Contrasting understorey species responses to the canopy and root effects of a dominant shrub drive community composition

Abstract

Questions Contrasting understorey species responses to the effects of dominant species might occur within a single community even with neutral community‐level interactions. However, no studies have assessed the contribution of below‐ and above‐ground effects for all species of a community and their consequences for community composition. We tested the following hypotheses: (i) there are contrasting responses of understorey species to the canopy and root effects of a dominant shrub; (ii) the contrasting understorey responses to the canopy and root effects of the shrub are related to community composition. Location Species‐rich sub‐alpine community, eastern Tibet Plateau, China, dominated by Dasiphora fruticosa. Methods We used a removal procedure and shade cloth treatment to separate root from canopy effects and quantified the biomass responses of 41 species of the understorey community. Species‐level responses to the root and canopy effects were quantified with the relative interaction index. We conducted multivariate analyses to assess the relative contribution of root and canopy effects to community composition. Results We found contrasting species‐level responses to the canopy and root effects of D. fruticosa that could be grouped into six cluster groups. Dominant effects were positive for the roots and negative for the canopy, with a tendency for a trade‐off between the two. Community‐level effects were less strong and weakly significant, in particular for species richness. Root and canopy effects strongly explained understorey species composition but net shrub effects did not. Conclusions This study highlights that communities include species having contrasting responses to both the canopy and root effects of dominant species that importantly explain species composition.

Stature of dependent forbs is more related to the direct and indirect above‐ and below‐ground effects of a subalpine shrub than are foliage traits

“…() and Wang et al. () in a similar system dominated by D. fruticosa . However, in our study, three species groups showed positive indirect effects from either the shrub's canopy or its roots, and only one showed negative indirect effects from the shrub's canopy.…”

“…Wang et al. () disentangled above‐ and below‐ground direct effects of Dasiphora using shrub removal and light reduction. They showed that these effects balanced each other, partially explaining the weak occurrence of direct net effects at the community level.…”

Density-Dependent Plant–Plant Interactions Triggered by Grazing

“…According to the “shifting limitations hypothesis” (see Gibson, 2009) the decline of positive interactions is expected in habitats with high density of large-sized benefactor, because of the intensifying competition (Kelemen et al, 2013; Macek et al, 2016; Goldberg et al, 2017). Intense belowground competition for nutrients and water is not expected in benign environment characterized by moist and fertile soil (Wilson and Tilman, 1991; Kiær et al, 2013); therefore, similarly to the decline of flowering success, competition for light can be responsible for the loss of species richness in the terminal part of the gradient (Lepš, 1999; Borer et al, 2014; Wang et al, 2017). Moreover, the accumulated litter and the allelopathic effect can also contribute to this phenomenon (Barkosky and Einhellig, 2003; Deák et al, 2011; Miglécz et al, 2013).…”

Contrasting responses of different functional groups stabilize community responses to a dominant shrub under global change

“…The contrasting responses of species to neighbours observed within a single community have been shown to be related to species functional traits, in particular plant height, a good proxy of species' competitive ability for light (Díaz et al., 2016; Grime, 1974; Liancourt et al., 2005, 2009; Michalet et al., 2008; Wang, Michalet, et al., 2019), rather than traits related to growth rate such as leaf dry mass content (LDMC; Ackerly, 2004; Kunstler et al., 2016; Wright et al., 2004). Thus, it has been found that in species‐rich communities, particularly those from intermediate environmental conditions and characterized by high functional divergence, there are functionally different species, or group of species, with contrasting responses to their neighbours, which could balance the community‐level responses (Michalet et al., 2015; Wang et al., 2017). However, our knowledge is still limited on how changes in environmental conditions mimicking global change affect plant–plant interactions at both the species (including group of species) and community levels in communities living under intermediate stress conditions.…”