University of Tasmania

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Thermal optima of gross primary productivity are closely aligned with mean air temperatures across Australian wooded ecosystems

journal contribution
posted on 2023-05-21, 11:56 authored by Bennett, AC, Arndt, SK, Bennett, LT, Knauer, J, Beringer, J, Griebel, A, Hinko-Najera, N, Liddell, MJ, Metzen, D, Pendall, E, Silberstein, RP, Timothy WardlawTimothy Wardlaw, Woodgate, W, Haverd, V
Gross primary productivity (GPP) of wooded ecosystems (forests and savannas) is central to the global carbon cycle, comprising 67%-75% of total global terrestrial GPP. Climate change may alter this flux by increasing the frequency of temperatures beyond the thermal optimum of GPP (T-opt). We examined the relationship between GPP and air temperature (Ta) in 17 wooded ecosystems dominated by a single plant functional type (broadleaf evergreen trees) occurring over a broad climatic gradient encompassing five ecoregions across Australia ranging from tropical in the north to Mediterranean and temperate in the south. We applied a novel boundary-line analysis to eddy covariance flux observations to (a) derive ecosystem GPP-Ta relationships and T-opt (including seasonal analyses for five tropical savannas); (b) quantitatively and qualitatively assess GPP-Ta relationships within and among ecoregions; (c) examine the relationship between T-opt and mean daytime air temperature (MDTa) across all ecosystems; and (d) examine how down-welling short-wave radiation (Fsd) and vapour pressure deficit (VPD) influence the GPP-Ta relationship. GPP-Ta relationships were convex parabolas with narrow curves in tropical forests, tropical savannas (wet season), and temperate forests, and wider curves in temperate woodlands, Mediterranean woodlands, and tropical savannas (dry season). Ecosystem T-opt ranged from 15celcius (temperate forest) to 32celcius (tropical savanna-wet and dry seasons). The shape of GPP-Ta curves was largely determined by daytime Ta range, MDTa, and maximum GPP with the upslope influenced by Fsd and the downslope influenced by VPD. Across all ecosystems, there was a strong positive linear relationship between T-opt and MDTa (Adjusted R-2: 0.81; Slope: 1.08) with T-opt exceeding MDTa by >1celcius at all but two sites. We conclude that ecosystem GPP has adjusted to local MDTa within Australian broadleaf evergreen forests and that GPP is buffered against small Ta increases in the majority of these ecosystems.


Publication title

Global Change Biology










School of Natural Sciences


Wiley-Blackwell Verlag GmbH

Place of publication

United Kingdom

Rights statement

© 2021 John Wiley & Sons Ltd.

Repository Status

  • Restricted

Socio-economic Objectives

Hardwood plantations; Native forests; Other plant production and plant primary products not elsewhere classified