INFLUENCE OF THE HOST ON GROWTH AND BIOMASS ALLOCATION IN THE 2 FACULTATIVE ROOT HEMIPARASITES ODONTITES-VULGARIS AND EUPHRASIA-MINIMA

Growth, reproduction and biomass allocation were investigated in the f acultative root hemiparasites Odontites vulgaris and Euphrasia minima grown without a host and with the grass Lolium perenne or the legume M edicago sativa as hosts. In addition, the hosts were grown without par asites to analyze the effects of parasitization on host biomass and al location. Odontites vulgaris attached to the legume and E. minima atta ched to the grass produced more leaves and flowers and accumulated mor e biomass than unattached parasites. In contrast, the biomass of O. vu lgaris grown with the grass and that of E. minima grown with the legum e as host did not differ from that of unattached parasites. Odontites vulgaris attached to the grass were taller and invested relatively mor e biomass into stems and less into leaves than parasites without a hos t or with the legume as host. In contrast, reproductive allocation was highest and root allocation lowest in O. vulgaris attached to the leg ume. Euphrasia minima attached to a host invested more into reproducti on than unattached parasites. The two hemiparasites differed in their effects on the hosts. While E. minima had no negative effects on host growth, O. vulgaris reduced the biomass of both host species and also reduced total productivity per pot (parasite + host). Legumes parasiti zed by O. vulgaris allocated a lower proportion of total biomass to ro ots than unparasitized plants.