Photosynthesis in C4 plants is relatively less limited by atmospheric CO2 levels because
(1) there is effective pumping of CO2 into bundle sheath cells
(2) RuBisCO in C4 plants has higher affinity for CO2
(3) six carbon acids are the primary initial CO2 fixation products
(4) the primary fixation of CO2 is mediated via PEP carboxylase.