Low-temperature leaf photosynthesis of a Miscanthus germplasm collection correlates positively to shoot growth rate and specific leaf area

Background and Aims The C-4 perennial grass miscanthus has been found to be less sensitive to cold than most other C-4 species, but still emerges later in spring than C-3 species. Genotypic differences in miscanthus were investigated to identify genotypes with a high cold tolerance at low temperatures and quick recovery upon rising temperatures to enable them to exploit the early growing season in maritime cold climates. Suitable methods for field screening of cold tolerance in miscanthus were also identified. Methods Fourteen genotypes of M. sacchariflorus, M. sinensis, M. tinctorius and M. x giganteus were selected and grown under warm (24 A degrees C) and cold (14 A degrees C) conditions in a controlled environment. Dark-adapted chlorophyll fluorescence, specific leaf area (SLA) and net photosynthetic rate at a photosynthetically active radiation (PAR) of 1000 mu mol m(-2) s(-1) (A(1000)) were measured. Photosynthetic light and CO2 response curves were obtained from 11 of the genotypes, and shoot growth rate was measured under field conditions. Key Results A positive linear relationship was found between SLA and light-saturated photosynthesis (A(sat)) across genotypes, and also between shoot growth rate under cool field conditions and A(1000) at 14 A degrees C in a climate chamber. When lowering the temperature from 24 to 14 A degrees C, one M. sacchariflorus exhibited significantly higher A(sat) and maximum photosynthetic rate in the CO2 response curve (V-max) than other genotypes at 14 A degrees C, except M. x giganteus 'Hornum'. Several genotypes returned to their pre-chilling A(1000) values when the temperature was increased to 24 A degrees C after 24 d growth at 14 A degrees C. Conclusions One M. sacchariflorus genotype had similar or higher photosynthetic capacity than M. x giganteus, and may be used for cultivation together with M. x giganteus or for breeding new interspecies hybrids with improved traits for temperate climates. Two easily measured variables, SLA and shoot growth rate, may be useful for genotype screening of productivity and cold tolerance.