Leaf photosynthesis in the C4-grassMiscanthusxgiganteus, growing in the cool temperate climate of southern England

Previous studies have shown that both photoinhibition and low temperature impairment of leaf development occur in C4 species growing in temperate climates. These result in reductions in the maximum quantum efficiency (φ) and the light-saturated rate of CO2 uptake (Asat). The perennial C4-grass Miscanthus × giganteus has been shown to attain high productivity in northern Europe. This study examines and analyses the seasonal variation in photosynthetic gas exchange of M. × giganteus grown in southern England. Although the crop was exposed to chilling temperatures at the start of the season neither Asat nor φ were impaired, when assessed at a measurement temperature of 24°C. Between May and July the mean values of Asat and φ were 34 μmol m−2 s−1 and 0.067, respectively, declining to 20 μmol m−2, s−1 and 0.045 in October. In the field, on clear days between May and July, the typical midday rates of CO2, uptake ranged between 20–27 μmol m−2 S−1, although in late-June a peak mean value of 35 μmol m−2 s−1 was attained. The study shows that under the cool temperate conditions of southern England, M. × giganteus, unlike all C4 species previously examined, is able to realize the photosynthetic potential of the C4 process without suffering any apparent low temperature impairment, except possibly at the very end of the growing season.