Table S2.

Summary of plant material, growth conditions, CO₂ treatments, and measured D6^S/D6^R values for greenhouse and growth chamber experiments

Group	Species	Growth conditions, duration of CO2 treatment	Sugar analyzed	Samples	CO2 treatment, ppm	D6S/D6R
						Low CO2	High CO2	Difference	ANOVA P
A	sunflower	greenhouse, 2 d	leaf starch	a	180/280/450/700/1,500	see Table S1	see Table S1	see Table S1	—
B	sunflower	growth chamber, from germination	leaf structural carbohydrates	b	200 and 1,000	1.043 ± 0.018	0.862	0.0181	—
C	maize*	greenhouse, 2 d	leaf starch	c	450 and 1,200	1.269 ± 0.013	1.270 ± 0.001	−0.001	0.966
D	spinach	growth chamber, from germination	leaf starch	d	360 and 700	0.950 ± 0.007	0.865 ± 0.005	0.085	<0.001†
			leaf soluble sugars	e	360 and 700	0.968 ± 0.014	0.877 ± 0.015	0.091	0.007
			leaf soluble sugars	f	360‡		0.849	0.101‡	—
E	bean	growth chamber, from germination	leaf starch	g	360 and 700	1.032 ± 0.006	0.923 ± 0.007	0.109	<0.001†
			leaf soluble sugars	h	360 and 700	1.004 ± 0.022	0.906 ± 0.017	0.098	0.024
			seed starch	i	360 and 700	0.920 ± 0.013	0.868 ± 0.011	0.052	0.037

^*Plants with C₃, C₄, and crassulacean acid metabolism (CAM) show distinct overall D isotopomer patterns, and high D6^S/D6^R values are characteristic of C4 metabolism (28). Importantly, the D6^S/D6^R ratio of the maize metabolite is independent of [CO₂].

^†Two-way ANOVA with species (spinach or bean) and CO₂ treatment as variables shows that D6^S/D6^R ratios differ between species (P = 10⁻⁹) and depend on [CO₂] (P = 10⁻⁷), with no interaction between the variables (P = 0.14), indicating that although D6^S/D6^R values are species-dependent, their shifts as function of [CO₂] are conserved among species. Such variation may reflect species-dependent D fractionation connected to the regulation of carbon metabolism.

^‡Twelve percent O₂ and difference is taken relative to 360-ppm treatment, sample e.