Effect of elevated CO 2 on the carbon balance of a grass-clover mixture

Abstract

Experiments were carried out to investigate the effect of elevated CO 2 (780 μmol mol −1) on the C-balance and carbon release from the roots of a mixture of Dactylis glomerata and Trifolium pratense. The plants were grown for 67 days in a growth chamber with controlled watering and fertilisation, with an intermediate harvest after 41 days. Elevated CO 2 increased total net uptake of carbon (C) by about 30% by the end of regrowth. Total net C-uptake and the amount of C recovered in the second harvest were balanced at both CO 2 concentrations, and the root: shoot ratio was not affected by elevated CO 2. 13C-allocation to roots, and 13C released into the root environment were measured following pulse-labelling with was 1.6% and 13C released from roots was only 0.4%. No significant difference in these proportions was observed at elevated CO 2, but in absolute terms, plants grown at elevated CO 2 released more 13C from the roots.