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  • 1
    ISSN: 1615-6102
    Keywords: Root hemiparasite ; Olax ; Host-parasite interface ultrastructure ; Apoplastic tracers ; Transport pathway ; Water: solute uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.
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  • 2
    ISSN: 1573-5036
    Keywords: effect of combined N ; geocarpic legumes ; nitrogen fixation ; Rhizobium ; root nodule ; ureide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nodulation, nitrogen (N2) fixation and xylem sap composition were examined in sand cultured plants of Bambara groundnut (Vigna subterranea L.) and Kersting's bean (Macrotyloma geocarpum L.) inoculated with Bradyrhizobium strain CB756 and supplied via the roots for a 4 week period from the third week onwards with different levels of (15N)-nitrate (0–15 mM). The separate contributions of nitrate and N2 to plant nitrogen were measured by isotope dilution. Increasing levels of nitrate inhibited nodule growth (measured as dry matter or nodule N) of both species parallel with decreased dependence on symbiotically-fixed N. Specific nodule activity (N2 fixed g nodule dry−1 d−1 of nodules) was reduced progressively with time in V. subterranea at higher (5 or 15 mM) levels of NO3, but this was not so for M. geocarpum. Root xylem bleeding sap of both species showed ureides (allantoin and allantoic acid) as predominant (〉90%) solutes of nitrogen when plants were relying solely on atmospheric N. Levels of ureide and glutamine decreased and those of asparagine and nitrate in xylem increased with increasing level of applied nitrate. Relative levels of xylem ureide-N were positively correlated (R2=0.842 for M. geocarpum and 0.556 for V. subterranea), and the ratio of asparagine to glutamine in xylem exudate negatively correlated (R2=0.955 for M. geocarpum and 0.736 for V. subterranea) with plant reliance on nitrogen fixation. The data indicate that xylem sap analyses might be useful for indirect field assays of nitrogen fixation by the species and that Kersting's bean might offer some potential as a symbiosis in which N2 fixation is relatively tolerant of soil N.
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  • 3
    ISSN: 1573-5036
    Keywords: natural ecosystems ; nutrient acquisition ; roots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This paper examines the general biology of mycorrhizal associations alongside the wide range of alternative trophic adaptations which higher plants may employ when competing for limited resources of specific nutrients within an ecosystem. All examples described come from highly nutrient-impoverished heathlands or open woodlands of the kwongan of southwest Australia. An account is given of the general patterns of rooting morphology and their association with various mycorrhizal and non-mycorrhizal nutrient-acquiring strategies, including various forms of parasitism, epiparasitism, autotrophy with or without mycorrhizal association. Taxonomic affinities of each grouping are examined alongside growth and life form characteristics. A case study of patterns of utilization of a specific nutrient, nitrogen in a Banksia woodland ecosystem is presented to illustrate how a multifaceted approach can be used for studying species responses and interactions. The study categorizes species according to nitrate-utilizing ability and suggests how 15N natural abundance of soil and plant components and organic solutes of nitrogen is xylem might be utilized to separate species into different trophic categories. Response of the ecosystem to fire is examined in respect of the nutritional interrelationships of component species as the ecosystem changes from being nitrate dominant immediately after fire to increasingly ammonium-producing thereafter. The paper concludes by examining generally trophic relationships within whole ecosystems and outlines some of the challenges for future research in this connection.
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  • 4
    ISSN: 1573-5036
    Keywords: cowpea ; intercropping ; maize ; 15N methods ; N economy ; N2-fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Yields of above ground biomass and total N were determined in summer-grown maize and cowpea as sole crops or intercrops, with or without supplementary N fertilizer (25 kg N ha−1, urea) at an irrigated site in Waroona, Western Australia over the period 1982–1985. Good agreement was obtained between estimates of N2 fixation of sole or intercrop cowpea (1984/85 season) based on the15N natural abundance and15N fertilizer dilution techniques, both in the field and in a glasshouse pot study. Field-grown cowpea was estimated to have received 53–69% of its N supply from N2-fixation, with N2-fixation onlyslightly affected by intercropping or N fertilizer application. Proportional reliance on N2-fixation of cowpea in glasshouse culture was lower (36–66%) than in the field study and more affected by applied N. Budgets for N were drawn up for the field intercrops, based on above-ground seed yields, return of crop residues, inputs of fixed N and fertilizer N. No account was taken of possible losses of N through volatilization, denitrification and leaching or gains of N in the soil from root biomass. N2-fixation was estimated tobe 59 kg N ha−1 in the plots receiving no fertilizer N, and 73 kg N ha−1 in plots receiving 25 kg N ha−1 as urea. Comparable fixation by sole cowpea was higher (87 and 82 kg N ha−1 respectively) but this advantage was outweighed by greater land use efficiency by the intercrop than sole crops.
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  • 5
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary If a nodulated legume is decapitated immediately after a brief period of photosynthesis in C14O2 a highly reproducible pattern of labelling is detected among the amino compounds of the root bleeding sap. The sequences of this pattern apparently reflect the consequences of the exchange of labelled carbohydrate with various morphological and metabolic compartments of the root. The progress of the exchange is greatly influenced by diurnal variations in root metabolism. An endogenous component is described for the rhythmic discharge of amino compounds into the bleeding sap. At 24°C the period of the rhythm is slightly greater than 24 hours. Plants with branched shoots are used to study environmental influences on the translocation of labelled assimilates from a shoot, and the utilisation of these materials in synthesis of organic compounds of nitrogen in the nodulated root. One half of the branched shoot is fed with C14O2 and its unlabelled partner removed for collection of bleeding sap. A progressive enrichment of bleeding sap with radiocarbon occurs only if the plants are exposed to normal photoperiods and ambient temperatures. Similar plants retained in darkness in constant temperature exhibit a rapid decline in the specific activity of the amino fraction of the bleeding sap, suggesting that translocation from the pool of labelled carbohydrate in the shoot has failed to keep pace with root synthesis.
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  • 7
    ISSN: 1573-5036
    Keywords: choline phosphate ; glycero phosphate ; inositol phosphate ; lupins ; phosphatase ; phosphorus availability ; pyro phosphate ; RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Inositol phosphate is at least equal to KH2PO4 as a source of P for the growth of lupins in sand but a much poorer source in soil. RNA and glycerophosphate were excellent sources of P for lupin growth in a P-fixing soil. Soil and root phosphatase activity were not altered by amendment of soils with either inorganic- or organic-P. The difference in availability of differing P-sources is related to their solubility in soils rather than susceptibility to phosphatases.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 15 (1961), S. 329-346 
    ISSN: 1573-5036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The influence of combined nitrogen (as ammonium nitrate) on the symbiotic performances of selected bacterial associations of four legumes was examined using sand culture. In barrel medic (Medicago tribuloides Desr.) and vetch (Vicia sativa L. andV. atropurpurea Desf.) bacterial partnerships of a host plant varied greatly in their nodulation responses to a range of amounts of nitrogen applied at sowing. Some bacterial strains exhibited varying degrees of stimulation of nodule number, growth and fixation by low or medium amounts of nitrogen. Higher levels of combined nitrogen depressed symbiosis. Other strain responses showed a severe restriction of symbiosis with any amount of added nitrogen. Seasonal influences conditioned symbiotic responses to combined nitrogen in an association of cowpea (Vigna sinensis End.) With a summer sowing small amounts of ammonium nitrate added at sowing benefited later symbiotic development. No such stimulation was evident in an autumn sowing and symbiotic injury from high levels of nitrogen was greater than in the summer sowing. The developing association of cowpea was found to be most sensitive to ammonium nitrate added just as the first leaves unfolded. Here damage was manifest in a permanent elevation of the top: root ratio with subnormal growth and functioning of nodules. Greatest benefit from added inorganic nitrogen followed applications made as the first nodules appeared on the primary root. In this case added combined nitrogen acted as an investment providing returns in additional fixation equivalent to 5–10 times the amount of nitrogen originally fed to the seedling and representing some 50 per cent greater total fixation than in minus-nitrogen controls.
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  • 9
    ISSN: 1573-5036
    Keywords: competition ; crop rotation ; farming systems ; ley farming ; soil nitrogen ; Trifolium subterraneum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Annual pasture legumes play a key role in ley farming systems of southern Australia, providing biologically fixed nitrogen (N) to drive the production of the pastures as well as subsequent crops grown in rotation. Seasonal inputs of biologically fixed N in shoot biomass of the subterranean clover (Trifolium subterraneum) component of grazed annual pastures were assessed using the15N natural abundance technique and appropriately timed sampling of herbage dry matter (DM) for N accumulation. At three study sites spanning a gradient across the Western Australian wheatbelt from 300 to 600 mm annual rainfall the performance of the clover and non-legume herbs and grasses was examined as paired comparisons involving two management treatments expected to give contrasting effects on pasture productivity, botanical composition and N2 fixation. The proportion of clover N derived from atmospheric N2 fixation (%Ndfa) ranged from 65 to 95% across sites, treatments and sampling times. Amounts of fixed N accumulated in clover shoot biomass ranged from 50 to 125 kg ha−1, and paralleled trends in clover production. Substantial increases in pasture production in high yielding treatments generally occurred without decrease in %Ndfa, suggesting that N2 fixation was essentially non-limiting to performance of the clover component. Seasonal profiles for accumulation of fixed N were skewed towards the late winter and spring period, particularly in low plant density pastures following a cereal crop. There were seasonal, site and treatment-specific effects on the proportion of clover and non-legume pasture components and consequently clover yield and N2 fixation were variably affected by competition from non-legume species.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Agroforestry systems 45 (1999), S. 7-9 
    ISSN: 1572-9680
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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