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  • 1
    ISSN: 1432-1939
    Keywords: Echinochloa crus-galli ; Ecotypes ; Temperature ; CO2 enrichment ; C4 metabolism ; NADP+-malate dehydrogenase ; Energy of activation ; K m, V max/K m
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The apparent energy of activation (E a), Michaelis-Menten constant (K mfor oxaloacetate), V max/K mratios and specific activities of NADP+-malate dehydrogenase (NADP+-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO2 concentrations, 350 μl l-1 and 675 μl l-1. E avalues of NADP+-MDH extracted from QUE plants were significantly lower than those of MISS plants. K mvalues and V max/K mratios of the enzyme from both ecotypes were similar over the range of 10–30°C but reduced V max/K mratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO2 enrichment did not modify appreciably the catalytic properties of NADP+-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP+-MDH activities were always in excess of the amount required to support observed rates of CO2 assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP+-malate dehydrogenase among these ecotypes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant ecology 135 (1998), S. 31-41 
    ISSN: 1573-5052
    Keywords: Canonical correspondence analysis ; CO2 ; Multivariate analysis ; Open-top chambers ; Plant community ; Succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the response of a pasture community in southern Quebec (Canada) to long-term exposure of enriched atmospheric CO2 conditions. The study was conducted using open-top growth chambers directly placed on top of the natural pasture community. To investigate the change in the overall species composition in time and space, we used canonical correspondence analysis, a direct ordination method. Over the three years, the overall community responded significantly to enriched CO2. The analyses show that, after three years, CO2 was the most important environmental variable affecting the species composition. Initially the presence of the wall of the chambers influenced the composition but CO2 became more important by the third year. Soil and air temperatures only slightly influenced the community composition. The first two axes of the canonical correspondence analysis explained a large proportion of the variation in the three years and these trends appeared to increase with time. Species such as Agropyron repens appeared to be positively influenced by the presence of the wall (slightly warmer conditions). However, the analyses suggest that Phleum pratense and Trifolium repens, for example, were favored by the increase in atmospheric CO2. The variation in species composition in enriched versus ambient CO2 chambers suggests that the effect of the environmental factors, particularly CO2, were important in affecting the rate and pattern of succession. Furthermore, the temporal increase in importance of the variable CO2 in the present analyses indicates that there might be a time-lag in response to atmospheric enrichment.
    Type of Medium: Electronic Resource
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