Abstract
Two naturally coexisting grassland species - Centaurea jacea (often predominating) and Fragaria vesca (subordinate) were grown together in a pot experiment of factorial design, where competition and arbuscular mycorrhiza (AM) inoculation were used as treatments. The effects of competition were one-sided, i.e. the mass of F. vesca decreased relatively more than that of C. jacea as a result of competition. The root and total mass of C. jacea increased with AM inoculation while F. vesca did not respond. The mass difference between C. jacea and E vesca in a particular pot increased when plants were mycorrhizal, mostly due to the mass increase of C. jaceae. This can be explained by the differential response of these species to AM. We did not find any indirect indication of the interplant transfer of resources. The results of this experiment show the more unbalanced competition (larger differences in biomass) resulting from AM infection of plants.