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  • 1
    ISSN: 1432-1939
    Keywords: Nitrogen use efficiency ; C3 grasses ; C4 grasses ; Biomass production ; Competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two C3 grasses (Hordeum vulgare L., Avena sativa L.) and two C4 grasses (Panicum miliaceum L., Panicum crus-galli L.) were cultivated in standard soil in the open air in pure cultures and in various mixed cultures at low and high nitrogen fertilization levels. After three months the dry weight, length and nitrogen content of the aboveground and below-ground parts of the plants and the shoot/root ratios were determined. Hordeum vulgare was the most successful species irrespective of the nitrogen fertilization level, and also exhibited in most cases the highest nitrogen concentrations. Panicum miliaceum, on the other hand, was the species least able to compete. The production of biomass was reduced in cultures growing under nitrogen starvation conditions, this phenomenon being more pronounced with respect to the C4 than to the C3 species. The decrease in the production of biomass at low N conditions was most drastic with Panicum crus-galli, the species with the lowest nitrogen content and thus assumed to be best adapted to nitrogen starvation conditions. In cultures growing at low nitrogen fertilization levels the shoot/root ratios of all species.shifted in favour of an increasing root proportion. The extent of this shift, however, differed from species to species.
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  • 2
    ISSN: 1432-1939
    Keywords: Nitrogen use efficiency ; C3 plant ; C4 plant ; Biomass production ; Nitrate metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Pure and mixed cultures of the dicotyledons Atriplex hortensis L. (C3 plant) and Amaranthus retroflexus L. (C4 plant) were maintained under open air conditions in standard soil at low and high nitrogen supply levels. A comparison of shoot dry weight and shoot length in the various series shows that the growth of the aboveground parts of both species was severely reduced under low N conditions. In both pure and mixed cultures the differences resulting from low N vs. high N conditions was less pronounced with Atriplex (C3 plant) than with Amaranthus (C4 plant). The root dry weight of the two species was not reduced so much under low N conditions as was the shoot dry weight. The low N plants were found to contain a larger proportion of their biomass in the roots than did the high N plants. In general the root proportion of Atriplex was greater than that of Amaranthus. The contents of organic nitrogen and nitrate and the nitrate reductase activity (NRA) per g dry weight of both species decreased continually throughout the experiments. With the exception of young plants, the low N plants always had tower contents of organic nitrogen and nitrate and nitrate reductase activities than did the high N plants. The highest values of NRA were measured in the leaf laminae. The eaves also exhibited the highest concentrations of organic nitrogen. The highest nitrate concentrations, however, were observed in the shoot axis, and in most cases the lowest nitrate values were found in the laminae. At the end of ne growing season this pattern was found to have been reversed with Atriplex, but not with Amaranthus. Thus Atriplex was able to maintain a higher NRA in the laminae than Amaranthus under low N conditions. The transpiration per leaf area of the C4 plant Amaranthus during the course of a day was substantially lower than that of the C3 plant Atriplex. There were no significant differences in transpiration between the low N and high N series of Amaranthus. The low N plants of Atriplex, however, clearly showed in most cases higher transpiration rates than the corresponding high N plants. These different transpiration rates of the high N and the low N Atriplex plants were also reflected in a distinct 13C discrimination. The sum of these results points to the conclusion that the C3 plant Atriplex hortensis can maintain a better internal inorganic nitrogen supply than the C4 plant Amaranthus retroflexus under low N conditions and an ample water supply, due to the larger root proportion and the more pronounced and flexible transpiration of the C3 plant.
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  • 3
    ISSN: 1432-1939
    Keywords: Biomass production ; CAM plants ; Leaf conductance ; Nitrogen use efficiency ; Water supply
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two CAM plant species (Kalanchoe daigremontiana and K. tubiflora) were cultivated in pure cultures with two different levels of nitrogen and water supply. A comparison of the plant dry weight showed that the productivity was severely reduced under low nitrogen or/and water conditions. Additionally the proportion of the different organs contributing to the total biomass, and thus the ratio of root/shoot dry weight shifted substantially. At the same time the production of leaf buds in ratio to leaf biomass was increased. Concentrations of organic nitrogen and nitrate in the shoots were drastically reduced under low nitrogen or/and water conditions, but organic nitrogen concentration in the roots remained relatively high. The leaf conductance over a day was investigated only for K. daigremontiana, and decreased with reduced water and nitrogen supply. The results indicate that CAM plants do not have the predicted high nitrogen use efficiency. Under environmental stress they change from biomass production towards provisions for life preservation.
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