Photosynthesis, immediate export and carbon partitioning in source leaves of C3, C3‐C4 intermediate, and C4Panicum and Flaveria species at ambient and elevated CO2 levels
Immediate export in leaves of C 3 -C 4 intermediates were compared with their C 3 and C 4 relatives within the Panicum and Flaveria genera. At 35 Pa CO 2 , photosynthesis and export were highest in C 4 species in each genera. Within the Panicum, photosynthesis and export in type I' C 3 -C 4 intermediates were greater than those in C 3 species. However, type I' C 3 -C 4 intermediates exported a similar proportion of newly fixed 14 C as did C 4 species. Within the Flaveria, type II' C 3 -C 4 intermediate species had the lowest export rather than the C 3 species. At ambient CO 2 , immediate export was strongly correlated with photosynthesis. However, at 90 Pa CO 2 , when photosynthesis and immediate export increased in all C 3 and C 3 -C 4 intermediate species, proportionally less C was exported in all photosynthetic types than that at ambient CO 2 , All species accumulated starch and sugars at both CO 2 levels. There was no correlation between immediate export and the pattern of 14 C-labelling into sugars and starch among the photosynthetic types within each genus. However, during CO 2 enrichment, C 4 Panicum species accumulated sugars above the level of sugars and starch normally made at ambient CO 2 , whereas the C 4 Flaveria species accumulated only additional starch.