White poplar (Populus alba L.) leaf waste recovery and intercropping outcome on its polyphenols

The growing need for biomass recovery suggests forest waste leaf material for technological applications in a circular economy scenario. In this context, white poplar (Populus alba L.) foliar material was recovered in a forest site planted on a former agricultural land was identified in Tuscany (Italy), and intercropping eventually occurred was also valuated. In fact, the mixed plantation was characterized by tree different associations consisting of broad-leaf trees, including Populus alba L. intercropped with another valuable species (walnut, Juglans regia L.), and different nurse species (Italian alder, Alnus cordata (Loisel.); hazelnut, Corylus avellana L., Autumn olive, Elaeagnus umbellata (Thunb.)). Thus, Populus albaleaves were investigated for their lignin and phenol content, and for their anti-radical activity by (2,2-diphenyl-1-picrylhydrazyl) DPPH and [2, 2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)] ABTS assays. Furthermore, Populus alba extracts were profiled by liquid chromatography hyphenated to high-resolution tandem mass spectrometry (LC-HRMS/MS), in order to deepen into the intercropping influence on specialized metabolites’ content. In particular, it was observed that when Populus alba grows in presence of the nurse species Elaeagnus umbellata, a decrease in the aforementioned parameters was observed, as well as a negative impact on the polyphenol profile. Thus, our findings are in line with the observation that white poplar leaf residue has a high potential for achieving bioactive polyphenol compounds, and that an intercropped nurse species such as Alnus cordata could favourably augment flavonoids and chlorogenic acids to be used as multifunctional ingredients.