Effect of a switch from elevated to ambient CO2 on growth and carbohydrate allocation of Plantago major ssp. pleiosperma.

Transfer of plants of Plantago major ssp. pleiosperma (L.) Pilger to elevated CO2 (700 mul l(-1)) showed a transient stimulation of the relative growth rate (RGR). Thereafter the RGR of the plants grown at elevated CO2 was the same as for plants grown at ambient CO2 (350 mul l(-1)). At that time starch level in the leaves of plants grown at elevated CO2 was still higher, and the RGR of the developing secondary shoots was still stimulated. In order to obtain more insight into the effect of elevated CO2 on the partitioning of photosynthetic carbohydrates between storage and growth, elevated CO2-grown plants were switched to ambient CO2, when the RGR was no longer stimulated. A growth analysis of the whole plant and of the secondary shoots was conducted, together with determinations of soluble sugar and starch levels in shoot and root. The increase in total fresh weight (TFW) and of the fresh weight of the secondary shoots (FWsec) of the switched plants was equal to that of the plants which were grown at elevated CO2 continuously during the first days after the switch. Two days after the switch of the elevated CO2-grown plants to ambient CO2, shoot starch level had decreased to that of plants grown at ambient CO2 continuously. We conclude that the storage non-structural carbohydrates, present in the elevated CO2-grown plants, can be used for growth upon a switch to ambient CO2.