What shapes the altitudinal range of a high mountain Mediterranean plant? Recruitment probabilities from ovule to seedling stage

Recruitment is a complex process consisting of sequential stages affected by biotic interactions and abiotic factors. Assessment of these sequential stages and corresponding subprocesses may be useful in identifying the most critical stages. Accordingly, to assess the factors that may determine the altitudinal range limits of the high mountain Mediterranean plant Silene ciliata, a set of demographic stages, from flower production to establishment of 2‐yr‐old plants, and their influence on recruitment probability were examined using a step‐by‐step approach. We integrated florivory, pollination and pre‐dispersal seed predation as pre‐dispersal factors, and seedling emergence and survival as post‐dispersal determinants of recruitment. Three populations were monitored at the southernmost margin of the species along its local altitudinal range. Previous studies suggest that seediness is strongly limited by summer drought especially at the lower boundary of the species, a situation that may worsen under current global warming. Our results showed that recruitment was mainly limited by low seed production in the pre‐dispersal stage and low seedling emergence and survival in the post‐dispersal stage, probably due to environmental harshness in summer. By contrast, biotic factors responsible for propagule loss, such as flower and fruit predation, had a minor effect on the probability of plant recruitment. Although the relative importance of transition probabilities was similar among populations along the altitudinal range, comparatively lower flower production significantly reduced the number of recruited plants at the lowest altitude population. This demographic bottleneck, together with increased competition with other species favoured by climate warming, might collapse population growth and limit persistence at the lower altitudinal range of the species, raising its low local altitudinal edge.     

Negative evidence of local adaptation to the establishment conditions in a perennial herb

The differential adaptation of populations of the same species to their local environmental conditions through divergent selection, known as local adaptation, is a key step in the process of diversification of species. Here, we explore the local adaptation of the perennial mountain herb Helleborus foetidus to variable environmental conditions of seedling emergence and establishment at two different spatial scales (habitats and regions) with special attention to the role of physical and chemical soil properties. The possibility of local adaptation was evaluated under the ??local versus foreign?? and the ??home versus away?? criteria. Reciprocal sowing experiments were carried out by cross-sowing seeds among habitats and regions, controlling for maternal effects by means of seed mass, and recording seedling emergence and survival. Several topsoil properties were measured linked to each sowing point. Only partial patterns of local adaptation were found, which were insufficient to eventually state the existence of local adaptation at any spatial scale or under any criteria assessed. Here, we discuss how soil properties and selection on seed size may be related to the non-achievement of local adaptation criteria. Negative evidence of local adaptation seems to be due to a congruency in the selective pressures exerted by the different soil environments on seedling emergence and survival.     

Unravelling genetics at the top: mountain islands or isolated belts?

Background and Aims

In mountain plant populations, local adaptation has been described as one of the main responses to climate warming, allowing plants to persist under stressful conditions. This is especially the case for marginal populations at their lowest elevation, as they are highly vulnerable. Adequate levels of genetic diversity are required for selection to take place, while high levels of altitudinal gene flow are seen as a major limiting factor potentially precluding local adaptation processes. Thus, a compromise between genetic diversity and gene flow seems necessary to guarantee persistence under oncoming conditions. It is therefore critical to determine if gene flow occurs preferentially between mountains at similar altitudinal belts, promoting local adaptation at the lowest populations, or conversely along altitude within each mountain.

Methods

Microsatellite markers were used to unravel genetic diversity and population structure, inbreeding and gene flow of populations at two nearby altitudinal gradients of Silene ciliata, a Mediterranean high-mountain cushion plant.

Key Results

Genetic diversity and inbreeding coefficients were similar in all populations. Substantial gene flow was found both along altitudinal gradients and horizontally within each elevation belt, although greater values were obtained along altitudinal gradients. Gene flow may be responsible for the homogeneous levels of genetic diversity found among populations. Bayesian cluster analyses also suggested that shifts along altitudinal gradients are the most plausible scenario.

Conclusions

Past population shifts associated with glaciations and interglacial periods in temperate mountains may partially explain current distributions of genetic diversity and population structure. In spite of the predominance of gene flow along the altitudinal gradients, local genetic differentiation of one of the lower populations together with the detection of one outlier locus might support the existence of different selection forces at low altitudes.     

Altitude and woody cover control recruitment of Helleborus foetidus in a Mediterranean mountain area

This study explores how variation of macro- and micro-climatic conditions associated with changes in altitude affect early recruitment dynamics of the perennial herb Helleborus foetidus (Ranunculaceae). We also analyse the relevance of facilitation by woody vegetation on seedling recruitment along altitudinal gradient. We conducted a sowing experiment testing the effect of altitude (using three populations located at 1100, 1400 and 1650 m a.s.l.) and woody cover (open areas vs cover of woody species) on seedling emergence during two years and survival three years after sowing. Simultaneously, we characterised elevations and cover types in terms of climatic factors (surface air temperature and relative humidity) throughout a whole year, and light conditions (global site factor and red/infrared ligh ratio) using hemispheric photographs. We detected a significant effect of elevation on seedling emergence, with a higher emergence at lowest altitude. Woody cover greatly affected seedling survival and recruitment, both rates being higher under woody species than in open areas. Emergence was negatively correlated with winter stress factors, which increased with elevation. Survival and recruitment were negatively correlated with summer stress factors, which were ameliorated by woody cover and with altitude. Amelioration of climatic factors by woody cover was not influenced by altitude. Implications for species persistence in Mediterranean mountains under climate change scenarios are discussed.     

Strong microsite control of seedling recruitment in tundra

The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided.     

Short delay in timing of emergence determines establishment success in Pinus sylvestris across microhabitats

BACKGROUND AND AIMS: The date of emergence may have far-reaching implications for seedling performance. Seedlings emerging early in the growing season often have a greater rate of survival or grow better if early emergence provides advantages with respect to an environmental cue. As a result, the benefits of early emergence may be lost if the environmental stress creating the differences among cohorts disappears. The experimental manipulation under field conditions of the factors that constitute the main sources of stress for seedling establishment is thus a straightforward method to evaluate the impact of date of emergence on seedling establishment under realistic conditions. METHODS: Two field experiments were performed to analyse the effect of emergence date on survival and first-year growth of Scots pine seedlings in natural mountain forests in south-east Spain. Two main environmental factors that determine seedling success in these mountains were considered: (1) microhabitat type (monitoring the effect of date of emergence in the three most common microhabitats where seedlings recruit); (2) summer drought (monitored by an irrigation treatment with control and watered sampling points). KEY RESULTS: Overall, early emergence resulted in a higher probability of survival and better growth in the two experiments and across microhabitats. However, the reduction in summer drought did not diminish the differences observed among cohorts: all cohorts increased their survival and growth, but early cohorts still had a clear advantage. CONCLUSIONS: Date of emergence determines establishment success of Pinus sylvestris seedlings, even if cohorts are separated by only a few days, irrespective of the intensity of summer drought. The experimental design, covering a gradient of light intensity and soil moisture that simulates conditions of the regeneration niche of Scots pine across its geographical range, allows the results to be extrapolated to other areas of the species. Date of emergence is thus likely to have a large impact on the demography of Scots pine across its geographical range.     

Mountain invasions on the way: are there climatic constraints for the expansion of alien woody species along an elevation gradient in Argentina?

Aims Increasing evidence worldwide indicates that high mountain regions are not immune to invasion by alien plants. Here, we aimed to address whether three major woody invaders of low-mountain areas are constrained to lower altitudes due to climatic restrictions or just by low propagule pressure. We hypothesize that the increasing climatic harshness towards higher altitudes restricts seedling establishment and survival of these woody invaders and thus their potential for altitudinal expansion.Methods The study was carried out in the Sierras Grandes Mountains, Córdoba, central Argentina (32o50′S, 64o90′W). We addressed the hypothesis with an experimental approach, dissociating the effect of the environmental gradient from that of propagule pressure, by discarding the influence of seed sources. We translocated seeds of Gleditsia triacanthos L., Ligustrum lucidum W.T. Aiton. and Pyracantha angustifolia (Franch.) C.K.Schneid. along the altitudinal gradient (from 900 to 2700 m asl). Seven sites were selected along the altitudinal gradient, spaced every 200–400 m. Three plots (4×4 m) were selected within each altitudinal site and excluded from livestock; 100 seeds of each species were sown within each plot (6300 seeds in total). Seedling emergence and survival was monitored during two growing seasons and soil temperature and moisture was recorded as well. The field experiment was complemented with lab assays.Important findings Climate along this altitudinal gradient might be least restrictive at mid elevations, as a result of the intersection between opposite soil temperature and moisture gradients. Sown seeds germinated along the whole altitudinal gradient and seedlings successfully established and over-wintered well above their current altitudinal distribution (up to 2200 m for Ligustrum and 2400 m for Gleditsia and Pyracantha). Additional lab assays confirmed field patterns and gave some insights into contrasting regeneration strategies between these invaders that might help to overcome stochastic environmental constraints in the germination stage. Overall, seedlings of three major woody invaders of low-mountain woodlands can establish and survive at higher elevations than their current distribution. In contrast to natives, they seem to be broad climate tolerators, rather than specialized stress tolerators, capable of germinating and growing across a wide elevational range. While long-term experiments might be necessary to fully address the potentials for altitudinal expansion, out results on early lifecycle stage suggest that the invaders studied here would have mostly a dispersal barrier rather than a climate barrier to establish in the upper belt of the Sierras Grandes.     

Effects of the duration of cold stratification on early life stages of the Mediterranean alpine plant Silene ciliata

Cold stratification provided by snow cover is essential to break seed dormancy in many alpine plant species. The forecast reduction in snow precipitation and snow cover duration in most temperate mountains as a result of global warming could threaten alpine plant populations, especially those at the edge of their species distribution, by altering the dynamics of early life stages. We simulated some effects of a reduction in the snow cover period by manipulating the duration of cold stratification in seeds of Silene ciliata, a Mediterranean alpine specialist. Seeds from three populations distributed along an altitudinal gradient were exposed to different periods of cold stratification (2, 4 and 6 months) in the laboratory and then moved to common garden conditions in a greenhouse. The duration of the cold stratification treatment and population origin significantly affected seed emergence percentage, emergence rate and seedling size, but not the number of seedling leaves. The 6‐month and 4‐month cold stratification treatments produced higher emergence percentages and faster emergence rates than seeds without cold stratification treatment. No significant cold stratification duration x seed population origin interactions were found, thus differential sensitivity to cold stratification along elevation is not supported.     

Microclimate predicts frost hardiness of alpine Arabidopsis thaliana populations better than elevation

In mountain regions, topological differences on the microscale can strongly affect microclimate and may counteract the average effects of elevation, such as decreasing temperatures. While these interactions are well understood, their effect on plant adaptation is understudied. We investigated winter frost hardiness of Arabidopsis thaliana accessions originating from 13 sites along altitudinal gradients in the Southern Alps during three winters on an experimental field station on the Swabian Jura and compared levels of frost damage with the observed number of frost days and the lowest temperature in eight collection sites. We found that frost hardiness increased with elevation in a log‐linear fashion. This is consistent with adaptation to a higher frequency of frost conditions, but also indicates a decreasing rate of change in frost hardiness with increasing elevation. Moreover, the number of frost days measured with temperature loggers at the collection sites correlated much better with frost hardiness than the elevation of collection sites, suggesting that populations were adapted to their local microclimate. Notably, the variance in frost days across sites increased exponentially with elevation. Together, our results suggest that strong microclimate heterogeneity of high alpine environments can preserve functional genetic diversity among small populations. Synthesis: Here, we tested how plant populations differed in their adaptation to frost exposure along an elevation gradient and whether microsite temperatures improve the prediction of frost hardiness. We found that local temperatures, particularly the number of frost days, are a better predictor of the frost hardiness of plants than elevation. This reflects a substantial variance in frost frequency between sites at similar high elevations. We conclude that high mountain regions harbor microsites that differ in their local microclimate and thereby can preserve a high functional genetic diversity among them. Therefore, high mountain regions have the potential to function as a refugium in times of global change.     

Seedling emergence responds to both seed source and recruitment site climates: a climate change experiment combining transplant and gradient approaches

Seedling recruitment allows genetic recombination and production of dispersal units. Both the climate experienced by the source populations (seed source effect) and the weather experienced by the seeds during germination and seedling emergence (recruitment site effects) are important for seedling recruitment. Separating these effects in the field is essential to assess potential climate change impacts on plant population. We combine experimental seed transplant and gradient analyses to separate the effects of seed source and recruitment site temperature and precipitation for the seedling emergence of two alpine/lowland species pairs (Viola biflora/Viola palustris, Veronica alpina/Veronica officinalis). Combining these approaches allows us to compare local responses versus responses along environmental gradients, but also tests for local adaptation and/or pre-conditioning effects (adaptive seedling emergence responses). Veronica officinalis emergence increased with increasing seed source temperature in both the experimental and the gradient approaches, and showed adaptive seedling emergence. Viola biflora, Viola palustris and Veronica alpina emergence decreased with recruitment site temperature in both approaches. Both Violas emergences increased with recruitment site precipitation, in both approaches for the alpine violet, and in the gradient approach for lowland one. Emergence was primarily affected by the environment of the recruitment site, whereas seed source climate and adaptive seedling emergence impacted recruitment in only one of our species. The responses to recruitment site temperatures were negative, whereas the response to seed source temperature was positive. Ignoring the distinctions between these different mechanisms can lead to erroneous conclusions regarding potential climate change impacts on plant recruitment.     

Adding a third dimension to the edge of a species' range: altitude and genetic structuring in mountainous landscapes

In addition to the topographical and ecological barriers, other landscape features may also subtly influence the patterns of gene flow and spatial genetic structuring at species' borders. This paper focuses on the role played by altitudinal gradients that characterize mountainous landscapes. We formulate and test the hypothesis that when the distribution boundaries of plant species intersect mountainous landscapes, altitudinal gradients in ecological conditions may considerably enhance population subdivision and genetic structuring at the regional level. Using amplified fragment length polymorphism markers, we studied genetic diversity and differentiation in a set of 21 peripheral populations of the evergreen shrub Lavandula latifolia Med. (Labiatae) at its southernmost distribution limit in the Betic mountain ranges of southern Spain. Population size and abundance, and within-population genetic diversity, varied predictably with altitude, being highest at middle elevations and declining steadily towards both the upper and lower altitudinal distribution margins. Genetic differentiation tended to follow the opposite trend. These altitudinal patterns result from variation with elevation in the relative influence of gene flow and drift on the distribution of genetic variation. Genetic drift prevails around the upper and lower altitudinal limits, whereas a situation closer to a drift-gene flow equilibrium exists at the center of the altitudinal distribution. Altitudinal variation in the relative influences of gene flow and drift appears as an essential element in the interpretation of regional genetic structuring of L. latifolia at its mountainous distribution edge, and a factor which may influence the evolutionary potential of peripheral populations and the likelihood of local adaptation.     

Seedling establishment of Asteraceae forbs along altitudinal gradients: a comparison of transplant experiments in the native and introduced ranges

Aim Since ecological and evolutionary context changes when a plant species is introduced to a new area, it can be assumed that responses of alien plants to changing conditions along environmental gradients differ from those in their native range. Even if seed availability is not limited, the distribution of alien plants along such a gradient might still be restricted by their ability to germinate and establish as seedlings. In the present study, we aim at testing what factors promote or limit plant invasions during early establishment by using altitude as a model gradient. Location Altitudinal gradients in the Wallowa Mountains (Oregon, USA) and the Swiss Alps (Valais, Switzerland). Methods In transplant experiments along altitudinal gradients, we investigated the early establishment success of eight invasive alien Asteraceae species in their native and introduced ranges in the Wallowa Mountains and the Swiss Alps. Results Seedling recruitment was not restricted to relatively lower altitudes in the introduced range. In addition, we found no evidence for genetic adaptation along the altitudinal gradient in the introduced range, highlighting the importance of phenotypic flexibility for invasions. Furthermore, seedling recruitment was only enhanced by disturbance in the native range where vegetation was comparably dense but not in the introduced range. However, plant development was strongly delayed in the introduced range, probably due to low seasonal water availability. Main Conclusions We conclude that introduced plants, due to their ability to tolerate a wide range of environmental conditions, are not necessarily more restricted in their altitudinal limits than they are in their native range. Furthermore, due to other interacting factors (e.g. different competition situations among ranges), attempts to predict distributions of alien plants in the introduced range that are based on their distributions in the native range may be misleading.     

The importance of biotic interactions and local adaptation for plant response to environmental changes: field evidence along an elevational gradient

Predicting the response of species to environmental changes is a great and on‐going challenge for ecologists, and this requires a more in‐depth understanding of the importance of biotic interactions and the population structuration in the landscape. Using a reciprocal transplantation experiment, we tested the response of five species to an elevational gradient. This was combined to a neighbour removal treatment to test the importance of local adaptation and biotic interactions. The trait studied was performance measured as survival and biomass. Species response varied along the elevational gradient, but with no consistent pattern. Performance of species was influenced by environmental conditions occurring locally at each site, as well as by positive or negative effects of the surrounding vegetation. Indeed, we observed a shift from competition for biomass to facilitation for survival as a response to the increase in environmental stress occurring in the different sites. Unlike previous studies pointing out an increase of stress along the elevation gradient, our results supported a stress gradient related to water availability, which was not strictly parallel to the elevational gradient. For three of our species, we observed a greater biomass production for the population coming from the site where the species was dominant (central population) compared to population sampled at the limit of the distribution (marginal population). Nevertheless, we did not observe any pattern of local adaptation that could indicate adaptation of populations to a particular habitat. Altogether, our results highlighted the great ability of plant species to cope with environmental changes, with no local adaptation and great variability in response to local conditions. Our study confirms the importance of taking into account biotic interactions and population structure occurring at local scale in the prediction of communities’ responses to global environmental changes.     

Phenotypes and environment predict seedling survival for seven co‐occurring Great Basin plant taxa growing with invasive grass

Trait–environment correlations can arise from local adaptation and can identify genetically and environmentally appropriate seeds for restoration projects. However, anthropogenic changes can disrupt the relationships between traits and fitness. Finding the best seed sources for restoration may rely on describing plant traits adaptive in disturbed and invaded environments, recognizing that while traits may differ among species and functional groups, there may be similarities in the strategies that increase seedling establishment. Focusing on three grass genera, two shrub species, and two forb genera, we collected seeds of all taxa from 16 common sites in the sagebrush steppe of the western United States. We measured seed and seedling characteristics, including seed size, emergence timing, and root and shoot traits, and compiled a suite of environmental variables for each collection site. We described trait–environment associations and asked how traits or environment of origin were associated with seedling survival in invaded gardens. Sampling seven taxa from the same sites allowed us to ask how trait–environment–performance associations differ among taxa and whether natural selection favors similar traits across multiple taxa and functional groups. All taxa showed trait–environment associations consistent with local adaptation, and both environment of origin and phenotypes predicted survival in competitive restoration settings, with some commonalities among taxa. Notably, rapid emergence and larger seeds increased survival for multiple taxa. Environmental factors at collection sites, including lower slopes (especially for grasses), greater mean annual temperatures (especially for shrubs and forbs), and greater precipitation seasonality were frequently associated with increased survival. We noted one collection site with high seedling survival across all seven taxa, suggesting that conditions within some sites may result in selection for traits that increase establishment for multiple species. Thus, choosing native plant sources with the most adaptive traits, along with matching climates, will likely improve the restoration of invaded communities.     

Effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura, central Japan

We investigated the effects of roads on alpine and subalpine plant species distribution along an altitudinal gradient on Mount Norikura (3026 m a.s.l.), Japan. We examined the vegetation of herb and tree species shorter than 1.3 m along roadsides and adjacent natural vegetation at 200 m intervals between 1600 and 3000 m a.s.l. The timberline was at 2500 m a.s.l. Although the canopy opening was greater at the roadsides than in the natural vegetation, it was similar above the timberline. Soil cover and litter depth of the soil surface were less at roadsides than the natural vegetation, and gravel and rock cover were greater at roadsides. Species composition changed in similar directions from natural vegetation to roadsides along the altitudinal gradient. This direction was related to canopy opening and litter depth. Liliaceae, Ericaceae and Pinaceae were dominant families in the natural vegetation, and Asteraceae and Poaceae were greatest at the roadsides. Roadside plants were mostly herb species, while tree species increased in natural vegetation. Five exotic species were also observed at the roadsides. Sunny plant species gradually increased with altitude in the natural vegetation, indicated by the increase in canopy opening. By contrast, roadside plants were mostly sunny plant species irrespective of altitude. The number of lowland and montane species increased at the roadsides in the subalpine zone. Thus, roads strongly altered species composition of the natural vegetation along the altitudinal gradient probably because of changes in light and soil-surface conditions for growth and seedling establishment.     

Floral adaptation to local pollinator guilds in a terrestrial orchid

Background and Aims

Studies of local floral adaptation in response to geographically divergent pollinators are essential for understanding floral evolution. This study investigated local pollinator adaptation and variation in floral traits in the rewarding orchid Gymnadenia odoratissima, which spans a large altitudinal gradient and thus may depend on different pollinator guilds along this gradient.

Methods

Pollinator communities were assessed and reciprocal transfer experiments were performed between lowland and mountain populations. Differences in floral traits were characterized by measuring floral morphology traits, scent composition, colour and nectar sugar content in lowland and mountain populations.

Key Results

The composition of pollinator communities differed considerably between lowland and mountain populations; flies were only found as pollinators in mountain populations. The reciprocal transfer experiments showed that when lowland plants were transferred to mountain habitats, their reproductive success did not change significantly. However, when mountain plants were moved to the lowlands, their reproductive success decreased significantly. Transfers between populations of the same altitude did not lead to significant changes in reproductive success, disproving the potential for population-specific adaptations. Flower size of lowland plants was greater than for mountain flowers. Lowland plants also had significantly higher relative amounts of aromatic floral volatiles, while the mountain plants had higher relative amounts of other floral volatiles. The floral colour of mountain flowers was significantly lighter compared with the lowland flowers.

Conclusions

Local pollinator adaptation through pollinator attraction was shown in the mountain populations, possibly due to adaptation to pollinating flies. The mountain plants were also observed to receive pollination from a greater diversity of pollinators than the lowland plants. The different floral phenotypes of the altitudinal regions are likely to be the consequence of adaptations to local pollinator guilds.     

The response of forest plant regeneration to temperature variation along a latitudinal gradient

Background and Aims

The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming.

Methods

Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments.

Key Results

Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted.

Conclusions

Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics.     

Microgeographic variation in early fitness traits of Pinus sylvestris from contrasting soils

Premise

The possibility of fine-scale intraspecific adaptive divergence under gene flow is established by theoretical models and has been confirmed empirically in tree populations distributed along steep altitudinal clines or across extreme edaphic discontinuities. However, the possibility of microgeographic adaptive divergence due to less severe but more frequent kinds of soil variation is unclear.

Methods

In this study, we looked for evidence of local adaptation to calcareous versus siliceous soil types in two nearby Mediterranean Pinus sylvestris populations connected via pollen flow. Using a greenhouse experiment, we tested for variation in early (up to three years of age) seedling performance among open-pollinated maternal families originating from each edaphic provenance when experimentally grown on both types of natural local substrate.

Results

Although seedlings were clearly affected by the edaphic environment, exhibiting lower and slower emergence as well as higher mortality on the calcareous than in the siliceous substrate, neither the performance on each substrate nor the plasticity among substrates varied significantly with seedling edaphic provenance.

Conclusions

We found no evidence of local adaptation to a non-extreme edaphic discontinuity over a small spatial scale, at least during early stages of seedling establishment. Future studies on microgeographic soil-driven adaptation should consider long-term experiments to minimize maternal effects and allow a potentially delayed expression of edaphic adaptive divergence.     

Phenology and polyploidy in annual Brachypodium species (Poaceae) along the aridity gradient in Israel

Local adaptation of plants along environmental gradients provides strong evidence for clinal evolution mediated by natural selection. Plants have developed diverse strategies to mitigate stress, for example, drought escape is a phenological strategy to avoid drought stress, while polyploidy was proposed as a genomic adaptation to stress. Polyploidy as an adaptation to aridity (an environmental parameter integrating temperature and precipitation) was previously documented in annual Brachypodium spp. (Poaceae) in the Western Mediterranean. Here, we examined whether polyploidy or phenology are associated with aridity in annual Brachypodium spp. along the aridity gradient in the Eastern Mediterranean. Using flow cytometry, we determined ploidy levels of plants from natural populations along the Israeli gradient, spanning ∼424 km from mesic Mediterranean to extreme desert climates. In a common garden we recorded time of seedling emergence, flowering and senescence. We tested whether the proportion of allotetraploids in the populations and phenological traits were associated with aridity. Contrary to a previous study in the Western Mediterranean, we found no effect of aridity on the proportion of allotetraploids and diploids within populations. Interestingly, phenology was associated with aridity: time of emergence was later, while flowering and senescence were earlier in desert plants. Our results indicate that in the Eastern Mediterranean, adaptation of Brachypodium to aridity is mediated mainly by phenology, rather than ploidy level. Therefore, we suggest that genome duplication is not the main driver of adaptation to environmental stress; rather, phenological change as a drought escape mechanism may be the major adaptation.     

Detection of Climate-Sensitive Zones and Identification of Climate Change Indicators: A Case Study from the Bavarian Forest National Park

We determined the climate-sensitive zones along an altitudinal gradient in a low mountain range forest, the Bavarian Forest National Park in south-eastern Germany, and studied which vascular plant species are likely to respond to climate change. Plants were recorded on 273 plots along four straight transects. The composition of the plant species and their environmental correlates were detected using unconstrained correspondence analysis (DCA) with post-hoc correlation of axes against site variables. We tested the effect of site variables on species composition using maximally selected rank statistics, which allow the simultaneous identification of a threshold and assessment of its significance. Species turnover within the vascular plant community along the altitudinal gradient was assessed using the same method on the basis of the DCA sample scores. Using geostatistical models of local temperature and Bayesian methods with binomial errors that account for spatial structure, we tested the influence of temperature on selected single vascular plant species and assessed the suitability of the species as climate change indicators. Temperature was the most important factor explaining the variability in vascular plant community composition, which changed discretely along the altitudinal gradient, with a climate-sensitive zone found between 1,100 and 1,200 m a.s.l. The distribution of ten species with their lower or upper altitudinal limit in this zone was significantly driven by temperature. To track vegetation responses to climate change effectively, we suggest a three-level monitoring program, flexible with regard to the volume of required sampling effort.