The toxic weed Heliotropium europaeum L.: Germination ecology, soil seed bank, and emergence dynamics in diversified cropping systems

Abstract

AbstractHeliotropium europaeum is a toxic annual weed that has been found with increasing frequency in the Mediterranean agro‐environment. We investigated, both in laboratory and in field, the ecological aspects of this species in order to verify a possible connection between cropping systems and population increase. Its germination, characterized by a high thermal optimum (about 35°C) is markedly reduced by burial. Strong depth‐mediated germination inhibition was observed with over 2 cm of burial. Nongerminated seeds undergo a secondary dormancy highlighting their ability to form a persistent seed bank. Indeed the seed bank analysis carried out in an agroecosystem based on minimum tillage cropping systems showed a seed accumulation in the shallowest soil layers. The hypothesis that poor seed burial plays a crucial role in the population dynamics of this species was confirmed by the drastic reduction in seedling emergence after only 1 year of plowing. A strongly reduced emergence percentage was shown which causes not only a lower seedling density but also a lower inflorescence density and respective seed ripening. In conclusion, there is a clear relationship between an increase in this species and cultivation systems based on minimum tillage.