Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre‐adapted to serpentine soils.     

Serpentine ecotypic differentiation in a polyploid plant complex: shared tolerance to Mg and Ni stress among di- and tetraploid serpentine populations of <Emphasis Type="Italic">Knautia arvensis</Emphasis> (Dipsacaceae)

Background and aims

Serpentine soils impose limits on plant growth and survival and thus provide an ideal model for studying plant adaptation under environmental stress. Despite the increasing amount of data on serpentine ecotypic differentiation, no study has assessed the potential role of polyploidy. We tested for links between polyploidy and the response to serpentine stress in Knautia arvensis, a diploid-tetraploid, edaphically differentiated complex.

Methods

Variation in growth, biomass yield and tissue Mg and Ni accumulation in response to high Mg and Ni concentrations were experimentally tested using hydroponic cultivation of seedlings from eight populations of different ploidy and edaphic origin.

Results

Regardless of ploidy level, serpentine populations exhibited higher tolerance to both Mg and Ni stress than their non-serpentine counterparts, suggesting an adaptive character of these traits in K. arvensis. The effect of ploidy was rather weak and confined to a slightly better response of serpentine tetraploids to Mg stress and to higher biomass yields in tetraploids from both soil types.

Conclusions

The similar response of diploid and tetraploid serpentine populations to edaphic stress corresponded with their previously described genetic proximity. This suggests that serpentine tolerance might have been transmitted during the local autopolyploid origin of serpentine tetraploids.

     

No effect of elevation and fragmentation on genetic diversity and structure in Polylepis australis trees from central Argentina

Phenological differences in flowering arising along elevational gradients may be caused by either local adaptation or phenotypic plasticity. Local adaptation can lead to reproductive isolation of populations at different elevational zones and thus produce elevational genetic structuring, while phenotypic plasticity does not produce elevational genetic structuring. In this study, we examined the effects of elevation and fragmentation on genetic diversity and structure of Polylepis australis populations, where individuals exhibit phenological differences in flowering along an elevational gradient. We assessed the polymorphism of amplified fragment length polymorphism markers in adults and saplings from one conserved and one fragmented forest covering elevations from 1600 to 2600 m asl. Over 98% of variation was found within populations, and we found very low and similar genetic differentiation along elevational gradients for adults and saplings in both continuous and fragmented forests. In addition, there was no significant relationship between genetic diversity and elevation. Results indicated that phenological differences along elevational gradients are more likely caused by phenotypic plasticity than local adaptation, and fragmentation does not appear to have affected genetic diversity and differentiation in the studied populations. Results therefore imply that if necessary, seeds for reforestation purposes may be collected from different elevations to the seeding or planting sites.     

表型可塑性与外来植物的入侵能力

外来植物的入侵能力与其性状之间的关系是入侵生态学中的基本问题之一。成功的入侵种常常能占据多样化的生境,并以广幅的环境耐受性为特征。遗传分化(包括生态型分化)和表型可塑性是广布性物种适应变化、异质性生境的两种不同但并不矛盾和排斥的策略。越来越多的实验证据表明,表型可塑性具有确定的遗传基础,本身是一种可以独立进化的性状。许多入侵种遗传多样性比较低,但同时又占据了广阔的地理分布区和多样化的生境,表型可塑性可能在这些物种的入侵成功和随后的扩散中起到了关键作用。本文首先介绍表型可塑性的含义,简述表型可塑性和生物适应的关系,然后从理论分析和实验证据两个方面论述了表型可塑性与外来植物入侵能力的相关性,最后针对进一步的研究工作进行了讨论。当然,并非所有入侵种的成功都能归因于表型可塑性,作者认为对于那些遗传多样性比较低同时又占据多样化生境的入侵种,表型可塑性和入侵能力的正相关可能是一条普遍法则,而非特例。     

Rapid Plant Invasion in Distinct Climates Involves Different Sources of Phenotypic Variation

When exotic species spread over novel environments, their phenotype will depend on a combination of different processes, including phenotypic plasticity (PP), local adaptation (LA), environmental maternal effects (EME) and genetic drift (GD). Few attempts have been made to simultaneously address the importance of those processes in plant invasion. The present study uses the well-documented invasion history of Senecio inaequidens (Asteraceae) in southern France, where it was introduced at a single wool-processing site. It gradually invaded the Mediterranean coast and the Pyrenean Mountains, which have noticeably different climates. We used seeds from Pyrenean and Mediterranean populations, as well as populations from the first introduction area, to explore the phenotypic variation related to climatic variation. A reciprocal sowing experiment was performed with gardens under Mediterranean and Pyrenean climates. We analyzed climatic phenotypic variation in germination, growth, reproduction, leaf physiology and survival. Genetic structure in the studied invasion area was characterized using AFLP. We found consistent genetic differentiation in growth traits but no home-site advantage, so weak support for LA to climate. In contrast, genetic differentiation showed a relationship with colonization history. PP in response to climate was observed for most traits, and it played an important role in leaf trait variation. EME mediated by seed mass influenced all but leaf traits in a Pyrenean climate. Heavier, earlier-germinating seeds produced larger individuals that produced more flower heads throughout the growing season. However, in the Mediterranean garden, seed mass only influenced the germination rate. The results show that phenotypic variation in response to climate depends on various ecological and evolutionary processes associated with geographical zone and life history traits. Seeing the relative importance of EME and GD, we argue that a “local adaptation vs. phenotypic plasticity” approach is therefore not sufficient to fully understand what shapes phenotypic variation and genetic architecture of invasive populations.     

Characterizing the contribution of plasticity and genetic differentiation to community‐level trait responses to environmental change

The match between functional trait variation in communities and environmental gradients is maintained by three processes: phenotypic plasticity and genetic differentiation (intraspecific processes), and species turnover (interspecific). Recently, evidence has emerged suggesting that intraspecific variation might have a potentially large role in driving functional community composition and response to environmental change. However, empirical evidence quantifying the respective importance of phenotypic plasticity and genetic differentiation relative to species turnover is still lacking. We performed a reciprocal transplant experiment using a common herbaceous plant species (Oxalis montana) among low‐, mid‐, and high‐elevation sites to first quantify the contributions of plasticity and genetic differentiation in driving intraspecific variation in three traits: height, specific leaf area, and leaf area. We next compared the contributions of these intraspecific drivers of community trait–environment matching to that of species turnover, which had been previously assessed along the same elevational gradient. Plasticity was the dominant driver of intraspecific trait variation across elevation in all traits, with only a small contribution of genetic differentiation among populations. Local adaptation was not detected to a major extent along the gradient. Fitness components were greatest in O. montana plants with trait values closest to the local community‐weighted means, thus supporting the common assumption that community‐weighted mean trait values represent selective optima. Our results suggest that community‐level trait responses to ongoing climate change should be mostly mediated by species turnover, even at the small spatial scale of our study, with an especially small contribution of evolutionary adaptation within species.     

Within- and trans-generational plasticity affects the opportunity for selection in barbed goatgrass (Aegilops triuncialis)

• Premise of the study: Environments are composed of selective agents, and environments may also modify the efficacy of these agents. Environments affect the rate of maximum evolutionary change by influencing variation in relative fitness (i.e., the opportunity for selection, or I). Within- and transgenerational plastic environmental responses may affect I, speeding or slowing processes of local adaptation. • Methods: We determined whether environmental factors affected the opportunity for selection (I) in Aegilops triuncialis (barbed goatgrass) by measuring I as a within- and transgenerational plastic response to two maternal glasshouse environments (serpentine/dry and loam/moist). We also determined whether this species’ two most common genetic lineages (determined by DNA microsatellite length polymorphism) varied in response to glasshouse treatments. • Key Results: Opportunity for selection was less for plants grown in the dry serpentine environment than for plants grown in the moist loam environment. This response varied between genetic lineages. The east lineage exhibited a within-generation response to the dry serpentine environment. For both seed mass and average seed weight in this lineage, the opportunity for selection was lower in dry serpentine than in moist loam. The west lineage had a transgenerational response to the dry serpentine such that the opportunity for selection for seed number and seed mass was lower for plants produced by mothers grown in dry serpentine than for plants produced by mothers in moist loam. • Conclusions: Phenotypic variation in relative fitness is constrained by the dry serpentine environment, which leads to lower evolvability in this environment. Within- and transgenerational effects of the environment may slow local adaptation to serpentine soils.     

Jack-and-Master Trait Responses to Elevated CO2 and N: A Comparison of Native and Introduced Phragmites australis

Global change is predicted to promote plant invasions world-wide, reducing biodiversity and ecosystem function. Phenotypic plasticity may influence the ability of introduced plant species to invade and dominate extant communities. However, interpreting differences in plasticity can be confounded by phylogenetic differences in morphology and physiology. Here we present a novel case investigating the role of fitness trait values and phenotypic plasticity to global change factors between conspecific lineages of Phragmites australis. We hypothesized that due to observed differences in the competitive success of North American-native and Eurasian-introduced P. australis genotypes, Eurasian-introduced P. australis would exhibit greater fitness in response to global change factors. Plasticity and plant performance to ambient and predicted levels of carbon dioxide and nitrogen pollution were investigated to understand how invasion pressure may change in North America under a realistic global change scenario. We found that the introduced Eurasian genotype expressed greater mean trait values in nearly every ecophysiological trait measured – aboveground and belowground – to elevated CO₂ and nitrogen, outperforming the native North American conspecific by a factor of two to three under every global change scenario. This response is consistent with “jack and master” phenotypic plasticity. We suggest that differences in plant nitrogen productivity, specific leaf area, belowground biomass allocation, and inherently higher relative growth rate are the plant traits that may enhance invasion of Eurasian Phragmites in North America. Given the high degree of genotypic variability within this species, and our limited number of genotypes, our results must be interpreted cautiously. Our study is the first to demonstrate the potential importance of jack-and-master phenotypic plasticity in plant invasions when facing imminent global change conditions. We suggest that jack-and-master invasive genotypes and/or species similar to introduced P. australis will have an increased ecological fitness, facilitating their invasion in both stressful and resource rich environments.     

Genetic diversity inferred from AFLP fingerprinting in populations of Onosma echioides (Boraginaceae) from serpentine and calcareous soils

Abstract

Onosma echioides is a non-obligate serpentinophytic borage occurring discontinuously on calcareous and serpentine outcrops at the northwest limit of its range. Mean concentrations of Ca, Mg and heavy metals in root and shoot samples of eight populations from the two soil types were first determined. Subsequently, the genetic polymorphism of the same accessions was estimated by means of Amplified Fragment Length Polymorphism (AFLP) fingerprinting technique. Root and shoot samples from serpentine outcrops showed higher levels of Ni, Cr and Mg, and lower Ca/Mg ratios compared with those from calcareous soils. Based on 353 polymorphic AFLP bands, the two edaphic groups of populations showed comparable levels of genetic diversity. A remarkable genetic differentiation between populations and a high level of within-population genetic variance were found. Results of Mantel's test supported a significant correlation between genetic and geographical distances, while no difference in relation to the edaphic factor was detected. Molecular data suggested isolation as the key factor shaping the infraspecific genetic structure of O. echioides, which may be in relation with the short-distance, zoochorous systems of seed dispersal and pollination of this species.     

CHARACTERIZING SELECTION ON PHENOTYPIC PLASTICITY IN RESPONSE TO NATURAL ENVIRONMENTAL HETEROGENEITY

Adaptive genetic differentiation and adaptive phenotypic plasticity can increase the fitness of plant lineages in heterogeneous environments. We examine the relative importance of genetic differentiation and plasticity in determining the fitness of the annual plant, Erodium cicutarium, in a serpentine grassland in California. Previous work demonstrated that the serpentine sites within this mosaic display stronger dispersal‐scale heterogeneity than nonserpentine sites. We conducted a reciprocal transplant experiment among six sites to characterize selection on plasticity expressed by 180 full‐sibling families in response to natural environmental heterogeneity across these sites. Multivariate axes of environmental variation were constructed using a principal components analysis of soil chemistry data collected at every experimental block. Simple linear regressions were used to characterize the intercept, and slope (linear and curvilinear) of reaction norms for each full‐sibling family in response to each axis of environmental variation. Multiple linear regression analyses revealed significant selection on trait means and slopes of reaction norms. Multivariate analyses of variance demonstrated genetic differentiation between serpentine and nonserpentine lineages in the expression of plasticity in response to three of the five axes of environmental variation considered. In all but one case, serpentine genotypes expressed a stronger adaptive plastic response than nonserpentine genotypes.     

Pre-adaptation or genetic shift after introduction in the invasive species Impatiens glandulifera?

Invasive exotic plants often grow fast, reproduce rapidly and display considerable phenotypic plasticity in their invasive range, which may be essential characteristics for successful invasion. However, it remains unclear whether these characteristics are already present in native populations (pre-adaptation hypothesis) or evolve after introduction (genetic shift hypothesis).To test these hypotheses we compared means and phenotypic plasticity of vegetative and reproductive traits between populations of Impatiens glandulifera collected from either the invasive (Norway) or native range (India). Seeds were sown and the resulting plants were exposed to different experimental environments in a glasshouse. We also tested whether trait means and reaction norms harbored genetic variation, as this may promote fitness in the novel environment.We did not find evidence that invasive populations of I. glandulifera grew more vigorously or produced more seeds than native populations. Phenotypic plasticity did not differ between the native and invasive range, except for the number of nodes which was more plastic in the invasive range. Genetic variation in the slope of reaction norms was absent, suggesting that the lack of change in phenotypic plasticity between native and invasive populations resulted from low genetic variation in phenotypic plasticity initially harbored by this species. Post-introduction evolution of traits thus probably did not boost the invasiveness of I. glandulifera. Instead, the species seems to be pre-adapted for invasion.We suggest that differences in habitat between the native and invasive range, more specifically the higher nutrient availability observed in the new environment, are the main factor driving the invasion of this species. Indeed, plants in the more nutrient-rich invasive range had greater seed mass, likely conferring a competitive advantage, while seed mass also responded strongly to nutrients in the glasshouse. Interactions between habitat productivity and herbivore defense may explain the lack of more vigorous growth in the new range.     

Intraspecific spatial genetic differentiation of a Daphnia species within a long narrow reservoir

Environmental gradients influence the distribution and taxonomic composition of planktonic taxa, including Daphnia. In canyon-shaped reservoirs with pronounced horizontal gradients of food supply, predation pressure and other factors, not only species and interspecific hybrids but also clones within these taxa are non-randomly distributed. Using a long-term data set from a reservoir mostly dominated by a single Daphnia species, we evaluated whether intraspecific genetic differentiation can be frequently detected between upstream and downstream reservoir regions with different environmental conditions. We analysed variation at four allozyme loci (two species-specific and two polymorphic) to assess the taxonomic composition and intraspecific variation of Daphnia collected in different years (between 1995 and 2005) and periods of the growing season. D. galeata dominated in all samples, although other species and hybrids with D. galeata were also occasionally detected. Despite limited variation at the analysed loci, D. galeata from upstream and downstream regions were significantly genetically differentiated on seven out of twelve sampling dates. Although genetic drift in geographically distant subpopulations may contribute to differentiation, we presume that the observed patterns are primarily due to different selection regimes. We predict that a significant genetic differentiation within planktonic populations also occurs more frequently in natural water bodies.     

Light and Nutrient Dependent Responses in Secondary Metabolites of Plantago lanceolata Offspring Are Due to Phenotypic Plasticity in Experimental Grasslands

A few studies in the past have shown that plant diversity in terms of species richness and functional composition can modify plant defense chemistry. However, it is not yet clear to what extent genetic differentiation of plant chemotypes or phenotypic plasticity in response to diversity-induced variation in growth conditions or a combination of both is responsible for this pattern. We collected seed families of ribwort plantain (Plantago lanceolata) from six-year old experimental grasslands of varying plant diversity (Jena Experiment). The offspring of these seed families was grown under standardized conditions with two levels of light and nutrients. The iridoid glycosides, catalpol and aucubin, and verbascoside, a caffeoyl phenylethanoid glycoside, were measured in roots and shoots. Although offspring of different seed families differed in the tissue concentrations of defensive metabolites, plant diversity in the mothers'' environment did not explain the variation in the measured defensive metabolites of P. lanceolata offspring. However secondary metabolite levels in roots and shoots were strongly affected by light and nutrient availability. Highest concentrations of iridoid glycosides and verbascoside were found under high light conditions, and nutrient availability had positive effects on iridoid glycoside concentrations in plants grown under high light conditions. However, verbascoside concentrations decreased under high levels of nutrients irrespective of light. The data from our greenhouse study show that phenotypic plasticity in response to environmental variation rather than genetic differentiation in response to plant community diversity is responsible for variation in secondary metabolite concentrations of P. lanceolata in the six-year old communities of the grassland biodiversity experiment. Due to its large phenotypic plasticity P. lanceolata has the potential for a fast and efficient adjustment to varying environmental conditions in plant communities of different species richness and functional composition.     

Genetic differences in the elevational limits of native and introduced Lactuca serriola populations

Aim Differences in phenological timing might explain why populations of the annual Lactuca serriola reach higher elevational limits in a part of its introduced range than in its native range. I investigated (1) whether this difference in elevational limits has a genetic basis, (2) the importance of clinal genetic differentiation and phenotypic plasticity in phenology as responses to elevation in L. serriola, and whether these responses differ between regions, and (3) whether the realized temperature niche of L. serriola differs between the two regions. Location Plant material was collected in Canton Valais, Switzerland (native range) and the Wallowa Mountains, Oregon, USA (introduced range). The field experiment was conducted in Canton Grisons, Switzerland. Methods Plants from 20 populations collected along elevational gradients were grown in eight common gardens established at 200‐m elevational intervals (600–2000 m a.s.l.). The timing of phenological transitions was monitored and analysed with mixed‐effects models to determine differences in (1) elevational limits, and (2) clinal genetic differentiation and phenotypic plasticity as responses to elevation for plants from each region. The limits of the species along five temperature gradients were derived from generalized linear models using published occurrence data to quantify regional differences in the realized temperature niche. Results The limit of seed set (1400 m a.s.l.) was the same for plants of both regions. However, the limit of flowering, probably a better reflection of elevational limits in this study, was 400 m higher for plants from the introduced region due to their faster development. Native populations showed clines in development time with elevation consistent with expectations. However, these were weaker in introduced populations, the responses of which were rather characterized by phenotypic plasticity. Thus, although introduced populations grow at considerably cooler sites than in the native region, this is unlikely to have resulted from direct selection for tolerance of high‐elevation conditions. Main conclusions This study supports a genetic basis for differences in the elevational limits of L. serriola populations between two parts of its native and introduced range. Although it is not yet clear whether these differences evolved in the introduced range, these findings highlight the potential of alien species for gaining insights into niche evolution.     

Edaphic microsatellite DNA divergence in wild emmer wheat, Triticum dicoccoides, at a microsite: Tabigha, Israel

Twenty eight microsatellite markers were used to analyze genetic divergence in tandem dinucleotide repeated DNA regions between two edaphic subpopulations of Triticum dicoccoides growing on the contrasting terra rossa and basalt soilsfrom a microsite at Tabigha, north of the Sea of Galilee, Israel. The terra rossa soil niche was drier and more stressful than the basalt throughout the growing season (November to May). Significant microsatellite divergence in allele distribution, repeat length, genetic diversity, and linkage disequilibria were found between emmer wheat from the two soil types over two short transects of 100 m each. Soil-specific and -unique alleles and linkage disequilibria were observed in the terra rossa and basalt subpopulations. A permutation test showed that the effects of random genetic drift were very low for the significant genetic diversity at microsatellite loci between the two subpopulations, suggesting that an adaptive molecular pattern derived by edaphic selection may act upon variation of the microsatellites. Received: 4 February 2000 / Accepted: 31 March 2000<@head-com-p1a.lf>Communicated by H.F. Linskens     

Variable effects on growth and defense traits for plant ecotypic differentiation and phenotypic plasticity along elevation gradients

Along ecological gradients, phenotypic differentiation can arise through natural selection on trait diversity and magnitude, and environment‐driven plastic changes. The magnitude of ecotypic differentiation versus phenotypic plasticity can vary depending on the traits under study. Using reciprocal transplant‐common gardens along steep elevation gradients, we evaluated patterns of ecotypic differentiation and phenotypic plasticity of several growth and defense‐related traits for two coexisting but unrelated plant species, Cardamine pratensis and Plantago major. For both species, we observed ecotypic differentiation accompanied by plasticity in growth‐related traits. Plants grew faster and produced more biomass when placed at low elevation. In contrast, we observed fixed ecotypic differentiation for defense and resistance traits. Generally, low‐elevation ecotypes produced higher chemical defenses regardless of the growing elevation. Yet, some plasticity was observed for specific compounds, such as indole glucosinolates. The results of this study may suggest that ecotypic differentiation in defense traits is maintained by costs of chemical defense production, while plasticity in growth traits is regulated by temperature‐driven growth response maximization.     

Fine-scale spatial genetic structure across a strong environmental gradient in the saltmarsh plant <Emphasis Type="Italic">Puccinellia maritima</Emphasis>

Saltmarsh forms the transition between maritime and terrestrial environments where biotic and abiotic conditions vary substantially along a gradient in elevation. Theoretical and empirical population genetics studies have focused on the influence of environmental gradients on intra-specific genetic variation. Contrastingly, only a few studies have focused on genetic variation in saltmarsh plants, despite the potentially strong influence of environmental gradients shaping diversity in these species. In the present paper, we assess the genetic structure of the saltmarsh plant Puccinellia maritima collected across an elevation gradient in restored and natural saltmarsh. Both spatial autocorrelograms of genetic variation and spatial analysis of principal components detected genetic structure in the natural saltmarsh organized along the gradient in elevation, yet no such pattern was identified considering distance between individuals without taking elevation into account. In combination with previous phenotypic analyses, our results imply that ecological divergence likely plays a key role in shaping genetic structure within saltmarsh species. Comparison of restored and natural saltmarsh indicated that interspecific competition plays an important role in shaping the genetic structure observed on the natural saltmarsh. The results of this study demonstrate that saltmarshes are valuable models in which to test effects of ecological differentiation and, by extension, provide a better understanding of the functioning of this threatened environment.     

Plant resource-use strategies: the importance of phenotypic plasticity in response to a productivity gradient for two subalpine species

Background and Aims

Functional traits are indicators of plant interactions with their environment and the resource-use strategies of species can be defined through some key functional traits. The importance of genetic variability and phenotypic plasticity in trait variations in response to a common environmental change was investigated in two subalpine species.

Methods

Two species with contrasted resource-use strategies, Dactylis glomerata and Festuca paniculata, were grown along a productivity gradient in a greenhouse experiment. Functional traits of different genotypes were measured to estimate the relative roles of phenotypic plasticity and genetic variability, and to compare their levels of phenotypic plasticity.

Key Results

Trait variability in the field for the two species is more likely to be the result of phenotypic plasticity rather than of genetic differentiation between populations. The exploitative species D. glomerata expressed an overall higher level of phenotypic plasticity compared with the conservative species F. paniculata. In addition to different amplitudes of phenotypic plasticity, the two species differed in their pattern of response for three functional traits relevant to resource use (specific leaf area, leaf dry matter content and leaf nitrogen content).

Conclusions

Functional trait variability was mainly the result of phenotypic plasticity, with the exploitative species showing greater variability. In addition to average trait values, two species with different resource-use strategies differed in their plastic responses to productivity.     

Phenotypic effects of the nurse Thylacospermum caespitosum on dependent plant species along regional climate stress gradients

Contrasting phenotypes of alpine cushion species have been recurrently described in several mountain ranges along small‐scale topography gradients, with tight competitive phenotypes in stressful convex topography and loose facilitative phenotypes in sheltered concave topography. The consistency of phenotypic effects along large‐scale climate stress gradients have been proposed as a test of the likely genetic bases of the differences observed at small‐scale. Inversely, plastic phenotypic effects are more likely to vanish at some points along climate stress gradients. We tested this hypothesis for two phenotypes of the alpine cushion species Thylacospermum caespitosum at four points along regional gradients of cold and drought stress in northwest China. We measured the traits of the two cushion phenotypes and quantified their associated plant communities and environmental variables along the regional temperature and aridity gradients. Cushion height, convexity and stem density overall showed significant effect of phenotypes. Difference in tightness of cushions between phenotypes was consistent across climate conditions, whereas differences in cushion convexity and height between phenotypes increased with increasing cold stress. Phenotypic effects on species richness and abundance were consistent along both climate gradients but not effects on species composition, while there were no phenotypic effects on environmental variables. Additionally, RII (relative interaction index) curves were linear along the drought gradient but unimodal along the temperature gradient, likely due to the occurrence of contrasting species pools at the different sites. We conclude that the consistency of phenotypic effects of T. caespitosum was high for species richness and abundance and mainly explained by differences in interference mediated by likely heritable differences in cushion tightness. Additionally, our study shows that the shapes of the relationship between plant responses to neighbours and environmental stresses are not necessarily driven by niche‐based deterministic factors.