Abstract
Cushion plants can have positive impacts on plant richness in severe environments and possibly across trophic levels on arthropods, an under-studied topic. This study examined whether soil communities under cushions have higher richness and abundance of soil microarthropods than adjacent non-cushion vegetation, and whether differences in collembolan and mite abundance and species richness between cushions and adjacent vegetation increase with elevation. Paired soil samples were taken under cushions of Silene acaulis along the elevation gradient (1000, 1100, 1200, 1300, 1400 m a.s.l.), under cushions of Diapensia lapponica on the exposed ridge above the treeline (1000 m a.s.l.), and under adjacent non-cushion plant vegetation. In total, 5853 individuals of collembolans (n = 1705) and mites (n = 4148) were obtained from soil samples and identified to order/species level. S. acaulis cushions had a positive effect on species richness and abundance of collembolans, with richness effects from 1100 m a.s.l. upwards. Oribatid mite richness and abundance were also higher under cushions compared with adjacent vegetation. Species richness of collembolans and oribatids declined with increasing elevation from 1200 m a.s.l. Collembolan abundance peaked at mid-elevation (1200 m a.s.l.) under cushions and adjacent vegetation, while oribatid mite abundance peaked at 1300 m a.s.l. under both vegetation types. D. lapponica cushions on the exposed ridge had significant positive effects on species richness, abundance and diversity index of collembolans, and abundance of oribatids. Cushion plants play an important role in supporting the biodiversity of soil fauna in severe alpine environments, with the positive effects of cushion plants increasing with environmental severity.
Highlights
Facilitation is defined as an interaction in which the presence of one species alters the environment in a way that enhances growth, survival, or reproduction of a second, neighboring species (Bronstein 2009)
The aims of the present study were to: i) compare soil microarthropod communities inhabiting soil under two cushion plant species, S. acaulis along an elevation gradient and Diapensia lapponica on an exposed ridge, with those inhabiting soil under adjacent non-cushion vegetation; and ii) evaluate the effect of elevation gradient and facilitation by cushion plants on microarthropod communities under these two types of vegetation
Comparison of Silene acaulis and adjacent vegetation along an elevation gradient In total, 3807 soil mites and 1392 collembolans were recorded along the elevation gradient, in association with S. acaulis cushions and adjacent vegetation
Summary
Facilitation is defined as an interaction in which the presence of one species alters the environment in a way that enhances growth, survival, or reproduction of a second, neighboring species (Bronstein 2009). Facilitation effects tend to occur in high-stress environments such as Arctic and alpine ecosystems (Antonsson et al 2009), and the impact of facilitation tends to increase with environmental stress (Choler et al 2001; Brooker et al 2008). Plant-arthropod interactions in natural alpine habitats have been studied, but mainly for pollinators and benthic or soil surface species (Cardinale et al 2002; Molina-Montenegro et al 2006; Sieber et al 2011; Molenda et al 2012; Reid and Lortie 2012), with fewer studies on cushion plant-soil arthropod interactions (Coulson et al 2003; Minor et al 2016). 338 cushion plant species have been recorded in 34 families and 78 genera, mainly in harsh alpine and other cold regions (Hauri and Schröter 1914; Arredondo-Núñez et al 2009). Predicted changes associated with a changing climate in regions with a high cushion plant abundance make such plants very appropriate for ecological observations and experiments
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