Effects of long‐term exposure to elevated CO2 conditions in slow‐growing plants using a 12C‐enriched CO2‐labelling technique

Despite their relevancy, long-term studies analyzing elevated CO2 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 (Chamaeropshumilis and Cycasrevoluta) exposed to ambient (ca. 400 µmol mol−1) and elevated (ca. 800 µmol mol−1) CO2 conditions over a long-term period (20 months). The ambient isotopic 13C/12C composition (δ13C) of plants exposed to elevated CO2 conditions was modified (from ca. −12.8‰ to ca. −19.2‰) in order to study carbon allocation in leaf, shoot and root tissues. Elevated CO2 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 CO2 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 CO2 stimulatory effect on dry mass) in Cycas plants exposed to elevated CO2 enabled the enhancement of their photosynthetic capacity. The δ13C values determined in the different plant tissues (leaf, shoot and root) suggest that Cycas plants grown under elevated CO2 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.