Nitrogen relations of natural and disturbed plant communities in tropical Australia |
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Authors: | S Schmidt G R Stewart M H Turnbull P D Erskine N Ashwath |
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Institution: | (1) Department of Botany, The University of Queensland, Brisbane, QLD 4072, Australia, AU;(2) Environmental Research Institute of the Supervising Scientist, Environmental Protection Agency, Locked Bag 2, Jabiru NT 0886, Australia, AU |
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Abstract: | Nitrogen relations of natural and disturbed tropical plant communities in northern Australia (Kakadu National Park) were
studied. Plant and soil N characteristics suggested that differences in N source utilisation occur at community and species
level. Leaf and xylem sap N concentrations of plants in different communities were correlated with the availability of inorganic
soil N (NH+
4 and NO−
3). In general, rates of leaf NO−
3 assimilation were low. Even in communities with a higher N status, including deciduous monsoon forest, disturbed wetland,
and a revegetated mine waste rock dump, levels of leaf nitrate reductase, xylem and leaf NO−
3 levels were considerably lower than those that have been reported for eutrophic communities. Although NO−
3 assimilation in escarpment and eucalypt woodlands, and wetland, was generally low, within these communities there was a suite
of species that exhibited a greater capacity for NO−
3 assimilation. These “high- NO−
3 species” were mainly annuals, resprouting herbs or deciduous trees that had leaves with high N contents. Ficus, a high-NO−
3 species, was associated with soil exhibiting higher rates of net mineralisation and net nitrification. “Low-NO−
3 species” were evergreen perennials with low leaf N concentrations. A third group of plants, which assimilated NO−
3 (albeit at lower rates than the high-NO−
3 species), and had high-N leaves, were leguminous species. Acacia species, common in woodlands, had the highest leaf N contents of all woody species. Acacia species appeared to have the greatest potential to utilise the entire spectrum of available N sources. This versatility in
N source utilisation may be important in relation to their high tissue N status and comparatively short life cycle. Differences
in N utilisation are discussed in the context of species life strategies and mycorrhizal associations.
Received: 5 July 1997 / Accepted: 13 July 1998 |
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Keywords: | Nitrate Nitrogen utilisation Tropical woodland Tropical monsoon forest Xylem sap |
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