Seeming field allelopathic activity of Cynara cardunculus L. reduces the soil weed seed bank

Weeds are one of the most important pests in agroecosystems, causing considerable economic losses on the production. The widespread use of herbicides during the last decades has led to an increased search for more environmentally sustainable methods for weed management. The manipulation of allelopathic interactions between crops and weeds, such as the introduction of an allelopathic species within a crop rotation, represents a valid alternative. In a multidisciplinary approach, we evaluated the effects resulting from three consecutive years of cultivation, in two different areas, with the three botanical varieties of Cynara cardunculus L. (globe artichoke, cultivated and wild cardoon), compared with a classic Mediterranean wheat/faba bean rotation and an olive grove, on the quali/quantitative weed soil seed bank and the changes in the eubacterial communities. Furthermore, the in vitro antibacterial activity of aqueous, methanolic, and ethanolic leaf extracts of cultivated cardoon against three bacteria involved in the soil N-cycle was investigated. In both areas, C. cardunculus caused a significant reduction (from − 34 to − 50%) on the amount of weed seeds in all treatments compared to controls; in some cases, a reduction of the number of weed species was observed. On one hand, the presence of cultivated cardoon had a negative influence towards Bacillus subtilis, while on the other, a positive one towards the beneficial soil bacteria Pseudomonas putida and Azospirillum brasilense. Moreover, methanolic and ethanolic leaf extracts from cultivated cardoon showed an inhibitory activity on B. lichenoformis, while there were no negative effects on Rhizobium leguminosarum and Sinorhizobium meliloti, two important bacteria involved in biological N2 fixation. These results confirmed, for the first time, the field allelopathic activity of C. cardunculus in monoculture and the possibility of introducing it within a crop rotation as an indirect method for a chemical-free weed seed bank control while respecting soil eubacterial communities.