could
explain the reduced growth of Acorus plants under high N and sole NH4+–N nutrition described previously. 相似文献
18.
Tomato growth was examined in solution culture under constant pH and low levels of NH4+ or NO3?. There were five nitrogen treatments: 20 mmoles m?3 NH4+, 50 mmoles m?3 NO3?, 100 mmoles m?3 NH4+ 200 mmoles m?3 NO3?, and 20 mmoles m?3 NH4++ 50 mmoles m?3 NO3?. The lower concentrations (20 mmoles m?3 NH4+ and 50 mmoles m?3 NO3?) were near the apparent Km for net NH4+ and NO3? uptake; the higher concentrations (100 mmoles m?3 NH4+ and 200 mmoles m?3 NO3?) were near levels at which the net uptake of NH4+ or NO3? saturate. Although organic nitrogen contents for the higher NO3? and the NH4++ NO3? treatments were 22.2–30.3% greater than those for the lower NO3? treatment, relative growth rates were initially only 10–15% faster. After 24 d, relative growth rates were similar among those treatments. These results indicate that growth may be only slightly nitrogen limited when NH4+ or NO3? concentrations are held constant over the root surface at near the apparent Km concentration. Relative growth rates for the two NH4+ treatments were much higher than have been previously reported for tomatoes growing with NH4+ as the sole nitrogen source. Initial growth rates under NH4+ nutrition did not differ significantly (P≥ 0.05) from those under NO3? or under combined NH4++ NO3?. Growth rates slowed after 10–15 d for the NH4+ treatments, whereas they remained more constant for the NO3? and mixed NH4++ NO3? treatments over the entire observation period of 24–33 d. The decline in growth rate under NH4+ nutrition may have resulted from a reduction in Ca2+, K+, and/or Mg2+ absorption. 相似文献
19.
Summary Significantly lower amounts of exchaneable NH4, soluble NO3 and clay-fixed NH4 forms of N were observed in the unfertilized fields with high rather than low-density cropped plots. Irrespective of planting
densitites, the fixed NH4 content in soil increased with increase in the period of crop growth. N uptake by plant and total bacterial population of
rhizosphere soil were significantly higher in the plots with the high than with the low-density planting. Availability of
native fixed NH4
+ to crops and biological utilization of a considerable amount of recently mineralized NH4
+ in fixed form is indicated. 相似文献
20.
Fertilization rates and clay fixed ammonium in two Quebec soils 总被引:5,自引:0,他引:5
Clay fixed NH4
+ can provide a significant sink for fertilizer N, as well as a source of N for plant uptake. Knowledge or soil NH4
+ fixing capacity and release for crops is necessary to develop long-term fertilizer programs. Field experiments with corn (Zea mays L.) were carried out to investigate soil NH4
+ fixing capacity and subsequent release as influenced by fertilizer rates using 15N in a Ste. Rosalie clay (fine, mixed, frigid, Typic Humaquept) and a Chicot sandy clay loam (fine-loamy, mixed, frigid, Typic Hapludalf). With high N rates increased NH4
+ fixation occurred only in the Ste. Rosalie soil. At the end of the first growing season, fertilizer N recovery as clay fixed NH4
+ for high and normal rates of fertilizer in the Ste. Rosalie soil was 17.8% and 28.7%, respectively and the recovery for the high and normal rates in the Chicot soil was 4.6 and 10.5%, respectively. Significant amounts of clay fixed NH4
+-N were released in the soil profile in the second year after 15N application on the Chicot soil. Recently clay fixed fertilizer NH4
+N was released more rapidly than that of the native fixed NH4
+, from the surface layer of the Ste. Rosalie soil. The fertilizer fixed NH4
+ seems to be in a more labile N pool than the native fixed NH4
+-N in the Chicot soil. 相似文献