共查询到20条相似文献,搜索用时 31 毫秒
1.
Fu-Cang Zhang Shao-Zhong Kang Fu-Sheng Li Jian-Hua Zhang 《植物学报(英文版)》2007,49(4):455-462
In the present study, we investigated whether growth and main nutrient ion concentrations of cabbage (Brassica campestris L.) could be increased when plants were subjected to different NH4^+/NO3- ratios. Cabbage seedlings were grown in a greenhouse in nutrient solutions with five NH4^+/NO3- ratios (1:0; 0.75:0.25; 0.5:0.5; 0.25:0.75; and 0:1). The results showed that cabbage growth was reduced by 87% when the proportion of NH4^+-N in the nutrient solution was more than 75% compared with a ratio NH4^+/NO3- of 0.5:0.5 35 d after transplanting, suggesting a possible toxicity due to the accumulation of a large amount of free ammonia in the leaves. When the NH4+/NO3- ratio was 0.5:0.5, fresh seedling weight, root length, and H2PO4- (P), K^+, Ca^2+, and Mg^2+ concentrations were all higher than those in plants grown under other NH4^+/NO3- ratios. The nitrate concentration in the leaves was the lowest in plants grown at 0.5: 0.5 NH4^+/NO3-. The present results indicate that an appropriate NH4^+/NO3- ratio improves the absorption of other nutrients and maintains a suitable proportion of N assimilation and storage that should benefit plant growth and the quality of cabbage as a vegetable. 相似文献
2.
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
3.
Combination Effect of NaCl Salinity and Nitrogen Form on Mineral Composition of Sunflower Plants 总被引:2,自引:0,他引:2
The effect of two N-forms (NH4
+ and NO3
–) and NaCl on pattern of accumulation of some essential inorganic nutrients was examined in sunflower (Helianthus annuus L.) cv. Hisun 33. Eight-day-old plants of were subjected for 21 d to Hoagland's nutrient solution containing 8 mM N as NH4
+ or NO3
·, and salinized with and addition of NaCl to the growth medium had no significant effect on total leaf N. However, root N of NH4-supplied plants decreased significantly with increase in NaCl concentration, whereas that of NO3-supplied plants remained unaffected. There was no significant effect of NaCl on leaf or root P, but the NO3-supplied plants had significa concentration of leaf P than that of NH4-supplied plants at varying salt treatments. Salinity of the rooting med did not show any significant effect on Na+ concentrations of leaves or roots of plants subjected to two differen N. NH4-treated plants generally had greater concentrations of Cl– in leaves and roots and lower K+ content in leaves than NO3-supplied plants. Ca2+ concentrations of leaves and roots and Mg2+ concentrations of leaves decreased in NH4-supplied plants due to NaCl, but they remained unaffected in NO3-treated plants. 相似文献
4.
N. A. Startsev V. J. Lieffers S. M. Landhäusser A. Velazquez-Martinez 《Plant and Soil》2008,311(1-2):51-59
When fertilizer is broadcast in boreal forest stands, the applied nutrients must pass through a thick layer of either feather moss or leaf litter which covers the forest floor. In a growth chamber experiment we tested the transfer of N through living feather moss or aspen litter when fertilized with urea ((NH2)2CO) or NH4NO3 at a rate of 100 kg ha?1 and under different watering regimes. When these organic substrates were frequently watered to excess they allowed the highest transfer of nutrients through, although 72% of the applied fertilizer was captured in the substrates. In a field experiment we also fertilized moss and aspen litter with urea ((NH2)2CO) or NH4NO3 at a more operationally relevant rate of 330 kg ha?1. We captured the NO3 ? or NH4 + by ion exchange resin at the substrate–mineral soil interface. In contrast to the growth chamber experiment, this fertilizer rate killed the moss and there was no detectable increase in nutrient levels in the aspen litter or feather moss layers. Instead, the urea was more likely transferred into the mineral soil; mineral soil of the urea treatment had 1.6 times as much extractable N compared to the NH4NO3 treatment. This difference between the growth chamber and field studies was attributed to observed fertilizer-damage to the living moss and possibly damage to the litter microflora due to the higher rate of fertilization in the field. In addition, the early and substantial rainfall after fertilization in the field experiment produced conditions for rapid leaching of N through the organic layers into the mineral soil. In the field, only 8% of the urea-N that was applied was captured by the ion exchange resin, while 34% was captured in for the NH4NO3 fertilization. Thus, the conditions for rapid leaching in the field moved much of the N in the form of urea through the organic layers and into the mineral soil before it was hydrolyzed. 相似文献
5.
Vasavi Singareddy Vijay Reddy Sheri Tarakeswari Muddanuru Revathi Tatineni Rakesh Kumar Jain Chander Rao Sankaraneni Varaprasad S. Kodeboyina Sujatha Mulpuri 《Plant Cell, Tissue and Organ Culture》2018,133(2):263-273
Nitrogen is a major driver of plant growth and the nitrogen source can be critical to good growth in vitro. A response surface methodology mixture-component design and a data mining algorithm were applied to nitrogen (N) nutrition for improving the micropropagation of Prunus armeniaca Lam. Data taken on shoot cultures included a subjective quality rating, shoot number, shoot length, leaf characteristics and physiological disorders. Data were analyzed using the Classification and Regression Tree data mining algorithm. The best overall shoot quality as well as leaf color were on medium with NO3??>?25 mM and NH4+/Ca+ >?0.8. Improving shoot length to15 mm required 25?<?NO3? ≤?35 mM with NH4+/Ca2+ ≤?2.33. The most shoots (11.6) were produced with NO3? >?25 mM and NH4+/Ca2+ ≤ 0.8, but there were 5–10 shoots at other NO3? concentrations regardless of NH4+/Ca2+ proportion. Leaves increased in size with higher NO3? concentrations (>?55 mM). Physiological disorders were also influenced by the nitrogen components. Shoot tip necrosis was rarely present with NO3? > 45 mM. Callus production decreased somewhat with NH4+/Ca2+ >?2.33. Suggested concentrations for an improved medium considering all of these growth characteristics would be 25?<?NO3? ≤?35 mM and NH4+/Ca+ ≤ 0.8. Validation experiments comparing WPM and three trial media showed improvements in several shoot growth parameters on medium with optimized mesos and optimized nitrogen components. 相似文献
6.
In many forests of Europe and north-eastern North America elevated N deposition has opened the forest N cycle, resulting in NO3 ? leaching. On the other hand, despite this elevated N deposition, the dominant fate of NO3 ? and NH4 + in some of these forests is biotic or abiotic immobilization in the soil organic matter pool, preventing N losses. The environmental properties controlling mineral N immobilization and the variation and extent of mineral N immobilization in forest soils are not yet fully understood. In this study we investigated a temperate mixed deciduous forest, which is subjected to an average N deposition of 36.5 kg N ha?1 yr?1, but at the same time shows low NO3 ? concentrations in the groundwater. The aim of this study was to investigate whether the turnover rate of the mineral N pool could explain these low N leaching losses. A laboratory 15N pool dilution experiment was conducted to study gross and net N mineralization and nitrification and mineral N immobilization in the organic and uppermost (0–10 cm) mineral layer of the forest soil. Two locations, one at the forest edge (GE) and another one 145 m inside the forest (GF1), were selected. In the organic layers of GE and GF1, the gross N mineralization averaged 10.9 and 11.1 mg N kg?1 d?1, the net N mineralization averaged 6.1 and 6.8 mg N kg?1 d?1 and NH4 + immobilization rates averaged 3.8 and 3.6 mg N kg?1 d?1. In the organic layer of GE and GF1, the average gross nitrification was 3.8 and 4.6 mg N kg?1 d?1, the average net nitrification was ?25.2 and ?31.3 mg N kg?1 d?1 and the NO3 ? immobilization rates averaged 29.0 and 35.9 mg N kg?1 d?1. For the mineral (0–10 cm) layer the same trend could be observed, but the N transformation rates were much lower for the NH4 + pool and not significantly different from zero for the NO3 ? pool. Except for the turnover of the NH4 + pool in the mineral layer, no significant differences were observed between location GE and GF1. The ratio of NH4 + immobilization to gross N mineralization, gross N mineralization to gross nitrification, and NO3 ? immobilisation to gross nitrification led to the following observations. The NH4 + pool of the forest soil was controlled by N mineralization and NO3 ? immobilization was importantly controlling the forest NO3 ? pool. Therefore it was concluded that this process is most probably responsible for the limited NO3 ? leaching from the forest ecosystem, despite the chronically high N deposition rates. 相似文献
7.
We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH4+, NO3?, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO3? and NH4+ grown cells had similar growth rates and C and X quotas. Therefore, NO3? grown cells used up to 48% more energy than NH4+ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a?1, we suggest that NO3?, grown cells do not compensate for the greater energy requirements of NO3? reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO3?, compared to NH4+ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh4+ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO3?, or urea. 相似文献
8.
Seasonal and spatial patterns of S,Ca, and N dynamics of a Northern Hardwood forest ecosystem 总被引:1,自引:1,他引:0
Seasonal dynamics of S, Ca and N were examined at the Huntington Forest, a northern hardwood ecosystem in the central Adirondacks
of New York for a period of 34 months (1985–1988). Solute concentrations and fluxes in bulk precipitation, throughfall (TF)
and leachates from the forest floor, E horizon and B horizon were quantified. Both above and below-ground elemental fluxes
mediated by vegetation (e.g. uptake, litter inputs, and fine roots production) were also determined. The roles of abiotic
and biotic processes were ascertained based on both changes in solute concentrations through the strata of the ecosystem as
well as differences between dormant and growing seasons. Concentrations of SO4
2−, NO3
−, NH4
+ and Ca2+ were greater in TF than precipitation. Forest floor leachates had greater concentrations of SO4
2−, NO3
− + NH4
+ and Ca2+ (9, 6 and 77 μeq L−1, respectively) than TF. There were differences in concentrations of ions in leachates from the forest floor between the dormant
and growing seasons presumably due to vegetation uptake and microbial immobilization. Concentrations and fluxes of NO3
− and NH; were greatest in early spring followed by a rapid decline which coincided with a demand for N by vegetation in late
spring. Vegetation uptake (44.7 kg N ha−1 yr−1 ) could account for the low leaching rates of N03
−. Within the mineral soil, changes with soil depth and the absence of seasonal patterns suggest that cation exchange (Ca+) or anion sorption (SO4
2−) are primarily responsible for regulating solute concentrations. The increase in SO4
2− concentration after leachates passed through the mineral soil may be attributed to desorption of sulfate that was adsorbed
during an earlier period when SO4
2− concentrations would have been greater due to elevated S inputs. 相似文献
9.
Wheat leaf growth is known to be spatially affected by salinity. The altered spatial distribution of leaf growth under saline
conditions may be associated with spatial changes in tissue mineral elements. The objective of this study was to evaluate
the spatial distributions of mineral elements and their net deposition rates in the elongating and mature zones of leaf 4
of the main stem of spring wheat (Triticum aestivum L. cv. Lona) during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty
loam with 0 and 120 mM NaCl. Three days after emergence of leaf 4, sampling was begun at 3 and 13 h into the 16-h light period.
Spatial distributions of fresh weight (FW), dry weight (DW), and Na+, K+, Cl−, NO−
3, Ca2+, Mg2+, total P, and total N in the elongating and mature tissues were determined on a millimeter scale. The patterns of spatial
distribution of Na+, Cl−, K+, NO3
−, and Ca2+ in the growing leaves were affected by salinity, while those of Mg2+, total P, and total N were not. Sodium, K+, Cl−, Ca2+, Mg2+, and total N concentrations (mmol · kg−1 FW) were consistently higher at 120 mM NaCl than at 0 mM NaCl along the leaf axis from the leaf base, whereas NO3
− concentration was lower at 120 mM NaCl. Deposition rates of all nutrients were greatest in the elongation zone. The elongation
zone was the strongest sink for mineral elements in the leaf tissues. Local net deposition rates of Na+, Cl−, Ca2+, and Mg2+ (mmol · kg−1 FW · h−1) in the most actively elongating zone were enhanced by 120 mM NaCl, whereas for NO3
− this was depressed. The lower supply of NO−
3 to growing leaves may be responsible for the inhibition of growth under saline conditions. Higher tissue concentrations of
Na+ and Cl− may cause ion imbalance but probably did not result in ion toxicity in the growing leaves. Potassium, Ca2+, Mg2+, total P, and total N are less plausibly responsible for the reduction in leaf growth in this study. Higher tissue K+ and Ca2+ concentrations at 120 mM NaCl are probably due to the presence of high Ca2+ in the soil of this study.
Received: 13 March 1997 / Accepted: 9 June 1997 相似文献
10.
The growth of Salvinia molesta D.S. Mitchell was studied in a greenhouse using controlled-temperature water-baths at 16, 19 and 22°C and 4 different nitrogen compounds (NO3?, NH4+, NH4NO3 and urea) at levels up to 60 mg N l?1. Little growth occurred at 16°C even if 20 mg N l?1 was supplied together with other nutrients including phosphorus (2 mg H2PO4-P l?1). The highest relative growth rate and total dry matter production occurred at 22°C when plants were supplied with 20 mg NH4-N l?1. At this temperature, the NH4+ ion was superior to the NO3? ion or urea as a nitrogen source (almost doubling the biomass), but was not significantly better than NH4NO3. Over a period of 19 days for plants receiving 0.02 mg NH4-N l?, biomass increased 4-fold at 16°C, 9-fold at 19°C and 10-fold at 22°C. In contrast, for plants receiving 20 mg NH4-N l?1, biomass increased 4-fold at 16°C, 18-fold at 19°C and 38-fold at 22°C. 相似文献
11.
The effect of ectomycorrhizal association of Pinus pinaster with Hebeloma cylindrosporum was investigated in relation to the nitrogen source supplied as mineral (NH4+ or NO3?) or organic N (L ‐glutamate) and at 5 mol m?3. Plants were grown for 14 and 16 weeks with mineral and organic N, respectively, and samples were collected during the last 6 weeks of culture. Total fungal biomass was estimated using glucosamine amount and its viability was assessed using the glucosamine to ergosterol ratio. Non‐mycorrhizal plants grew better with NH4+ than with NO3? and grew very slowly when supplied with L ‐glutamate. The presence of the fungus decreased the growth of the host plant with mineral N whereas it increased it with L ‐glutamate. Whatever the N source, most of the living fungal biomass was associated with the roots, whereas the main part of the total biomass was assayed outside the root. The form of mineral N did not significantly affect N accumulation rates over the 42 d in control plants. In mycorrhizal plants grown on either N source, the fungal tissues developing outside of the root were always the main N sink. The ectomycorrhizal association did not change 15NH4+ uptake rate by roots, suggesting that the growth decrease of the host‐plant was related to the carbon cost for fungal growth and N assimilation rather than to a direct effect on NH4+ acquisition. In contrast, in NO3?‐grown plants, in addition to draining carbon for NO3? reduction the fungus competed with the root for NO3? uptake. With NH4+ or NO3? feeding, although mycorrhizal association improved N accumulation in shoots, we concluded that it was unlikely that the fungus had supplied the plant with N. In L ‐glutamate‐grown plants, the presence of the fungus increased the proportion of glutamine in the xylem sap and improved both N nutrition and the growth rate of the host plant. 相似文献
12.
Fabiano Daniel De Bona Fabiana Schmidt Francisco Antonio Monteiro 《Plant and Soil》2013,373(1-2):201-216
Background and aims
Plant responses to S supply are highly dependent on N nutrition. We investigated the effect of S status on metabolic, nutritional, and production variables in Brachiaria brizantha treated with different N forms. Additionally, 15N and 34S root influx were determined in plants under short- and long-term S deprivation.Methods
Plants were submitted to soil fertilization treatments consisted of combinations of N forms [without N, ammonium (NH4 +), nitrate (NO3 ?) or NH4 ++NO3 ?] at S rates (0, 15, 30, or 45 mg dm?3). N and S influx capacity was determined in hydroponically-grown plants.Results
Shoot production due to S supply increased 53, 145 and 196 % with NH4 +, NH4 ++NO3 ? and NO3 ? treatments, respectively. No or low S impaired protein synthesis and led to high accumulation of N-NO3 ? and asparagine in NO3 ?-fed plants, both alone and with NH4 +. Proline accumulation was observed in NH4 +-fed plants. Short- and long-term S deprivation did not promote considerable changes in 15N influx. 34S absorption decreased depending on the N form provided: NH4 ++NO3 ? > only NH4 + > only NO3 ? > low N.Conclusions
Including both NH4 + and NO3 ? forms in fertilizer increases N and S intake potential and thereby enhances plant growth, nutritional value and production. 相似文献13.
NH4+ and NO3? uptake were measured by continuous sampling with an autoanalyzer. For Hypnea musciformis (Wulfen) Lamouroux, NO3?up take followed saturable kinetics (K2=4.9 μg-at N t?1, Vmax= 2.85 μg- at N, g(wet)?1. h?1. The ammonium uptake data fit a trucatd hyperbola, i.e., saturation was not reach at the concentrations used. NO3? uptake was reduced one-half in the presence of NH4+, but presence of NO3? had no effect on NH4+ uptake. Darkness reduced both NO3? and NH4+ uptake by one-third to one-half. For Macrocystis pyrufera (L) C. Agardh, NO3? uptake followed saturable kinetices: K2=13.1 μg-at N. l?1. Vmax=3.05 μg-at N. g(wet)?1. h?1.NH4+ uptake showed saturable kinetics at concentration below 22 μg-at N l -1 (K2=5.3 μg-at N.1–1, Vmax= 2.38 μg-at N G (wet)?1.h?1: at higher concentration uptake increased lincarly with concentrations. NO3?and NH4+ were taken up simulataneously: presence of one form did not affect uptake of the other. 相似文献
14.
K. E. Savage E. A. Davidson R. Z. Abramoff A. C. Finzi M.-A. Giasson 《Biogeochemistry》2018,139(1):53-68
Sediment porewater nutrients often occur at concentrations that are orders of magnitude higher than nutrients in overlying waters, and accordingly may subsidise growth of benthic macroalgal mats in estuarine ecosystems. The relative contribution of porewater nutrients is expected to be particularly important for macroalgae entrained in intertidal mudflat sediments, where access to water column nutrients is tidally constrained. In this study, filamentous Gracilaria chilensis thalli were simultaneously exposed to sediment and overlying water nutrient sources, labelled using 15N tracers (15NH4+ or 15NO3?) during a 5-day experiment. Dissolved inorganic N (DIN) uptake from porewater and overlying water accounted for 33 and 52%, respectively, of the N estimated as necessary to support the growth of G. chilensis, despite the two-fold lower DIN concentration of the overlying water and its periodic availability (8 h day?1). Of the total N assimilated by the plants,?~?15% could not be accounted for, supporting the acquisition of other N forms in order to meet demand. We also found that regardless of background NH4+:NO3? ratios (i.e. 1:3 in overlying water and 12:1 in porewater), plants accumulated 15NH4+ significantly more readily than 15NO3?, indicating a preference for NH4+. This ability to utilise multiple sources and species of N relatively rapidly may partly explain the competitive success of entrained macroalgae relative to non-entrained species and historically abundant seagrass beds in these environments. These results underscore the significance of both internal nutrient loading and external inputs as important in sustaining opportunistic macroalgal blooms in shallow estuaries. 相似文献
15.
The uptake and translocation of macro- and microelements in rape and wheat seedlings as affected by selenium supply level 总被引:2,自引:0,他引:2
Maria Filek Maria Zembala Andrzej Kornaś Stanisław Walas Halina Mrowiec Helinä Hartikainen 《Plant and Soil》2010,328(1-2):303-312
Plant growth in saline soils may be increased by fertilisation, but little is known about the effect of different forms of N on wheat growth in soils with different salinity levels. The aim of this study was to investigate the response of wheat (Triticum aestivum L., cv Krichauff) to (NH4)2SO4 or KNO3 or NH4NO3 at 0 (N0), 50 (N50), 100 (N100) and 200 (N200) mg N?kg?1 soil in a saline sandy loam. Salinity was induced using Na+ and Ca2+ salts to achieve three ECe levels, 2.8, 6.6 and 11.8 dS m?1 denoted S1, S2 and S3, respectively, while maintaining a low SAR (>1). Dry weights of shoot and root were reduced by salinity in all N treatments. Addition of N significantly increased shoot and root dry weights with significant differences between N forms. Under non-saline conditions (S1), addition of NO3???N at rates higher than N50 had a negative effect, while N100 as NH4???N or NH4NO3???N increased shoot and root dry weights. At N100, shoot concentrations of N and K were higher and P, Ca, Fe, Mn, Cu and Zn were lower with NO3???N than with NH4???N nutrition. The concentration of all nutrients however fell in ranges did not appear to be directly associated with poor plant growth with NO3???N. At all N additions, calculations indicated that soil salinity was highest with N addition as NO3???N and decreased in the following order: NO3?N > NH4?N > NH4NO3?N. Addition of greater than N50 as NO3???N, compared to NH4???N or NH4???NO3, increased soil salinity and reduced micronutrient uptake both of which likely limited plant growth. It can be concluded that in saline soils addition of 100 mg N?kg?1 as NH4???N or NH4NO3???N is beneficial for wheat growth, whereas NO3???N can cause growth depression. 相似文献
16.
Segregation of nitrogen use between ammonium and nitrate of ectomycorrhizas and beech trees
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Martin Leberecht Michael Dannenmann Javier Tejedor Judy Simon Heinz Rennenberg Andrea Polle 《Plant, cell & environment》2016,39(12):2691-2700
Here, we characterized nitrogen (N) uptake of beech (Fagus sylvatica) and their associated ectomycorrhizal (EM) communities from NH4+ and NO3?. We hypothesized that a proportional fraction of ectomycorrhizal N uptake is transferred to the host, thereby resulting in the same uptake patterns of plants and their associated mycorrhizal communities. 15N uptake was studied under various field conditions after short‐term and long‐term exposure to a pulse of equimolar NH4+ and NO3? concentrations, where one compound was replaced by 15N. In native EM assemblages, long‐term and short‐term 15N uptake from NH4+ was higher than that from NO3?, regardless of season, water availability and site exposure, whereas in beech long‐term 15N uptake from NO3? was higher than that from NH4+. The transfer rates from the EM to beech were lower for 15N from NH4+ than from NO3?. 15N content in EM was correlated with 15N uptake of the host for 15NH4+, but not for 15NO3?‐derived N. These findings suggest stronger control of the EM assemblage on N provision to the host from NH4+ than from NO3?. Different host and EM accumulation patterns for inorganic N will result in complementary resource use, which might be advantageous in forest ecosystems with limited N availability. 相似文献
17.
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
18.
We examined the effect of soil NH4+ and NO3? content upon the root systems of field-grown tomatoes, and the influence of constant, low concentrations of NH4+ or NO3? upon root growth in solution culture. In two field experiments, few roots were present in soil zones with low extractable NH4+ or NO3?; they increased to a maximum in zones having 2μg-N NO3? g?1 soil and 6 μg-N NO3= g?1 soil, but decreased in zones having higher NH4+ or NO3? levels. Root branching was relatively insensitive to available mineral nitrogen. Plants maintained in solution culture at constant levels of NH4+ or NO3?, had similar shoot biomass, but all root parameters – biomass, length, branching and area – were greater under NH4 nutrition than under NO3?. These results suggest that the size of root system depends on a functional equilibrium between roots and shoots (Brouwer 1967) and on the balance between soil NH4+ and NO3?. 相似文献
19.
Ammonia (NH3) is the third most abundant N species in the atmosphere and, due to various natural and anthropogenic sources, can reach high concentrations in some areas. While some plants show effects of toxicity, others are capable of using this N-form and grow well without any utilization of soil-N. Acquisition of atmospheric NH3 will affect the acid-base balance of the plants as absorption and dissolution causes an alkalinisation (production of OH?) and assimilation of NH3 results in an acidification (generation of H+). As there is only a limited capacity for biochemical disposal of excess H+ in shoots, pH regulation may involve H+/OH? extrusion into the media via roots and transport of (in)organic ions between roots and above-ground parts of the plant. Our aim therefore was to assess NH3 acquisition by Lolium perenne and to study the effects of gas phase NH3 on growth, acid-base balance and mineral composition of the plants. The experiments therefore included application of a range of 14NH3 to the shoots and of 15N as NO3?, NH4+ or NH4NO3 to the roots, from which the amount of gas phase NH3 acquisition could be quantified. Analysis of the mineral composition provided data for calculation of acid-base balance as well as for water use efficiencies of the plants. The results indicate that over the range of NH3 supplied, plants from all treatments could utilize gas-phase NH3 as demonstrated by increases in growth and in N and C use efficiencies. Plants receiving NO3? via their roots had a higher capacity to use gaseous NH3 than those growing with NH4+. NH3 assimilation in shoots reduced both the acid load with NH4+ nutrition and the alkaline load with NO3? supply to the roots. The results of the experiments are discussed in relation to possible acid-base regulation mechanisms of the whole plant. 相似文献
20.
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