Biotic and abiotic factors influence secondary metabolite accumulation and allelopathic potential of grapevine (Vitis vinifera) against cosmopolitan weeds

Viticulture generates significant pruning wastes, which can be valorized as bioherbicides for sustainable weed management, and as a means to advance the circular economy. Allelopathy, an environmentally friendly approach in which plants release secondary metabolites that suppress the growth of other species, presents a means to managing weed growth in agricultural systems. Our study aimed to assess whether biotic (grapevine variety and mycorrhization) and abiotic (atmospheric CO ₂ level, air temperature or water availability) factors influence the accumulation of secondary metabolites in grapevine ( Vitis vinifera L.) pruning wastes and their allelopathic effects on three cosmopolitan weeds ( Sisymbrium irio, Solanum nigrum and Sonchus oleraceus ). Two grapevine varieties, Tempranillo and Cabernet Sauvignon, inoculated (M) or not (NM) with mycorrhizal fungi, were grown under two environmental conditions: CATA (current CO ₂ and temperature conditions i.e., 400 ppm CO ₂ and ambient air temperature) and CETE (700 ppm CO ₂ and ambient air temperature + 4˚C). Within each grapevine variety and environmental condition, half of the M and NM plants were subjected to either full irrigation (WW) (90–100% substrate field capacity, FC) or limited irrigation (D) (cycles from 90–100% to 20–30% FC). Characterization of the methanolic extracts of the grapevine wastes revealed significant variations in phenolics, flavonoids, flavonols, and anthocyanins across treatments, with higher accumulation and free radical scavenging activity under elevated CO₂ and temperature conditions. Within each variety, the accumulation of secondary compounds was also influenced by the level of irrigation and the presence or absence of root-associated mycorrhizal fungi. Aqueous extracts of grapevine leaves used in germination bioassays strongly inhibited seed germination and seedling growth of the weeds, with the pronounced effects observed in S. irio . The presence of these secondary metabolites contributes to their allelopathic effect, highlighting the potential of grapevine pruning waste as bioherbicides and an alternative to synthetic herbicides. However, further studies are needed to determine optimal extract concentrations and assess their effects on crops under field conditions.