Root hemiparasites and plant diversity in experimental grassland communities

Abstract

Summary1 We studied the relationship between the diversity of grassland communities and the eects of the generalist hemiparasitic plant Rhinanthus alectorolophus. We compared resistance against biomass loss as a consequence of infection, performance of the parasite and resistance of the parasitized communities to invasion by other plant species. Seeds of the parasite were sown into experimental plots containing 1, 2, 4, 8 or 32 plant species belonging to one or more of three functional groups (grasses, legumes and non-leguminous herbs). 2 We predicted that infection will reduce host biomass, total community biomass and resistance to invasion, particularly in host communities with low diversity, but that the performance of the parasite will be at its lower level in such communities. 3 The presence of the parasite caused an overall reduction in host biomass per plot, which was mainly due to a strong reduction in the biomass of grasses. As predicted, the eect was smaller in communities with greater functional diversity. However, total community biomass (including the parasite biomass) was increased by more than a third in infected communities of one or two host species, while the parasite had no eect on total biomass of species-rich communities. 4 Germination of the parasite was hardly in¯uenced by the diversity of its host community, but early survival decreased with increasing number of functional groups and was lower in plots with legumes than without. However, our hypothesis that the performance of the surviving parasites would bene®t from a high functional diversity of hosts was supported. Parasite biomass per individual and per m 2 increased with the number of functional groups in the host community, as did reproductive potential. 5 Death of the parasite led to a higher proportion of bare ground in communities when the previously infected communities had low functional diversity, thus enabling subsequent colonization by weeds.

Biology, chance, or history? The predictable reassembly of temperate grassland communities

“…Our experiment confirms previous findings, that experimental communities with higher numbers of resident species are more resistant to invasion from both internal and external invaders than species-poor communities (Tilman 1997, Knops et al 1999, Joshi et al 2000, Levine 2000, Naeem et al 2000, Hector et al 2001, Kennedy et al 2002, Fargione et al 2003, van Ruijven et al 2003, Pfisterer et al 2004, Maron and Marler 2008, Roscher et al 2009a). We also found that the invasion process was highly non-random on the functional group level.…”

Interactions of inbreeding and stress by poor host quality in a root hemiparasite

“…The buffering of ID by functional diversity of hosts suggests that the deficits of inbred R. alectorolophus may be better compensated for if hosts from different functional groups are available. This supports the view that for hemiparasites such as R. alectorolophus the diversity of communities is of particular importance (Marvier and Smith, 1997;Joshi et al, 2000).…”

Ecosystem Effects of Biodiversity Manipulations in European Grasslands

“…Sites differed widely in climate, soil conditions, and other major environmental factors (Hector et al 1999, Joshi et al 2001. For more detailed information on single sites, for Switzerland see Diemer et al (1997), Joshi et al (2000), Koricheva et al (2000), Spehn et al (2000a, b), Stephan et al (2000), Diemer and Schmid (2001), Pfisterer et al (2004); for Sweden see Mulder et al (1999Mulder et al ( , 2002, Koricheva et al (2000), and Jumpponen et al (2002); for Germany see Gastine et al (2003) and Scherer-Lorenzen et al (2003); for Greece see Troumbis et al (2000Troumbis et al ( , 2002; for Portugal see Caldeira et al (2001); and for Silwood see Hector et al (2000aHector et al ( , 2001a.…”