Doubling genome size of energy willow affects woody stem cell wall structure, chemistry, and biogas yield

Effectiveness in woody biomass utilization is highly dependent on its genetics and physiology. We performed morpho-anatomical, chemical, and biomethane productivity characterizations of one-year-old woody stems in three shrub Salix viminalis genotypes: a diploid (Energo) and its two autotetraploid derivatives (PP-E7 and PP-E13). Tetraploidization affected changes in stem morpho-anatomy and corresponding improved chemical features and biomethane productivity, considerably more pronounced in tetraploid PP-E13, while PP-E7 was more similar to diploid Energo. Compared to diploid Energo, in tetraploid PP-E13 morphometric analysis showed increased stem diameter and higher wood fiber radial double wall thickness, while microscopic analysis suggested higher syringyl to guaiacyl (S:G) ratio of the wood fiber cell wall. Presented changes in stem morpho-anatomy of tetraploid PP-E13 compared to diploid Energo correspond to the improved chemical features: the lower Klason lignin content and higher S:G ratio, the higher cellulose and xylan content, and lower cellulose crystallinity (Crl). Presented improved chemical features, along with the increase in ash content, resulted in a 7.3% (10.3 CH₄ mL/g VS) increase in biomethane productivity in tetraploid PP-E13, compared to diploid Energo, suggesting tetraploid PP-E13 as an optimal raw material for fermentation technologies. In addition, besides the well-known chemical markers of willow biomass quality, the presented results highlight key stem morpho-anatomical parameters, which can serve as additional markers in energy willow improvement.