How do ecosystems gain most of the carbon?

Ecosystems primarily gain carbon through the process of photosynthesis, where plants, algae, and certain bacteria convert carbon dioxide from the atmosphere into organic matter using sunlight. This carbon is then transferred through the food web as organisms consume plants and each other. Additionally, carbon can be deposited in soils and sediments, contributing to long-term carbon storage. Overall, photosynthesis is the key mechanism through which ecosystems capture and store carbon.