The influence of elevated carbon dioxide concentrations on the partitioning of carbon in source leaves of Phaseolus vulgaris

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Abstract
Plants may alter their growth pattern in response to being grown in elevated CO2 concentrations. The nature of the change in carbon partitioning underlying those alterations was investigated in Phaseolus vulgaris cv. Gold Crop grown to the third trifoliate leaf stage in CO2 concentrations of 380, 800, and 1400 ppm. There was no effect of the CO2 concentration on plant height, leaf area, or dry weight, but the specific leaf weight increased significnatly as teh CO2 level increased. A primary leaf was pulse labelled with 14CO2 and the depletion of label from that source leaf was monitored with a GM tube. The depletion of the count rate with time was described by a nonlinear curve fitting procedure that allowed the derivation of rate constants to describe the partitioning of carbon in a two-compartment model. Rates of carbon storage decreased in th elight with increasing CO2 concentrations with no effect on the rates of export or remobilization. Both export and storage were reduced in the dark at all CO2 levels, with an increase in the residence time of carbon in the export pool. Reducing the CO2 concentration around the source leaf just after labelling did not change carbon partitioning compared to controls. Increasing the CO2 concentration around the source leaf just after labelling increased all carbon flux rates and reduced the residence times in the leaf pools.