Alpine Botany最新文献

Global warming may pose a serious threat to seed germination and establishment in alpine ecosystems, given that temperature is a primary factor in stimulating seed germination and regulating changes in seed dormancy. However, to date, little is known about the relative importance of temperatures experienced by parents versus by the seeds (after dispersal). In this study, we tested the effects of warming at different stages on germination success and timing in the Australian alpine herb Wahlenbergia ceracea. To decouple the effect of parental warming from that of offspring warming, we raised parental plants (in both outcrossed and selfed lines) in both current (benign, cool) and future (warm) temperature conditions, and then sowed the seeds they produced back in either current or future conditions. We quantified (1) the effects of parental and/or offspring warming on (i) the percentage of germination and (ii) the season of germination (i.e. effects on dormancy); (2) whether the season of germination affected seedling growth; and (3) the effects of inbreeding and its interaction with temperature. We found that the percentage of germination decreased slightly with parental warming, but increased greatly with offspring warming. Parental warming also increased the fraction of dormant seeds, indicating a shift from predominately autumn to spring emergence. Spring-emerged seedlings grew slower than autumn-emerged seedlings, but the growth rate of spring-emerged seedlings were not detrimentally affected by warm offspring temperatures. In this facultatively autogamous species, inbreeding magnified the negative effects of both parental and offspring warming. Our results illustrate the value of tests of the effects of warming across generations and on multiple life stages for improving our understanding of the ecological processes behind plant germination and establishment, and of plant responses to climate warming.

While climatic research about treeline has a long history, the climatic conditions corresponding to the upper limit of closed alpine grasslands remain poorly understood. Here, we propose a climatic definition for this limit, the ‘grassline’, in analogy to the treeline, which is based on the growing season length and the soil temperature. Eighty-seven mountain summits across ten European mountain ranges, covering three biomes (boreal, temperate, Mediterranean), were inventoried as part of the GLORIA project. Vascular plant cover was estimated visually in 326 plots of 1 × 1 m. Soil temperatures were measured in situ for 2–7 years, from which the length of the growing season and mean temperature were derived. The climatic conditions corresponding to 40% plant cover were defined as the thresholds for alpine grassland. Closed vegetation was present in locations with a mean growing season soil temperature warmer than 4.9 °C, or a minimal growing season length of 85 days, with the growing season defined as encompassing days with daily mean ≥ 1 °C. Hence, the upper limit of closed grasslands was associated with a mean soil temperature close to that previously observed at the treeline, and in accordance with physiological thresholds to growth in vascular plants. In contrast to trees, whose canopy temperature is coupled with air temperature, small-stature alpine plants benefit from the soil warmed by solar radiation and consequently, they can grow at higher elevations. Since substrate stability is necessary for grasslands to occur at their climatic limit, the grassline rarely appears as a distinct linear feature.

This study examined the morphological variation in Senecio subalpinus W.D.J. Koch. (Asteraceae) along a 950-m elevation gradient in the Tatra Mountains, Central Europe, with emphasis on floral allocation patterns. Fifteen morphological traits were measured in 200 plants collected in the field from 20 sites then the findings were modelled by elevation using linear mixed-effects models. Plant aboveground biomass and height decreased steadily with increasing elevation; however, the most distinctive feature was the elevational shift in floral allocation patterns. Low-elevation plants had greater numbers of smaller flower heads with a lower overall number of flowers, while high-elevation plants had smaller numbers of bigger flower heads and a greater overall number of flowers. Accordingly, the mean individual flower mass increased significantly with increasing elevation. Interestingly, the width of the outer ligulate flowers also increased considerably with increasing elevation, increasing the fill of the overall circumference of the flower head. Results of this study confirmed that elevation is an important ecological gradient driving variation in vegetative and floral traits of S. subalpinus. Possible causes of the observed variations are subsequently discussed, including the varying effects of both abiotic and biotic factors with elevation gradients.

Flower preformation is a widespread phenomenon in perennial plants from temperate and cold regions. An advanced preformation status reduces the prefloration period and thus increases the chance to mature seeds in time. Despite the particular importance of this strategy for high-mountain plants, studies are rare. Here we investigated how the length of the growing season impacts floral development, and to what extent floral development is synchronized with reproductive phenophases in the arctic-alpine species Ranunculus glacialis L. The study was carried out in the alpine-nival ecotone in the European Central Alps at sites with different snowmelt dates. Individuals were sampled at regular intervals throughout the growing season, and shoot architecture and changes in floral structures were analysed in detail using different microscopic techniques. R. glacialis individuals consist of a cluster of independent ramets, comprising 3 sympodia each. Floral initiation terminates the vegetative growth of each sympodium 2–3 years before flowers become functional. A specific feature is that basal and distal leaves on a sympodium mature in different years. The date of snowmelt did not affect the speed of development but flower size and the number of lateral flowers within an inflorescence. Belowground floral preformation is closely linked to aboveground reproductive processes, however, continues below the snow in case winter conditions set in too early. The staggered preformation of architectural units creates a permanent belowground reserve pool of floral structures which might be advantageous in the climatically harsh and unpredictable high-mountain environment.

Climate change impacts are of a particular concern in small mountain ranges, where cold-adapted plant species have their optimum zone in the upper bioclimatic belts. This is commonly the case in Mediterranean mountains, which often harbour high numbers of endemic species, enhancing the risk of biodiversity losses. This study deals with shifts in vascular plant diversity in the upper zones of the Sierra Nevada, Spain, in relation with climatic parameters during the past two decades. We used vegetation data from permanent plots of three surveys of two GLORIA study regions, spanning a period of 18 years (2001–2019); ERA5 temperature and precipitation data; and snow cover durations, derived from on-site soil temperature data. Relationships between diversity patterns and climate factors were analysed using GLMMs. Species richness showed a decline between 2001 and 2008, and increased thereafter. Species cover increased slightly but significantly, although not for endemic species. While endemics underwent cover losses proportional to non-endemics, more widespread shrub species increased. Precipitation tended to increase during the last decade, after a downward trend since 1960. Precipitation was positively related to species richness, colonisation events, and cover, and negatively to disappearance events. Longer snow cover duration and rising temperatures were also related to increasing species numbers, but not to cover changes. The rapid biotic responses of Mediterranean alpine plants indicate a tight synchronisation with climate fluctuations, especially with water availability. Thus, it rather confirms concerns about biodiversity losses, if projections of increasing temperature in combination with decreasing precipitation hold true.

Elevation gradients provide an ideal setting to infer species' functional trait responses to predicted future climate change. In plants, leaf functional traits help assess their capacity to cope with varying resources. Variation in abiotic conditions over short vertical distances can influence plant phenology, particularly leafing and flowering durations, and leaf functional traits at both inter- and intra-specific levels. However, studies examining relationships between leaf functional traits and phenology duration along elevation gradients are limited. We tested the relationship between leaf size, leaf thickness, specific leaf area, and leafing durations in 10 Rhododendron species in the Sikkim Himalaya. All the investigated traits varied significantly across species, but intra-specific variation in functional traits was observed only among a few. Leaf size and thickness showed significant negative relationships with elevation and a comparative phylogenetic method exhibited a strong relationship between leaf traits and leafing duration. We observed higher leaf thickness and size in species with longer leafing durations and less overlap in leafing and flowering durations. In contrast, species with shorter leafing durations and relatively more overlap in their flowering and leafing durations showed lower leaf thickness and leaf size. Leaf traits such as leaf thickness and leaf size also exhibited a strong phylogenetic signal across 10 Rhododendron species. Overall, from our findings, we infer that along an elevation gradient, the magnitude of leaf trait responses to future increases in temperature may vary depending on species phenology durations and phylogeny.

While the high elevation limit of trees is commonly related to low temperature, the rear edge of their distribution is often associated with drought. Here we explore phenology traits that contribute to a mechanistic explanation of both these edges of the fundamental niche in the broad leaved evergreen Quercus pannosa s.l. Populations of this species reach a drought limit (DL) at 2510 m in the semi-arid upper Yangtze valley, and a cold limit (CL) at 4270 m, very close to the conifer treeline, within a short geographical distance. Trees reach a height of only 4–7 m at both climatic limits, and > 30 m height at optimum site (OS) at 3440 m. At OS, flushing starts in mid-May and at the summer solstice at CL (after late frosts end), suggesting a photoperiod control. At DL, oak phenology tracks the (irregular) arrival of the monsoon. Shoots and leaves grew fastest and for the shortest period at DL, and slowest at CL, in both cases forming 4–7 cm long new shoots per year, contrasted by 12–13 cm a⁻¹ at OS. Maturation of leaves (length and specific leaf area, SLA) was again fastest at DL, followed by CL and slowest at OS, with a much longer shoot growth duration per year and bigger leaves. We conclude that the period favorable for growth and maturation was more than halved at both range limits (by frost or drought) compared to the optimum site, pointing at a common range restriction by the duration of the growing season.

Mountain plant species are changing their ranges in response to global warming. However, these shifts vary tremendously in rate, extent and direction. The reasons for this variation are yet poorly understood. A process potentially important for mountain plant re-distribution is a competition between colonizing species and the resident vegetation. Here, we focus on the impact of this process using the recent elevational shift of the sedge Carex humilis in the northern Italian Alps as a model system. We repeated and extended historical sampling (conducted in 1976) of the species in the study region. We used the historical distribution data and historical climatic maps to parameterize a species distribution model (SDM) and projected the potential distribution of the species under current conditions. We compared the historical and the current re-survey for the species in terms of the cover of important potential competitor species as well as in terms of the productivity of the resident vegetation indicated by the Normalized Difference Vegetation Index (NDVI). We found that Carex humilis has shifted its leading range margin upward rapidly (51.2 m per decade) but left many sites that have become climatically suitable since 1976 according to the SDM uncolonized. These suitable but uncolonized sites show significantly higher coverage of all dwarf shrub species and higher NDVI than the sites occupied by the sedge. These results suggest that resistance of the resident vegetation against colonization of migrating species can indeed play an important role in controlling the re-distribution of mountain plants under climate change.

Abandonment of pastures and successional shrub expansion are widespread in European mountain regions. Moderate shrub encroachment is perceived beneficial for plant diversity by adding new species without outcompeting existing ones, yet systematic evidence is missing. We surveyed vegetation along 24 transects from open pasture into shrubland across the Swiss Alps using a new protocol distinguishing different spatial scales, shrub cover of each plot (2 × 2 m) and larger-scale zonal cover along the transect. Data were analysed using generalized linear models of shrub cover, shrub species and environmental conditions, such as geology, aspect or soil. Most shrub communities were dominated by Alnus viridis (62% of transects) and Pinus mugo (25%), and the rest by other shrub species (13%). These dominant shrub species explained vegetation response to shrub cover well, without need of environmental variables in the model. Compared to open pasture, A. viridis resulted in an immediate linear decline in plant species richness and a marginal increase in beta-diversity (maximally + 10% at 35% cover). Dense A. viridis hosted 62% less species than open pasture. In P. mugo, species richness remained stable until 40% shrub cover and dropped thereafter; beta-diversity peaked at 35% cover. Hence, scattered P. mugo increases beta-diversity without impairing species richness. In transects dominated by other shrubs, species richness and beta-diversity peaked at 40–60% shrub cover (+ 23% both). A. viridis reduced species richness in a larger area around the shrubs than P. mugo. Therefore, effects of shrub encroachment on plant diversity cannot be generalized and depend on dominant shrub species.

Ongoing changes in temperature and precipitation regime may have a strong impact on vulnerable life-history stages such as germination, especially in alpine regions. Differences in germination patterns among species and populations may reflect their adaptation to conditions of their origin or may be determined by the phylogenetic constraints. These two effects are, however, rarely separated. All the germination patterns may also be modified by seed mass. We studied 40 populations of 14 species of Impatiens coming from different elevations in the Himalayas. Three home site temperatures were simulated and one warmer temperature according to a climate change scenario were used. We also studied the combined effect of shorter stratification and warmer temperature as another possible effect of climate change. Interactions of home site and germination conditions affected total germination and germination speed, but not seed dormancy. Seed mass and home site conditions’ interaction indicated different germination strategies in light and heavy seeds. Only seed mass was affected by phylogenetic relationships among the species, while germination response (except T30) was driven primarily by home site conditions. This study is the first to show that the effect of seed mass interacts with home site conditions in determining species’ germination patterns under changing climate. The differences in seed mass are thus likely crucial for species’ ability to adapt to novel conditions since seed mass, unlike seed germination patterns, is strongly phylogenetically constrained. Further studies exploring how seed mass modifies species’ germination under changing climate are needed to confirm generalisability of these findings.