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Parasitic and Competitive Interactions between the Hemiparasites Rhinanthus Serotinus and Odontites Rubra and their Host Medicago Sativa
Journal of Ecology
Vol. 83, No. 2 (Apr., 1995), pp. 245-251
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2261563
Page Count: 7
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1 Host plants are for hemiparasites both their main source of water and nutrients and potential competitors for light. To investigate the balance between costs and benefits of host presence a greenhouse experiment was performed with the two facultative root hemiparasites Rhinanthus serotinus and Odontites rubra and their host Medicago sativa. Above-ground (light competition) and below-ground (parasitic) interactions were separated and the host plants were killed 4, 8 and 12 weeks after planting by cutting off the shoots. 2 R. serotinus remained smaller than O. rubra when grown autotrophically and its growth was more stimulated by the presence of the host, indicating that R. serotinus has a higher degree of host dependence. The marked reduction in root allocation by both hemiparasites in the presence of the host was more pronounced in R. serotinus. 3 Above-ground competition by the host reduced the growth of both hemiparasites by more than 30%. However, the negative effect of removing the host after 4, 8 and 12 weeks of development indicated that the beneficial effects of the host predominated at all stages. 4 Both parasites had negative effects on host growth that were much stronger than that of another M. sativa individual. Above-ground separation of parasites and hosts had no effect on host biomass, indicating that the negative effect was due exclusively to parasitism. 5 Host root biomass was reduced more strongly than host shoot biomass by the parasites, resulting in a lower biomass allocation to roots. 6 The presence of the hemiparasites reduced the total productivity per pot. This suggests that the parasites have a lower efficiency of resource utilization than the hosts. 7 It is suggested that the balance between the effects of root parasitism on the host (e.g. via nutrient competition) and the effects of light competition by the host on the parasite restricts hemiparasites to relatively nutrient-poor habitats.
Journal of Ecology © 1995 British Ecological Society