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  • Nitrogen  (2)
  • CO2 assimilation  (1)
  • Storage
  • Springer  (4)
  • 1985-1989  (4)
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  • Springer  (4)
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  • 1
    ISSN: 1432-1939
    Keywords: Biennial plants ; Carbon partitioning ; Nitrogen partitioning ; Storage ; Harvest index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data. Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.
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  • 2
    ISSN: 1432-1939
    Keywords: CO2 assimilation ; stomatal responses ; soil drying rate ; cowpea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Well watered plants of Vigna unguiculata (L.) Walp cv. California Blackeye No. 5 had maximum photosynthetic rates of 16 μmol m-2 s-1 (at ambient CO2 concentration and environmental parameters optimal for high CO2 uptake). Leaf conductance declined with increasing water vapour concentration difference between leaf and air (Δw), but it increased with increasing leaf temperature at a constant small Δw. When light was varied, CO2 assimilation and leaf conductance were correlated linearly. We tested the hypothesis that g was controlled by photosynthesis via intercellular CO2 concentration (c i). No unique relationship between (1) c i, (2) the difference between ambient CO2 concentration (c a) and c i, namely c a-c i, or (3) the c i/c a ratio and g was found. g and A appeared to respond to environmental factors fairly independently of each other. The effects of different rates of soil drying on leaf gas exchange were studied. At unchanged air humidity, different rates of soil drying were produced by using (a) different soils, (b) different irrigation schemes and (c) different soil volumes per plant. Although the soil dried to wilting point the relative leaf water content was little affected. Different soil drying rates always resulted in the same response of photosynthetic capacity (A max) and corresponding leaf conductance (g(Amax)) when plotted against percent relative plant-extractable soil water content (W e %) but the relationship with relative soil water content (W e ) was less clear. Above a range of W e of 15%–25%, A max and g(Amax) were both high and responded little to decreasing W e . As soon as W e fell below this range, A max and g(Amax) declined. The data suggest root-to-leaf communication not mediated via relative leaf water content. However, g(Amax) was initially more affected than A max.
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  • 3
    ISSN: 1432-1939
    Keywords: Mimicry ; Nitrogen ; Herbivory ; Mistletoe ; Australia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Leaves from many misletoe species in Australia strongly resemble those of their hosts. This cryptic mimicry has been hypothesized to be a means of reducing the likelihood of mistletoe herbivory by vertebrates. Leaf Kjeldahl nitrogen contents (a measure of reduced nitrogen and thus amines, amino acids and protein levels) of mistletoes and their hosts were measured on 48 mimetic and nonmimetic host-parasite pairs to evaluate hypotheses concerning the significance of crysis versus noncrypsis. The hypothesis that mistletoes mimicking host leaves should have higher leaf nitrogen levels than their hosts is supported; they may be gaining a selective advantage through crypsis (reduced herbivory). The second hypothesis that mistletoes which do not mimic their hosts should have lower leaf nitrogen levels than their hosts is also supported; they may be gaining a selective advantage through noncrypsis (reduced herbivory resulting from visual advertisement of their reduced nutritional status).
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  • 4
    ISSN: 1432-1939
    Keywords: Forest decline, Spruce (Picea abies) ; Nitrogen ; Magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A declining Picea abies (L.) Karst. stand produced as much foliage and branches as a healthy stand but less stemwood at a similar leaf area index and climate. Nutrient analyses revealed that most biomass components at the declining site had lower concentrations of calcium and magnesium, but similar nitrogen and potassium (except for lower potassium in younger needles) and higher phosphorus, manganese and aluminum than the respective components at the healthy site. Comparison of these data with the results from studies on the nutrition and growth of P. abies seedlings (Ingestad 1959) led to the conclusion that the healthy stand is in a balanced nutritional state, while trees at the declining stand have only 56% of the foliar magnesium concentration required to permit growth at a rate which could be achieved at their nitrogen status. It appears that acidic deposition, which involves an input of nitrogen and a leaching of cations from the soil, causes an imbalance in the availability of nitrogen and magnesium. Growth is eventually reduced as magnesium becomes limiting.
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