Drought Response in <i>Miscanthus</i> : Breeding Increases Radiation and Water Use Efficiency Over Three Contrasting Years in Central Germany

ABSTRACT More and new sources of biomass are needed for renewable energy and renewable products for the bioeconomy. A leading new source of biomass is the highly sustainable perennial grass crop Miscanthus. The majority of the Miscanthus crop comprises a clone of Miscanthus × giganteus ( M × g ) of limited genetic variation and poor yield under dry growth conditions. The parental species of M × g , M. sacchariflorus and M. sinensis , are distributed over a large geographical range in Eastern Asia and may be used to improve on M × g . From breeding trials, we selected seven novel hybrids and two control genotypes including M × g . We grew these in a field experiment on drought‐prone soil in Germany with and without irrigation. To identify superior Miscanthus types, we estimated radiation use efficiency (RUE), yield and water use efficiency (WUE) from within‐season measurements made over three contrasting growing seasons. Temporal variations in RUE and WUE for different genotypes varied significantly and two novel hybrids, WAT6 and WAT8, achieved the highest yields. To achieve goodness of fit to yield measurements, genotype‐specific parameters for process descriptions in the model MiscanFor were adjusted for the two superior genotypes. These parameters included earlier shooting and an increased threshold of overheating. When the model was run over ten years, despite generating the highest yield values, WAT8 accumulated less biomass than WAT6 over the longer term. The response of WUE to variation in soil capillary pressure and vapour pressure deficit was examined. WUE of M × g increased with the severity of water stress then declined again. The superior yielding genotypes were more able to sustain biomass accumulation and/or water use under the highest stress. We believe that combining physiology with crop modelling is a powerful way to inform genetic and agronomic improvements needed to secure the future supply of biomass for the bioeconomy.