05/02/2014

Faster Decomposition Under Increased Atmospheric CO2 Limits Soil Carbon Storage

Summary

Carbon dioxide (CO₂) is released to the atmosphere when humans burn oil, coal, and gasoline, and it is the major cause of global warming. Soils can store carbon, helping to counteract rising CO₂. Carbon accumulates in soil through many years of plant photosynthesis, but also is lost from soil as microscopic organisms, mostly bacteria and fungi, decompose soil carbon, converting it back to CO₂ and releasing it to the atmosphere. The balance of these two processes and the future of the soil carbon sink are uncertain. How much will soil organic carbon persist, and how much will soil microorganisms convert back to CO₂, returning it to the atmosphere? This study compared data gathered from experiments around the world with models of the soil carbon cycle to test how carbon release from soil by microorganisms responds to rising CO₂. The main finding was surprising: increased plant growth caused by rising atmospheric CO₂ was associated with higher rates of CO₂ release from soil. On balance, the findings suggest that if rising CO₂ enhances carbon storage in soil at all, the effect will be small. These results indicate that soil carbon may not be as stable as previously thought, and that soil microorganisms exert more direct control on long-term carbon accumulation than currently represented in global models.

References

Van Groenign, K. J., X. Qi, C. W. Osenberg, Y. Luo, and B. A. 2014. “Faster Decomposition Under Increased Atmospheric CO₂ Limits Soil Carbon Storage,” Science 344(6183), 508-509. DOI:10.1126/science.1249534.