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1.
The mineralization of native soil organic matter and the simultaneous diffusion of zero NH+4 and NO?3 to a solution sink of zero N concentration was analysed experimentally and theoretically for a fine sandy loam soil. Experimentally, the NH4 and NO3 ions produced in an incubated unsaturated soil column were allowed to diffuse through a sintered glass plate into a stirred solution sink. The distribution of NH+4 and NO?3 in the soil column was measured after various incubation times. The rate of ammonification was measured directly during incubation and the rate of nitrification modelled from nitrifier growth kinetics. A Freundlich equation was used to describe the equilibrium between soluble and exchangeable NH+4 in the soil. Terms for the microbial transformation of N and the adsorption-desorption of NH+4 were combined with diffusion equations which were solved numerically using finite difference methods. The model constructed was used to predict the NH+4 and NO?3 con-centration distributions in the soil column, and good agreement was obtained between the experimental and predicted concentration profiles. The use of the model for predicting the diffusive flux of mineral N to the outer surfaces of soil peds, where it is vulnerable to leaching, was demonstrated.  相似文献   

2.
Chickpea plants (Cicer arietinum L cv. ILC 195) were grown for 24 days in water culture under two regimes of nitrogen nutrition (NO3 or NH4‐N) with or without Fe. For plants fed with NO3‐N, Fe stress severely depressed fresh weight accumulation and chlorotic symptoms of Fe‐deficiency developed rapidly. Little difference in growth occurred in the NH4‐fed plants, whether or not Fe was withheld, with no visual evidence of Fe‐deficiency indicating a beneficial effect of NH4 in depressing the symptoms of Fe chlorosis. Typical pH changes were measured in the nutrient solution of the control plants in relation to nitrogen supply, increasing with NO3 and decreasing with NH4‐nutrition. With both forms of nitrogen, plants acidified the nutrient solution in response to Fe‐stress. Under NH4‐nutrition, acidification was enhanced by withholding Fe. In the NO3‐fed plants the uptake of all nutrients was reduced by the stress but proportionally NO3‐ and K+ were most affected. Total anion uptake was depressed more than that of cation uptake. For the NH4‐fed plants withholding Fe resulted in an increased uptake of all ions except NH4 + which was depressed. Regardless of the form of N‐supply, when Fe was withheld from the nutrient solution the net H+ efflux calculated from the (C‐A) uptake values was closely balanced by the OH” added to the nutrient solution to compensate for the pH changes. Evidence of accumulation of organic acids in the Fe‐stressed plants was found, especially in the NO3‐fed plants, indicating a role for these internally produced anion charges in balancing cation charge in relation to the depression of NO3 uptake associated with Fe‐stress.  相似文献   

3.
The contribution of bacteria and fungi to NH4+ and organic N (Norg) oxidation was determined in a grassland soil (pH 6.3) by using the general bacterial inhibitor streptomycin or the fungal inhibitor cycloheximide in a laboratory incubation study at 20°C. Each inhibitor was applied at a rate of 3 mg g?1 oven‐dry soil. The size and enrichment of the mineral N pools from differentially (NH415NO3 and 15NH4NO3) and doubly labelled (15NH415NO3) NH4NO3 were measured at 3, 6, 12, 24, 48, 72, 96 and 120 hours after N addition. Labelled N was applied to each treatment, to supply NH4+‐N and NO3?‐N at 3.15 μmol N g?1 oven‐dry soil. The N treatments were enriched to 60 atom % excess in 15N and acetate was added at 100 μmol C g?1 oven‐dry soil, to provide a readily available carbon source. The oxidation rates of NH4+ and Norg were analysed separately for each inhibitor treatment with a 15N tracing model. In the absence of inhibitors, the rates of NH4+ oxidation and organic N oxidation were 0.0045 μmol N g?1 hour?1 and 0.0023 μmol N g?1 hour?1, respectively. Streptomycin had no effect on nitrification but cycloheximide inhibited the oxidation of NH4+ by 89% and the oxidation of organic N by more than 30%. The current study provides evidence to suggest that nitrification in grassland soil is carried out by fungi and that they can simultaneously oxidize NH4+ and organic N.  相似文献   

4.
Changes in soil solution composition and concentrations of exchangeable cations and mineral N in undisturbed cores of pasture soil were investigated in two experiments following applications of sheep urine to the cores. The major cations applied in the urine were K+ and Na+, and the major anions were HCO3? and Cl?. Addition of urine increased concentrations of exchangeable K+, Na+ and NH4+ and measured ionic strength of the soil solution throughout the surface 15 cm of soil, demonstrating that the urine moved through the core by macropore flow immediately following addition. Immediately following urine application the ionic strength in soil solution in the surface 2.5 cm of soil increased from 4–6 MM to 24–41 mM. Hydrolysis of urine-urea was extremely rapid, and in less than 1 d high concentrations of NH4+-N (i.e. 270–370 mg N kg?1) had accumulated in the surface 0–2.5 cm of the urine patch, and soil pH had risen by over one unit. Nitrification then proceeded and, after approximately 15 d, NO3? became the dominant form of mineral N present. During nitrification, soil pH declined and the ionic strength of the soil solution increased substantially with NO3? becoming the dominant anion present in solution. There were concomitant increases in the concentrations of Ca2+ and, to a lesser extent, Mg2+ in the soil solution as NO3? concentrations increased. After approximately 30 d, concentrations of exchangeable NO3? had risen to 250–330 mg N kg?1, soil solution NO3? concentrations had increased to about 80 mmol, dm?3, and ionic strength in the soil solution had increased to 130–140 mM. These results demonstrate the dominating effect of N transformations in causing large fluctuations in the pH, ionic composition and ionic strength of the soil solution in the urine patch. It was concluded that nutrient availability in the patch was affected directly by nutrient addition in urine, and also probably indirectly through the fluctuations in soil solution pH and ionic strength that occur.  相似文献   

5.
Reasons for chlorosis of vine (Vitis vinifera L.) under field conditions
  • 1 Analysis of leaf and soil samples from green and chlorotic vineyards did not result in a clear correlation between chlorosis and one of the soil factors determined (pH, concentration of HCO3?, water soluble P, DTPA-extractable Fe, Mn, Zn, Cu).
  • 2 In severe chlorotic leaves the concentration of all elements investigated was increased, while in weak chlorotic leaves the concentration of Fe, Mn, Zn, Cu and P stayed unchanged.
  • 3 There was no change neither in the P: Fe nor in the K: Ca ratio of the leaves due to chlorosis, but significant differences existed in the ratio extractable Fe: total Fe and total P: extractable Fe between green and chlorotic leaves.
  • 4 The increased amount of Mn and Zn in severe chlorotic leaves reached a 100 %, the also increased amount of Fe only a 20% extractability by 0,5 n HCl, which together with the high P-concentration can be assumed as a main reason for chlorosis.
  相似文献   

6.
‘Tifblue’ (V. ashei Reade) and US 280 (V. elliotti Chapman) blueberry plants were exposed to 2×2×2 factorial treatments of high and low phosphate and micronutrients (Cu, Zn, Mn, and B) and excess or stoichiometric concentrations of a chelator (EDDHA) added to Fe(NO3)3 in pH 6.8 solution cultures. Phosphorous was applied at 20 (low) or 400 (high) μM levels, micronutrients at low or high levels and either a 1:1 or 10:1 ratio of chelator to Fe concentrations.

Excess chelator in the nutrient solution always increased the severity of chlorosis except for US 280 plants grown under low P and stoichiometric chelator where neither micronutrient level resulted in chlorosis. Increased P concentration usually resulted in more severe chlorosis except for ‘Tifblue’ plants grown under low micronutrients and stoichiometric chelator where chlorosis did not develop with either P level. ‘Tifblue’ and US 280 differed in there response to excess solution Cu levels.

Unlike highbush blueberries (V. corymbosum L.), these two species of blueberries responsed to excess chelator in a manner similar to that reported for monocots.  相似文献   

7.
陈沂岭  赵学强  张玲玉  沈仁芳 《土壤》2019,51(2):243-250
NH_4~+和NO_3~–是对植物有效的两种主要无机氮源。水稻一般被认为是偏好NH_4~+的植物,但是在NO_3~–条件下,水稻也能良好地生长。大多数关于水稻铵硝营养的报道是在pH 6.0左右的水培条件下开展的,但是对于酸性条件下水稻铵硝营养研究很少。随着土壤酸化的加重及一些边际酸性土壤被用作水稻种植,研究酸性条件下水稻的铵硝营养具有重要意义。本文采用水培试验,在pH 5.0的条件下,通过添加和不添加pH缓冲剂MES(2-(N-吗啡啉)乙磺酸),研究了NH_4~+和NO_3~–对水稻生长、氮效率和矿质养分(N、P、K、Ca、Mg、Fe、Zn、Cu、Mn)吸收的影响。结果表明,在不添加MES的条件下,水稻地上部生长(株高、叶绿素含量、干重)在NH_4~+和NO_3~–之间没有显著差异,而添加MES后,NH_4~+处理的水稻地上部生长优于NO_3~–。不管是否添加MES,NO_3~–处理的水稻地下部生长(根长、根表面积和根物质量)优于NH_4~+。水稻含氮量和氮利用效率在不同NH_4~+和NO_3~–处理之间没有显著差异,但是NH_4~+处理的水稻氮吸收效率高于NO_3~–。与NO_3~–相比,NH_4~+增加了水稻地上部P和Fe含量,而降低了水稻地上部Ca、Mg、Zn、Cu和Mn含量,对K含量影响较小。上述结果表明,NH_4~+有利于改善水稻地上部生长,提高氮吸收效率、地上部P和Fe含量,而NO_3~–则有利于水稻发根,提高地上部Ca、Mg、Zn、Cu和Mn含量。  相似文献   

8.
Bush beans (Phaseolus vulgaris L. cv Contender) were grown on perlite with nutrient solution and 0, 1, 2.5 and 5 ppm levels of Na2CrO4 Significant decrease of top growth and chlorosis in trifoliated leaves were observed for 2.5 and 5 ppm Cr, with Cr concentrations (μg/g) in tops:≥ 12.1, in roots:≥ 509.9. Cr decreased K, Na, Mg and Fe concentrations, and increased P and Mn concentrations in roots. In tops decreased N, K, Na and Fe concentrations and increased Mn and Ca concentrations were observed, Translocation of P, Zn, Cu and Fe was inhibited; Ca and Mn translocation was generally enhanced. P/Fe ratio was increased up to 60% in chlorotic plants, indicating a shift from Fe2+ to Fe3+.  相似文献   

9.
ABSTRACT

Nutrient recycling in a space-based Bioregenerative Life Support System (BLSS) will require an understanding of nutrient dosage effects on crop production, plant tissue partitioning, and geochemical fates within crop systems. Sodium (Na+), fluoride (F?), and iodide (I?) are found in human waste streams. These elements were examined using crops in hydroponic systems. Lettuce, radish, spinach, and beet were used to study Na+ uptake and tolerance. Spinach, lettuce, and radish growth were inhibited at 8.0 × 10?2 M Na+ compared to the control. Beet growth improved at 2.0 and 4.0 × 10?2 M Na+ compared to the control. Rice plants were used to study F? and I? uptake and tolerance. Rice growth was inhibited at 5.0 × 10?4 M F? and at 5.0 × 10?6 M I?. Solution redox and sorption reactions were predicted with the aid of a chemical equilibrium model. A simulation model was used to predict element fates.  相似文献   

10.
The effect of soil and foliar application of different iron (Fe) compounds (FeSO4, Fe‐EDTA, Fe‐EDDS, and Fe‐EDDHA) on nutrient concentrations in lettuce (Lactuca sativa cv. Australian gelber) and ryegrass (Lolium perenne cv. Prego) was investigated in a greenhouse pot experiment using quartz sand as growth medium. Soil application was performed in both the acidic and alkaline pH range, and foliar application to plants grown in the alkaline sand only. Lettuce growth was depressed by Fe deficiency in the alkaline sand, whereas the treatments had no effect on ryegrass growth. Soil‐applied Fe compounds raised the Fe concentrations in lettuce. This was especially true for the Fe chelates, which also increased yields. Soil‐applied Fe compounds had no statistically significant effect on Fe concentrations in ryegrass. Concentrations of manganese (Mn) in lettuce were equally decreased by all soil‐applied chelates. In the alkaline sand, soil application of Fe‐EDDHA elevated copper (Cu) and depressed zinc (Zn) concentrations in lettuce. The chelates increased Zn concentration in ryegrass. Foliar application of Fe‐EDDS increased Fe concentrations in lettuce and in ryegrass most. Fe‐EDDHA depressed Mn and Zn concentrations in lettuce more than other Fe compounds, suggesting the existence of another mechanism, in addition to Fe, that transmits a corresponding signal from shoot to roots with an impact on uptake of micronutrients.  相似文献   

11.
ABSTRACT

The source of nitrogen (N) used in soil fertility practices affects plant growth, nutrient absorption, and the availability of nutrients. Consequently, the potential of plants to extract zinc (Zn) from soils may be increased by controlling the ratio of NH4 + to NO3 ? to maximize growth and Zn accumulation. The objectives of this research were to determine the effects of Zn supply and different molar ratios of NH4 + to NO3 ? on growth and Zn accumulation in Indian mustard (Brassica juncea Czern.). In a factorial experiment with solution culture, Indian mustard (accession 182921) was supplied with two concentrations of Zn (0.05 and 4.0 mg L?1) in combination with six N treatments with different molar percentage ratios of NH4 + to NO3 ? (0:100, 10:90, 20:80, 30:70, 40:60, and 50:50) for three weeks. Zinc supplied at 0.05 mg Zn L?1 represented a common concentration of Zn in solution culture, whereas 4.0 mg Zn L?1 was excessive for plant nutrition. If the supply of Zn in solution was excessive, plants developed symptoms of foliar chlorosis, which became severe if plants were supplied with 80% of N as NO3 ?. Supplying high proportions of NO3 ? in the nutrient medium stimulated Zn accumulation, whereas increasing proportions of NH4 + (up to 50% of the total N) enhanced shoot growth. The pH of nutrient solutions generally decreased with increasing proportion of NH4 + in solutions and with increased Zn supply. The Zn phytoextraction potential of Indian mustard was maximized, at about 15 mg Zn plant?1, if plants received 10% of the total N as NH4 + and 90% as NO3 ?.  相似文献   

12.
ABSTRACT

The effects of partial and complete substitution of potassium (K+) by rubidium (Rb+) and sodium (Na+) on plant growth and ion accumulation and partitioning was studied in bean young plants cultivated in nutrient solution with or without bicarbonate (HCO3 ?)-induced alkalinity. Plant growth was significantly decreased due to alkalinity and the substitution of K+, being leaves more affected than roots. Rubidium caused a severe toxicity reflected in a reduction in root dry mass and total chlorophyll concentration. Ion partitioning was markedly altered by alkalinity. Content of nitrogen (N), calcium (Ca), magnesium (Mg), iron (Fe), K, and Na were more accumulated in the roots in HCO3 ?-treated plants, while decreased in the shoot. Iron (Fe) was accumulated at similar extent in plants with and without high alkalinity, except in plants grown in Rb+ solutions. However, Fe was more accumulated in the roots, suggesting that chlorophyll synthesis was impaired by reduced translocation or internal inactivation of Fe. Zinc total uptake was severely reduced under high alkalinity in plants grown in Na+ solutions, maybe due to decreased Zn activity. Calcium was translocated more actively to the leaves and Mg was accumulated more in the roots of plants in Na+solutions. Despite the severe decrease in plant dry mass caused by Rb+, there was a higher translocation of N, phosphorus (P), Ca, Mg, Fe, zinc (Zn), copper (Cu), and manganese (Mn) from the roots to the leaves.  相似文献   

13.
This study was to investigate peanut response to application of nitric oxide (NO) at different growth stages and the effects of NO application on peanut yield and quality in calcareous soil. Sodium nitroprusside (SNP, a NO donor) solution was poured into calcareous soil at sowing, seedling, flowering, and podding stages, respectively, or at each aforesaid critical stage. Results showed that NO application increased the content of active Fe and leaf chlorophyll, which improved the photosynthesis of peanut; enhanced the ability of resistance to oxidative stress by decreased the accumulation of O2??, H2O2, and MDA and increased the activity of antioxidant enzymes. Nitric oxide increased the content of soil available Fe and root FCR activity, which can promote peanut absorb more Fe from the calcareous soil. What's more, peanut plants may pump a large amount of H+ from root cell membrane to consume in neutralization of HCO3?, and decrease the pH in apoplast, cytoplasm, and xylem, finally balance the mineral elements (Fe, Ca, Mg, Zn, and Cu) uptake and distribution. These results indicated that NO could improve peanut growth and development, increase peanut yield and quality. Furthermore, the application of NO at sowing or seedling stage did the most obvious effect on alleviating chlorosis of peanut in calcareous soil.  相似文献   

14.
Exchangeable and soluble soil aluminum (Al) is limiting plant growth in many soils worldwide. This study evaluated the effects of increasing rates of dolomite and magnesium carbonate (MgCO3) on Al3+, pH, dissolved organic carbon, cations, anions, and Al speciation on oil palm Deli dura × AVROS pisifera root growth. Dolomite and MgCO3 additions significantly raised linearly soil solution pH, magnesium (Mg2+), nitrate (NO3 ?) and chlorine (Cl?) concentrations; exponentially decreased the activity of phytotoxic Al species [aluminum (Al3+), aluminum sulfate (Al2SO4), and aluminum fluoride (AlF3)]; and reduced manganese (Mn) concentration and activity. High activity of those species exponentially reduced root dry weight. Optimum oil palm growth was achieved at: <50 μM monomeric Al, < 30 μM Mn, and <0.20 unit of the ratio Al+Mn to calcium (Ca)+Mg. High activity of Al species and Mn in acidic soil solution cause significant reduction of the root growth. Soil acidity alleviation either with dolomite or MgCO3 mitigates the toxic effect of Al and Mn.  相似文献   

15.
The relations between pH, different fractions of Fe and A1 and Na4P2O7-soluble C and the amount of adsorbed SO2-4 were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of adsorbed SO2-4 was significantly better correlated with the calculated amount of the inorganic fraction of Fe and A1 oxides obtained by subtracting Na4P2O7-soluble Fe and A1 from oxalate-soluble Fe and Al than with the oxalate extraction alone. There was a close correlation between C and organically-bound S in the Na4P2O7 extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically-complexed Fe and Al increases, the ability of the soil to adsorb SO2-4 decreases. The amount of adsorbed SO2-4 expressed on the basis of the amounts of oxalate-soluble Fe and Al was generally smaller in areas with low S deposition (< 60 mmol m-2 a-1). The ratio between pyrophosphate-soluble C and oxalate-extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic matter cannot adsorb SO2-4 and that the degree of this association is pH dependent. These observations have important implications regarding the effects of anthropogenic acidification.  相似文献   

16.
Eight species of tropical foliage plants were screened to determine their response to Fe‐stress conditions. Plants were grown for 120 days in modified Hoagland's nutrient solution at pH 6.3 containing either 0, 0.22 or 5.52 mg/liter Fe (as Fe+3‐HEEDTA). Araucaria heterophylla and Dracaena marginata showed leaf chlorosis and decreased growth at 0 and 0.22 mg/liter Fe. Ficus benjamina and Nephrolepis exaltata ’Bostoniensis’ showed little or no chlorosis or growth differences at either 0 or 0.22 mg/liter Fe. Over a 3 week period, F. benjamina and N. exaltata ’Bostoniensis’ decreased nutrient solution pH approximately 1 to 1.5 units lower than either D. marginata or A. heterophylla at all Fe levels. Codiaeum variegatum var. pictum, Dieffenbachia maculata ’Camille’, Epipremnum aureum, and Philodendron scandens oxycardium were intermediate in growth, chlorosis and lowering of the nutrient solution pH. One explanation for the differential Fe response between these species may be their ability to lower pH of the rhizosphere.  相似文献   

17.
《Journal of plant nutrition》2013,36(10-11):2295-2305
Abstract

Five dry bean cultivars (Coco blanc, Striker, ARA14, SVM29‐21, and BAT477) were evaluated for their resistance to iron deficiency on the basis of chlorosis symptoms, plant growth, capacity to acidify the external medium and the root‐associated Fe3+‐reduction activity. Plants were grown in nutrient solution supplied or not with iron, 45 µM Fe(III)EDTA. For all cultivars, plants subjected to iron starvation exhibited Fe‐chlorosis. These symptoms were more severe and more precocious in BAT477 and Coco blanc than in the others cultivars. An important acidification of the culture medium was observed between the 4th and the 8th days of iron starvation in Striker, SVM29‐21 and, particularly, ARA14 plants. However, all Fe‐sufficient plants increased the nutrient solution pH. This capacity of acidification appeared more clearly when protons extrusion was measured in 10 mM KCl + 1 mM CaCl2. The above genotypic differences were maintained: ARA14 showed the higher acidification followed by Coco blanc and BAT477. Iron deficiency led also to an increase of the root‐associated Fe(III)‐reductase activity in all lines. However, genotypic differences were observed: Striker shows the highest capacity of iron reduction under Fe deficiency condition.  相似文献   

18.
This trial was carried out to study the evolution of the nutrient parameters of the nutrient solution applied to tomato plants (Lycopersicum sculentum Mill. Forteza) cultivated in Mediterranean greenhouse conditions under different fertigation management models. The dynamic model is based on soil water content, which was measured by tensiometers, and on soil solutions obtained with suction cups (porous ceramic cup water samplers). The local traditional method consists of following technical recommendations, and the classical model requires the estimation of Crop Factor (Kc) and knowing the nutrient extraction. Nutrient solution and water applied are functions of the fertigation management criteria. The water used for fertigation was classified as C4-S3 according to the Riverside classification system. The cultivation period lasted from 15 August to 20 April. The nutrient parameters studied in nutrient and soil solution were pH, electrical conductivity (EC), nitrate (NO3 ?), phosphate (H2PO4 ?), potassium (K+), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and chloride (Cl?). The pH shows similar trends under the different treatments. Electrical conductivity is in the range of 2.8–4.5 dS m?1. Chloride, sodium, magnesium, and sulfate are exclusively modified by the salt concentration in the irrigation water, so it can be assumed that the three treatments vary equally. Nitrate, potassium, phosphate, and calcium are modified depending on each fertigation management method. Soil solution is modified by the nutrient solution applied. Dynamic management allows low nutrient concentration in the nutrient solution to be maintained and keeps soil nutrient concentration low, reducing fertilizer losses and therefore aquifer contamination.  相似文献   

19.
Studies were conducted to determine the efficacy of K salts in alleviating lime‐induced chlorosis. Greenhouse studies using a Gibbon silt loam [fine‐silty, mixed (calcareous), mesic Typic Haplaquoll] and a 1: 1 mixture of Gibbon soil and washed sand were conducted with KCl, KNO3, K2SO4, K2HPO4, or KHCO3 applied at rates of 0, 250, and 500 mg K/kg soil. An FeEDDHA treatment was included for comparison. Similar studies were conducted at two field sites known to produce lime‐induced chlorosis. Potassium salts were applied at 0, 20, and 40 g K/m of row. In the greenhouse, plants treated with KCl, KNO3, and K2SO4 on Gibbon soil were less chlorotic than controls or plants treated with K2HPO4, or KHCO3. No K treatment totally alleviated chlorosis except FeEDDHA. Chlorophyll correlated positively with chlorosis rating. No relationship was found between leaf Fe uptake and chlorosis. Plants grown in soil/sand exhibited no chlorosis and had lower Fe uptake than plants grown in Gibbon soil. Thus chlorosis was not due strictly to low soil‐Fe availability or inadequate Fe uptake. Bicarbonate in the soil solutions of both growth media treated with KCl was lower than controls which may explain the reduced chlorosis associated with this treatment.

One field site showed positive effects of K treatments on chlorosis rating, chlorophyll concentration, and seed yield. No treatment was as effective as FeEDDHA in influencing plant growth or yield. Total leaf Fe concentration was unrelated to leaf chlorophyll concentration. Inorganic cation/anion ratios in the plant were from 4.4–8.4 which could cause net H+ efflux by the plant and alkalinization of plant tissues. One possibility is that H+ efflux solubilizes P in the rhizosphere, which after uptake could immobilize Fe in the plant. Application of KCl, KNO3, and K2SO4 generally lowered HCO3 content of the upper 15 cm of both soils. High bicarbonate could increase rhizosphere P availability and increase immobilization of Fe in the plant.  相似文献   

20.
A study was made of the influence of substrate on the root releases of hydrogen ions (H+) and bicarbonate ions (HCO3 ) by corn (Zea mays, cv.Dea) grown between the 5/6 leaf and the 9/10 leaf stage in two different growth media, siliceous or calcareous sand. Different nutrient solutions were supplied in separate experiments, but in all cases, nitrogen was in the form of nitrate (NOg"), and iron chelates were present in solution.

In siliceous sand the pH generally increased, but acidification appeared with low NO3 nutrition. Roots released H+ and HCO3 simultaneously, and these ions partially reacted to form H2CO3. The pH variations depended on the balance of the released ions and on the low buffer capacity in this slightly acidic pH range. The algebraic sum of the ion effluxes was approximately equal to the sum of the ion uptakes; no stoichiometric coupling between the total H+ effluxes and the NO3 or potassium (K+) uptakes was recorded.

In calcareous sand HCO3 was released by the roots, but the H+ seedling effluxes always acidified the solutions with regard to the reference solutions in calcareous sand without plants. Even though HCO3 was released in great quantities by plants, the pH of the solutions did not become alkaline because of the high buffer capacity of the solution in contact with the calcareous medium. In this environment the plants reacted to the high levels of HCO3 and showed symptoms of lime‐induced chlorosis. To overcome the poor physicochemical conditions, H+ was released from the corn roots, and this H+ efflux was correlated to the total alkalinity of the solution.  相似文献   

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