EFFECT OF ELEVATED ATMOSPHERIC CO2 CONCENTRATION ON C-PARTITIONING AND RHIZOSPHERE C-FLOW FOR 3 PLANT-SPECIES

The effects of elevated atmospheric CO2- concentration on the partitio ning of dry matter and recent assimilate was investigated for three pl ant species (rye grass, wheat and Bermuda grass). This was evaluated i n plant-soil microcosm systems maintained at specific growth condition s, under two CO2 regimes (450 and 720 mu mol mol(-1)). The distributio n of recent assimilate between plant, microbial and soil pools was det ermined by (CO2)-C-14 pulse chase, for each plant species at both CO2 concentrations. Growth of rye grass and wheat (both C-3) was Ca. doubl ed al the higher CO2 concentration. Dry matter partitioning was also s ignificantly affected, with an increased root-to-shoot ratio for heat (0.72-1.03), and a decreased root-to-shoot ratio for rye grass (0.68-0 .47) at elevated CO2. For Bermuda grass (C-4), growth and partitioning of dry matter and C-14 were not affected by CO2 concentration. C-14-a llocation to the rhizospheres of rye-grass and wheat was found to be i ncreased by 62 and 19%, respectively, at the higher CO2 concentration. The partitioning of C-14 within the rhizospheres of the two C-3 speci es was also found to be affected by CO2 concentralion. At the higher C O2 concentration. proportionately less C-14 was present in the microbi al fraction, relative to that in the soil. This indicates altered micr obial utilisation of root-released compounds at the higher CO2 concent ration, which may be a consequence of altered quantity or quality of r hizodeposits derived from recent assimilate.