Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

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

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

Australian Journal of Plant Physiology 25(4) 413 - 425
Published: 1998

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.

Keywords: carbon and nitrogen isotope ratios, nitrogen concentration, specific leaf area, drought, burning, grazing, plant functional types, Eucalyptus.

https://doi.org/10.1071/PP97113

© CSIRO 1998


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