Rice (a C3 crop) and barnyard grass (Echinochloa crusgalli L.)(a C4 weed) were grown in a 1:1 mixture in a paddy field in ambient condition and with supplemented free air carbon dioxide enrichment (FACE, CO2concentration + 200 μmol mol − 1), in order to evaluate the impact of rising atmospheric carbon dioxide on nutrient competition between rice crop and weed. (judithcurry.com)
On Mars oxygen and fuel are in short supply, but there might be a way to make both from carbon dioxide in the air (newscientist.com)
Plant and Animal Decay - Decomposition of plants and animals releases carbon dioxide back into the air (carbonzero.ca)