Water use efficiency and biomass partitioning of three different Miscanthus genotypes with limited and unlimited water supply

Miscanthus species, which are C-4 perennial grasses, have a high biomass po tential but yields at many sites in Europe can be limited by insufficient w ater supply and plant survival is endangered under extreme summer drought. A pot experiment was conducted to measure the influence of reduced water su pply on the water use efficiency (WUE) and biomass partitioning of three Mi scanthus genotypes (M. x giganteus, M. sacchariflorus, and a M. sinensis hy brid) in a controlled environment. The experiment consisted of three phases (phase 1 = 0-20 d; phase 2 = 21-39 d; phase 3 = 40-54 d) punctuated by des tructive harvests. In phase 1, soil moisture was non-limiting. In the secon d and third phases. lowered soil moisture contents induced water deficits. Air vapour pressure deficit (VPD) was 0.49 +/- 0.05 kPa. Water deficits cau sed leaf senescence in M. x giganteus and M. sacchariflorus, but not in the M. sinensis hybrid. Green leaf conductances were lowest in M, sinensis und er water deficit, indicating stomatal regulation. Water use efficiency for whole plants of each genotype ranged from 11.5 to 14.2 g dry matter (DM) kg (-1) H2O but did not differ significantly between genotypes or water treatm ents under the conditions of this experiment. However, differences in dry m atter partitioning to the shoot (the harvestable component) resulted in gen otypic differences in WUE, calculated on a harvestable dry matter basis, wh ich ranged from 4.1 g DM kg(-1) H2O for M. sacchariflorus to 22 g DM kg(-1) H2O for M. x giganteus. (C) 2000 Annals of Botany Company.