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1.
A prerequisite to investigate the importance of osmotic potential (Ψo) in relation to matric potential (Ψm) in the soil for water uptake is the existence of a method that measures the temporal and spatial dynamics of Ψo in the vicinity of roots. One method for measuring Ψoin situ is the collection of soil solution with micro suction cups, the spatial resolution of which is suitable for rhizosphere studies. A major drawback of soil solution sampling is the disturbance of soil solution equilibrium, which makes frequent measurements impossible, so another method is required to provide information on the temporal dynamics of Ψo. The time‐domain reflectometry (TDR) technique might be suitable as the signal attenuation (σ) shows a close linear correlation with the salt concentration for a known soil water content. The temporal resolution of the TDR technique is high and the measurement has no impact on soil solution equilibrium. However, the spatial resolution of the TDR technique is too coarse to be used on its own in rhizosphere studies. We used a combination of TDR (fine temporal resolution) and micro suction cups (fine spatial resolution) to measure Ψo in a model system with Zea mays grown in quartz substrates. Osmotic potential changed continuously with time, and a steep gradient between bulk soil and the root compartment developed during the 39‐day growing period. The steepest gradient measured over a distance of 6 mm across the nylon net, separating the bulk soil from the root compartment, was ?365 kPa. The combination of both methods made it possible to extend the time interval between micro suction cup samplings and thus minimize the impact of sampling on soil solution equilibrium. Problems of separate calibration were avoided by calibrating the TDR measurements against the results obtained with the micro suction cups within the same experiment. 相似文献
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Solute transport from the bulk soil to the root surface is, apart from changes in soil moisture and plant nutrient uptake, a prerequisite for changes in soil osmotic potential (Ψo). According to the convection‐diffusion equation, solute transport depends on a number of parameters (soil moisture–release curve, hydraulic conductivity, tortuosity factor) which are functions of soil texture. It was thus hypothesized that soil texture should have an effect on the formation of Ψo gradients between bulk soil and the root surface. The knowledge about such gradients is important to evaluate water availability in the soil‐plant‐atmosphere continuum (SPAC). A linear compartment system with maize grown under controlled conditions in two texture treatments (T1, pure sand; T2, 80% sand, 20% silt) under low and high initial application of salts (S1, S2) was used to measure the development of Ψo gradients between bulk soil and the root surface by microscale soil‐solution sampling and TDR sensors. The differences in soil texture had a strong impact on the formation of Ψo gradients between bulk soil and the root surface at high and low initial salt application rate. At high initial salt application, a maximum osmotic‐potential gradient (ΔΨo) of –340 kPa was observed for the texture treatment T2 compared to ΔΨo of –180 in T1. The steeper gradients in osmotic potential in treatment T2 compared to T1 corresponded to higher cumulative water consumption in this treatment which can partly be explained by higher soil hydraulic conductivity in the range of soil matric potentials covered during the duration of the experiments. Differences between texture treatments in Ψo at the root surface did not result in differences in plant‐water relations measured as gas‐exchange parameters (transpiration rate, water‐use efficiency) and leaf osmotic potential. If soil osmotic and matric potential are regarded as additive in calculating the driving force for water movement from the soil into the root, the observed differences in water flux between treatments cannot be explained. 相似文献
4.
Sofie F. Kostandi Magdi F. Soliman Wolfgang Merbach 《Archives of Agronomy and Soil Science》2013,59(8):903-913
Replacing new corn genotypes in agricultural practices requires adequate information on the reaction of the selected hybrids to Cd uptake in Cd-polluted soil and an understanding of interactions with N fertilizers. A 2 × 2 × 3 factorial pot experiment with limed soil (pH 8), two maize (Zea mays) hybrids (Pioneer cultivar yellow and Pioneer cultivar white), two N fertilization forms (NH4 + and NO3 ?) and three Cd exposures (0, 2 and 5 mg kg?1 soil) was conducted under greenhouse conditions. Shoot dry mass increased significantly with NH4 + nutrition compared with NO3 ? nutrition in both maize hybrids, with greater negative influence of Cd application combined with NH4 + nutrition. The yellow cultivar had significantly greater shoot dry mass and lower Cd uptake than the white cultivar. Both hybrids exhibited similar N uptake in shoots and roots, with the exception of yellow cultivar with NH4 + nutrition without Cd application. NO3 ? nutrition always decreased Cd uptake in both cultivars compared with NH4 + nutrition. The N balance (mean across cultivars and Cd supply) after harvest showed most N uptake with NH4 + nutrition (63.4%) and Nmin remains in the soil with NO3 ? nutrition (48.7%). Soil pH decreased more with NH4 + (?0.95 pH units) than NO3 ? nutrition (?0.21). 相似文献
5.
《Journal of plant nutrition》2013,36(3):599-612
Physiological responses to salt stress were investigated in two cotton (Gossypium hirsutum L.) cultivars (Pora and Guazuncho) grown hydroponically under various concentrations of NaCl. Dry matter partitioning, plant water relations, mineral composition and proline content were studied. Proline and inorganic solutes were measured to determine their relative contribution to osmotic adjustment. Both leaf water potential (Ψw) and osmotic potential (Ψs)decreased in response to NaCl levels. Although Ψwand Ψs decreased during salt stress, pressure potential Ψp remained between 0.5 to 0.7 MPa in control and all NaCl treatments, even under 200 mol m?3 NaCl. Increased NaCl levels resulted in a significant decrease in root, shoot and leaf growth biomass. Root / shoot ratio increased in response to salt stress. The responses of both cultivars to NaCl stress were similar. Increasing salinity levels increased plant Na+ and Cl?. Potassium level remained stable in the leaves and decreased in the roots with increasing salinity. Salinity decreased Ca2+ and Mg2+ concentrations in leaves but did not affect the root levels of these nutrients. The K/Na selectivity ratio was much greater in the saline treated plants than in the control plants. Osmotic adjustment of roots and leaves was predominantly due to Na+ and Cl? accumulation; the contribution of proline to the osmotic adjustment seemed to be less important in these cotton cultivars. 相似文献
6.
The effects of NaCl salt (EC = 16 dS m−1) on water potential, and accumulation of proline, Na+ and K+ in leaves on the main stem of 30 wheat cultivars (Triticum aestivum L.) at awn appearance and 20 days after anthesis (20 DAA) were evaluated in a greenhouse experiment. Plants were arranged
in a according to a randomized complete block design with factorial treatments in three replications. Proline accumulation
at 20 DAA increased with increasing salt stress. This increase was 27.4-fold with the salt-sensitive cultivar “Ghods,” while
the mean was 5.2-fold for 19 salt-resistant cultivars. Positive correlations between proline, and K+ + Na+ concentrations associated with higher sensitivity to salt stress indicated that proline may not have a protecting role against
salt stress. No correlation was observed between leaf proline and water potential. Almost no contribution to the osmotic adjustment
seems to be made by proline. The contribution made by proline to the osmotic adjustment of plants at 20 DAA was 0.69 bar,
whereas that made by K+ and Na+ was 2.11 and 4.48 bar, respectively. The 30 wheat CVs used in this experiment showed different performances regarding the traits observed. Eleven of them showing the higher stress
sensitivity indices had the highest level of proline and Na+ concentrations. They were considered to be salt-sensitive cultivars. Among the others, nine cultivars showed salt tolerance
with almost the same Na+ and proline concentrations, but a higher K+/Na+ selectivity of ions from leaf to grains. In 10 of the cultivars, Na+ and proline concentrations were low, indicating the presence of a salt avoiding mechanism. 相似文献
7.
Roots can induce significant changes in the rhizosphere soil. The aim of the present study was to investigate the influence of beech (Fagus silvatica L.) roots on the chemistry of the rhizosphere soil solution. Special emphasis was given to the effect of the NH4+ supply since many forest soils presently receive high NH4+ inputs from atmospheric deposition. In a mature beech stand, a non‐mycorrhized long root was forced to grow into a rhizotrone filled with homogenized acidic forest soil from the Bw horizon of a Dystric Cambisol. Beside the control, a NH4+ enriched treatment was installed. Thirty micro suction cups of 1 mm diameter and 0.5 cm length were placed in a systematic grid of 5 × 10 mm in each rhizotrone to enable root growth through the grid. The water potential of the soil was kept constant by supplying a synthetic soil solution. Small amounts of soil solution were sampled periodically from May to October 1999 and analyzed by capillary electrophoresis for major cations and anions. Furthermore, pH and conductivity were measured by micro electrodes. In the laboratory experiments, beech seedlings were grown in rhizotrones in a control and in a NH4+ fertilized soil. The equipment for sampling soil solutions and the soil conditions in the laboratory was similar to the field experiment. In each rhizotrone a single long root grew through the lysimeter grid. The laboratory conditions induced higher rates of nitrification as compared to the field. Thus, the overall concentration range of the soil solution was not comparable between field and laboratory studies. In all treatments average soil solution concentrations of H+ and Al3+ were significantly higher in the rhizosphere than in the bulk soil. The NH4+ treatment resulted, in the field and laboratory, in a strong increase of the H+ and Al3+ concentrations in the rhizosphere, accompanied by an accumulation of Ca2+, Mg2+, and NO3—. The observed rhizosphere gradients in soil solution chemistry were highly dynamic in time. The results demonstrate that the activity of growing beech roots results in an acidification of the soil solution in the rhizosphere. The acidification was enhanced after the addition of NH4+. 相似文献
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Salt stress reduces grain yield of maize (Zea mays L.) due to poor kernel setting but not due to decreased grain filling. In the present study, it was tested whether acid invertase activity is decreased in developing kernels of maize under salt stress, and if assimilate supply is limited. The relatively salt‐sensitive maize hybrid Pioneer 3906 was compared with the more salt‐resistant hybrid SR 12. Salt stress caused a significant decrease in grain yield which was due to a 50% decrease in kernel number. No source limitation was observed, as the sucrose concentrations in kernels were significantly increased under salt stress for both genotypes. In contrast, glucose and fructose concentrations in kernels were significantly decreased. Salt stress caused a significant inhibition of soluble acid invertase activity to 19% in hydroponics 5 d after pollination (5 DAP) and to 50% in the soil culture experiment (2 DAP). The decrease in enzyme activity was the same for both genotypes. In the soil experiment, the highest soluble acid invertase activity was found 2 DAP with a steep decline until 8 DAP in Pioneer 3906. It is concluded that a decrease in acid invertase activity is a key factor associated with limited kernel setting under salt stress but additional factors may be responsible for genotypic differences. 相似文献
9.
苗期干旱胁迫下施氮对玉米氮素吸收和土壤生物化学性质的影响 总被引：1，自引：0，他引：1
研究苗期干旱胁迫下施氮对东北春玉米氮素吸收利用和土壤生物化学性质的影响,为区域玉米养分管理与逆境调控提供依据。研究设置水、氮二因素盆栽试验,土壤水分包括3个水平:田间持水量的30%(W0),50%(W1)和70%(W2);施氮量包括2个水平:不施氮(N0)和施氮0.24 g/kg(N1),测定不同水氮条件下玉米苗期的植株干重和氮素吸收、根际和非根际土壤的化学性质、微生物量碳、氮(MBC、MBN)及土壤酶活性。结果表明:干旱胁迫显著降低玉米苗期植株干重和氮素吸收量,其中W0条件降幅最大(分别为51.1%,43.8%)。施氮促进各水分条件下植株生长,且与水分存在显著交互作用,W2条件下施氮后植株干重和氮素吸收量的增幅最高(分别为53.7%,83.2%)。干旱胁迫提高植株的水分利用效率,但降低氮肥利用效率。施氮显著提高W2条件植株的水分利用效率,但干旱条件下则无显著影响。水、氮及其交互作用对土壤性质的影响较为复杂。总体上,苗期干旱胁迫暂时提高了根际和非根际土壤pH,显著增加根际土壤的铵态氮和硝态氮含量。MBC、MBN对干旱胁迫的响应在根际与非根际土壤之间存在相反趋势,根际土壤随干旱程度增加而提高,非根际土壤则随之下降。土壤酶活性方面,干旱胁迫显著影响根际土壤的硝酸还原酶和亚硝酸还原酶活性。施氮增加所有水分条件下根际和非根际土壤的pH和铵态氮、硝态氮含量,其中根际土壤的增幅高于非根际土壤。施氮显著增加各水分条件下根际和非根际土壤的MBC、MBN、脲酶和硝酸还原酶活性,但显著降低根际和非根际土壤亚硝酸还原酶活性。水氮交互作用显著影响根际土壤的亚硝酸还原酶、非根际土壤的脲酶、亚硝酸还原酶和FDA水解酶活性。根际、非根际土壤各生物化学性质之间均存在显著的相关关系,而且根际土壤除土壤亚硝酸还原酶外的各指标均与植株氮素吸收和氮肥利用效率呈正相关。苗期干旱显著抑制玉米植株生长和氮素吸收,并对土壤生物、化学性质造成显著影响。施氮对植株和土壤性质的影响在不同水分条件下存在差异,而且植株表现与土壤生物、化学性质之间存在显著相关关系。 相似文献
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In this study, salt‐induced changes in the growth rate of maize (Zea mays L.) were investigated during the first phase of salt stress. Leaf growth was reduced in the presence of 100 mM NaCl, and effects were more pronounced for the salt‐sensitive cv. Pioneer 3906 in comparison to the hybrid SR03. While hydrolytic activity of plasma membrane remained unaffected, H+‐pumping activity was reduced by 47% in Pioneer 3906, but was unchanged in SR03. Changes in apoplastic pH were detected by ratiometric fluorescence microscopy using the fluorescent dye fluorescein isothiocyanate‐dextran (50 mM). Pioneer 3906 responded with an increase of 0.2 pH units in contrast to SR03 for which no apoplastic alkalization was found. With respect to the hypothesis that the apoplastic pH is influenced by salinity, it is suggested that salt resistance is partly achieved due to efficient H+‐ATPase proton pumping, which results in cell‐wall acidification and loosening. 相似文献
12.
The effect of soil ESP on soil moisture retention and volume change of montmorillonitic type clay soil (vertisol) in the 10–58 ESP range showed increase in moisture retention with soil ESP in 10-bar suction range. Soil moisture suction (h) – water content (θ)relationship of the form h = ho(θ/θs)?b, where ‘ho’is air entry suction and ‘b’ is a constant, was obtained at all ESP levels. Soil bulk density at low moisture contents increased considerably with soil ESP due to dispersion and decreased linearly with increase in soil water content because of mineral swelling. The soil water diffusivity and conductivity in the 0.15–0.35 g/g moisture content range followed an exponential increase with soil moisture content recording a sharp decrease at soil ESP 10. The effect of high exchangeable sodium, however, was mitigated, to a large extent, by the increase in electrolyte concentration of permeating water to 5 mmhos/cm or greater. Decrease in water transmission parameters ascribed to exchangeable Na+ in the drier moisture regime was accounted for by dispersion of soil particles at low ESP. Whereas adsorbed Na+ – induced swelling was regarded as the major factor modifying soil water relations at relatively high ESP under wet moisture regime. Soil ESP of 10 may be treated as critical for swelling clay soil from soil and water – management view point. 相似文献
13.
Maize (Zea mays L.) plants in the early stage of development were treated with 80 mM sodium chloride (NaCl) with or without supplemental calcium (Ca2+) (8.75 mM) for a seven day period. The effects of salinity on dry matter production and shoot and root concentrations of sodium (Na+), Ca2+, and potassium (K+) were measured for seven Pioneer maize cultivars. Salinity significantly reduced total dry weight, leaf area, and shoot and root dry weight below control levels. For all seven cultivars, Na+concentrations were reduced and leaf area was significantly increased by supplementing salinized nutrient solutions with 8.75 mM calcium chloride (CaCl2). The two cultivars with the lowest shoot and root Na+ concentrations under NaCl‐salinity showed the greatest increases in total, shoot and root dry weights with the addition of supplemental Ca. Shoot fresh weight/dry weight ratios for all cultivars were decreased significantly by both salinity treatments, but supplemental Ca2+ increased the ratio relative to salinity treatments without supplemental Ca. Root fresh weight/dry weight ratios were decreased only by salinity treatments with supplemental Ca. With NaCl‐salinity, cultivars which had lower shoot and root Na+ concentrations were found to be more salt sensitive and had significantly lower amounts of dry matter production than those cultivars which had higher shoot and root Na+ concentrations. It was concluded that Na+ exclusion from the shoot was not correlated with and was an unreliable indicator of salt tolerance for maize. 相似文献
14.
Mohammad Hossein Izadi Javad Rabbani Yahya Emam Mohammad Pessarakli Ahmad Tahmasebi 《Journal of plant nutrition》2014,37(4):520-531
An experiment with factorial arrangement of treatments on a randomized complete block (RCB) design basis with three replications was conducted in a greenhouse during Spring 2010 to investigate changes in sodium ion (Na+), potassium ion (K+), Na+/K+ and to determine proline, protein content, and superoxide dismutase (SOD) of four wheat and four barley cultivars. Three salt levels {1, control (no salt), 7, and 13 dS m?1 [2.5 and 5 g salt [sodium chloride (NaCl) and sodium sulfate (Na2SO4) in 1:1 ratio] per kg of soil, respectively]} were used in this investigation. Salt stress treatments were applied 4 weeks after planting (at 2 leaf stage). Leaf samples were taken four weeks after imposition of salt treatment. The results showed that salinity caused an increased in proline and protein content, and SOD in all wheat and barley cultivars. The highest proline and protein content of barley and wheat cultivars at all salinity levels were observed in ‘Nimrooz’ and ‘Bam’ cultivars, respectively. At all salinity levels, wheat and barley cultivars ‘Kavir’ and ‘Nimrooz’, respectively, had the lowest Na+ content. Barley cultivar ‘Kavir’ and wheat cultivar ‘Bam’ had higher K+ and K+:Na+ ratios. This might be related to salt tolerance in these two cultivars. Wheat and barley cultivars showed differences with regard to proline, protein, and SOD content, Na+, K+, and K+:Na+ ratio, indicating existence of genetic diversity among the cultivars. These findings indicated that higher K+, K+:Na+ ratio, proline, protein, and SOD content could be the key factors, which offer advantage to barley over wheat for superior performance under saline conditions. 相似文献
15.
The effect of soil heating on the dynamics of soil available nutrients in the rhizosphere was evaluated. A pot experiment was carried out by using a rhizobox; a pot which enables to sample soils and soil solutions not only temporally with plant growth but also spatially depending on the distance from the root-accumulating compartment. The experiment consisted of 4 treatments; soils with or without heating treatment (150°C, 3 h), each of which was either planted with maize (Zea mays L.) or not. During the 17-d experiment, soil solutions at 0–2 mm from the root-accumulating compartment were collected 5 times. Soils depending on the distance from the root-accumulating compartment and plants were also collected after the experiment. The ionic concentrations of the soil solutions and soil water extracts, and the nutrient contents of plants were analyzed. Immediately after soil heating, the concentrations of cations, SO4 2-, CI-, water-soluble P, and water-soluble organic carbon increased significantly. With plant growth, the total ionic concentration in the rhizosphere soil solution increased for heated soil, whereas it decreased for unheated soil. The increase of the concentrations of cations and SO4 2- in the rhizosphere of heated soil was appreciable, suggesting that the movement of cations such as Ca2+ and Mg2+ by mass flow was regulated by that of SO4 2-. Moreover soil heating inhibited nitrification, resulting in the supply of N mainly in the form of NH4 + within 10 mm from the root-accumulating compartment. As a result, the soil pH decreased in the rhizosphere of heated soil. The amount of nutrients absorbed by plants, on the other hand, did not change significantly by soil heating except for an increase of P uptake. The increase of P uptake could be explained not only by the immediate increase of the water-soluble P concentration but also by the dissolution of Ca-bound P and the hydrolysis of water-soluble organic P in the rhizosphere. 相似文献
16.
In previous studies, a relation between plant growth during the first phase of salt stress and cell‐wall acidification was shown for differently resistant maize genotypes. In the present study, plants of the salt‐sensitive maize (Zea mays L.) cv. Pioneer 3906 and the salt‐resistant genotype SR 12, grown under 100 mM NaCl, showed a similar decrease in plasmalemma H+‐ATPase activity, while SR 12 showed less growth reduction than Pioneer 3906. From this it is concluded that maintenance of apoplast acidification is not necessary for better plant growth during the first phase of salt stress. 相似文献
17.
Cadmium (Cd) uptake by lettuce (Lactuca sativa L.) was studied in a hydroponic solution study at concentrations approaching the total concentration in contaminated soil solutions. Four cultivars of lettuce were tested (Divina, Reine de Mai, Melina, and J.44). Ten 12‐day old seedlings, pretreated in 0.5 μM CdCl2 solution, were labelled with carrier free 109CdCl2 (from 0.05 μM to 5 μM Cd in nutrient solution) in the presence and absence of metabolic inhibitors, DNP and DCCD. Cadmium taken up by the roots was determined after a 30 min desorption in unlabelled CdCl2 solution. In the absence of metabolic inhibitors and at 5 μM Cd, root absorbed from 2.5 to 8 mg Cd/g root dry weight. Exchangeable Cd measured after desorption represented less than 1% of the total Cd absorbed by the root. Cadmium absorption in presence of DNP showed that approximately 80% of the Cd enters the cell through an active process. This mechanism seems to be directly associated with H+‐ATPase as observed with DCCD inhibition. Varietal differences in shoot Cd uptake were only demonstrated at concentrations below 0.1 μM. Screening lettuce cultivars only by the Cd level in the tissue seems not to be possible for these cultivars except at concentrations close to that in the soil solution. But differences in relative contribution of uptake mechanisms in total Cd absorption were observed. High levels of Cd in roots were correlated with high contri‐ butions from H+‐ATPase in the active process of Cd uptake. 相似文献
18.
Effects of NaCl, KC1, and CaCl2 alone, and in combinations of NaCl/KCl and NaCl/CaCl2 on growth and ion uptake by ‘Kallar'grass in soil and in solution cultures were studied. In soil up to 150 mM NaCl and KCl had little effect on growth but CaCl2 depressed growth strongly. Dry weights in 150 mM NaCl/KCl decreased but remained little affected in NaCl/CaCl2. Plant response to Na+ was little affected by Ca++ or K+ and no interactions between Na+ and Ca++ or Na+ and K+ were observed. Plant tissue exhibited a strong selectivity for K+ over Na+ Concentrations of Na and Cl in the tops exceeded those in the roots. Leaf transections are presented providing some information on the tissue anatomy. 相似文献
19.
Plant genotypes differ in their capacity to grow in soils with low manganese (Mn) availability. The physiological mechanisms underlying differential tolerance to Mn deficiency are poorly understood. To study the relationship between Mn content in soil, plant genotypes, and rhizosphere microorganisms in differential Mn efficiency, two wheat (Triticum aestivum L.) cultivars, RAC891 (tolerant to Mn deficiency) and Yanac (sensitive), were grown in a Mn‐deficient soil to which 5, 10, 20 or 40 mg Mn kg–1 were added. The shoot dry matter of both cultivars increased with increasing Mn addition to the soil. At all soil Mn fertilizer levels, the tolerant RAC891 had a greater shoot dry matter and a higher total shoot Mn uptake than the sensitive Yanac. The concentration of DTPA‐extractable Mn in the rhizosphere soil of RAC891 at Mn20 and Mn40 was slightly lower than in the rhizosphere of Yanac. The population density of culturable microorganisms in the rhizosphere soil was low (log 6.8–6.9 cfu (g soil)–1) in both cultivars and neither Mn oxidation nor reduction were observed in vitro. To assess the non‐culturable fraction of the soil microbial community, the ribosomal intergenetic spacer region of the bacterial DNA in the rhizosphere soil was amplified (RISA) and separated in agarose gels. The RISA banding patterns of the bacterial rhizosphere communities changed markedly with increasing soil Mn level, but there were no differences between the wheat cultivars. The bacterial community structure in the rhizosphere was significantly correlated with the concentration of DPTA‐extractable Mn in the rhizosphere, fertilizer Mn level, shoot dry matter, and total shoot Mn uptake. The results obtained by RISA indicate that differential tolerance to Mn deficiency in wheat may not be related to changes in the composition of the bacterial community in the rhizosphere. 相似文献
20.
The increase of rhizosphere pH in the course of nitrate nutrition results from H+ consumption in the external medium during uptake of NO3? in a H+ co-transport and from internal OH? production during nitrate reduction. Synthesis of organic acids for NH4+ assimilation as well as strong partial depolarization of membrane potential with NH4+ uptake are the important reasons for rhizosphere acidification during ammonium nutrition. Despite differences in proton balance depending on N form, cytoplasmic pH changes are small due to physico-chemical buffering, biochemical pH regulation, H+ inclusion in vacuoles, and H+ release into the rhizosphere. Because of the large capacity for proton excretion the plasmalemma H+ ATPase of root cells plays an essential role during ammonium nutrition. An increase of the kinetic parameter Vmax after ammonium nutrition relative to nitrate nutrition suggests that the capacity of H+ release may be adjusted to the particular requirements of ammonium nutrition. Moreover, H+ ATPase is adjusted not only quantitatively but also qualitatively. The increase of the kinetic parameter km as well as the capability of the plasmalemma vesicles in vitro to establish a steeper pH gradient favours the supposition that H+ ATPase isoforms are formed which allow H+ release into the rhizosphere under conditions of low pH or poor H+ buffering of the soil. In this respect species differences exist, e.g. between maize (efficient adaptation) and faba bean (poor adaptation). 相似文献