Proc. R. Soc. B doi:10.1098/rspb.2007.1012 (2007)

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According to a new study, the amount of carbon stored in plant roots could be almost 70% greater than previously thought.

David Robinson of the University of Aberdeen in the UK used a theoretical model combined with realistic measurements of root to shoot mass ratios to explore the implications of a revised global root carbon pool on estimates of global carbon sources and sinks. These are assessed using two methods: the global carbon flux, based on changes in atmospheric carbon dioxide, and the inventory method, based on land-use changes. The study predicted a pool of at least 268 petagrams (1 Pg = 1 gigatonne), compared with previous estimates of about 160 Pg. On this basis, the land-based carbon sink is estimated at 2.7 Pg per year — 0.1 Pg per year greater than current estimates, suggesting it is stronger than previously recognized.

Alternatively, a larger root pool within existing global carbon budgets could mean that stocks of soil carbon are smaller than is thought and are depleting globally by up to 0.7% per year, possibly because of land-use change or climate change. This uncertainty highlights the urgent need to better understand the global carbon cycle to predict how it will respond to climate change.