Question

how c4 plants get their co2 on the closing of their stomata​

Answer 1

Most c4 plants open stomata during the day, but are adapted to hot and dry climate by relocating the c3 calvin cycle to the lower O2 cells in the interior of the leaf, while surrounding them with c4 cells that increase CO2. With lower O2 and higher CO2, carbon fixing is favored in the Calvin cycle.