Multiple choice: hemiparasite performance in multi‐species mixtures

Abstract

Hemiparasitic plants have green leaves, but extract water and solutes from neighbouring plants. It is still poorly understood how different host plants in communities contribute to parasite performance, as species that are good hosts in single‐host experiments may not necessarily be preferred hosts in mixtures. We grew the root hemiparasite Rhinanthus alectorolophus (Orobanchaceae) together with each of 13 host species (experiment 1) and with 15 different four‐species mixtures of these hosts (experiment 2) that differed in the number of legumes and of host functional groups. Parasites profited from mixtures including more legumes and from mixtures including different host functional groups. Some host species and mixtures were very tolerant of parasitism and supported large parasites without being strongly suppressed in their own growth, but the suppression of a species in the single‐host experiment did not explain the suppression of a species in a host mixture. We thus calculated for each host species an index of the difference in suppression between the two experiments which may be related to host use in a mixture. Host quality (mean parasite biomass with a host species) in the single‐host experiment could explain 64% of the variation in parasite biomass with a host mixture when it was weighted by the proportion of the host species in the mixture without the parasite and by the suppression difference index. Our results suggest that plant species which are the best hosts in single‐host experiments are not always those used most strongly by a parasite growing with a mixture. Together with the finding that hemiparasites benefit from a mixed diet based on hosts from different functional groups this suggests that parasites prefer certain host species to obtain a mixed diet.

Effects of drought and N level on the interactions of the root hemiparasite Rhinanthus alectorolophus with a combination of three host species

“…In contrast, in another experiment with R. alectorolophus and combinations of hosts at least some less‐preferred species (e.g. Anthyllis vulneraria , Taraxacum officinale , Trisetum flavescens ) were not suppressed or even increased in size when the hemiparasite was present, which was suggested as due to competitive release (Sandner & Matthies ). Similarly, when hemiparasites were experimentally removed from natural communities, some species increased in abundance, whereas others became less abundant ( e.g .…”

“…; Ameloot et al . ; Matthies ; Sandner & Matthies ). The reduction in overall productivity by hemiparasites has been attributed to a low resource‐use efficiency of hemiparasites (Matthies ; Ameloot et al .…”

“… for other grass species). However, the observation that D. glomerata was the most strongly suppressed species does not imply that it was also the host species most beneficial to the hemiparasite (Sandner & Matthies ). Although there is often a positive relationship between the suppression of a host species and the benefit to the hemiparasite, some species are suppressed more strongly than others by parasites of the same size (Matthies ; Sandner & Matthies ), i.e .…”

“…Although R. alectorolophus has a wide host range, the performance of the hemiparasite strongly depends on host species (Matthies & Egli ; Hautier et al . ; Sandner & Matthies ). The three perennial species selected as hosts for the experiment ( D. glomerata , M. sativa and S. minor ) frequently occur together with R. alectorolophus (personal observation) and are known to be good to medium quality hosts (Matthies & Egli ; Rowntree et al .…”

“…The three perennial species selected as hosts for the experiment ( D. glomerata , M. sativa and S. minor ) frequently occur together with R. alectorolophus (personal observation) and are known to be good to medium quality hosts (Matthies & Egli ; Rowntree et al . ; Sandner & Matthies ). Seeds of R. alectorolophus and the host species were obtained from a commercial seed supplier (Appels Wilde Samen, Darmstadt, Germany).…”