Open gas exchange system for simultaneous determination of the apparent CO2 assimilation by means of URAS technique and incorporation of 14C into plants

Apparent CO2 assimilation and 14C incorporation into intact plants (Hordeum distichon L., Beta vulgaris L., and Vicia faba L.) were simultaneously measured on the same leaf, using a simple combination of the URAS technique (infrared absorption recorder) and 14CO2 fumigation in an open system. As a result of 14C discrimination during the CO2 incorporation and respiration losses during harvest and post-harvest treatment, the 14C method gave always lower CO2 assimilation values (by 17 to 25%) than the URAS technique. Nevertheless, the results obtained by both methods were closely correlated. Therefore, for quantifying the assimilated CO2 properly and simultaneously tracing the assimilates synthesized from CO2, it is not sufficient to measure solely 14C incorporation, but to combine both techniques. The system presented is qualified to meet these requirements. (author)