Plants of Solanum curtilobum (from high altitude) and Solanum tuberosum (from low altitude) were grown in open-top chambers in a greenhouse at either ambient (AC, 360 µmol mol-1) or ca. twice ambient (EC, 720 µmol mol-1) CO2 concentrations for 30 d. CO2 treatments started at the reproductive stage of the plants. There were similar patterns in the physiological response to CO2 enrichment in the two species. Stomatal conductance was reduced by 59 % in S. tuberosum and by 55 % in S. curtilobum, but such a reduction did not limit the net photosynthetic rate (PN), which was increased by approximately 56 % in S. curtilobum and 53 % in S. tuberosum. The transpiration rate was reduced by 16 % in both potato species while instantaneous transpiration efficiency increased by 80 % in S. tuberosum and 90 % in S. curtilobum. Plants grown under EC showed 36 and 66 % increment in total dry biomass, whereas yields (dry mass of tubers) were increased by 40 and 85 % in S. tuberosum and S. curtilobum, respectively. EC promoted productivity by increasing PN. Thus S. tuberosum, cultivated around the world at low altitudes, and S. curtilobum, endemic of the highland Andes, respond positively to EC during the tuberisation stage. and N. Olivo, C. A. Martinez, M. A. Oliva.
Clusia is a widely distributed neotropical genus with 321 currently described species. This remarkable genus is the only one known to contain trees sensu stricto with CAM photosynthesis. To survey the occurrence of CAM in Clusia species from Colombia, we determined the leaf stable carbon isotope composition (δ13C) of 568 specimens from 114 species deposited in 12 Colombian herbaria. In the vast majority of specimens, δ13C values indicated that C3 photosynthesis was the principal contributor to carbon gain. δ13C values typical of strong CAM (less negative than -20‰) were observed in only five species, in four of them for the first time. All samples with CAM-type isotopic signatures were collected below 1,000 m a.s.l., whereas species with predominantly C3 occurred from sea level to 3,500 m a.s.l. Together with information already available in the literature, we conclude that CAM is present in 22% (35/156) of the species of Clusia investigated thus far.