This is a view through the undergrowth in tropical forest at the study site in Panama. Credit: Dr. Emma Sayer
A new study shows that as climate change enhances tree growth in tropical forests, the resulting increase in litterfall could stimulate soil micro-organisms leading to a release of stored soil carbon.
The researchers used results from a six-year experiment in a rainforest at the Smithsonian Tropical Research Institute in Panama, Central America, to study how increases in litterfall - dead plant material such as leaves, bark and twigs which fall to the ground - might affect carbon storage in the soil. Their results show that extra litterfall triggers an effect called 'priming' where fresh carbon from plant litter provides much-needed energy to micro-organisms, which then stimulates the decomposition of carbon stored in the soil.
Lead author Dr Emma Sayer from the UK's Centre for Ecology & Hydrology said, "Most estimates of the carbon sequestration capacity of tropical forests are based on measurements of tree growth. Our study demonstrates that interactions between plants and soil can have a massive impact on carbon cycling. Models ofclimate change must take these feedbacks into account to predict future atmospheric carbon dioxide levels."
This is leaf litter around the buttress roots of a tropical tree at the study site in Panama. Credit: Dr. Emma Sayer
Tropical forests play an essential role in regulating the global carbon balance. Human activities have caused carbon dioxide levels to rise but it was thought that trees would respond to this by increasing their growth and taking up larger amounts of carbon. However, enhanced tree growth leads to more dead plant matter, especially leaf litter, returning to the forest floor and it is unclear what effect this has on the carbon cycle.
Measuring CO2 efflux from the soil in subplots where the forest floor has been replaced with litter with a distinct isotopic signature. A wire mesh tent excludes forest litter from the subplots. Credit: Dr. Emma Sayer
Co-author Dr Edmund Tanner, from the University of Cambridge, said, "This priming effect essentially means that older, relatively stable soil carbon is being replaced by fresh carbon from dead plant matter, which is easily decomposed. We still don't know what consequences this will have for carbon cycling in the long term."
More information: ‘Soil carbon release enhanced by increased tropical forest litterfall’ will be published online in the journal Nature Climate Change on 14 August 2011. DOI: 10.1038/nclimate1190
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