Comparative study of biomass determinants of 12 poplar (Populus) genotypes in a high-density short-rotation culture

The success of the production of renewable bioenergy with short-rotation coppice (SRC) cultures primarily depends on their sustainability and biomass yield. The choice of the genotypic materials largely determines how much biomass can be produced; therefore there is a need to study the performance of genotypes in situ to select the best performing ones. Twelve poplar (Populus) genotypes, of which two only recently commercialized, were planted in a large-scale operational SRC culture for the production of biomass for bioenergy. The objectives of the study were: (i) to describe and compare the 12 genotypes based on their growth, structural and developmental characteristics, and (ii) to analyze causal relationships between determining traits and productivity characteristics assessed at leaf, tree and population level by performing a hierarchical cluster analysis. The clustering of the poplar genotypes was clearly determined by parentage and genetic origin. Distinct differences between clusters were expressed in the biomass related traits; genotypes of similar parentage and origin showed comparable characteristics. Populus nigra genotypes were the least performing among the studied genotypes. The recently commercialized P. trichocarpa×P. maximowiczii hybrids on the other hand, were among the most productive genotypes. The P. deltoides×P. nigra hybrids showed intermediary results, with genotype Hees showing the highest biomass production among the 12 genotypes. As higher heating value was rather uniform among the genotypes, biomass production appeared the primary trait with regard to bioenergy production. This has significant implications for SRC cultures aiming at maximization of biomass production for maximum bioenergy yield. Besides the direct measurements of woody biomass growth (i.e. stem diameter), leaf area index is one of the most important early selection criteria for poplar with bioenergy purposes. The negative correlation of biomass and leaf rust infection reconfirmed the importance of disease vulnerability in breeding and selection programs.