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The importance of species-specific and temperature-sensitive parameterisation of A / C i models: a case study using cotton ( Gossypium hirsutum L.) and the automated ‘OptiFitACi’ R-package.
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  • Demi Sargent,
  • Jeffrey Amthor,
  • Joseph R. Stinziano,
  • John Evans,
  • Spencer Whitney,
  • Michael P. Bange,
  • David Tissue,
  • Warren C. Conaty,
  • Robert Sharwood
Demi Sargent
Western Sydney University Hawkesbury Institute for the Environment

Corresponding Author:[email protected]

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Jeffrey Amthor
Northern Arizona University Center for Ecosystem Science and Society
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Joseph R. Stinziano
Canadian Food Inspection Agency
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John Evans
Australian National University Research School of Biology
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Spencer Whitney
Australian National University Research School of Biology
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Michael P. Bange
Cotton Seed Distributors Ltd
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David Tissue
Western Sydney University Hawkesbury Institute for the Environment
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Warren C. Conaty
CSIRO Agriculture and Food
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Robert Sharwood
Western Sydney University Hawkesbury Institute for the Environment
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Abstract

Leaf gas exchange measurements provide an important tool for inferring a plant’s photosynthetic biochemistry. In most cases, the responses of photosynthetic CO 2 assimilation to variable intercellular CO 2 concentrations ( A/ Ci response curves) are used to model the maximum rate of carboxylation by ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, V cmax) and the rate of electron transport at a given photosynthetically active radiation (PAR; J PAR). The standard Farquhar-Von Caemmerer-Berry model is typically used with default parameters of Rubisco kinetic values and mesophyll conductance to CO 2 ( g m) derived from tobacco that impairs analytical reliability across species. To study this, here we measured the temperature responses of key in vitro Rubisco catalytic properties and g m in cotton ( Gossypium hirsutum cv. Sicot 71) and derived V cmax and J 2000 ( J at 2000 µmol m -2 s -1 PAR) from cotton A/ Ci curves incrementally measured at 15°C to 40°C using cotton and tobacco parameters with our new automated fitting R package ‘OptiFitACi’. When applied to cotton, the tobacco parameters produced unrealistic J 2000: V cmax ratio of <1 at 25°C, two- to three-fold higher estimates of V cmax, approximately 50% higher estimates of J 2000 and more variable estimates of V cmax and J 2000, compared to model parameterisation with cotton-derived values. We determined that errors arise when using a g m of 0.23 mol m -2 s -1 bar -1 or below and Rubisco CO 2-affinities under ambient O 2 ( K C 21%O2) outside 461 µbar to 627 µbar to model A/ C i responses in cotton. We show how the multi- A/ C i modelling capabilities of ‘OptiFitACi’ serves as a robust, user-friendly extension of ‘plantecophys’ by providing simplified temperature-sensitivity and species-specificity parameterisation capabilities to enable higher accuracy estimates of V cmax and J 2000.
05 Aug 2023Submitted to Plant, Cell & Environment
07 Aug 2023Submission Checks Completed
07 Aug 2023Assigned to Editor
07 Aug 2023Review(s) Completed, Editorial Evaluation Pending
23 Aug 2023Reviewer(s) Assigned
27 Sep 2023Editorial Decision: Revise Minor
10 Nov 20231st Revision Received
14 Nov 2023Submission Checks Completed
14 Nov 2023Assigned to Editor
19 Nov 2023Review(s) Completed, Editorial Evaluation Pending