Environmental Factors Affecting the Loss of Carbon from the Roots of Wheat and Barley Seedlings

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Abstract
The amounts of carbon released into soil from roots of wheat and barley seedlings grown under three environmental conditions for 3 weeks with shoots in constant specific activity 14CO2 are reported. This carbon loss was measured as respired 14CO2 from both the root and the accompanying microbial population and as root derived 14C-labelled organic C compounds in the soil. With a 16 h photoperiod, growth at 15 °C constant or 18 °C day/14 °C night gave a loss of 33–40% of the total net fixed carbon (defined as 14C retained in the plant plus 14C lost from the root). The proportion of 14C translocated to the roots that was released into the soil did not change with temperature, so carbon distribution within the plant must have changed. With a 12 h photoperiod and a temperature regime of 18 °C/14 °C carbon loss from the roots was decreased to 17–25% of the total fixed carbon.