Temperature response of bundle-sheath conductance in maize leaves

Highlight Bundle-sheath conductance, g bs , is commonly assumed to be independent of temperature. We report that temperature response of maize g bs followed a peaked or non-peaked Arrhenius equation, triggering further investigations on this response.

14 The O 2 partial pressure in eqn (A4), O c , is described as where O m is the mesophyll O 2 partial pressure (which we set here the same as O i , the 17 intercellular air-space O 2 partial pressure). The variable u oc in eqn (A5) represents the 18 coefficient that lumps diffusivities and solubilities of CO 2 and O 2 in water (von Caemmerer & 19 Furbank 1999), and its possible dependence on temperature is quantified in Appendix B.

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In the context of the modified model, eqn (1) in the main text, V p is described by: The analytical solutions for individual terms of eqn (1) where V p is given by xJ atp /2. In this solution, x 1 , x 2 and x 3 are defined according to the text 6 below eqn (A4), depending on whether the rate of the C 3 cycle is limited by the Rubisco 7 activity or by etransport.
where d, f and k are expressed as In this solution, x 1 , x 2 and x 3 are defined according to the text below eqn (A4), depending on 26 whether the rate of the C 3 cycle is limited by Rubisco activity or by etransport.

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Three roots for the above cubic equation are: We found the root A 1 suitable for calculating either A EE or A ET under any combinations of C i , 6 I inc and O i . The coefficient u oc in eqn (A5) in Appendix A actually lumps: where D O2 and D CO2 are the diffusivities for O 2 and CO 2 in water, respectively, and S O2 and 6 S CO2 are their respective solubilities in water. u oc at 25°C is 0. where the universal gas constant R = 0.008314 kJ K -1 mol -1 . The data provided at the same 14 website also allows quantifying the decrease of S O2 with increasing temperature:

Supplementary appendix C. Model and data for describing PEPc limited rates of photosynthesis within the initial section of A-C i curves
The photosynthetic rate in the initial part of an A-C i curve can be approximated by (von Caemmerer & Furbank 1999): where C m is the level of CO 2 in the mesophyll cells. Because g bs is low (0.0009 to 0.0065 mol m -2 s -1 in our cases, Fig. 6) and the CO 2 levels for the initial part of an A-C i curve are also low ( Fig. S1), the last term of the above equation is negligible.
The difference in C m from C i is described by: C m = C i -A/g m (see Eqn A3). Combining this equation with Eqn (C1) yields a model: The advantage of this model, eqn (C2), compared with the one described in the main text dA/dC i = K p V pmax /(C i +K p ) 2 , is that it does not assume that g m is infinite and the initial part of the A-C i curves is strictly linear. Its disadvantage is that g m has to be assumed beforehand.  Table S1.