Research Highlights

Nature Reports Climate Change
Published online: 4 February 2008 | doi:10.1038/climate.2008.10

The root problem

Anna Barnett

Science doi:10.1126/science.1151382 (2008)

SETH PRITCHARD

The amount of carbon naturally sequestered underground by the delicate roots of plants remains hugely uncertain, suggests a new study. This casts doubt on predictions of how much the soil carbon sink can buffer carbon dioxide emissions and mitigate future warming.

Images from miniature underground cameras have shown that tiny roots die and are replaced within one year, suggesting that they may rapidly transfer atmospheric carbon to the soil. In contrast, experiments measuring the rate at which certain carbon isotopes are incorporated into new roots have indicated that the roots persist for over four years. Seth Pritchard of the College of Charleston, South Carolina, and co-workers tested possible explanations for the discrepancy, comparing images they captured from forest plots to previously published isotope data from the same plots. They found that, in general, short-term imaging studies overestimated root growth, whereas isotopic data — now used in some global climate models — substantially underestimated it.

Reinterpreting isotopic results from past studies could increase the expected size of the soil carbon sink, suggest the authors, though this also depends heavily on hard-to-predict carbon cycling by soil microbes. The potential for soil carbon storage to mitigate the greenhouse effect is therefore still unclear, they say.