Influence of the host on three sub-Arctic annual facultative root hemiparasites

I. Growth, mineral accumulation and above-lground dry-matter partitioning



Growth, mineral accumulation and above-ground dry-matter partitioning were measured in three sub-Arctic annual facultative root hemiparasites, Rhinanthus minor L., Euphrasia frigida L. and Melampyrum sylvaticum L., growing either unattached or attached to a host plant. Attached plants were at least an order of magnitude taller than unattached plants, and individuals produced a total above-ground biomass up to three orders of magnitude greater than that produced by unattached plants. Attached plants produced a greater number of branches, leaves, buds, flowers and ripe seed capsules. Leaf size was greater in attached than unattached plants. For two species, Rhinanthus minor and Euphrasia frigida, the response of individuals attached to a legume was compared to the response of those attached to a grass. Stimulation of parasite growth was greater with a legume host than with a grass. The architecture of parasites on legume hosts differed greatly from those either on grasses or unattached, with those on legumes often having a considerably greater number of second order branches. Above-ground biomass partitioning was affected by attachment to a host, and was a function of host type. Unattached plants of all three species of parasite accumulated foliar element concentrations within the same order of magnitude as their hosts. Element concentrations in attached plants were sometimes, but not always, greater than those of their hosts. Element concentrations, especially N, were greatest in those parasites attached to a legume.