Leaf photosynthesis in the C-4-grass Miscanthus x giganteus, 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 C-4 species growing in temperate climates, These result in reductions in the maximum quantum efficiency (phi) and the light-saturated rate of CO2 uptake (A(sat)). The perennial C-4-grass Miscanthus x 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, x giganteus grown in southern England. Although the crop was exposed to chilling temperatures at the start of the season neither A(sat) nor phi were impaired, when assessed at a measurement temperature of 24 degrees C. Between May and July the mean values of A(sat) and phi were 34 mu mol m(-2) s(-1) and 0.067, respectively, declining to 20 mu mol 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 mu mol m(-2) S-1, although in late-June a peak mean value of 35 mu mol m(-2) s(-1) was attained, The study shows that under the cool temperate conditions of southern England, M. x giganteus, unlike all C-4 species previously examined, is able to realize the photosynthetic potential of the C-4 process without suffering any apparent low temperature impairment, except possibly at the very end of the growing season.