CARBON STORAGE BY INTRODUCED DEEP-ROOTED GRASSES IN THE SOUTH-AMERICAN SAVANNAS

ESTIMATES of the global carbon dioxide balance have identified a subst antial 'missing sink' of 0.4-4.3 Gt per year(1). It has been suggested that much of this may reside in the terrestrial biosphere(2). Here we present an analysis of the carbon stored by pastures based on deep-ro oted grasses which have been introduced in the South American savannas . Although the deep-rooted grasses were chosen principally for agricul tural reasons(3), we find that they also sequester significant amounts of organic carbon deep in the soil. If our study sites are representa tive of similar pastures throughout South America, this process could account for the sequestration of 100-507 Mt carbon per year-a substant ial part of the 'missing sink'. Thus, although some land-use changes(4 ) (such as burning tropical rainforests) contribute to the atmospheric CO2 burden, we conclude that the introduced pastures studied here hel p to offset the effect of anthropogenic CO2 emissions.