Effects of long‐term exposure to elevated CO 2 conditions in slow‐growing plants using a 12 C‐enriched CO 2 ‐labelling technique

Despite their relevancy, long‐term studies analyzing elevated CO 2 effect in plant production and carbon (C) management on slow‐growing plants are scarce. A special chamber was designed to perform whole‐plant above‐ground gas‐exchange measurements in two slow‐growing plants ( Chamaerops humilis and Cycas revoluta ) exposed to ambient (ca. 400 µmol mol −1 ) and elevated (ca. 800 µmol mol −1 ) CO 2 conditions over a long‐term period (20 months). The ambient isotopic 13 C/ 12 C composition ( δ 13 C) of plants exposed to elevated CO 2 conditions was modified (from ca. −12.8‰ to ca. −19.2‰) in order to study carbon allocation in leaf, shoot and root tissues. Elevated CO 2 increased plant growth by ca. 45% and 60% in Chamaerops and Cycas , respectively. The whole‐plant above‐ground gas‐exchange determinations revealed that, in the case of Chamaerops , elevated CO 2 decreased the photosynthetic activity (determined on leaf area basis) as a consequence of the limited ability to increase C sink strength. On the other hand, the larger C sink strength (reflected by their larger CO 2 stimulatory effect on dry mass) in Cycas plants exposed to elevated CO 2 enabled the enhancement of their photosynthetic capacity. The δ 13 C values determined in the different plant tissues (leaf, shoot and root) suggest that Cycas plants grown under elevated CO 2 had a larger ability to export the excess leaf C, probably to the main root. The results obtained highlighted the different C management strategies of both plants and offered relevant information about the potential response of two slow‐growing plants under global climate change conditions. Copyright © 2008 John Wiley & Sons, Ltd.