Can miscanthus C4 photosynthesis compete with festulolium C3 photosynthesis in a temperate climate?

Miscanthus, a perennial grass with C4 photosynthesis, is regarded as a promising energy crop due to its high biomass productivity. Compared with other C4 species, most miscanthus genotypes have high cold tolerances at 14ºC. However, in temperate climates, temperatures below 14ºC are common and our aim was to elucidate cold tolerances of different miscanthus genotypes and compare with a C3 perennial grass - festulolium. Eleven genotypes of M. sacchariflorus, M. sinensis, M. tinctorius, M. x giganteus as well as festulolium were grown under warm (24/20ºC, day/night) and three under cold (14/10ºC, 10/8ºC and 6/4ºC) conditions in a controlled environment. Measurements of photosynthetic light response curves, operating quantum yield of photosystem II (ΦPSII), net photosynthetic rate at a PAR of 1000 lmol m-2 s-1 (A1000) and dark-adapted chlorophyll fluorescence (Fv/Fm) were made at each temperature. In addition, temperature response curves were measured after the plants had been grown at 6/4ºC. The results showed that two tetraploid M. sacchariflorus and the standard triploid M. x giganteus cv. Hornum retained a significantly higher photosynthetic capacity than other miscanthus genotypes at each temperature level and still maintained photosynthesis after growing for a longer period at 6/4ºC. Only two of five measured miscanthus genotypes increased photosynthesis immediately after the temperature was raised again. The photosynthetic capacity of festulolium was significantly higher at 10/8ºC and 6/4ºC than of miscanthus genotypes. This indicates that festulolium may be more productive than the currently investigated miscanthus genotypes in cool, maritime climates. Within miscanthus, only one M. sacchariflorus genotype exhibited the same photosynthetic capacity as Hornum at both cold conditions and when the temperature was raised again. Therefore, this genotype could be useful for breeding new varieties with an improved cold tolerance vis-a-vis Hornum, and be valuable in broadening the genetic diversity of miscanthus for more widespread cultivation in temperate climates