Leaf-level productivity traits in Populus grown in short rotation coppice for biomass energy

Populus is a genus of extremely fast-growing trees originating in the northern hemisphere, with potential as a source of renewable, biomass energy. The aim of this work was to physiologically characterize genotypes of hybrid poplar, informing future selection, breeding and the development of process-based yield models. Two experiments - a short rotation coppice field trial at two contrasting UK sites and a glasshouse experiment - were conducted on five different genotypes of Populus. The field trial experiment showed that stemwood yields varied between 5.8 and 11.8 t ha(-1) a(-1) and that the genotype, Hoogvorst (Populus trichocarpa x P. deltoides) was the most productive. This production was characterized at a physiological level by rapid rates of leaf expansion and slow rates of leaf production and, at a cellular level, by the largest epidermal cell number per leaf. The glasshouse experiment confirmed the superior productivity of Hoogvorst, with this genotype producing the largest individual leaf areas (P 0.005) that were highly correlated with biomass production (R-2 = 0.7). There was no correlation between leaf-level photosynthesis measurements and total biomass production. In general, leaf level photosynthetic characteristics were less able to differentiate between the most productive and less productive genotypes than morphological traits.