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15 N natural abundance of plant and soil components of a Banksia woodland ecosystem in relation to nitrate utilization, life form, mycorrhizal status and N 2 ‐fixing abilities of component species
Author(s) -
PATE J. S.,
STEWART G. R.,
UNKOVICH M.
Publication year - 1993
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1993.tb00882.x
Subject(s) - woodland , abundance (ecology) , ecosystem , banksia , nitrate , mycorrhizal fungi , environmental chemistry , environmental science , natural (archaeology) , ecology , chemistry , botany , biology , horticulture , inoculation , paleontology
Studies of the variation in δ 15 N values for plants from a fire‐prone Banksia woodland in South West Australia showed that pioneer herbaceous, non‐mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81%c). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence between the δ 15 N values of soil nitrate, xylem nitrate and leaf total nitrogen, suggesting an exclusive reliance on nitrate ions as nitrogen source. These pioneer species also showed a preponderance of the chloroplastic isoform of glutamine synthetase while woody species generally had higher activity associated with the cytosolic isoform. The group comprising monocotyledonous hemicryptophytes and geophytes contained species with slightly positive δ 15 N values and moderately active in nitrate reduction and storage. Nitrogen‐fixing species had the lowest δ 15 N values (–0.36‰), irrespective of their apparent utilisation of nitrate. However, woody resprouter species which had low levels of nitrate reduction and storage had δ 15 N values which fell within the range of values obtained for the miscellaneous assemblage of N 2 ‐fixing species. Consequently, 15 N abundance values failed to distinguish N 2 fixing from non‐fixing woody species, and therefore, could not be used in the ecosystem to determine the dependence of putative nitrogen fixing species on N 2 fixation. The study demonstrated complex patterns of nitrogen utilization in the ecosystem in which exploitation of different nitrogen resources related to plant life form and the physiological attributes of nitrogen assimilation by component species.