Influence of the host on growth and biomass allocation in the two facultative root hemiparasites Odontites vulgaris and Euphrasia minima

Abstract

Growth, reproduction and biomass allocation were investigated in the facultative root hemiparasites Odontites vulgaris and Euphrasia minima grown without a host and with the grass Lolium perenne or the legume Medicago sativa as hosts. In addition, the hosts were grown without parasites to analyze the effects of parasitization on host biomass and allocation. Odontites vulgaris attached to the legume and E. minima attached to the grass produced more leaves and flowers and accumulated more biomass than unattached parasites. In contrast, the biomass of O. vulgaris grown with the grass and that of E. minima grown with the legume as host did not differ from that of unattached parasites. Odontites vulgaris attached to the grass were taller and invested relatively more biomass into stems and less into leaves than parasites without a host or with the legume as host. In contrast, reproductive allocation was highest and root allocation lowest in O. vulgaris attached to the legume. Euphrasia minima attached to a host invested more into reproduction 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 parasitized by O. vulgaris allocated a lower proportion of total biomass to roots than unparasitized plants.