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

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.

Photosynthetic physiology of eucalypts along a sub-continental rainfall gradient in northern Australia

“…Leaves were collected at sites ranging from approximately 12 • S to 25 • S latitude, encompassing MAP ranging from approximately 1800 to 200 mm. Over most of this range, little variation was observed in leaf 13 C, with a marked response only becoming apparent when MAP declined to below about 400 mm (Miller et al, 2001;Schulze et al, 1998). A similarly flat response of eucalypt 13 C to variation in MAP has also been observed in south-western Australia (Schulze et al, 2006a;Turner et al, 2008).…”

“…Eucalypts, comprising species in the closely related genera Eucalyptus and Corymbia, dominate the over-stories of these savannas. The height and abundance of the over-story eucalypts decrease with declining MAP from north to south Schulze et al, 1998;Williams et al, 1996). Where MAP declines to less than about 500 mm, the eucalypt-dominated savannas tend to give way to Acacia-dominated shrublands (Bowman and Connors, 1996).…”

“…Previous investigations of leaf-level responses of eucalypts to variation in MAP in the Northern Territory of Australia have focussed on measurements of stable carbon isotope discrimination ( 13 C) in leaf dry matter (Miller et al, 2001;Schulze et al, 1998). Leaves were collected at sites ranging from approximately 12 • S to 25 • S latitude, encompassing MAP ranging from approximately 1800 to 200 mm.…”

Relationships Between Tree Height and Carbon Isotope Discrimination

“…Correlations between D and precipitation are routinely found in regional or global scale studies (e.g. Schulze et al 1998;Warren et al 2001;Bowling et al 2002) due to the dominant effect of water availability on g s and p c . The lack of freezing temperatures in tropical regions may also allow higher g s and p c because xylem vessels can grow larger and have subsequently greater hydraulic conductance .…”

Structural and functional leaf traits of two Gochnatia species from distinct growth forms in a sclerophyll forest site in Southeastern Brazil

“…Normally, leaves with a lower SLA invest a lot in non-photosynthetic tissues, such as the cuticle and leaf epidermis (Dijkstra 1990;Fahn & Cutler 1992), and have leaves with a lower leaf area. These aspects may be important in high-light environments where conservation of water resources leads to ecological success (Schulze et al 1998), but also to a lower A mass . In contrast, the higher values of SLA for G. barrosii may suggest a mesophytic aspect of its leaves, which also has lower leaf thickness and higher leaf area as a strategy to increase the capture of the diffuse light that penetrates the the border of the canopy (Grime & Hunt 1975).…”