Effect of CO₂Concentration on Growth, Carbon Distribution and Loss of Carbon from the Roots of Maize

The effects of three ranges of CO2 concentration on growth, carbon distribution and loss of carbon from the roots of maize grown for 14 d and 28 d with shoots in constant specific activity 14CO2 are described. Increasing concentrations of CO2 led to enhancement of plant growth with the relative growth rate (RGR) of the roots affected more than the RGR of the shoots. Between 16% and 21% of total net fixed carbon (defined as 14C retained in the plant plus 14C lost from the root) was lost from the roots at all CO2 concentrations at all times but the amounts of carbon lost per unit weight of plant decreased with time. Possible mechanisms to account for these observations are discussed.