Are the tentative proxy traits themselves affected by
CO2 level?
Linear correlations for the three tentative proxy traits measured under
elevated vs. ambient CO2 levels were similar among the
traits (Fig. 6A). Overall across the 17 genotypes, the slope was near 1,
indicating the absence of a generic effect. However, with R² values
between 0.5 and 0.6, there was considerable scatter, and the SEM error
bars indicated that for some genotypes, there was an effect of
CO2 level on the proxy trait value.
In fact, there generally was a clear negative trend (in some cases
significant at P<0.05) in the relationship between the
plasticity of the proxy traits (expressed as the difference between
elevated and ambient CO2 levels) vs. the Amax or
grain yield ratio observed between the CO2 levels (Fig.
S1, supplemental materials). Consequently, those genotypes that had a
reduced proxy trait value under e-CO2 due to phenotypic
plasticity showed a smaller Amax or yield gain under
e-CO2.
Correlations across genotypes of the other measured variables under
elevated vs. ambient CO2 levels are shown in Fig. S2
(supplemental materials).