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  • 1
    ISSN: 1432-2048
    Keywords: Brassica (photoinhibition) ; Chilling ; Crop growth analysis ; Freezing ; Photoinhibition ; Photosynthesis (quantum yield)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The maximum quantum yield of CO2 uptake (Φ), as a measure of light-limited photosynthetic efficiency, of a Brassica napus crop was measured on most days from mid-October until mid-April. During the winter, Φ was decreased by up to 50%. From January to March, leaves exposed to direct sunlight on days with minimum air temperatures near or below 0° C showed significant reductions in Φ. However, control leaves, artificially shaded from direct sunlight on these days, did not show any decrease. This provides statistical evidence for a light-dependent inhibition of CO2 uptake in the field, termed here photoinhibition. Recovery of Φ during warmer interludes was slow, requiring approx. 2–3 d. Concurrent measurements of light interception by the crop canopy and dry-matter accumulation showed that the efficiency with which intercepted light was converted into dry matter varied, declin between January and March to 33% of the value recorded in the warmer autumn months. Conversion efficiency was significantly and positively correlated with quantum yield. In a closed crop canopy during winter, light will be limiting for photosynthesis for much of the time. Under these conditions depression of Φ at the leaf level may contribute significantly to decreased dry-matter accumulation at the crop level, since the light-limited rate of CO2 uptake is likely to govern canopy photosynthetic rate.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5036
    Keywords: biomass ; decomposition ; Distichlis spicata ; Echinochloa polystachya ; Eulalia trispicata ; Lophopogon intermedius ; Pennisetum mezianum ; primary production ; primary productivity ; Themeda triandra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Studies of net primary production in four contrasting tropical grasslands show that when full account is taken of losses of plant organs above- and below-ground these ecosystems are far more productive than earlier suggested. Previous values have mainly been provided by the International Biological Programme (IBP), where estimates of production were based on a change in vegetation mass alone and would not necessarily have taken full account of organ losses and turnover. Calculation at three of our sites based on estblished methodology using changes in plant mass alone (i.e. that used by the International Biological Programme, IBP) proved to be serious underestimates of when acount was taken of losses simultaneously with measurement of change in plant mass. Accounting for the turnover of material at these three sites resulted in productivities up to five times higher than were obtained using the standard IBP procedure. An emergent C4 grass stand at a fourth site in the Amazon achieved a productivity which approached the maximum recorded for agricultural crops. In this case, productivity values, when organ losses were taken into account, only slightly exceeded that obtained with IBP methods. The findings reported here have wider implications, in prediction of global carbon cycling, remote sensing of plant productivity and impact assessment of conversion to arable cropping systems.
    Type of Medium: Electronic Resource
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