Fig. 3.

Leaf ¹³CO₂ net discrimination and discrimination fractions in the light, and ¹³CO₂ photorespiratory fractionation for gdch-KD versus WT plants determined based on Evans and von Caemmerer (2013). (A) Observed leaf net ¹³CO₂ discrimination in the light (Δ_o), and modeled ¹³C discrimination fractions for gdch-KD (n=3) and the WT (n=4) at an atmospheric pO₂ of 18.4 kPa. Δ_i is the additive ¹³CO₂ discrimination during CO₂ diffusion from atmosphere to intercellular air space and due to carboxylation; Δ_i−Δ_o is comprised of three terms: Δ_gm, which is the ¹³CO₂ fractionation fraction during CO₂ diffusion in the liquid phase to chloroplast stroma, and Δ_e and Δ_f, which are the ¹³C fractionation fractions associated with light mitochondrial non-photorespiratory respiration and photorespiration, respectively. Δ_f was calculated as Δ_f=Δ_i−Δ_o−Δ_gm−Δ_e. Values are mean ±SE. (B) ¹³CO₂ fractionation for photorespiration (f) in gdch-KD plants calculated at an atmospheric pO₂ of 18.4 kPa from ${\mathrm{\Delta }}_{\mathrm{f}}=\frac{1+t}{1-t}\left(f\frac{{\mathrm{\Gamma }}^{\ast }}{C_{\mathrm{a}}}\right)$ versus f of 16.2‰ in the WT. Values for gdch-KD plants are the mean ±SE (n=3). Significance (P<0.05) of the effect of plant type on the variables in (A) was evaluated by SAS PROC MIXED as a one-way ANOVA; * for 0.01<P<0.05; ** for P<0.01. Significance in (B) was evaluated by one-sample t-test (P<0.05). ** for P<0.01.