Cushion Plants Research Articles

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.

Azorella Cushion Plants and Aridity are Important Drivers of Soil Microbial Communities in Andean Ecosystems

Cushion plants are specialized keystone species of alpine environments that can have a positive effect on ecosystem structure and function. However, we know relatively little about how cushion plants regulate the diversity and composition of soil microbial communities, major drivers of soil processes and ecosystem functioning. Identifying what factors drive the diversity and composition of soil microbial communities in high-elevation ecosystems is also fundamental to predict how global changes will affect their conservation and the services and functions they provide. Thus, we sampled four sites along the southern Andes following the vegetation belt of Azorella cushion species. The field sites spread along a latitudinal gradient and had contrasting levels of aridity, UV-B radiation, mean temperature and soil properties. Overall, Azorella, as well as aridity and UV-B radiation, were the major drivers of the distribution, composition and diversity of soil microbial communities in the studied ecosystems of the Chilean Andes. UV-B radiation affected particularly soil fungi, while soil properties such as pH, total C and N content, essential predictors of microbial diversity globally, had a much lower effect on the composition of soil microbial communities. Understanding the factors driving the structure and composition of microbial communities, particularly the role of cushion plants and the feedbacks between plant, climate and soil is of uttermost importance for the preservation of the functionality of high-elevation ecosystems threatened by climate change.

Co-ordination between xylem anatomy, plant architecture and leaf functional traits in response to abiotic and biotic drivers in a nurse cushion plant.

Plants in dry Mediterranean mountains experience a double climatic stress: at low elevations, high temperatures coincide with water shortage during summer, while at high elevations temperature decreases and water availability increases. Cushion plants often act as nurses by improving the microclimate underneath their canopies, hosting beneficiary species that may reciprocally modify their benefactors' microenvironment. We assess how the nurse cushion plant Arenaria tetraquetra subsp. amabilis adjusts its hydraulic system to face these complex abiotic and biotic constraints. We evaluated intra-specific variation and co-ordination of stem xylem anatomy, leaf functional traits and plant architecture in response to elevation, aspect and the presence of beneficiary species in four A. tetraquetra subsp. amabilis populations in the Sierra Nevada mountains, southern Spain. Xylem anatomical and plant architectural traits were the most responsive to environmental conditions, showing the highest mutual co-ordination. Cushions were more compact and had smaller, more isolated conductive vessels in the southern than in the northern aspect, which allow minimization of the negative impacts of more intense drought. Only vessel size, leaf mass per area and terminal branch length varied with elevation. Nurse cushions co-ordinated plant architecture and xylem traits, having higher canopy compactness, fewer leaves per branch and fewer, more isolated vessels than non-nurse cushions, which reflects the negative effects of beneficiary plants on nurse water status. In non-nurse cushions, plant architecture co-ordinated with leaf traits instead. The interacting effects of aspect and elevation on xylem traits showed that stress due to frost at high elevation constrained xylem anatomy in the north, whereas stress due to drought had a parallel effect in the south. Trait co-ordination was weaker under more demanding environmental conditions, which agrees with the hypothesis that trait independence allows plants to better optimize different functions, probably entailing higher adjustment potential against future environmental changes.

Plant size of the alpine cushion Thylacospermum caespitosum affects soil amelioration at different elevations

Cushion plants (as nurse species) can ameliorate soil conditions under their canopy in alpine environments. However, this amelioration (or the intensity of soil fertility islands) related with the size of plants is rarely studied. To assess size effects of Thylacospermum caespitosum on soil fertility islands, soil properties (pH; electric conductivity, EC; soil organic carbon, SOC; available nitrogen, AN; available phosphorus, AP; available potassium, AK) and microbial biomass (soil microbial biomass carbon, SMBC; soil microbial biomass nitrogen, SMBN) were investigated at three different elevations in the Qilian Mountains. Plant size significantly influenced (P < 0.001) soil properties (pH, EC, SOC, AN, AP, AK) and microbial biomass (SMBC and SMBN) at all three elevations. A size-dependent fertile island effect occurred beneath T. caespitosum, where the relative interaction index (RII) of soil properties and SMBC was affected (P < 0.001) by plant size at the three elevations. Moreover, most parameters of soil nutrition and microbial biomass under T. caespitosum were reduced (P < 0.001) with increases in elevation, but the RII was increased (P < 0.05). In short, soil amelioration by T. caespitosum was clearly dependent on plant size at all elevations, and this effect on soil increased with elevation. Thus, the existence of size-dependent fertility islands together with elevation should be regarded as a central mechanism of the nurse effect of T. caespitosum in harsh alpine ecosystems, where many ecological processes rely on the nurse effect of cushion plants.

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

BackgroundAbandoned 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.ResultsS. 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.ConclusionsS. 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.

Creating Your Own Environment: Ecosystems Sustained by Cushion Plants

Photo 1: Mountains such as the Spanish Sierra Nevada are biodiversity hotspots teeming with endemic species. At high altitude (3200 m asl), these environments are sustained by cushion plants. Photo credit: Gianalberto Losapio. Photo 2: Ecosystem engineers Arenaria tetraquetra (left) and Hormathophylla spinosa (right) can tolerate stress, ameliorate the environment and facilitate other plant species. Photo credit: Gianalberto Losapio. Photo 3: The cushions of Arenaria tetraquetra hosts different blooming plants such as Jasione amethistina, Lotus corniculatus subsp. glacialis, Galium pyrenaicum, Anthyllis vulneraria subsp. pseudoarundana, Leontodon boryi, and Nevadensia purpurea. Photo credit: Gianalberto Losapio. Photo 4: The flower visitor network is characterized by more than 50 species of insects. These include the cosmopolitan honeybees (Apis mellifera), which moved at high altitude for foraging on flowers of Sideritis glacialis. Photo credit: Gianalberto Losapio. Photo 5: Not all the insects visiting flowers are actual pollinators, but they are also predators, parasitoids, or herbivores, like the weevils Otiorhynchus (Curculionidae). This way, cushion plants enrich also the functional diversity and complexity of insect communities. Photo credit: Gianalberto Losapio. These photographs illustrate the article “An experimental approach to assessing the impact of ecosystem engineers on biodiversity and ecosystem functions” by Gianalberto Losapio, Bernhard Schmid, Jordi Bascompte, Richard Michalet, Pierfilippo Cerretti, Christoph Germann, Jean-Paul Haenni, Rainer Neumeyer, Francisco Javier Ortiz-Sánchez, Adrian C. Pont, Pascal Rousse, Jürg Schmid, Daniele Sommaggio, and Christian Schöb in Ecology. https://doi.org/10.1002/ecy.3243

Species Distribution in Cenofloras of the Cryophytic Steppes and Cushion Plants with the Participation of Stellaria pulvinata Grub. in the Mongolian Altai

The distribution of the vascular plants species occurring in the composition of high mountain communities with the participation of stitchwort polster (Stellaria pulvinata Grub.) are analyzed. They form a separate altitudinal belt in the altitudinal-zonation range of vegetation and belong to the arid class of zonality types in the central Mongolian Altai (2700–3300 m a.s.l. Baltic System (BS)). The analysis identified cenotically active species in the cenofloras of cryophytic steppes and cryophytes–forb cushion plants, which include distinctive elements of cryo-xerophytic conditions, such as Oxytropis oligantha, O. chionophylla, Saussurea leucophylla, Chamaerhodos altaica, Arenaria meyeri, and Androsace septentrionalis; montane species confined to the high mountain areas of southern Siberia and central Asia (Festuca kryloviana and Poa altaica) and bunchgrasses, which are represented by widely distributed species typical of the steppe (Festuca lenensis and Koeleria cristata). Modeling of the spatial distribution revealed that the ecological–cenotic optimum for the majority of species in the region is found outside of the cryophytic steppes and cushion-plant growth area. According to the identified potential distribution ranges of species accompanying Stellaria pulvinata, a close relationship has been established between the vegetation of the central Mongolian Altai high mountains and the mountains of southern Siberia.

Vegetation science during hectic times

Vegetation science during hectic times

Root biomass and production by two cushion plant species of tropical high-elevation peatlands in the Andean páramo

High-elevation peatlands in the Andes are receiving increasing attention for their biodiversity and their high rates of carbon accumulation. However, the ecology of these peatlands and the environmental factors that control their carbon dynamics remain under-studied. Here we report on the patterns of root biomass productivity and turnover rates for two cushion plant species (Distichia muscoides, Plantago rigida) that commonly dominate high-elevation peatlands (> 4200 m a.s.l.) in the Andean paramo landscape of Northern Ecuador. Root biomass for P. rigida ranged from 680 to 864 g m-2 and was approximately 40 % higher than for D. muscoides (507–620 g m-2). In contrast, root production was almost twice as high for D. muscoides (2000–2800 g m-2 yr-1) than for P. rigida (1030–1080 g m-2 yr-1). These patterns resulted in high root turnover rates, especially for D. muscoides (0.98–1.90 yr-1). Below-ground productivity (as C) at our sites conservatively ranged from 0.55 to 1.5 kg m–2 yr–1, representing approximately 30 % of the estimated total productivity for these species, which only accounts for root production down to 50 cm depth. These high productivity rates are in accordance with the extremely high rates of carbon accumulation that have been reported for high-elevation peatlands of the Andes.

Morphological variability of cushion plant Lyallia kerguelensis (Caryophyllales) in relation to environmental conditions and geography in the Kerguelen Islands: implications for cushion necrosis and climate change

In recent decades, climate change has been faster in various parts of the world. Within species, to counter rapid climatechanges shift of geographical area, individuals’ plastic responses or populations’ genetic adaptation might occur. The sub-Antarctic islands are subject to one of the most rapid climate changes on earth, with already visible impacts on nativevegetation. Such might be the case of Lyallia kerguelensis a cushion plant strictly endemic to the Kerguelen Islands. In L.kerguelensis, necrotic parts were observed in cushions these last decades and possibly related to water stress. We analysedmorphological variability of L. kerguelensis, including necrosis extent, across 19 populations spanning a wide range ofenvironments across the Kerguelen Islands. Inter-population variations in the cushion surface area, shape and compactnesswere well explained by topography, degree of wind exposure, slope aspect, proportions of coarse sand and bare soil, andgeographical distance between populations. All these variables are related to wind intensity and water availability. Moreover,in cushions with less than 10% necrosis in surface area, necrosis extent was positively correlated to soil sodium. Sodiumavailability might reduce the plant’s capacity for osmotic adjustment in face of other abiotic stresses, such as water stress. Weconclude that cushion morphology may have the capacity to adjust to environmental variation, including aspects of climatechange, but that cushion necrosis may be accelerated in the driest and most saline environments.

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.

Environmental controls over Holocene carbon accumulation in Distichia muscoides-dominated peatlands in the eastern Andes of Colombia

The long-term carbon (C) and vegetation dynamics of tropical, high-Andean cushion peatlands are poorly understood. Here, we present radiocarbon-dated paleoecological records and modern microclimate data from high-elevation peatlands currently dominated by the cushion plant Distichia muscoides in the páramo (alpine tundra) of the eastern Colombian Andes. Focusing on a well-dated 4300-year-old peat core collected at 4194 m elevation from the Sierra Nevada del Cocuy, we investigated the response of peatland vegetation to hydroclimate changes and environmental controls on C accumulation. In addition, we carried out a regional synthesis of existing C accumulation data from northern Andean peatlands to place our new results in broad geographic and temporal context over the last 17,000 years. Our results show that the current Distichia-dominated peatlands are a recent landscape feature on El Cocuy occurring only during the last ∼250 years. The Distichia peatlands have extremely high sediment accumulation rates of up to 1 cm yr−1 and C accumulation rates between 183.7 and 849.5 g C m−2 yr−1, decreasing with the elevation of a site. These rates far exceed an expected modern C accumulation rate of 110 g C m−2 yr−1, calculated by extrapolating an exponential function from a late Holocene average C accumulation rate of 48.6 g C m−2 yr−1 for the northern Andes. This suggests that recent Distichia establishment represents an acceleration of C accumulation at a rate higher than expected from decomposition-related autogenic effects. Before the modern climate warming period, our record indicates that Distichia cushions have only grown intermittently, often after the peatland was flooded with mineral sediments. Mineral sediment deposits at 3290, 2590, 1620, 930, and 860 cal. yr BP correspond with wet intervals from lake-derived records of hydroclimate change in the northern Andes and indicate increases in precipitation and subsequent in-wash of mineral sediments. However, within the last 150 years, mineral sediment deposition has increased in frequency, likely due to warming-induced melting of permanent snow and ice mobilizing exposed fluvio-glacial sediments. Increased mineral nutrients, rising temperatures, and strong diurnal temperature contrast in the tropical mountains may explain the rapid C accumulation rates. Taken together, we show that Andean peatlands have experienced the largest shift in vegetation and C accumulation rates in the last 250 years than at any other time during the last 4000 years.

The presence of a foreign microbial community promotes plant growth and reduces filtering of root fungi in the arctic-alpine plant Silene acaulis

ABSTRACT Background Climate change is expected to drive trailing-edge range redistributions of arctic-alpine plant populations, bringing together immigrant plant ecotypes and soil microbial communities associated with already resident ecotypes. Aims The goal of the present study was to assess growth performance and plant–microbe interactions between seedlings and native and foreign microbial communities in ecotypes of the cushion plant Silene acaulis from Europe and North America. Methods Using seed sourced from Colorado, USA, and Ireland we grew Silene seedlings in sterile bulk soil with live inocula added from their own local soil and each other’s soil. We measured above-ground plant growth metrics, and analysed fungal and bacterial community composition using marker gene sequencing and microscopy. Results Seedlings growing in foreign soil inocula showed significantly greater biomass or shoot length compared to growth in home soil inocula. While seedling root microbiomes were overall convergent with each other compared to source soil inocula, significantly lower filtering of fungal taxa from the soil was observed for seedlings growing in foreign compared to home soil inocula. Conclusions Foreign plant ecotypes from distant habitats may experience competitively beneficial effects when growing in local soil communities; however, the nature and generality of these interactions requires further analysis.

The positive effects of the alpine cushion plant Arenaria polytrichoides on insect dynamics are determined by both physical and biotic factors

Cushion plants' significant role for alpine biodiversity has been demonstrated in particular through their positive effects on plant diversity. However, their effects on higher trophic levels (e.g. insects) remain largely unclear. In this study, by field sampling in the Hengduan Mountains (HDM) in southwestern China, we evaluated the effects of an alpine gynodioecious cushion species, Arenaria polytrichoides (Carophyllaceae), on insect richness, abundance and population dynamics at two different elevations (4427 m vs. 4732 m) separately at two time periods (day vs. night) and in two growing seasons (early vs. late). The results showed that the total insect diversity decreases from low to high elevation sites. Some insect species were exclusively detected within A. polytrichoides cushions, leading to an increase in local insect richness from 7% to 35%. The positive effects of cushions on insect diversity could be attributed to unique biotic properties provided by cushions. Firstly, the effects were determined by the sexual dimorphism of the cushion with hermaphroditic cushions supporting higher insect diversity than female cushions. This could be because hermaphroditic cushions provide more resources, such as nectar and pollen grains, for insects than female cushions. Secondly, the cushions' associated beneficiary plants can also provide extra resources for attracting more insects, but this effect was mediated by the micro-environmental conditions. Finally, the magnitude of cushions' positive effects on insect dynamics were stronger under higher than under lower environmental stress. This study confirmed that facilitation by A. polytrichoides cushions in HDM plays an important role in constructing the alpine insect community and further regulating its dynamics. Moreover, the positive effects of cushions on insect dynamics increase with increasing environmental stress. Therefore, the distribution range of insects would quite possibly be expanded into higher elevation under future climate changes, which will induce new challenges for the local alpine ecosystems.

Widespread dieback in a foundation species on a sub‐Antarctic World Heritage Island: Fine‐scale patterns and likely drivers

AbstractUnder anthropogenic climate change, emerging diseases and pathogens are increasingly prevalent in high latitude and altitude regions that were previously protected by cold winter temperatures. Ongoing island‐wide dieback of a foundation species, the cushion plant Azorella macquariensis, on World Heritage listed Macquarie Island provides the first sub‐Antarctic example. To better understand the island‐wide progression of cushion dieback and its drivers, we established and quantified plant condition classes and measured microclimate across 62 sites. We then tested whether the drivers of cushion dieback were associated with (i) water stress: represented by vapour pressure deficit, wind exposure and gravel content, (ii) pathogen virulence: using freezing days and extreme humidity as empirically supported surrogates, or (iii) both. There was a strong north‐south progression in cushion condition, with dieback most active in the centre of the island and advanced in the north. Dieback was most extensive at sites with fewer freezing days and high humidity. Natural southern refugia were explained by the significantly colder temperatures, associated with a north‐south temperature gradient. It is expected that under current climate change trajectories, where Macquarie is likely to continue to become warmer and wetter, cushion dieback will remain pervasive, expanding most slowly in the south and potentially outpacing recovery. We emphasise the need for increased awareness to prevent the establishment of pathogens into and across the landscapes of newly susceptible high latitude and altitude regions. Areas of high conservation significance need to be prioritised for management, to prevent further landscape‐scale change under current climate trajectories.

Andes, Bofedales, and the Communities of Huascarán National Park, Peru

Mountain wetlands are abundant in the high elevations of the tropical Andes. Wetlands occupy ~11% of the total park area and are mostly found in the large mountain valleys. Wetlands occur up to 5000 m asl, but most occur between 4,000–4,700 m asl. The highest elevation wetlands are typically dominated by cushion plants, while lower elevation wetlands are more commonly occupied by graminoids. About 60% of all wetlands are peatlands and the remainder are mineral soil wet meadows. The peatlands are up to 11 m deep and 12,000 years old, storing an average of 2,101 Mg C ha-1, which is comparable to lowland tropical peatlands. Our work in Huascarán National Park in Peru is also showing the importance of wetlands in a coupled natural-human system. These wetlands and alpine landscapes are shaped in part by legacies of past human land use, including ancient pastoralism and farming, and are also affected by millions of downstream users dependent upon wetlands and glacier-fed streams for water and energy production. Biodiversity and endemism is high among taxonomic groups such as plants, birds, fish, amphibians and insects. Currently the tropical Andes are in ecological flux due to rapid land cover changes caused by both biophysical and socioeconomic drivers. In addition, the high Andes are experiencing warming and rapid glacial retreat that is resulting in hydroecological changes and socioeconomic changes to the traditional Andean societies that feed back to changes in wetland sustainability.

Peatlands of the Central Andes Puna, South America

The Andean puna is the highest elevation mountain and plateau region in the western hemisphere, extending from northern Peru to central Chile and Argentina, with vast areas above 4,250 m elevation. The Atacama Desert on the western side of the Andes is the world’s most arid region, and this aridity extends across the mountains. The upland vegetation is mostly continuous in the more humid north but becomes more and more patchy and barren composed only of bunch grasses in the central and southern region. Extensive upland talus, moraines, and colluvial deposits of the mountains produces perennial ground water flow systems that support thousands of peatlands and other wetlands that are regionally termed “bofedales” or “vegas”. The peatlands are dominated by several species in the family Juncaceae, most famously Distichia muscoides, that forms dense clonal cushions that characterize the alpine peatlands and landscapes. Being close to the equator, the growing season extends across the entire year, and continuous growth of the cushion plants have produced high carbon accumulation rates and peat bodies 7-10 m thick in many areas. The region supports unique plants and animals, and ecosystems, and the wetlands are threatened by overuse for livestock grazing, and climate changes that could reduce water provision may lead to some bofedales completely drying.

Testing the role of functional trait expression in plant–plant facilitation

AbstractPositive biotic interactions between plant species may strongly affect species and community‐level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that plant–plant facilitation could occur through the impact of benefactor species on the functional trait expression of beneficiary species. Indeed, plant species that affect local conditions can modify functional trait expression of interacting species, thereby improving their performance and resulting in a facilitative interaction. However, the response of intraspecific trait variation to biotically driven microhabitat modification, and its role in determining the outcome of plant–plant interactions, has rarely been explored.Here, we test whether growing with benefactor species affects the expression of functional traits of eight species, encompassing different plant growth forms, in two contrasting study systems. This is achieved using a paired sampling approach to compare values of seven functional traits of conspecific individuals growing within and adjacent to cushion plants (i.e. benefactor species which are known to strongly alter microhabitat conditions and to have positive effects on some of the focal species). In addition, we test whether the effect of biotic interactions on functional trait expression changes along elevational gradients, as the outcome of biotic interactions is expected to vary with elevation.Contrary to predictions, in both systems, intraspecific trait variation was not well explained by the biotic interaction with the cushion plant species or the variation in abiotic conditions associated with elevational gradients. Where biotic interactions did affect functional trait expression and bivariate trait relationships, traits responded variably between species, suggesting that context specificity may be a constraint to predicting how intraspecific trait variation responds to plant–plant interactions, adding to the growing body of literature that challenges the generality and predictability of the drivers of intraspecific trait variation.This research, therefore, suggests that benefactor species’ facilitative process is likely not through an impact on intraspecific trait expression, and that instead other processes may be more important for translating beneficial microhabitat modification or increased resource availability by benefactor species into positive impacts on beneficiary species.A freePlain Language Summarycan be found within the Supporting Information of this article.

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

AimsThe 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.MethodsComputational 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.ResultsAirflow 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.ConclusionThis 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.

Disentangling Large- and Small-Scale Abiotic and Biotic Factors Shaping Soil Microbial Communities in an Alpine Cushion Plant System.

Microorganisms play a crucial role in biogeochemical cycles and ecosystem processes, but the key factors driving microbial community structure are poorly understood, particularly in alpine environments. In this study, we aim to disentangle the relative contribution of abiotic and biotic factors shaping bacterial and fungal community structure at large and small spatial and integration scales in an alpine system dominated by a stress-tolerant cushion species Thylacospermum ceaspitosum. These effects were assessed in two mountain ranges of northwest China and for two contrasting phenotypes of the cushion species inhabiting two different microtopographic positions. The large- and small-scale abiotic effects include the site and microhabitat effects, respectively, while the large- and small-scale biotic effects include the effects of cushion presence and cushion phenotype, respectively. Soil microbial communities were characterized by Illumina Miseq sequencing. Uni- and multivariate statistics were used to test the effects of abiotic and biotic factors at both scales. Results indicated that the site effect representing the soil pH and abiotic hydrothermal conditions mainly affected bacterial community structure, whereas fungal community structure was mainly affected by biotic factors with an equal contribution of cushion presence and cushion phenotype effects. Future studies should analyze the direct factors contributing to shaping microbial community structure in particular of the cushion phenotypes.