But the terrestrial biosphere serves as a 'carbon sponge', absorbing large amounts of carbon dioxide from the atmosphere. Some estimate that this 'carbon sink' can take up as much as two and a half billion tonnes of carbon annually. Even this, however, obscures the true magnitude of carbon cycling between the terrestrial biosphere and the atmosphere. So even a small shift in the balance of carbon cycling in the terrestrial biosphere could have a large impact on climate. Understanding how vegetation responds to changes in climate is critical to future predictions.
Some forests are carbon sinks, others sources.
Plants release carbon dioxide through a respiratory process analogous to that of our own breathing. Microbes decompose dead plants breaking down the carbon-rich matter to carbon dioxide. The second study analysed decomposition. Christian Giardina of the University of Hawaii and Michael Ryan of the US Department of Agriculture Forest Service in Colorado suggest that decomposition processes in forest soils don't depend on temperature. Giardina and Ryan's findings contrast with an earlier suggestion that global warming might increase the release of carbon from soils by speeding up microbial activity.