Can perennial C₄ grasses attain high efficiencies of radiant energy conversion in cool climates?

Although C₄ plants are considered to have higher conversion efficiency and productivity than C₃, plants, this advantage may not be realized under sub‐optimal conditions. Two perennial C₄ rhizomatous grasses of cool temperate origin, Miscanthus × giganteus and Spartina cyno‐suroides, have been suggested as potential fuel crops for north‐western Europe. The conversion efficiencies of these species were examined for 2 years in fertilized, irrigated, replicated plots in south‐eastern England. In the second year, the energy conversion efficiencies for shoot and total biomass production were 0.040 and 0.051, respectively, for S. cynosuroides, with significantly higher values of 0.060 and 0.078, respectively, for M. × giganteus. The M. × giganteus crop attained shoot productivity of 2.87 kg m⁻² between April and September, exceeding the highest values typically obtained with intensively managed C₃, crops. Canopy development was early, and high interception and conversion efficiencies were maintained over most of the growing season. This study provides the evidence that the superior potential light conversion efficiencies associated with C₄ photosynthesis can be realized under cool temperate conditions and that such climatic conditions do not Inherently impair the C₄ process.