Salix species and varieties affect the molecular composition and diversity of soil organic matter

Background and aims Most studies of the relationships between the composition of soil organic matter and plant cover have been carried out at the plant genera level. Yet, they have largely overlooked the potential effects that plant varieties belonging to the same genus can have on soil organic matter. Methods We investigated whether plant varieties belonging to different Salix species ( S. dasyclados and S. viminalis) impacted the composition of organic matter using mid-infrared spectroscopy and pyrolysis GC/MS. Top-soils (0-20 cm) were taken from an 18 year-old long-term field trial where six Salix varieties were grown as short-rotation coppice under two fertilisation regimes. Results Significant differences in the molecular composition and diversity of the soil organic matter were observed in the fertilised plots. The effects were mostly visible at the species level, i.e. between varieties from S. dasyclados and S. viminalis , though smaller differences among varieties from the same species were also observed. No significant effects of Salix varieties were observed in the unfertilised plots, possibly due to the relatively high degree of spatial variability in several soil properties (pH, total N and total organic C contents). Conclusion This study provides evidence that the taxonomic distance, at the species level, among Salix plant varieties can affect the molecular composition and diversity of soil organic matter. Such an effect should be considered in breeding programmes for managing soil organic C, as it is one of the potential driver of organic C persistence in soils.