Whole-plant CO2 exchange, carbon partitioning and growth in Quercus robur seedlings exposed to elevated CO2

Abstract

Pedunculate oak acorns (Quercus robur L.) were germinated and grown under nonlimiting nutritional and water conditions in controlled-environment greenhouses with ambient (350 μmol mol −1 ) or elevated (700 μmol mol −1 ) CO 2 concentrations. A semi closed gas exchange measurements, and 13 CO 2 labelling, system (1.5% 13 CO 2 ) was used to simultaneously assess (a) the CO 2 exchange of both aerial and below-ground (roots plus soil) compartments of the soil-plant system and (b) the partitioning of the recently photo-assimilated carbon. Measurements were made during the fast aerial prowth phase (July 30) and at the end of the growing season (October 15). On July 30, whole-plant dry mass had been increased by 44% since the beginning of the growing season in the elevated CO 2 treatment, whereas at the end of the growing season the enhancing was only 17%. Elevated CO 2 stimulated net CO 2 assimilation rate per unit leaf area (A) in July (+ 40%), whereas in October this stimulation had disappeared. The respiratory CO 2 evolution of the root-soil compartment (individual plant basis) was stimulated 35% under the elevated CO 2 conditions on July 30, but not on October 15. In July, relative specific allocation (RSA), a parameter expressing the sink strength, was higher in all compartments under 700 μmol mol −1 compared to 350 μmol mol −1 . Moreover in root tips, the RSA values determined 4 h after the labelling were particularly high (7.8%) with elevated CO 2 , whereas under ambient CO 2 RSA values were close to zero