Hemiparasite-density effects on grassland plant diversity, composition and biomass

Abstract

Hemiparasitic plants are considered as ecosystem engineers because they can modify the interactions between hosts and other organisms. Thereby, they may affect vegetation structure, community dynamics and facilitate coexistence as they are able to reduce interspecific competition by parasitizing selectively on competitive species and promote subordinate ones. In agri-environmental schemes, introducing the hemiparasite Rhinanthus has therefore been suggested as a low-cost method to increase grassland plant diversity, which is still subject to debate. 2 The majority of previous studies simply compared sites with and without hemiparasites. However, as hemiparasite effects are most likely density-dependent, we present a novel approach assessing the effect of Rhinanthus alectorolophus density on grassland plant diversity, yield and biomass quality. Moreover, we investigated whether functional plant composition and community mean traits are affected, which has been largely neglected in previous studies. The relationship between species richness and relative Rhinanthus biomass followed an optimum curve with highest values at 31% relative Rhinanthus biomass. At this Rhinanthusbiomass level, species richness was increased by 12% and yield decreased by 26% compared with plots without Rhinanthus. At relative Rhinanthus biomass > 60%, species richness was even lower than in plots without Rhinanthus. Overall, the biomass of grasses and the cumulative cover of legumes decreased linearly with increasing relative Rhinanthus biomass. Community mean trait analysis revealed that an increasing Rhinanthus density shifts the community composition towards smaller plant species. Biomass quality was not affected by increasing relative Rhinanthus biomass. In summary, our results of increased plant diversity − in line with a slightly lower yield but similar biomass quality − indicate that Rhinanthus is a suitable biological tool for grassland restoration.

Direct and indirect effects of land use on bryophytes in grasslands

“…If we assume that plant biomass negatively correlates with the light available for bryophytes, our results suggest that an increase in light competition from vascular plants partially explains the negative effect of fertilization on bryophyte diversity. Feßel et al (2016), who measured light transmittance to the ground in German grasslands, found sward cover and aboveground biomasstwo positively related factors (Heer et al, 2018) to be the most important factors explaining lower light levels on the ground, supporting our assumption that higher biomass means less light. Our results indicate that fertilization affects bryophyte diversity through several mechanisms and that the impacts may be more complex than previously thought.…”

Parasitism induces negative effects of physiological integration in a clonal plant

“…Parasitism and clonal integration each have strong community‐level effects on their own. For example, through differential effects on hosts and nonhosts and by decreasing the density of vegetation, parasitic plants can change plant community structure (Press & Phoenix, 2005), promote plant species diversity (Grewell, 2008; Heer et al ., 2018), and control invasive plant species (Shen et al ., 2007; Yu et al ., 2008; Cirocco et al ., 2017; Tĕšitel et al ., 2017, 2020; Li et al ., 2019). Clonal integration may modify the response of plants to grazing (Liu et al ., 2020) and help explain why increased dominance by tall, wide‐spreading clonal plants accounts for much of the negative effects of elevated N levels on diversity in some grasslands (Gough et al ., 2012; Dickson et al ., 2014), and why clonal growth in plants is associated with invasiveness (Pyšek et al ., 1995; Pyšek, 1997; Liu et al ., 2006; Song et al ., 2013).…”

Seedling recruitment in mountain grassland restoration: Effects of soil preparation and grazing

“…Rhinanthus alectorolophus has a wide range of hosts that includes grasses and legumes (Sandner & Matthies, 2018). The species is used as a tool in restoration of species‐rich grasslands as it reduces competition by grasses and may thus have a positive effect on plant diversity (Bullock & Pywell, 2005; Heer et al, 2018). In all sown plots (four plots per site), ten randomly chosen seedlings of both species were tagged in May 2019 using coloured rings and poles (Appendix ).…”