- Carbon fixation is a fundamental biological process by which inorganic carbon (typically in the form of carbon dioxide, CO₂) is converted into organic compounds, primarily by autotrophic organisms such as plants, algae, and certain bacteria. This transformation lies at the heart of the carbon cycle, serving as the primary mechanism through which carbon enters the biosphere and supports life on Earth.
- The fixed carbon becomes part of essential biomolecules like glucose, starches, proteins, and lipids, forming the energetic and structural foundation of virtually all ecosystems.
- The most well-known and widespread pathway of carbon fixation is the Calvin-Benson cycle, which occurs in the chloroplasts of plants and algae during photosynthesis. In this cycle, the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) captures atmospheric CO₂ and incorporates it into a five-carbon compound, ribulose bisphosphate (RuBP), ultimately producing glyceraldehyde-3-phosphate (G3P), a simple sugar that can be used to build more complex carbohydrates. The energy and reducing power needed for this reaction are supplied by ATP and NADPH, which are generated during the light-dependent reactions of photosynthesis.
- In addition to the Calvin cycle, there are other carbon fixation pathways used by certain microorganisms. These include the reverse Krebs cycle, the 3-hydroxypropionate cycle, and the reductive acetyl-CoA pathway—each adapted to specific environmental niches, such as hydrothermal vents or anaerobic conditions. These alternative pathways are especially important in chemoautotrophic bacteria and archaea, which do not rely on sunlight but instead derive energy from chemical reactions to fix carbon.
- Carbon fixation is not only crucial for individual organisms but also has profound implications for global climate regulation. By removing CO₂ from the atmosphere, autotrophs act as carbon sinks, mitigating the accumulation of greenhouse gases and helping to stabilize Earth’s climate. Forests, grasslands, oceans (via phytoplankton), and wetlands are all major sites of carbon fixation and carbon sequestration. The balance between carbon fixation and carbon release (through respiration, decomposition, and combustion) determines the net flow of carbon in the environment.
- However, human activities—especially the burning of fossil fuels and deforestation—have significantly disrupted this balance, leading to increased atmospheric CO₂ concentrations and contributing to climate change. Enhancing natural carbon fixation through practices such as reforestation, regenerative agriculture, or even artificial photosynthesis has become a key focus in efforts to reduce carbon footprints and restore ecological equilibrium.
