Cushion plants act as facilitators for soil microarthropods in high alpine Sweden

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.

Species interactions involving cushion plants in high-elevation environments under a changing climate

The effects of global warming are stronger in high-elevation environments than elsewhere. Here, we review recent advances in alpine plant ecology with a focus on dry mountain ranges, mainly in Mediterranean-type climate, with a global change perspective. Raising temperatures and changes in precipitation influence both plant growth and reproduction, and therefore the spatial distribution of species. Research in high-elevation systems evidenced that plant–plant interactions involving cushion plants play a crucial role in the assembly of plant communities, influencing species richness, genetic and phylogenetic diversity, and species persistence. By buffering environmental extremes and ameliorating biophysical conditions, cushion plant species acting as ecosystem engineers are fundamental in the response of alpine ecosystems to global warming, mitigating negative impacts on different plant species with narrow niche and small distribution range.

Cushion plant Silene acaulis is a pioneer species at abandoned coal piles in the High Arctic, Svalbard

Background Abandoned coal piles after the closure of mines have a potential negative influence on the environment, such as soil acidification and heavy metal contamination. Therefore, revegetation by efficient species is required. For this, we wanted to identify the role of Silene acaulis in the succession of coal piles as a pioneer and a nurse plant. S. acaulis is a well-studied cushion plant living in the Arctic and alpine environments in the northern hemisphere. It has a highly compact cushion-like form and hosts more plant species under its canopy by ameliorating stressful microhabitats. In this research, we surveyed vegetation cover on open plots and co-occurring species within S. acaulis cushions in coal piles with different slope aspects and a control site where no coal was found. The plant cover and the similarity of communities among sites were compared. Also, the interaction effects of S. acaulis were assessed by rarefaction curves. Results S. acaulis was a dominant species with the highest cover (6.7%) on the coal piles and occurred with other well-known pioneer species. Plant communities on the coal piles were significantly different from the control site. We found that the pioneer species S. acaulis showed facilitation, neutral, and competition effect in the north-east facing slope, the south-east facing slope, and the flat ground, respectively. This result was consistent with the stress gradient hypothesis because the facilitation only occurred on the north-east facing slope, which was the most stressed condition, although all the interactions observed were not statistically significant. Conclusions S. acaulis was a dominant pioneer plant in the succession of coal piles. The interaction effect of S. acaulis on other species depended on the slope and its direction on the coal piles. Overall, it plays an important role in the succession of coal piles in the High Arctic, Svalbard.

Oribatid mites (Acari: Oribatida) from the Sella massif (Dolomites, Trentino, Italy) with description of Trichoribates valeriae n. sp. (Ceratozetidae)

Results from collections of oribatid mites in the cushion plant belt of Sass Pordoi and Piz Boè in the Italian Dolomites (Prov. Trento) are presented. A total of 10 oribatid species belonging to seven families were found. Most have a wide general distribution, Anachipteria shtanchaevae is restricted to the Alps. Three species are frequently or mainly found in the montane to alpine zone (A. shtanchaevae, Camisia horrida, Oribatula interrupta). Remarkable findings are Camisia foveolata, hitherto only known from the boreal climate zone, which indicates a preglacial relict distribution, and Kunstidamaeus lengersdorfi as highest recorded altitude for this species. Trichoribates valeriae n. sp., found in large numbers on both mountains, is described and compared with other congeners, and its systematic position is discussed. This species is characterized by a lamellar structure with small ridges and widely separated cusps, rounded rostrum with nose-like protuberance, 10 pairs of medium long notogastral setae with short bristles, notogastral porose area A1 divided in two parts, porose areas present on all tibiae and tarsi. Additional morphological information on the presence of porose areas on tarsi of Trichoribates scilierensis Bayartogtokh and Schatz, 2008 is given.

Cushion plants act as facilitators for soil microarthropods in high alpine Sweden

1.Cushion plants can have positive impacts on plant richness in severe environments and possibly across trophic levels on arthropods, an under-studied topic. 2.This study examined whether soil communities under cushions of Silene acaulis and Diapensia lapponica have higher richness and abundance of soil microarthropods (Acari, Collembola) than adjacent non-cushion vegetation; and whether differences in collembolan and mite abundance and species richness between S. acaulis cushions and adjacent vegetation increase with elevation.3.In total, 5199 individuals of Collembola (n=1392) and mites (n=3807) were identified to order/species level in samples along an elevation transect (1000, 1100, 1200, 1300, and 1400 m a.s.l.), and an exposed ridge above the treeline (1000 m a.s.l.) in northern Sweden. Paired soil samples were taken within cushions of Silene acaulis (along the elevation gradient) and Diapensia lapponica (on the exposed ridge) and adjacent non-cushion plant vegetation. 4.Silene acaulis had a positive effect on species richness and abundance of Collembola, with richness effects from 1100 m a.s.l. upwards. Oribatid mite abundance and richness were also higher in S. acaulis compared with adjacent vegetation. 5.Species richness of Collembola and Oribatida declined with increasing elevation from 1200 m a.s.l. Collembola abundance peaked at mid-elevation (1200 m a.s.l.) in both S. acaulis and adjacent vegetation, while oribatid mite abundance peaked at 1300 m a.s.l. in both vegetation types. 6.Cushions of D. lapponica on the exposed ridge had a significant positive effect on species richness, abundance and diversity of Collembola, and abundance of Oribatida. 7.Alpine cushion plants play an important role in supporting biodiversity of soil fauna in severe alpine environments, with the positive effect of cushion plants increasing with environment severity.

Wind and seed: a conceptual model of shape-formation in the cushion plant Azorella Selago

Aims The sub-Antarctic cushion plant, Azorella selago, is usually hemispherical when small but frequently crescent-shaped when larger. Spatial variation in wind speed and in air-borne seed and sediment deposition is examined to determine if wind scouring and deposition patterns could contribute to the development of non-hemispherical shapes in cushion plants. Methods Computational fluid dynamic analyses were conducted for hemispherical and crescent-shaped cushion plants parameterizing models with data from A. selago habitats on Marion Island. Numerical data were contextualized with field observations to arrive at a conceptual model for shape development. Results Airflow modelling showed that both wind scouring and seed deposition of the commonly co-occurring grass Agrostis magellanica are greater on the windward side of the plant. By contrast, heavier sediment particles are predominantly deposited on the leeward side of plants, leading to burial of lee-side A. selago stems. This sediment accumulation may initiate the development of the crescent-shape in hemispherical plants by increasing stem mortality on the plant’s leeward edge. Once developed, the crescent-shape is probably self-reinforcing because it generates greater air recirculation (and lower air velocities) which enhances further deposition and establishment of A. magellanica grasses in the lee of the crescent. The conceptual model consists therefore of three stages namely, (1) negligible air recirculation, (2) sediment deposition and grass establishment, and (3) differential cushion growth. Conclusion This conceptual model of plant shape development may explain the occurrence and orientation of crescent-shaped cushion plants and highlights how predicted changes in wind patterns may affect vegetation patterns.