What is the amount of carbon dioxide which is fixed in the biosphere through photosynthesis annually ?

4 x 10¹³ kg

Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. According to one estimate 4 × 10¹³ kg of carbon is fixed annually in the biosphere through photosynthesis.

A considerable amount of carbon returns to the atmosphere as CO₂ through respiratory activities of the producers and consumers.

Decomposers also contribute substantially to CO₂ pool by their processing of waste materials and dead organic matter of land or oceans.