Generalised dose-response curves are essential to understand how plants acclimate to atmospheric CO 2 . We carried out a meta-analysis of 630 experiments in which C 3 plants were experimentally grown at different [CO 2 ] under relatively benign conditions, and derived dose-response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200-1200 µmol mol À1 CO 2 , some traits more than doubled (e.g. areabased photosynthesis; intrinsic water-use efficiency), whereas others more than halved (area-based transpiration). At current atmospheric [CO 2 ], 64% of the total stimulation in biomass over the 200-1200 µmol mol À1 range has already been realised. We also mapped the trait responses of plants to [CO 2 ] against those we have quantified before for light intensity. For most traits, CO 2 and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO 2 ], and some traits (such as area-based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO 2 ] at different integration levels and offers the quantitative dose-response curves that can be used to improve global change simulation models.

Parameters of Crassulacean Acid Metabolism (carbon isotope composition [δ13C values], diurnal acid cycles) were studied together with properties of phosphoenolpyruvate carboxylases (PEP‐C) in eight species of the genus Sedum. The δ13C values indicate a considerable variability of CAM capacity among the species investigated. The spectra of organic acids were similar in all species. Malate, citrate, and isocitrate were the main components of the acid fraction. Quinic acid occurred only during the light period. Molecular weights of PEP‐C were in the range of 160,000 and showed no correlation to CAM as indicated by the δ13C values. However, there were differences in the kinetic data of PEP‐C. Sedum species with less negative δ13C (i.e. with high CAM capacity) have PEP‐C with higher Vmax, higher Km (PEP) and higher sensitivity for malate inhibition.

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