Journal Article

Transport, storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia

Susanne Schmidt and George R. Stewart

in Tree Physiology

Volume 18, issue 6, pages 403-410
Published in print June 1998 | ISSN: 0829-318X
Published online June 1998 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/18.6.403
Transport, storage and mobilization of nitrogen by trees and shrubs in the wet/dry tropics of northern Australia

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Xylem sap from woody species in the wet/dry tropics of northern Australia was analyzed for N compounds. At the peak of the dry season, arginine was the main N compound in sap of most species of woodlands and deciduous monsoon forest. In the wet season, a marked change occurred with amides becoming the main sap N constituents of most species. Species from an evergreen monsoon forest, with a permanent water source, transported amides in the dry season. In the dry season, nitrate accounted for 7 and 12% of total xylem sap N in species of deciduous and evergreen monsoon forests, respectively. In the wet season, the proportion of N present as nitrate increased to 22% in deciduous monsoon forest species. These results suggest that N is taken up and assimilated mainly in the wet season and that this newly assimilated N is mostly transported as amide-N (woodland species, monsoon forest species) and nitrate (monsoon forest species). Arginine is the form in which stored N is remobilized and transported by woodland and deciduous monsoon forest species in the dry season. Several proteins, which may represent bark storage proteins, were detected in inner bark tissue from a range of trees in the dry season, indicating that, although N uptake appears to be limited in the dry season, the many tree and shrub species that produce flowers, fruit or leaves in the dry season use stored N to support growth. Nitrogen characteristics of the studied species are discussed in relation to the tropical environment.

Keywords: amides; monsoon forest; nitrate; nitrogen fixation; nitrogen transport; storage protein; tropical savanna woodland; ureides; xylem sap

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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