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

Alison C Bennett; Stefan K Arndt; Lauren T Bennett; Jürgen Knauer; Jason Beringer; Anne Griebel; Nina Hinko-Najera; Michael J Liddell; Daniel Metzen; Elise Pendall; Richard P Silberstein; Timothy J Wardlaw; William Woodgate; Vanessa Haverd

doi:10.1111/gcb.15760

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

Glob Chang Biol. 2021 Oct;27(19):4727-4744. doi: 10.1111/gcb.15760. Epub 2021 Jul 20.

Authors

Affiliations

¹ School of Ecosystem and Forest Science, University of Melbourne, Richmond, Vic., Australia.
² School of Ecosystem and Forest Science, University of Melbourne, Creswick, Vic., Australia.
³ CSIRO, Oceans and Atmosphere, Canberra, ACT, Australia.
⁴ School of Agriculture and Environment, The University of Western Australia, Crawley, WA, Australia.
⁵ Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, Australia.
⁶ Centre for Tropical Environmental and Sustainability Science and College of Science and Engineering, James Cook University, Cairns, Qld, Australia.
⁷ Centre for Ecosystem Management, School of Science, Edith Cowan University, Joondalup, WA, Australia.
⁸ ARC Centre for Forest Value, University of Tasmania, Hobart, TAS, Australia.
⁹ CSIRO, Land and Water, Canberra, ACT, Australia.
¹⁰ School of Earth and Environmental Sciences, The University of Queensland, St Lucia, Qld, Australia.

PMID: 34165839
DOI: 10.1111/gcb.15760

Abstract

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 15℃ (temperate forest) to 32℃ (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 R² : 0.81; Slope: 1.08) with T_opt exceeding MDTa by >1℃ 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.

Keywords: Eddy covariance; air temperature; broadleaved evergreen tree; climate change; forest; gross primary production; savanna; thermal optima.

MeSH terms

Australia
Carbon Cycle*
Ecosystem*
Forests
Seasons
Temperature