THE EFFECTS OF ELEVATED CO2 CONCENTRATIONS ON THE ROOT-GROWTH OF LOLIUM-PERENNE AND TRIFOLIUM-REPENS GROWN IN A FACE SYSTEM

Lolium perenne and Trifolium repens were grown in a Free Air CO2 Enric hment (FACE) system at elevated (600 mu mol mol(-1)) and ambient (340 mu mol mol(-1)) carbon dioxide concentrations during a whole growing s eason. Using a root ingrowth bag technique the extent to which CO2 enr ichment influenced the growth of L. perenne and T. repens roots under two contrasting nutrient regimes was examined. Root ingrowth bags were inserted for a fixed time into the soil in order to trap roots. It wa s also possible to follow the mortality of roots in bags inserted for different time intervals. Root ingrowth of both L. perenne and T. repe ns increased under elevated CO2 conditions. In L. perenne, root ingrow th decreased with increasing nutrient fertilizer level, but for T. rep ens the root ingrowth was not affected by the nutrient application rat e. Besides biomass measurements, root length estimates were made for T . repens. These showed an increase under elevated CO2 concentrations. Root decomposition appeared to decrease under elevated CO2 concentrati ons. A possible explanation for this effect is the observed changes in tissue composition, such as the increase in the carbon:nitrogen ratio in roots of L. perenne at elevated CO2 concentrations.