Showing papers in "Plant and Soil in 1969"

A theoretical study of the distribution of substances around roots resulting from simultaneous diffusion and mass flow

Abstract: The change in concentration of a solute in soil, moving near the surface of a root by both mass flow and diffusion, has been calculated by a numerical method with a computer. The effect of change in the plant controlled variables v0 (the solvent flux at the root surface) and k (the root absorbing power), and the soil variables b (the buffer power) and D (the diffusion coefficient) are described in turn. The concentration at the root surface, relative to the undisturbed soil solution, approaches a limiting value v0/k. As v0 is increased, the limiting value is approached more rapidly, and the zone of disturbance is more compressed. A steady state is reached if r0v0/bD>2, but if r0v0/bD<2 the disturbance continues to spread outwards even though the concentration at the root surface has nearly attained its limiting value. As k is increased, other factors being constant, the limiting relative concentration at the root surface is approached more rapidly, but the spread of the disturbance away from the root is little affected. As Db is decreased, corresponding to a decrease in soil moisture, the concentration at the root surface reaches its limit more rapidly and the zone of disturbance is compressed. If, because of increase in the concentration at the root surface, the efficiency of root absorption declines, the relative concentration will exceed v0/k, and may reach no limit — at least until the assumptions of the model used break down.

The supply of nutrient ions by diffusion to plant roots in soil

Abstract: Observation of soil grown roots of rye-grass shows that an approximately cylindrical volume of soil, the root hair cylinder, is densely occupied by root hairs. Estimates are given of the concentration of labile and solution potassium within the root hair cylinder during experiments measuring potassium uptake from two soils by single roots. Calculations, using a diffusion model, suggest that labile potassium concentrations may be reduced to between 99.3 and 53 per cent of the initial, depending on the diffusion characteristics of the soil and nutrient demand by the root. Of the total potassium absorbed by a root in 4 days, the proportion which is supplied from within the root hair cylinder is small (0.8 to 6.3 per cent) indicating that diffusion to the root from the soil outside the root hair cylinder is of paramount importance. When root demand is high, diffusion appears to limit uptake to between 71 and 59 per cent of that which roots of comparable physiology would be expected to absorb from stirred solution of the same concentration. Nevertheless, the presence of root hairs is calculated to have enhanced uptake by up to 77 per cent compared with roots without hairs because they virtually increase the root diameter. Diffusion does not appear to be a limiting factor when root demand is low and hairs can then add little to the efficiency of the root system in potassium absorption.

Effects of silica and nitrogen supply on some leaf characters of the rice plant

Abstract: While the degree of leaf erectness of the rice plant is a varietal characteristic, it can be changed greatly by silica and nitrogen nutrition. Nitrogen tends to make rice leaves more droopy and silica keeps them more erect. This effect of silica on leaf erectness is marked when the silica content of leaves is low. Leaf openness is well correlated with the light extinction coefficient of rice populations. Leaf thickness increases with increasing supply of silica whereas it decreases with increasing supply of nitrogen. Increased nitrogen supply markedly increases leaf length, width, and area. Silica has little effect on these characters.

Nutrient status effects on loss of amides and amino acids from pine roots

Abstract: Loss of amides and amino acids from pine roots was two and a half times greater from roots grown in phosphate-deficient nutrient solution than from those grown in complete nutrient solution and ten times greater than from plants grown in nitrogen-deficient solution. The major factor in increased loss from phosphate-deficient plants was an increase in free amides and amino acids in these plants. Increased amide and amino acid loss from phosphate-deficient plants may have important consequences in micro-organism—plant interactions.

Activity of phosphate-dissolving bacteria in Egyptian soils

Abstract: Phosphorus is applied to soils in inorganic fertilizers or in organic manures in the form of plant and animal residues. Of all forms of phosphorus occurring in soils, the monovalent anion H2PO4is the only one available to the growing plants. When soluble forms of inorganic phosphorus fertilizers are applied to soils, somewhat alkaline in reaction, such as Egyptian soils, they are rapidly converted to the non-available form. This transformation is a major problem of phosphate fertilization in U.A.R. Fortunately, soils of Egypt were found to harbour high densities of phosphate dissolving bacteria. T a h a et al. 2a suggested that they may play an important role in supplying the growing plants with their needs of phosphorus. The presence of soil microorganisms capable of transforming insoluble phosphorus to the available form was recorded by different investigators a 5 6 s 9 10 12 la 21 and many others. The USSR investigators had isolated an active phosphate dissolving strains of B. megatherium var. pho@haticum. This was propagated to form inoculant which was given the name 'Phosphobacterin'. I t was reported that such enhanced plant growth and phosphorus uptake 4 11 14 16 24 The present investigation was carried out to s tudy the qualitative and quantitative distribution of different groups of phosphate dissolvers in soils and rhizosphere of some field crops at different stages

The uptake of applied selenium by agricultural plants

Abstract: Elemental selenium and a series of selenites and selenates were applied in pot and field experiments. With the elemental selenium a small increase in concentration in the plants was found in both kinds of experiments with red clover, lucerne, mustard, andsugar beet as test plants, but not with barley. In the second year an increase in the concentration in the plants was found in lucerne only (field experiment). In a pot experiment eight successive cuts of clover all had nearly the same content.

The effect of low pH on different phases of nodule formation in pea plants

Abstract: A number of experiments was carried out with pea plants growing in a nutrient solution of low pH, inhibitory to nodule formation but not to plant growth when combined nitrogen was available. It has been found that on transferring plants from a neutral culture solution to an acid solution of pH 4.5 at different periods of time after inoculation, nodulation is reduced when the exposure to low pH takes place during the first days after inoculation, and particularly on the second or third day. Once nodulation has been initiated, nodule growth and nitrogen fixation proceed normally in an acid solution. Failure of nodulation at low pH, under the conditions of these experiments, was not due to the inhibition of bacterial growth. From these results an acid-sensitive period, occurring during the second or third day after inoculation, was demonstrated.

Soluble and total silicon in sugar cane

Abstract: The data presented throughout this paper indicate that soluble Si in plant tissues can give useful information about the Si-status of plants. In fact, this fraction of plant Si seems to be less subject to extraneous variation than does total Si. Silicon which can be extracted with dilute TCA is a discrete fraction. The amount extracted was little influenced by extraction time, amount of extractant, or number of extractions. The soluble-Si fraction was not stable before extraction. Concentration decreased with time. The rate of decrease was temperature related. Storage in a nitrogen atmosphere decreased Siimmobilization.

Effects of silicon on the chemical composition of rice plants

Abstract: Rice plants were grown in nutrient culture solutions. Silicon was supplied to these plants at different rates. The plant samples of early vegetative, vegetative and flowering stages were analysed for nitrogen, phosphorus, potassium, calcium, magnesium, iron, manganese, silicon, protein and carbohydrate contents. The application of silicon generally decreased the nitrogen, protein and potassium content of rice plants. Its application also decreased the iron and manganese contents. The use of silicon resulted in an increase in phosphorus, calcium, magnesium, silicon and carbohydrate contents of rice plants.

The supply of nutrient ions by diffusion to plant roots in soil. I. Absorption of potassium by cylindrical roots of onion and leek

Abstract: Plant uptake and distribution will depend both on the soil's ability to supply and plant demand. Supply is (normally) by mass flow and diffusion. The latter is generally the more important process for potassium (Barber et al *), and in this work mass flow was deliberately reduced to insignificance. Ability to supply depends on concentration in the soil and mobility, expressed as the diffusion coefficient. These were measured as nearly as possible under the conditions of the plant uptake experiments. Plant demand depends on plant-physiological factors, which cannot reliably be obtained separately. If uptake by a known surface at a given time is measured, plant demand can be calculated and the complete picture obtained. This should give concentration in the soil around the root as a function of distance and time, and also uptake as a function of time.

Uptake of phosphorus-32 by vesicular-arbuscular mycorrhizae

Abstract: The uptake and accumulation of phosphorus by mycorrhizal and nonmycorrhizal onion plants were compared. The results of the experiments indicate: 1. Mycorrhizal onion plants accumulated significantly more phosphorus in the roots and tops than nonmycorrhizal plants. 2. Vesicular-arbuscular mycorrhizae are sites of increased phosphorus accumulation compared to nonmycorrhizal roots. 3. A fungitoxicant (parachloronitrobenzene) reduced phosphate accumulation by mycorrhizae but did not significantly affect phosphate accumulation by nonmycorrhizal roots.

Effects of addition of copper, manganese, zinc and chromium compounds on ammonification and nitrification during incubation of soil

Abstract: The effects of adding 100, 1,000, and 10,000 ppm of copper, manganese, zinc and chromium as sulphates and of copper and zinc as carbonates on ammonification and nitrification during incubation (3) weeks) of an initially neutral soil under aerobic and anaerobic conditions were studied. Some stimulating but more usually inhibitory effects of trace elements on both processes were found. These effects varied considerably depending on the level and type of the cation added, whether the conditions were aerobic or anaerobic, and on the extent to which pH was altered by the treatments.

Non-photosynthetic effects of red and far-red light on root-nodule formation by leguminous plants

Abstract: Nodulation of pea and broad bean plants grown in the light was found to be reduced when the roots were exposed to far-red light for 5–15 minutes daily during 5 consecutive days following inoculation with nodule bacteria. Similar results were obtained following a single exposure to far-red light during a period of 15 minutes at the 3rd or 4th day after inoculation. When the roots were exposed to far-red light either before inoculation or during the first two days afterwards there were either no effects or only slight effects on nodulation The inhibitory effect of far-red light on nodulation was partly reduced by subsequent exposure to red light, provided that the same part of the plant was exposed to both red and far-red light,viz either the root or the shoot. When different parts of the plant were exposed to red and far-red light respectively, there was no interaction between the two kinds of light on nodulation. Plants whose roots were exposed to far-red light did not subsequently show stem elongation. Nodules were found to develop on the roots of pea plants grown in the dark, provided that the plants were kept at or below 22°C. At 25°C nodulation was almost absent. Nodulation was decreased by addition of kinetin and IAA. In contrast to plants grown in the light pea plants grown in the dark, inoculated with either an effective or ineffective strain of Rhizobium, developed equal numbers of nodules. Exposure to red light slightly increased the percentage of nodulated plants but decreased the number of nodules per plant. Exposure to far-red light slightly decreased both the percentage of nodulated plants and the number of nodules per plant. The effect of far-red light was counteracted by red light andvice versa.

The mucilaginous layer of citrus roots — Its delineation in the rhizosphere and removal from roots

Abstract: The presence of a mucilaginous layer adhering to the epidermal cells of young citrus roots was noted. Washing the roots with 1N NH4Cl for 1 minute removed this layer and the micro-organisms embedded in it. Chemical analysis of this extract yielded from 2–20% of the total specific root cations. It is thought that the mucilagenous layer and associated micro-organisms are a part of the rhizopshere and can act as a reservoir and supply of nutrients for the plant.

Chelating ability of fumarprotocetraric acid andParmelia conspersa

Abstract: Fumarprotocetraric acid andParmelia conspersa interact with granite to produce soluble colored complexes which shows that chemical weathering of the rock material takes place. The chelating ability ofP. conspersa may be due to the presence of fumarprotocetraric acid. Contrary to popular belief, many lichen acids are not very insoluble in water.

Uptake of silica byTrifolium incarnatum in relation to the concentration in the external solution and to transpiration

Abstract: The uptake of monosilicic acid by crimson clover (Trifolium incarnatum L.) was investigated using solution cultures in which the level ranged from 0.4 to 60 ppm SiO2, and soils in which the level in solution ranged from 7 to 67 ppm SiO2. With increasing levels of silica in the external solution there were systematic increases in uptake, but the quantities of silica in the tops were always less than those which were theoretically carried to the roots in the mass flow of water. The silica content of the roots was higher than in the corresponding tops and seemed to be largely associated with the epidermis. These findings and the observation that the concentration of monosilicic acid in the xylem sap is lower than that in the external solution, are regarded as evidence that the plant excludes a proportion of the monosilicic acid from the transpiration stream. This exclusion is attributed to a barrier in the root through which monosilicic acid passes at a slower rate than water.

Symbionts of alder nodules in New Zealand

Abstract: Micro-organisms capable of forming effective nodules on roots ofAlnus viridis have been found to be present in New Zealand soils. It is concluded that endemic soil organisms suitable for nodulation ofAlnus viridis occur, and cross inoculation trials have indicated that there are probably differences between organisms forming nodules with various species of alders.

Effects of nitrogen, phosphorus and potassium fertilizers on the assimilation capacity ofBeta vulgaris chloroplasts (I)

Abstract: Aspects of non-cyclic photophosphorylation and NADP photoreduction,viz (a) the effects produced on these processes by the three fertilizer elements: nitrogen, phosphorus and potassium; (b) variations in the catalase activity of reaction mixtures following fertilizer application, and (c) correlations between photosynthesis as measured on leaf-tissue discs and the assimilation capacity of chloroplast suspension, were studied. The role of catalase in the non-cyclic photophosphorylation processes was also studied.

Studies on the influence of foliar nutrient sprays on the root exudation pattern in four crop plants

Abstract: Studies conducted to examine the exudation pattern of amino acids and sugars in four crop plants,viz sorghum, sunnhemp, ragi, and tomato indicated that in all, 17 known amino acids and 4 sugars were exuded and that the number and nature of the exuded amino acids and sugars differed with the plant species and with the age of plant. Glutamic and aspartic acids were found to be present in the exudates of all the plant species at all stages of plant growth examined. The quantities of amino acids and sugars differed with plant species and the maximum quantity of the chemicals was exuded during the early stages of plant growth. Glutamic acid among amino acids, and glucose among sugars, were always present in higher concentrations than the others, in the exudates in all the four crop plants. Foliar application of nitrogen in the form of NaNO3 and phosphorus as Na2HPO4, was found to alter the exudation pattern of amino acids and sugars and such influence differed in different plant species. There was a general increase in the total concentration of amino acids and a decrease in sugar content in the exudates after treatment of the foliage with N, while a decrease in the amino acid content and increase in total sugars with P-treatment was observed.

Micro-organisms in the rhizosphere of plants inoculated withAzotobacter chroococcum

Abstract: The hypothesis that inoculation withAzotobacter chroococcum affects the growth of plants indirectly through changing the rhizosphere microflora was investigated. Inoculated and uninoculated wheat and tomato plants were grown in the glasshouse in two different soils, and total bacteria, chitinolytic bacteria, actinomycetes, glucosefermenting bacteria, aerobic cellulose-decomposing bacteria, and anaerobes were determined in intervals in the rhizosphere and in the soil. Root-surface fungi were studied using the Harley and Waid's root-washing technique10. Azotobacter became established in the rhizosphere of wheat and tomato plants and stimulated their growth. All the bacterial groups examined were more abundant in the rhizosphere than in the soil. Inoculation with Azotobacter delayed the colonization of roots by bacteria, actinomycetes, and fungi in the rhizosphere, but had no effect on other organisms. Inoculation did not affect the dominant root-surface fungi, and minor changes were not consistent.

Action of 2,4-DB and dalapon on the symbiotic properties ofLotus corniculatus (birdsfoot trefoil)

Abstract: Field trials carried out in 1965 and 1966 showed that 2,4-DB, alone or in combination with dalapon, reduced nodulation and tended to decrease the efficiency of nitrogen fixation in birdsfoot trefoil. Dalapon appeared to enhance the inhibitory action of 2,4-DB on nodulation. No obvious cytological differences could be detected in the nodules or in the isolated bacteroids of field-treated and untreated plants. Under growth chamber conditions, 2,4-DB drastically reduced trefoil growth and nodulation particularly in treatments where the herbicide came directly in contact with the plants. It appears that the reduction in nodulation and nitrogen fixation is a result of plant damage and abnormal root growth caused by 2,4-DB application.

Micro-organic colonization of forest soil after burning

Abstract: The results show that for some time, fire sites remain largely free of many of the micro-organisms that normally inhabit the soil and are then gradually colonized by species characteristic of burnt sites. Colonization was most pronounced at the margins due presumably to the invasion of the nutrient-rich soil of the fire site by mycellia from surrounding unburnt ground. The micro-organisms isolated from the centre of the burns during the early stages of succession, probably arise from spores brought in the wind and washed down by rain water.

Routine analysis of N15 in plant material by mass-spectrometry

Abstract: A routine analysis of N15 in plant material by means of the Dumas reaction in vacuum was compared with the classical one consisting of Kjeldahl digestion, distillation of ammonia and oxydation of it with NaBrO to N2. It was found that the systematic error introduced by non random pairing of N14 and N15 below 5% N15 atom excess is negligable.

The effect of Calothrix inoculation on vegetable crops

Abstract: The inoculation of the soil with the nitrogen fixing blue-green alga,Calothrix anomala had a positive effect onCapsicum annum andLactuca sativa, in terms of yield and percentage nitrogen. A combined application of urea and alga was more effective than their individual applications.

Interactions of azotobacter with rhizosphere and root-surface microflora

Abstract: Actinomycetes isolated from soil and from the rhizosphere of seedlings, some inoculated with Azotobacter and others not, were tested for antagonism againstAzotobacter chroococcum Antagonistic actinomycetes were initially fewer in the rhizosphere of inoculated than of uninoculated seedlings In the rhizospheres of inoculated and uninoculated seedlings, the number of antagonists increased with time, but not in the soil The proportion of isolates that showed antagonism was same in soil and rhizosphere Fungi isolated from root surfaces showed two types of antagonism against Azotobacter; bactericidal and bacteriostatic When inoculated to sterilized soil, only the strongly antagonistic actinomycete greatly checked initial Azotobacter multiplication The slow decline in the numbers of Azotobacter in the rhizosphere of older plants may reflect the increasing population of antagonists

Suspected copper deficiency in radiata pine

Abstract: Growth disorders in 3-year-old radiata pine associated with very low copper concentrations in the foliage are described. The low concentrations of copper appear to have been nitrogen induced. The effect of remedial measures is being investigated.

Loss of organic compounds from roots

Abstract: Nutritional factors, temperature and pH were investigated for their effects on embryo germination and seedling growth of axenic peanuts. Optimum temperature range for seedling growth was between 32°C and 35°C and pH optimum was between 6 and 7. Sucrose, gibberellin and either (NH4)2SO4 or KNO3 as nitrogen sources increased seedling growth. When a mixture of thiamin (0.01 ppm), riboflavin (0.1 ppm) and 2,4-D (0.01 ppm) was added to the nutrient medium dry weight and height of the seedlings was increased as much as 50 per cent. Plants were successfully grown from axenic embryos separated from the cotyledons to mature plants which produced axenic seed in plastic isolator chambers, but growth was delayed compared to plants developing from seed. Axenic seed was planted under sterile conditions and a second generation of axenic plants obtained which produced viable seed.

Iron metabolism of grasses

Abstract: 1. The relationship of iron supply to the tissue concentration of total iron, N, HCl soluble iron, Cu, Mn, P, Ca, K, N, chlorophyll, catalase and peroxidase have been studied in two grass species raised at graded levels of iron supply ranging from 0.04–10.24 ppm in purified sand culture. 2. An increase in the iron supply caused an increase in the content of both total and acid soluble iron in Yorkshire fog up to a level of 2.56 ppm iron supply, after which no further increase took place. In timothy, low levels of iron supply caused an accumulation of both total and acid soluble iron within the tissue. 3. Increasing iron supply caused an increase in the content of chlorophyll, catalase and peroxidase. Both catalase and peroxidase were in greater concentration in Yorkshire fog than in timothy. 4. In the leaves of both species there was a marked correlation between chlorophyll and both catalase and peroxidase at all levels of iron supply. 5. Iron deficiency produced a high concentration of Cu, Mn, Ca, P, K and N in both grasses. At low levels of iron supply there was a greater accumulation of these elements in timothy than in Yorkshire fog. 6. The most reliable chemical method of identifying iron deficiency in both grasses appeared to be the value of the Ca/K, and Fe/Mn ratios. 7. A significant correlation existed between the Cu and Mn content of both grasses and suggestions are advanced to explain the susceptibility of timothy, and the resistance of Yorkshire fog to iron chlorosis with respect to the Cu and Mn contents of both grasses.

Host specificity among five species in the cowpea cross-inoculation group

Abstract: In a cross-inoculation experiment using crushed nodules from cowpea (Vigna unguiculata), groundnut (Arachis hypogea), bambara groundnut (Voandzeia subterranea), lima bean (Phaseolus lunatus) and soybean (Glycine max.), it was found that soybean did not nodulate with Rhizobia from any of the other species whilst its Rhizobia nodulated with all species. Cowpea and lima bean, on the other hand, nodulated with Rhizobia from all species, but their Rhizobia nodulated only with each other. Groundnut and bambara groundnut nodulated with Rhizobia from all species except cowpea and lima bean, and their Rhizobia also nodulated with all species except soybean.

Relationships betweenAspergillus flavus, A. niger and some other fungi in the mycoflora of groundnut kernels

Abstract: The relationships betweenAspergillus flavus, A. niger, Penicillium funiculosum, P. rubrum, andFusarium solani have been studied in 234 samples and 5850 plates from fresh and stored kernels derived from 2 years' groundnut crops in Israel.