Effects of light availability on attachedRhinanthus minor (L.), an angiospermatic root hemiparasite

We studied the effect of light availability on the growth of an angiospermatic root hemiparasite,Rhinanthus minor. When attached to its host, height growth increased in response to shading, demonstrating thatR. minor was able to detect alterations in light quality and/or quantity. However, this reduced illumination did not affect its biomass, number of haustoria, or the amount of15N transferred from the hosts, compared with its performance under non-shaded conditions. Therefore,R. minor is unlikely to have difficulty in extracting host resources under shading. This result may have been mediated by a loweredR. minor transpiration rate in response to fluctuations in external conditions, including shading and water stress, compared with non-parasitic plants. Therefore, we suggest that, as long as the extent of resources diverted from host to parasite is not significantly altered by shading, growth of the attachedR. minor will be unaffected by reduced light availabilityper se.