There was once a proposal that "dark respiration" (i.e TCA cycle) was shut
down in the light. Tracer studies
GRAHAM D, DA WALKER 1962 Some effects of light on the interconversion of
metabolites in green leaves. Biochem J 82: 554-560
showed this not to be the case. Naturally an illuminated leaf will fix CO2
from whatever source. Carbon dioxide compensation points (cf C3 with C4) are
relevant to this question.