bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of Potassium Delivery to the Roots of Cereal Plants
Authors: Gäth Stefan , Meuser Helmut , Abitz Carl‐Andreas , Wessolek Gerd , Renger Manfred 
Published: February 2007

AbstractPotassium (K) delivery to the roots of cereal plants in soils is determined by both soil and plant factors, root growth and root length density in particular, being of major importance. In Part A of this paper an evaluative framework is shown for sandy and loamy‐silty soils for determination of root length density based on available field capacity, soil depth in 10 cm steps and the climatic water balance. A good correlation (r2 = 0.86) was found when the root length densities were determined at ear emergence. With the help of correction functions root length densities can be subsequently estimated for the other phenological stages (stem elongation, flowering and yellow ripeness). The method described is suited for determining root length densities in water and nutrient transport simulation models.In Part B exchange resins were used to simulate the K delivery from the soil to the root. Measurements were made for different soils and water contents. The depletion zone near the exchange resin was 6 mm thick after 4 days. This corresponds to results obtained from root measurements. Comparisons between a sandy and a loamy‐silty soil show, that K delivery by diffusion for equal concentrations depends primarily on soil moisture and pore tortuosity. This leads to the conclusion, that soil physical properties must be taken into consideration when evaluating chemical soil analysis and recommendating fertilizer applications.
The maize root system in situ: Evaluation of structure and capability of utilization of phytate and inorganic soil phosphates
Authors: Beck Erwin , Fußeder Anton , Kraus Michael 
Published: February 2007

Abstract
The dependence of the morphology of the maize (Zea mays L.) seminal root system on physical, chemical and biotic parameters was investigated with pot cultures in quartz sand and in a natural loamy sand soil. Low O2‐supply to the soil resulted in a substantially smaller root biomass despite a relative increase in total root length. Reduced N‐supply also stimulated root length growth, but also enhanced the formation of laterals. The presence of soil microorganisms, in comparison to sterile cultures, resulted in a reduced length of the main roots, and the production of slender laterals with a decreased root hair density. Generally, the structural variability of laterals in response to different growth conditions was much more pronounced than that of the main roots.
A major part of the work reported here was dedicated to a detailed study of phosphate (P) acquisition by the maize root system under field conditions. Radioactive labelling of the roots and radioautography of soil cores revealed the in situ distribution pattern of the maize root system. Controlled labelling of the soil with radioactive phosphate allowed the documentation of the development and replenishment of the phosphate depletion zone around roots. Finally, the longevity and phosphate uptake activity of the different parts and tissues of the primary root system of maize was examined by electron microscopy and tracer studies including pulse chase experiments. From these studies the phosphate‐acquiring strategy of the maize root system appears as follows: The capability of P uptake decreases in the order: root hairs, 1st order laterals, 2nd order laterals, main root. The life‐spans of the components of the maize root system increase by the sequence: root hairs, laterals, main root. Inorganic P uptake, therefore, mainly occurs during the first weeks of root development. Dying back of the root occurs in an ordered manner resulting in a relocation of stored P predominantly into the main root cortex. Furthermore, it could be shown that competition for P between roots of the same or of adjacent maize and/or lupin plants virtually does not occur in situ.
The utilization of phytate‐P was studied with 14C/32P‐labelled Camyo‐inositol‐hexaphosphate supplied to maize plants grown in sterile quartz sand or in hydroponic cultures. The ratio of P‐ and C‐uptake as well as the incidence of phytate hydrolysis products in the rooting medium indicated the capability of maize roots to acquire P from phytate by enzymatic hydrolysis. This was confirmed by enzyme studies of the root tissues. A specific hydrolyzing enzyme (phytase; molecular weight 51 kD) could be detected in the cell wall of the root, especially in the root tip, which initiates phytate dephosphorylation. Further breakdown is presumably accomplished by monophosphoric phosphohydrolases.
Phosphorus Efficiency of Buckwheat (Fagopyrum esculentum)
Authors: Amann Christine , Amberger Anton 
Published: February 2007

AbstractThe ability of buckwheat (Fagopyrum esculentum) roots to acquire phosphorus (P) was characterized by investigating P uptake, morphological features, and chemical changes in the rhizosphere.Over a range of nutrient solution P concentrations (5–500 μmol · L−1), maximum shoot growth was achieved with a P supply between 5 and 100 μmol · L−1. Root weight and root length, as well as length and frequency of root hairs, were higher at low P levels. Root surface and the root surface/shoot dry weight ratio reached high values.Though P uptake rates were only moderate (0.15 pmol · cm−1 root · sec−1), shoot P concentrations were high (1.8% of dry weight with 100 μM P) predominantly being inorganic (80%). Phosphorus efficiency was characterized by a high specific absorption rate (810 mmol P · kg−1 root dry wt · d−1) rather than by an efficient utilization for dry weight production.Root exudates of low‐P plants had lower pH values than exudates of high‐P plants and increased the solubility of FePO4 and MnO2 to a greater extent. Amounts of exuded organic acids and phenolics were low and could not account for the observed solubilization of FePO4 and MnO2.Enhanced hydrolysis of glucose‐6‐phosphate by exudates from low‐P plants was due to an increased “soluble” acid phosphatase activity, and root surface phosphatase activity was also slightly enhanced with P deficiency. In the rhizosphere soil of buckwheat, some depletion of organic P forms was observed, and in pot trials with quartz sand, buckwheat utilized glucose‐ 6‐phosphate as a P source at the same rate as inorganic P.
Role of root‐induced changes in the rhizosphere for iron acquisition in higher plants
Authors: Marschner Horst , Treeby Michael , Römheld Volker 
Published: February 2007

AbstractPlants can mobilize iron (Fe) in the rhizosphere by non‐specific and specific (adaptive) mechanisms. Non‐specific mechanisms are, for example, rhizosphere acidification related to high cation‐anion uptake ratios, or citric acid excretion. The specific mechanisms are root responses to Fe deficiency and can be classified into two different strategies. The Strategy I is typical for dicots and monocots except for grasses (graminaceous species) and is characterized by increased plasma membrane‐bound reductase activity, enhanced net excretion of protons and enhanced release of reducing compounds, mainly phenolics. The reductase activity is stimulated by low pH, and with supply of FeIII chelates, ferric reduction at the plasma membrane takes place prior to uptake. In contrast, in graminaceous species (Strategy II) these root responses are absent, but enhancement of release of FeIII chelating compounds ‐ phytosiderophores ‐ takes place. These phytosiderophores are very efficient in mobilizing FeIII from artificially prepared sparingly soluble inorganic compounds (e.g. FeIII hydroxide) and from calcareous soils. The ferrated phytosiderophores are taken up by grasses at rates 102 to 103 times higher than Fe supplied either as synthetic chelate or microbial siderophores (e.g. ferrioxamine B), indicating a specific membrane transport system for ferrated phytosiderophores in roots of grasses. In calcareous soils phytosiderophores not only mobilize Fe, but also Zn, Mn, and Cu by chelation. However, only the FeIII phytosiderophores are taken up preferentially by Fe deficient grasses. The ecological advantages and disadvantages of Strategy I and Strategy II for Fe acquisition from calcareous soils are discussed.
Effect of zinc deficiency in wheat on the release of zinc and iron mobilizing root exudates
Authors: Zhang Fusuo , Römheld Volker , Marschner Horst 
Published: February 2007

AbstractThe effect of Zn deficiency in wheat (Triticum aestivum L. cv. Ares) on the release of Zn mobilizing root exudates was studied in nutrient solution. Compared to Zn sufficient plants, Zn deficient plants had higher root and lower shoot dry weights. After visual Zn deficiency symptoms in leaves appeared (15–17 day old plants) there was a severalfold increase in the release of root exudates efficient at mobilizing Zn from either a selective cation exchanger (Zn‐chelite) or a calcareous soil. The release of these root exudates by Zn deficient plants followed a distinct diurnal rhythm with a maximum between 2 and 8 h after the onset of light. Re‐supply of Zn to deficient plants depressed the release of Zn mobilizing root exudates within 12 h to about 50%‐, and after 72 h to the level of the control plants (Zn sufficient plants).The root exudates of Zn deficient wheat plants were equally effective at mobilizing Fe from freshly precipitated FeIII hydroxide as Zn from Zn‐chelite. Furthermore, root exudates from Fe deficient wheat plants mobilized Zn from Zn‐chelite, as well as Fe from FeIII hydroxide. Purification of the root exudates and identification by HPLC indicated that under Zn as well as under Fe deficiency, wheat roots of the cv. Ares released the phytosiderophore 2′‐deoxymugineic acid. Additional experiments with barley (Hordeum vulgare L. cv. Europa) showed that in this species another phytosiderophore (epi‐3‐hydroxymugineic acid) was released under both Zn and Fe deficiencies.These results demonstrate that the enhanced release of phytosiderophores by roots of grasses is not a response mechanism specific for Fe deficiency, but also occurs under Zn deficiency. The ecological relevance of enhanced release of phytosiderophore also under Zn deficiency is discussed.
Carbon Turnover in the Rhizosphere
Authors: Helal Helal M. , Sauerbeck Dieter 
Published: February 2007

AbstractConsiderable progress has been made during the last decade towards understanding and quantifying the input and turnover of plant carbon in the rhizosphere. This was made possible by the development (partially by the authors) and combination of appropriate new methods, such as:

–homogeneous labelling of whole plants with 14C
–distinction between root and microbial respiration
–separation of soil zones of known distances from the roots
–determination of microbial soil biomass.
These methods were applied to study the following aspects:

–release of organic plant carbon into the soil by growing roots
–utilization of this plant carbon by the microbial biomass in the rhizosphere
–related influence on the turnover of soil organic matter, and
–spatial range of such root influence in the soil.
About 19% of the total photosynthetic production of the investigated plants was released into the rhizosphere as organic material. Most of this (15%) was transformed by the rhizosphere microorganisms into CO2, while only a small fraction (4%) remained in the soil, mainly as microbial cells (2.5%). As a result, microbial rhizosphere biomass increased considerably. Relative to the organic C‐input, however, the incorporation of root derived carbon by the microbial biomass was remarkably low (13%).Along with the increase in microbial rhizosphere biomass, the presence of plant roots also enhanced the decomposition of soil organic matter and affected soil aggregate stability. Root carbon and root influences were even detected up to 20 mm away from the roots. This may be partially attributed to the contribution of root derived volatiles. Accordingly, both the actual volume of the rhizosphere and its metabolic significance is greater than what has so far been assumed. Possible interactions involving root, soil and microbial carbon are discussed.
Interaction of maize roots and rhizosphere microorganisms
Authors: Schönwitz Roswitha , Ziegler Hubert 
Published: February 2007

AbstractThe interaction between the roots of Zea mays L. and its rhizosphere microflora was studied in nutrient solution with respect to two exemplary aspects ‐ water soluble vitamins and the four most frequent carbohydrates.The exudation of vitamins and sugars into the medium is increased in a solid substrate (glass‐ballotini simulating soil structure) in comparison with nutrient solution only. The amounts of vitamins released (1 to 421 ng per plant) are high enough for a pronounced influence on the rhizosphere microflora to be expected. However, the microbial population feeding on the exudates has very simple nutritional demands. In spite of appreciable amounts of vitamins found in the inoculated nutrient solution, the growth of vitamin requiring species is not stimulated compared to the soil population.The roots are mostly inhabited by shorter rods and occasionally by actinomycete‐like filaments. The percentage of the root area covered by its microflora, assuming a monolayer, is 4% in the root region where root hairs are just emerging, 7% in the root hair zone and 20% in the oldest part of the roots, 10 mm below the grain.In the presence of rhizosphere microorganisms, root dry weight is lower than that of axenically grown plants because the diameter of the primary root is diminished. In addition, the vitamin and sugar content of the root is affected by rhizosphere microorganisms. The results can be interpreted as an indication that phytohormones may participate in interactions between roots and bacteria.
Plant, Microbial and Soil Factors, Determining Nitrogen Fixation in the Rhizosphere
Authors: Werner Dietrich , Berggold Regine , Jaeger Dieter , Krotzky Arno , Papen Hans , Schenk Sigrid , Thierfelder Heidemarie 
Published: February 2007

AbstractA genotype effect on associative (rhizosphere) N2‐fixation was observed with two cultivars of Sorghum bicolor (nutans) with a maximum rate of 8 μmol C2H4 · h−1 · plant−1 in one genotype compared to 0.9 μmol in the other. Characteristics of the high fixing genotype were a reduced transpiration rate, a lower number of stomata and increased root exudate production per gram root dry weight with higher concentration of dicarboxylic acids. The bacterial rhizosphere composition revealed a three times higher number of N2‐fixing bacteria, a tenfold reduction of actinomycetes and a threefold reduction of Arthrobacter associated with the high fixing cultivar compared to the low fixing genotype. From these and other plant rhizospheres two new nitrogen fixing bacteria, Pseudomonas stutzeri and Erwinia herbicola, were characterized. With the N2‐fixing bacteria Azospirillum brasilense and Klebsiella pneumoniae an enhancement of specific nitrogenase activity by aromatic compounds, for example phenolics, the herbicide alachlor and the insecticide carbofuran was demonstrated. An oscillating nitrogenase activity in Azospirillum brasilense under microaerobic conditions was found, resulting from an encystation and deencystation under those conditions. Experiments with wheat roots demonstrated that reduced oxygen tensions, essential for a maximum rhizosphere N2‐fixation, reduced root growth significantly and altered the N‐metabolism of the roots.
Gas‐chromatographic Separation of Organic Acids and Electrophoretic Determination of Phosphatases from VA Mycorrhizal Roots
Authors: Fabig BjöRn , Vielhauer Konrad , Moawad Atef M. , Achtnich Wolfram 
Published: February 2007

AbstractA report is given on methods for separation and identification of organic acids, including phenolic acids, and on the determination of phosphatases from VA mycorrhizal (VAM) roots.For gas‐chromatographic preparation of the samples containing the organic acids silylation and methylation were tested, as well as various solvents and silylating reagents. Columns of different polarity were examined for their separation properties. Gas‐ chromatographic separation of the acids was incomplete on the packed column OV 7. With the capillary column PVMS 54 separation was much better, but improvements are still needed.Mycorrhiza‐specific phosphatases (MSP) appearing as three bands were found by electrophoresis with porosity‐gradient gels in mycorrhizal roots of Allium, Sorghum and Eupatorium plants. In these three species each MSP was located at the same position. Inoculated onion roots enzymatically digested with cellulase and pectinase showed no root‐specific phosphatases, but still revealed MSP. Further improvements in electrophoresis techniques are being investigated.
Distribution pattern of total lipids and lipid fractions in forest humus
Authors: Ziegler Frank , Zech Wolfgang 
Published: February 2007

AbstractMull, moder, and mor humus profiles were investigated for their total lipid contents and the behaviour of lipid‐phosphorus and of five neutral lipid classes identified by HPTLC. The quantitative distribution of total and neutral lipids among the humus types is, besides by natural differences between the various parent litter materials, mainly controlled by soil physicochemical properties. In particular strongly acidic conditions, i.e. conditions corresponding to a reduced biological activity, inhibit significantly the decomposition of lipid compounds in (moder and) mor humus. A feature of the lipid depth functions is the input of microbial and root litter‐derived lipid material in the fermentation layers and a considerable lipid accumulation in the A horizons, probably at least partly due to mechanical transport processes. Phospholipids show no distinct variation dependent on the humus type, as far as the organic layers are concerned. But obviously, lipid‐P in the mineral, soil is closely correlated with, and therefore is a valuable measure for, the overall biological activity increasing from mor to moder and mull humus.
Bodenanalytische Diagnose von K‐ und Mg‐Mangel in Fichtenbeständen (Picea abies Karst.)
Authors: Liu Jin‐Chen , Trüby Peter 
Published: February 2007

AbstractFür 44 Fichtenbestände Südwestdeutschlands wurden signifikante Beziehungen zwischen den Gehalten an austauschbarem K, Mg, Ca und Al im Boden und den entsprechenden Gehalten der Nadeln nachgewiesen. Enge Zusammenhänge ergaben sich außerdem zwischen dem austauschbaren Mg im Boden und dem Vergilbungsgrad älterer Nadeln. Anhand der in der Nadelanalyse gebräuchlichen Grenzwerte wurden kritische Gehalte an austauschbaren Nährelementen im Boden abgeleitet. Für Mg liegt der Bereich akuten Mangels bei Gehalten < 2 μeq/g Boden. Die Bodenanalyse kann hierfür alternativ zur Nadelanalyse eingesetzt werden. Für K ist eine ähnlich scharfe Abgrenzung des Mangelbereichs nicht möglich. Bei Gehalten < 2 μeq/g Boden ist jedoch ein Auftreten akuten K‐Mangels wahrscheinlich. Es kann aber auch bei höheren K‐Gehalten (2–5 μeq/g Boden) K‐Mangel auftreten. Für eine Diagnose von K‐Mangel stellt die Bodenanalyse daher lediglich eine Orientierungshilfe dar.
Effect of temperature on the fragmentation of humic acids in alkaline solutions
Authors: Khairy Ahmed H. , Ziechmann Wolfgang 
Published: February 2007

AbstractThe fragmentation of one synthetic and four soil humic acids was studied in solutions of sodium hydroxide (pH 13) at different temperature between 0 and 90°C. The dissolved parts of the initial amounts of humic acids decreased to a minimum with the increase in temperature from 0 to 10°C. The fragmentation in this region was a function of both; temperature and concentration. At 15–20°C all of the initial amounts of humic acids were dissolved. The rate of fragmentation increased rapidly between 15 and 20°C and later slowed down between 20 and 40°C. This was due to the reaggregation of the particles of the produced hymatomelanic acids into particles of similar solubilities as those of the residual nonfragmented parts of the humic acids. This reaggregation took place probably through the formation of hydrophobic bonds. The fragmentation increased at temperatures above 40°C, and reached a maximum between 50 and 70°C depending on the type of the humic acid. The decline in fragmentation at temperatures higher than those corresponding to the maxima is most probably due to chemical reactions, in which the fragmentation products especially fulvic acids recombine together at about 60°C. Importance of these results in analytical methods of extraction and characterisation of humic acids is discussed.
Direct determination of potassium‐calcium activity ratio in soils with two ion‐selective electrodes. II. Interactions of potassium and calcium ions with soils
Authors: Yu T. R. , Beyme B. , Richter J. 
Published: February 2007

AbstractThe interactions of potassium and calcium ions with two variable charge soils and one constant charge soil were examined by measuring the pK‐0.5pCa value with two ion‐selective electrodes, together with measurements of single ion activities. The constant charge soil showed a much higher preference for calcium relative to potassium than the variable charge soils. The relative affinities of potassium, calcium, sodium and aluminum ions with exchange sites were not constant, but were a function of surface properties of the soil. pH affected the pK‐0.5pCa value in both the variable charge soil and the constant charge soil. The strong competition of aluminum ions for exchange sites was the major cause of the higher preference of soils for calcium ions relative to potassium ions at low pH. The pK‐0.5pCa value was always smaller in sulfate systems than in chloride systems, with the difference more distinct in variable charge soils. In addition to an initial fast reaction, some potassium ions were immobilized at later times, even for the highly weathered variable charge soil.
Influence of various fertilization on the mineralogical composition of clay fractions in long‐term field experiments
Authors: Leinweber Peter , Reuter Gerhard 
Published: February 2007

AbstractSoil samples from several long‐term experiments in the German Democratic Republic (GDR) were taken from plots with and without K‐supply. The fine, medium and coarse clay fractions were isolated using ultrasonic dispersion and sedimentation techniques and then investigated by x‐ray. Comparisons between the mineralogical compositions found and the results of x‐ray analyses of clay fractions from untreated Ah‐horizons of the same sites point to accelerated mineral transformations in unfertilized plots. Reductions in the illite contents are proved using the x‐ray diffraction diagrams. In connection with the question of the transformational products of this accelerated illite weathering, a new possibility for evaluation by curve‐fitting Lp‐corrected x‐ray diffraction diagrams was tested on one example. The degradation of the illites is partly accompanied with drastic reductions in the amounts of Ca‐lactate soluble and adsorbed K. Organic fertilization with 10 to 15 tons of farmyard manure per hectare per year prevented these negative mineralogical changes.
Further evidence concerning the importance of soil air‐filled porosity, soil organic matter and plants for denitrification
Authors: Prade Klaus , Trolldenier Günter 
Published: February 2007

AbstractPrevious experiments with artificially compacted mixtures of soils derived from two horizons of a mollic luvisol have shown the significance of air‐filled porosity, organic C content and presence of roots for denitrification. To test the validity of these results for natural conditions undisturbed soil cores were taken during tillering from fields cropped to wheat. Denitrification was measured at different constant soil moisture levels. The denitrification rates were in agreement with those found in the earlier experiments. In the light of the new data the previously established regression function parameters were only slightly modified. This confirmed our former findings that the effect of low air‐filled porosity and high soil organic C on denitrification was greater in cropped than in uncropped soil.