Plasticity in reproduction and growth among 52 range‐wide populations of a Mediterranean conifer: adaptive responses to environmental stress

A plastic response towards enhanced reproduction is expected in stressful environments, but it is assumed to trade off against vegetative growth and efficiency in the use of available resources deployed in reproduction [reproductive efficiency (RE)]. Evidence supporting this expectation is scarce for plants, particularly for long‐lived species. Forest trees such as Mediterranean pines provide ideal models to study the adaptive value of allocation to reproduction vs. vegetative growth given their among‐population differentiation for adaptive traits and their remarkable capacity to cope with dry and low‐fertility environments. We studied 52 range‐wide Pinus halepensis populations planted into two environmentally contrasting sites during their initial reproductive stage. We investigated the effect of site, population and their interaction on vegetative growth, threshold size for female reproduction, reproductive–vegetative size relationships and RE. We quantified correlations among traits and environmental variables to identify allocation trade‐offs and ecotypic trends. Genetic variation for plasticity was high for vegetative growth, whereas it was nonsignificant for reproduction. Size‐corrected reproduction was enhanced in the more stressful site supporting the expectation for adverse conditions to elicit plastic responses in reproductive allometry. However, RE was unrelated with early reproductive investment. Our results followed theoretical predictions and support that phenotypic plasticity for reproduction is adaptive under stressful environments. Considering expectations of increased drought in the Mediterranean, we hypothesize that phenotypic plasticity together with natural selection on reproductive traits will play a relevant role in the future adaptation of forest tree species.     

High-elevation plants have reduced plasticity in flowering time in response to warming compared to low-elevation congeners

Global warming has caused shifts in the flowering time of many plant species. In alpine regions the temperature rise has been especially pronounced and together with decreasing winter precipitation has led to earlier snowmelt. The close association between time of snowmelt and plant growth at high elevations makes climate change for alpine plants particularly threatening. Here we transplanted eleven congeneric pairs of high- and low-elevation herbaceous species to common gardens differing c. 800 m in elevation, and c. 4 °C in mean growing season temperature to test whether reproductive phenologies of high- and low-elevation plants differ in their respective responses to temperature. Results indicate that high-elevation plants were less plastic in response to transplantation than their low-elevation congeners as the onsets of phenophases on average shifted 7 days less than in low-elevation plants. Plasticity of phenophase durations was overall weaker than that of phenophase onsets, and slightly stronger in high-elevation species compared to low-elevation congeners. We suggest that weaker plasticity in the onsets of early stages of reproductive phenology of high-elevation plants is related to spring frost, which constitutes a strong selective agent against early loss of winter hardiness. Some of the plastic responses of both low- and high-elevation species might potentially be adaptive under predicted climate change. However, the observed plasticity can be largely explained as a passive response to temperature and not as the result of natural selection in heterogeneous environments. The strong temperature-sensitivity of low-elevation species might promote their upward range expansion, but only to a certain threshold after which it becomes limited by the short growing season.     

The role of sexual and vegetative reproduction in the population maintenance of a monocarpic perennial herb,Cardiocrinum cordatum var. glehnii

Because monocarpic perennial plants have only one reproductive opportunity in their entire life, they need to ensure offspring production. Some plants reproduce both sexually and vegetatively, and vegetative reproduction could possibly compensate for seed production. Therefore, the role and significance of these reproductive modes is likely to differ between monocarps and polycarps, which can reproduce many times. Cardiocrinum cordatum var. glehnii is a monocarpic perennial that reproduces both sexually and vegetatively (bulblet formation). Here, we investigated the characteristics and contribution to population maintenance of sexual and vegetative reproduction to reveal the significance of these two reproductive modes in this species. First, we found that bulblet formation occurred in plants after the three‐leaved rosette stage. Second, resource allocation experiments revealed that although resources were mainly invested in fruit maturation after the flowering season, resource allocation was switched from sexual reproduction to vegetative reproduction if seed production was insufficient. Third, the outcrossing rate in this species varied greatly according to the environment surrounding the population. However, reproductive assurance by selfing kept seed production stable even if flowers did not receive sufficient pollen for full seed set via outcross pollination, and moreover, there was no intensive inbreeding depression. Finally, genotypic identification of ramets suggested that daughter ramets derived from vegetative reproduction received the space that the mother flowering ramet had occupied until the previous year.     

The role of biomass allocation strategy in diversity loss due to fertilization

Proposed mechanisms for explaining biodiversity loss due to fertilization include interspecific competition and assemblage-level thinning. The interspecific competition hypothesis (ICH) assumes a link between population changes and species competitive ability, which is related to functional traits such as biomass allocation patterns. Based on a 2-year fertilization experiment in an alpine meadow on the Tibetan Plateau, we attempted to explore the relationships between individual and population responses. Individual response was measured by changes in plant biomass and biomass allocation, and population response was estimated by changes in species abundance. The results suggested that following fertilization (1) changes in individual biomass differ among species and functional groups, (2) reproductive allocation tends to decrease for all species whereas leaf allocation generally increases for grasses but decreases for forbs, (3) a strong positive correlation exists between species relative abundance change and individual biomass response, and (4) species relative abundance change has a positive correlation with leaf allocation response, a negative correlation with stem allocation response, and no significant correlation with reproductive allocation response. We conclude that the individual biomass responses and biomass allocation strategy can partly explain diversity loss due to fertilization, a result consistent with the ICH.     

Are plasticity in functional traits and constancy in performance traits linked with invasiveness? An experimental test comparing invasive and naturalized plant species

The role of phenotypic plasticity in plant invasions is among the most often discussed relationships in invasion ecology. However, despite the large number of studies on this topic, there is little consistency. Reconsideration of the role of plasticity by distinguishing two substantially distinct trait-groups, performance traits (contributing directly to fitness) and functional traits (influencing fitness indirectly), could form a more operative framework for comparative studies. In the current study we expect that invasive species benefit from being plastic in functional traits, which allows them to maintain a more constant performance across different environmental conditions compared to non-invasive alien species. We compared invasive and naturalized non-invasive alien plant species by their germination (20 species), their vegetative (10 species) and their reproductive (four species) responses to three different levels of water, light and nutrient availability in a common garden experiment. Used traits were classified into performance (germination ratio, total biomass, seed number) and functional traits (time to germination, root:shoot ratio, specific leaf area, reproductive allocation). We found that invasive and non-invasive species responded similarly to environmental factors, except for example that invasive species germinated earlier with decreasing light conditions or, surprisingly, non-invasive species reacted more intensely to increased nitrogen availability by having a superior ability to achieve greater biomass. The two groups were equally plastic in all the germination and vegetative traits measured but the reproductive traits, since higher plasticity in relative reproductive allocation and higher constancy in reproductive performance showed a pronounced relation with invasiveness.     

高山植物繁殖策略的研究进展

高山地区通常被认为是陆地上最为极端的生境之一,但却拥有许多形态特化的植物和较高的物种多样性。高山植物如何在严酷的环境中实现成功繁殖,这一问题倍受研究者们的关注。本文综合了国内外高山植物在资源分配、花形态对非生物环境因子的响应、动物传粉及其适应机制、果实和种子及克隆繁殖等繁殖策略方面的文献。为应对低温多雨雪的恶劣环境,一些高山植物采取花向日性、花冠闭合及花序保温结构等繁殖策略。高山植物的传粉者类群也发生了改变,主要为蜂类和蝇类。熊蜂(Bombusspp.)传粉的高效性,减少了高山环境对植物传粉造成的不利影响。当传粉者不可得时,植物不仅通过延迟自交和自助自交等机制来提供繁殖保障,还借助克隆繁殖及其他传粉机制(风媒或风虫媒)来维持种群的繁衍。依赖动物传粉的高山植物,可以采取增加繁殖构件的资源分配、加大"广告"投入以及较大的花展示或较长的花寿命来提高传粉者的拜访几率,以及借助泛化的花结构和选择合适的开花时间等策略来提高繁殖成功率。此外,大部分高山植物产生干果且具有持久的种子库,有利于种子的传播以及种子寻找萌发及幼苗生长的最佳外界环境。在今后的研究中,可着重探讨以下几个问题:(1)非生物环境因子对花形态的选择;(2)季节变化与繁殖策略;(3)群落水平上植物与传粉者的关系;(4)高山生态系统对全球变暖的响应。     

Effects of grazing and fertilization on the relationship between species abundance and functional traits in an alpine meadow community on the Tibetan Plateau

Trait‐based approaches can provide a useful tool for linking plant attributes to community structure and ecosystem function. Seed mass and plant height play important roles in the dynamics of plant communities, but few empirical community level studies have tested this, especially in stressful environments. The aim of the present study was to determine if there is a relationship between functional traits (seed mass and plant height) and changes in species relative abundance (SRA) in response to grazing and fertilization. We measured SRA and plant functional traits for 40 common species in a Tibetan Plateau alpine meadow. In the fertilized meadow, seed mass and plant height was significantly positively correlated with the relative abundance of the species. In the grazed meadow, these variables were significantly negatively correlated. Our results demonstrates that plant functional traits can be used to predict the change of SRA in plant community. Grazing promotes the dominance of small‐seeded and short‐stature species, and fertilization facilitates the occurrence of large‐seeded and tall‐stature species.     

TEMPORAL VARIATION OF FLOWER AND FRUIT SIZE IN RELATION TO SEED YIELD IN CELANDINE POPPY (CHELIDONIUM MAJUS; PAPAVERACEAE)

Ecological and evolutionary studies typically consider variation in single reproductive characters in isolation, without considering how they might be correlated with other reproductive and vegetative characters. In our study, we examined temporal patterns of variation and correlation in flower diameter and fruit length during a reproductive phase in two Massachusetts populations of the herb, Chelidonium majus. We also examined the relationships of such variation to measurements of seed yield components (mean seed weight and number per fruit) and aspects of plant vegetative size. Most of the variation in the sizes of reproductive characters occurred within individual plants, instead of among plants or between populations. Flower and fruit sizes as well as seed number per fruit declined significantly during the season in both populations. Only mean seed size per fruit was relatively stable for individual plants in both populations. Conserving resources by a gradual reduction in the size of reproductive characters over the season may be a strategy for maternal plants to continue seed production. The strong, persistent patterns of correlation between certain characters, such as flower and fruit size, in spite of extensive phenotypic plasticity, was interpreted as indirect evidence for developmental correlation. Furthermore, vegetatively larger plants produced not only more flowers and fruits, but also consistently larger flowers and fruits. The results emphasize that variation in fitness characters, such as seed size and number, should not be viewed in isolation from vegetative characters, flower, and fruit sizes in ecological and evolutionary studies, if the goal is to understand the mechanisms of natural selection in wild populations.     

Facilitation and interference in subalpine meadows of the central Caucasus

Abstract. We studied the effects of neighbours on the biomass of seven randomly chosen species in species‐rich sub‐alpine meadows in the central Caucasus Mountains by comparing the performance of plants with neighbours removed experimentally to that of paired plants with their neighbours left intact. In most cases the removal of neighbours led to significant increases in vegetative and total above‐ground biomass implying the species were limited by competition. However, the neighbour removal led also to an increased leaf wilting for target plants, as well as to strong decline in reproductive effort for some species. We hypothesise that competition may be the prevailing type of interaction in species‐rich sub‐alpine meadow communities, but competitive effects on vegetative production may be balanced, if not outweighed, by facilitation, at least for some species. Such a balance may enhance species coexistence in communities.     

The effects of fertilization on the trait-abundance relationships in a Tibetan alpine meadow community

Aims Comparisons of the trait–abundance relationships from various habitat types are critical for community ecology, which can offer us insights about the mechanisms underlying the local community assembly, such as the relative role of neutral vs. niche processes in shaping community structure. Here, we explored the responses of trait–abundance relationships to nitrogen (N), phosphorus (P) and potassium (K) fertilization in an alpine meadow.Methods Five fertilization treatments (an unfertilized control and additions of N, P, K and NPK respectively) were implemented using randomized block design in an alpine Tibetan meadow. Species relative abundance (SRA), plant above-ground biomass and species richness were measured in each plot. For 24 common species, we measured species functional traits: saturated height, specific leaf area (SLA) and leaf dry matter content (LDMC) in each treatment but seed size only in the unfertilized control. Standard major axis (SMA) regression and phylogenetically independent contrasts (PICs) analysis were used to analyse species trait–abundance relationships in response to different fertilization treatments.Important findings Positive correlations between SRA and saturated height were raised following N, P and NPK fertilizations, which indicated an increase in light competition in these plots. In P fertilized plots, SRA was also positively correlated with LDMC because tall grasses with a nutrients conservation strategy often have a relative competitive advantage in capturing limited light and soil nutrients. In K fertilized plots, neither the trait–abundance relationships nor above-ground biomass or species richness significantly differed from that in the control, which suggests that K was not a limiting resource in our study site. These significant correlations between species traits and relative abundance in fertilized treatment suggest that trait-based selection plays an important role in determining species abundance within local communities in alpine meadows.     

How endangered is sexual reproduction of high-mountain plants by summer frosts? Frost resistance, frequency of frost events and risk assessment

In temperate-zone mountains, summer frosts usually occur during unpredictable cold spells with snow-falls. Earlier studies have shown that vegetative aboveground organs of most high-mountain plants tolerate extracellular ice in the active state. However, little is known about the impact of frost on reproductive development and reproductive success. In common plant species from the European Alps (Cerastium uniflorum, Loiseleuria procumbens, Ranunculus glacialis, Rhododendron ferrugineum, Saxifraga bryoides, S. moschata, S. caesia), differing in growth form, altitudinal distribution and phenology, frost resistance of reproductive and vegetative shoots was assessed in different reproductive stages. Intact plants were exposed to simulated night frosts between ?2 and ?14 °C in temperature-controlled freezers. Nucleation temperatures, freezing damage and subsequent reproductive success (fruit and seed set, seed germination) were determined. During all reproductive stages, reproductive shoots were significantly less frost resistant than vegetative shoots (mean difference for LT₅₀ ?4.2 ± 2.7 K). In most species, reproductive shoots were ice tolerant before bolting and during fruiting (mean LT₅₀ ?7 and ?5.7 °C), but were ice sensitive during bolting and anthesis (mean LT₅₀ around ?4 °C). Only R. glacialis remained ice tolerant during all reproductive stages. Frost injury in reproductive shoots usually led to full fruit loss. Reproductive success of frost-treated but undamaged shoots did not differ significantly from control values. Assessing the frost damage risk on the basis of summer frost frequency and frost resistance shows that, in the alpine zone, low-statured species are rarely endangered as long as they are protected by snow. The situation is different in the subnival and nival zone, where frost-sensitive reproductive shoots may become frost damaged even when covered by snow. Unprotected individuals are at high risk of suffering from frost damage, particularly at higher elevations. It appears that ice tolerance in reproductive structures is an advantage but not an absolute precondition for colonizing high altitudes with frequent frost events.     

Do clonal growth form and habitat origin affect resource-induced plasticity in Tibetan alpine herbs?

To investigate how growth form and habitat origin affect phenotypic plasticity to resource supply in the Tibetan alpine herbs, the phalanx-type species Stipa capillacea and the guerilla-type species Carex montis-everestii were sampled from two different habitats (alpine steppe and alpine scrubland) and grown under three levels of light intensity and two levels of nutrient supply. Interspecific differences in light-induced plasticity were detected only in number of ramets, specific leaf area and leaf sheath length. Plasticity in plant biomass, number of ramets and rhizome length in response to light intensity differed between the two habitats. Stipa plants were more plastic than Carex plants in number of ramets and specific leaf area in response to light intensity. Carex plants from the alpine scrubland expressed greater light-induced plasticity in plant biomass and number of ramets than those from the alpine steppe, and Stipa plants showed less interhabitat differences in plasticity, which may be closely related to their contrasting growth forms. Clonal growth form and habitat origin affected nutrient-induced plasticity in none of the measured traits. It may be the guerilla growth form that makes Carex plants more efficiently adapted to highly heterogeneous light conditions in scrubland, and less habitat-dependent plasticity contributes to success of the phalanx-type Stipa plants in alpine habitats. The results are discussed in the context of foraging for heterogeneously distributed essential resources and adaptation to habitat origin.     

Plant responses to simulated warming and drought: a comparative study of functional plasticity between congeneric mid and high elevation species

Aims Effects of climate change, especially changes in temperatures and precipitation patterns, are particularly pronounced in alpine regions. In response, plants may exhibit phenotypic plasticity in key functional traits allowing short-term adjustment to novel conditions. However, little is known about the degree of phenotypic plasticity of high elevation species relative to mid elevation congeners.Methods We transplanted 14 herbaceous perennial species from high elevation into two common gardens (1050 and 2000 m.a.s.l.) in the Swiss Alps, and we examined plastic responses in key functional traits to changes in temperature and soil water availability. This design was replicated with 14 congeneric species from mid elevation to assess if the degree of phenotypic plasticity differs between mid and high elevation species. Survival was assessed across two growing seasons, while aboveground biomass and specific leaf area (SLA) were measured after the first growing season, and biomass allocation to belowground and reproductive structures after the second. Moreover, a phenotypic plasticity index was calculated for the functional traits to compare the degree of plasticity between mid and high elevation species.Important findings Aboveground biomass was higher in mid elevation species relative to high elevation congeners in all treatments, yet decreased for both with elevation and drought. Similarly, SLA decreased with elevation and drought. Root mass fraction (RMF) was generally higher in high elevation species, and decreased with drought at the lower site. Drought increased the allocation to reproductive structures, especially when plants were grown at their elevation of origin. Interestingly, no difference was found in the degree of phenotypic plasticity averaged across mid and high elevation species for any of the studied functional traits. These results indicate that phenotypic plasticity in the focal traits did not depend on the elevation of origin of the species. Plasticity was not related to environmental heterogeneity, nor constrained by selective pressures at high elevation. However, both species groups showed a remarkable capacity for short-term acclimation to a prospective climate through rapid adjustments in key functional traits.     

Linking flowering and reproductive allocation in response to nitrogen addition in an alpine meadow

Aims Plants can change in phenology and biomass allocation in response to environmental change. It has been demonstrated that nitrogen is the most limiting resource for plants in many terrestrial ecosystems. Previous studies have usually focused on either flowering phenology or biomass allocation of plants in response to nitrogen addition; however, attempts to link flowering phenology and biomass allocation are still rare. In this study, we tested the effects of nitrogen addition on both flowering phenology and reproductive allocation in 34 common species. We also examined the potential linkage between flowering time and reproductive allocation in response to nitrogen addition.Methods We conducted a 3-year nitrogen addition experiment in Tibetan alpine meadow. We measured first flowering date and the reproductive allocation for 34 common plant species in control, low and high nitrogen added plots, respectively. One-way analysis of variance was used to examine differences of first flowering date and reproductive allocation among treatments. The relationships between the change in species first flowering date and change in reproductive allocation in response to nitrogen addition were examined by calculating Pearson correlation coefficients.Important findings For most species, both first flowering date and reproductive allocation significantly responded to nitrogen addition. Nitrogen addition significantly delayed the first flowering date and reduced the reproductive allocation for all graminoid species, but accelerated flowering and increased reproductive allocation for most forb species. We found that changes in first flowering date significantly negatively correlated with the changes in reproductive allocation over species in response to nitrogen, which indicated a positive relationship between flowering response and plant performance in reproductive allocation. Species that advanced their flowering time with nitrogen addition increased their reproductive allocation, whereas those that delayed flowering time tended to decline in reproductive allocation with nitrogen addition. Our results suggest that species-specific switch from vegetative growth to reproductive growth could influence species performance.     

Local adaptation and cogradient selection in the alpine plant, Poa hiemata, along a narrow altitudinal gradient

Alpine environments are particularly susceptible to environmental changes associated with global warming but there is potential for alpine plants to adapt to warming if local adaptation occurs and gene flow allows genotypes adapted to low altitudes to colonize higher altitude sites. Here we examine the adaptive potential of a common alpine grass, Poa hiemata, within the restricted alpine habitat of Australian mountains, across a narrow altitudinal gradient replicated in three areas. Grasses at high altitude sites had shorter leaf lengths and larger circumferences than those at lower sites. Transplant experiments with clonal material and plants grown from seed indicated that these differences were partly genetic, with environmental and genetic factors both contributing to the differences between altitudes. Differences in altitudinal forms were also evident in a common garden experiment. Plants showed a home-site advantage in terms of survival. A fitness analysis indicated that at high altitude sites, selection favored plants with short leaves and larger circumferences, whereas these traits were selected in the opposite direction at the low altitude sites. These findings indicate cogradient selection and potential for both plastic and genotypic shifts in response to climate change in P. hiemata.     

Phenotypic plasticity in vegetative and reproductive traits in an invasive weed, Lythrum salicaria (Lythraceae), in response to soil moisture

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.     

Patch configuration affects alpine plant distribution

The relative importance of niche requirements and dispersal limitation in controlling the landscape‐scale distribution of plants is still contentious. Local occurrence and abundance of alpine plants are commonly thought to be driven by abiotic site conditions due to pronounced environmental gradients over short distances. However, explicit tests of the additional role of dispersal‐related processes for alpine plant distribution patterns are lacking. Here, we combine niche‐based species distribution models with variables describing patch size and connectivity to evaluate if, besides abiotic limitations, spatial habitat configuration affects the occurrence and abundance of six plant species inhabiting patchy snowbed mosaics of the northeastern Calcareous Alps in Austria. Moreover, we assess if eventual effects of spatial patch configuration are more clearly detectable when calculating connectivity based on parameterized mechanistic dispersal kernels for both wind and animal vectors instead of using nearest neighbour metrics. We show that patch size and connectivity are significantly correlated to the occurrence of all and to the abundance of four out of six study species, although the relative importance of these variables, as compared to niche constraints, varies among species. In addition, connectivity measures derived from parameterized dispersal kernels were more closely related to occupancy, and in particular to abundance patterns than a simple nearest neighbour metric. The fitted kernels also suggest that dispersal by alpine chamois plays an important role for inter‐patch seed exchange. We conclude that, despite evident abiotic limitations, recurrent local extinctions and delayed re‐colonizations indeed play a role for the distribution of our study species, and that alpine plants may hence be less in equilibrium with their abiotic environment than commonly thought. Moreover, the relatively high long‐distance dispersal probabilities of animal kernels indicate that the ability of alpine plants to adapt their ranges to a rapidly warming climate may, among other factors, depend on the availability of dispersal services by large mammals.     

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.     

Soil warming increases plant species richness but decreases germination from the alpine soil seed bank

Global warming is occurring more rapidly above the treeline than at lower elevations and alpine areas are predicted to experience above average warming in the future. Temperature is a primary factor in stimulating seed germination and regulating changes in seed dormancy status. Thus, plant regeneration from seed will be crucial to the persistence, migration and post disturbance recruitment of alpine plants in future climates. Here, we present the first assessment of the impact of soil warming on germination from the persistent alpine soil seed bank. Contrary to expectations, soil warming lead to reduced overall germination from the soil seed bank. However, germination response to soil temperature was species specific such that total species richness actually increased by nine with soil warming. We further explored the system by assessing the prevalence of seed dormancy and germination response to soil disturbance, the frequency of which is predicted to increase under climate change. Seeds of a significant proportion of species demonstrated physiological dormancy mechanisms and germination of several species appeared to be intrinsically linked to soil disturbance. In addition, we found no evidence of subalpine species and little evidence of exotic weed species in the soil, suggesting that the soil seed bank will not facilitate their invasion of the alpine zone. In conclusion, changes in recruitment via the alpine soil seed bank can be expected under climate change, as a result of altered dormancy alleviation and germination cues. Furthermore, the alpine soil seed bank, and the species richness therein, has the potential to help maintain local species diversity, support species range shift and moderate species dominance. Implications for alpine management and areas for further study are also discussed.     

The role of spontaneous selfing in the pioneer species Saxifraga aizoides

A large variety of reproductive patterns is present among alpine plants to ensure the persistence of populations in such harsh environments. In the present study, the role of spontaneous selfing and its contribution to the actual reproductive success of an alpine pioneer plant was investigated. The results showed that Saxifraga aizoides is clearly self-compatible. Open-pollinated flowers exhibited higher seed numbers per capsules than selfing flowers, albeit the difference was not significant. Although seed weight seemed to be independent from the kind of pollination, open-pollinated flowers had a significantly higher proportion of germinated seeds than selfed ones. Furthermore, the ability of fast germination found in S. aizoides enables the seeds to take advantage of all possible opportunities for germination. In summary, S. aizoides exhibits a successful recruitment strategy for an alpine pioneer species.