Lolium perenne grasslands may function as a sink for atmospheric carbon dioxide

Model calculations and scenario studies suggest the existence of a consider able positive feedback between temperature and CO2 levels in the atmosphere . Rising temperatures are supposed to increase decomposition of soil organi c C leading to increased production of CO2 and this extra CO2 induces a pos itive feedback by raising the temperature still further. Evidence was found that negative feedback mechanisms also exist: more primary production is a llocated to roots as atmospheric CO2 rises and these roots decompose more s lowly than roots grown at ambient CO2 levels. Experimental data partly obta ined with C-14-techniques were applied in a grassland C model. The model re sults show that at an atmospheric CO2 concentration of 700 mu L L-1 increas ed belowground C storage will be more than sufficient to balance the increa sed decomposition of soil organic C in a ryegrass (Lolium perenne L.) grass land soil. Once a doubling of the present atmospheric CO2 concentration has been reached, C equivalent to 55% of the annual CO2 increase above 1 ha ry egrass can be withdrawn from the atmosphere. This indicates that grassland soils represent a significant sink for rising atmospheric CO2.