Carbon and nitrogen isotope discrimination and nitrogen nutrition of trees 
along a rainfall gradient in northern Australia

Schulze, E.-D.; Williams, R. J.; Farquhar, G. D.; Schulze, W.; Langridge, J.; Miller, J. M.; Walker, B. H.

doi:10.1071/pp97113

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Carbon and nitrogen isotope discrimination and nitrogen nutrition of trees along a rainfall gradient in northern Australia

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Schulze, E.-D.
Department Biogeochemical Processes, Prof. E.-D. Schulze, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Citation

Schulze, E.-D., Williams, R. J., Farquhar, G. D., Schulze, W., Langridge, J., Miller, J. M., et al. (1998). Carbon and nitrogen isotope discrimination and nitrogen nutrition of trees along a rainfall gradient in northern Australia. Australian Journal of Plant Physiology, 25(4), 413-425. doi:10.1071/pp97113.

Cite as: https://hdl.handle.net/11858/00-001M-0000-000E-CB8F-1

Abstract

Carbon isotope discrimination (Δ) and nitrogen isotope ratios, N-concentrations and specific leaf area of 50 tree species were investigated along a continental-scale transect through northern Australia over which annual rainfall varied from 1800 mm to 216 mm rainfall. Average specific leaf area (SLA, m2 kg-1) of leaves ranged from 10.7 ± 1.7 (av. ± s.d.) in N₂ fixing deciduous trees to 0.8 ± 0.4 in spinescent sclerophylls shrubs. SLA generally decreased with increasing aridity. N₂ fixing species had higher leaf N concentration (average N-concentration 20.1 ± 3.7 mgN g-1) than non- N₂ fixing (10.8 ± 3.3) or spinescent species (7.05 ± 1.8).
Community-averaged Δ was approximately constant at rainfalls above 475 mm (average Δ = 19.4 ± 1.2‰). Where rainfall was less than 475 mm, Δ decreased from 19‰ to 17‰ at 220 mm. Δ was positively correlated with SLA. Δ of deciduous N₂ fixing species and spinescent species were 1‰ and 2.4‰ lower than in evergreen sclerophyllous species. Δ in the N₂ fixing Allocasuarina was 1.2‰ lower than in non- N₂ fixing sclerophyllous species. The δ¹⁵N-values indicated N₂ fixation only at high rainfall. Burning of the field layer in a Eucalyptus forest had no effect on all measured tree parameters including δ¹⁵N, but δ¹⁵N increased under grazing conditions to >5‰.
The constant value of community averaged Δ between 1800 and 450 mm may be the result of replacement of functional types and species. The decline in Δ in the more arid section may be a function of both low species diversity, and a highly aseasonal and unpredictable rainfall regime.