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  • Nutrient cycling  (3)
  • ELECTRONICS AND ELECTRICAL ENGINEERING  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 82 (1990), S. 432-436 
    ISSN: 1432-1939
    Keywords: Grass ; Lolium perenne ; Nutrient cycling ; Phosphorus ; Roots
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous experiments, using 32P pulse labelling, showed that when roots of Lolium perenne were detached from the shoot, a substantial proportion of the phosphorus in the roots could within a few weeks be released and be captured by another, living plant. This paper describes experiments designed to confirm and further investigate this rapid nutrient transfer. Roots from plants grown with ample N and P were detached and placed in litter bags in soil. They lost up to 60% of their initial N and up to 70% of their P in three weeks. Even when roots were grown with deficient P supply, resulting in C:P ratios of 300–400, they lost 20–30% of their initial P. Time-courses of 32P loss from roots suspended in solution gave results which agreed with these figures. The initially rapid rate of 32P loss had declined greatly within three weeks. In a pot experiment small L. perenne plants showed a marked increase in their N and P content during 30 days after a neighbouring large plant's shoot was removed, supporting rapid capture of nutrients lost from the detached roots. To investigate P loss from roots while attached to the shoot, L. perenne shoots were clipped every four days and 32P loss from the roots measured. After the third clip the rate of loss increased, eventually to more than four times that from the control plants.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 84 (1990), S. 359-361 
    ISSN: 1432-1939
    Keywords: Nutrient cycling ; Phosphorus ; Roots ; Ryegrass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Lolium perenne was grown in solution culture with either ample or deficient phosphate supply (‘high-P’ and ‘low-P’ plants). The concentration in the roots of phosphorus as water-soluble compounds, phospholipid and insoluble residue was measured. A supplementary experiment showed that the concentration of each component in the roots of low-P plants was similar to that in plants grown in P-deficient soil. The time-course of the decline of each P component was determined in roots detached from the shoot and left hanging in solution. During the three weeks residue P concentration in the roots declined little. In contrast, both types of root lost about three-quarters of their lipid P in the first week. Low-P roots lost little of their water-soluble P. High-P roots contained much more water-soluble P and lost much of it during the first two weeks. By the end of three weeks their water-soluble P content was levelling out at a value similar to that in low-P roots, suggesting a ‘non-labile pool’. The rapid loss of lipid P from low-P roots comprised more than half of their total loss, and the possible ecological significance of this is discussed.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Mycorrhiza 1 (1992), S. 47-53 
    ISSN: 1432-1890
    Keywords: Competition ; Grassland ; Nutrient transfer ; Nutrient cycling ; Seedling establishment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We present and discuss evidence, mostly from our own research, on some possible roles of mycorrhizae in interactions between plants. Experiments investigating whether seedlings become more rapidly infected with mycorrhiza if they are near large, already infected plants have shown that contact between the seedling's roots and established mycelium sometimes speeds up infection but on other occasions it does not. The reason for the discrepancies is not clear. Mycorrhiza can substantially alter the balance between competing plant species in a way that would not be predicted from their response when growing separately. An experiment involving large and small plants of the same species growing together showed little effect of mycorrhiza on the balance between plants of different sizes. The rate of transfer of 32P between plants of Lolium perenne or Plantago lanceolata was so slow, even when they were mycorrhizal, that phosphorus transfer between living plants seems unlikely to be of major ecological importance. However, nitrogen was found to be transferred much more freely than phosphorus between P. lanceolata plants. Situations are discussed in which there could be a source-sink relationship between plants causing net flow of carbon or mineral nutrients from one to the other. If nutrients pass from dying roots to living plants via mycorrhizal links, this could result in preferential nutrient cycling between species that share the same type of mycorrhiza. Some evidence is presented that this does happen.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2019-06-27
    Description: Moment method solutions are considered for treating the problem of wire antennas in the presence of an arbitrary dielectric inhomogeneity. In the first method, the current on the wire and the electric field intensity in the inhomogeneity are treated as independent unknowns, while in the second and third methods they are treated as dependent unknowns. The third method is applied to the problem of strip antennas in an electrically thin dielectric slab. Numerical results are presented, and are in good agreement with measurements and previous calculations.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-CR-140854 , TR-2902-20
    Format: application/pdf
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