Interactions between a facultative annual root hemiparasite, Rhinanthus minor (L.) and its hosts
This thesis describes relationship of a facultative annual root hemiparasite, Rhinanthus minor with its hosts, and seeks to investigate how changes in the physical environment influence interactions between host and parasite. A field study reveals that the presence of R. minor reduces productivity of the host vegetation in a traditional Scottish hay meadow, in which grass species significantly suffer from the parasitism while the non-grass species do not. Photosynthetic rate, growth and nutrient status of R. minor are not affected by removal of above ground host vegetation. Growth of unattached R. minor is significantly poor compared to those attached to Lathyrus pratensis and Galium verum. Nutritional status and biomass allocation of R. minor are dependent on host species. Amongst host plants, L. pratensis, a legume, is a better host for R. minor, although it is most negatively affected by the parasitism. The sink strength of R. minor for host resources is not overridden by the sink activity in the hosts created by simulated grazing. It is also noted that recovery of host growth from grazing is negatively affected by infection with R. minor. Soil nitrogen has no direct effects on R. minor growth, number and size of haustoria. However, it has indirect beneficial effects on those parameters through improving host growth and nitrogen status. Increased nitrogen availability to host-parasite association does not alleviate negative effects of the parasitism. It is revealed that as a chlorophyllous parasite, R. minor can gain benefits from elevated CO2 in terms of carbon assimilation rate and growth, but increased CO2 availability to parasitised hosts fails to alleviate negative impacts of R. minor on host photosynthesis and growth. Shading does not negatively affect growth of attached R. minor, but stimulates height growth.