Carbon dioxide
The air component in soil provides plants with the carbon dioxide needed for photosynthesis.
Photosynthesis is the process by which plants and other autotrophs use light energy from sun to produce nutrients from carbon dioxide and water. Air component in soil mostly contains carbon dioxide, nitrogen, and oxygen. Plants absorb carbon dioxide from the air component in soil which it uses for photosynthesis and for its growth. Most of the substances that plant utilizes to develop new leaves, roots, and stems, are composed mainly of carbon.