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 potential but yields at many sites in Europe can be limited by insufficient water supply and plant survival is endangered under extreme summer drought. A pot experiment was conducted to measure the influence of reduced water supply on the water use efficiency (WUE) and biomass partitioning of three Miscanthus genotypes ( M. x giganteus, M. sacchariflorus , and a M. sinensis hybrid) 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 destructive harvests. In phase 1, soil moisture was non-limiting. In the second and third phases, lowered soil moisture contents induced water deficits. Air vapour pressure deficit (VPD) was 0.49 ± 0.05 kPa. Water deficits caused leaf senescence in M. x giganteus and M. sacchariflorus , but not in the M. sinensis hybrid. Green leaf conductances were lowest in M. sinensis under 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 H 2 O but did not differ significantly between genotypes or water treatments under the conditions of this experiment. However, differences in dry matter partitioning to the shoot (the harvestable component) resulted in genotypic differences in WUE, calculated on a harvestable dry matter basis, which ranged from 4.1 g DM kg −1 H 2 O for M. sacchariflorus to 2.2 g DM kg −1 H 2 O for M. x giganteus .