Respiration for maintenance and growth inReynoutria japonica ecotypes from different altitudes on Mt Fuji

Respiration for maintenance and growth ofReynoutria japonica ecotypes from altitudes of 700 and 2420 m on Mt Fuji were measured in two controlled thermal conditions. The maintenance respiration of the high-altitude ecotype at both 15 and 25°C was significantly (1.7-fold) higher than that of the low-altitude ecotype, whereas growth respiration was independent of both ecotype and temperature. The temperature coefficient (Q₁₀) of the maintenance respiration was about 1.9 in both ecotypes. The results show that there is ecotypic differentiation in the performance of maintenance respiration. It is suggested that the high maintenance respiration of the high-altitudeR. japonica ecotype is advantageous in severe upland environments but disadvantageous in a warm lowland climate in terms of carbon economy.     

Seed germination and seedling growth ofCarex doenitzii growing on alpine zone of Mt. Fuji

Carex doenitzii on the upper timberline of Mt. Fuji were studied to determine the effect of thermal conditions on their seed germination and seedling growth. Mature seeds collected at the end of the growing season were divided into five test groups, and each was germinated at constant temperature, the temperatures being 15 C, 20 C, 25 C, 30 C and 35 C. Seed germination percentage was highest (93%) at 25 C. Seedlings germinated at 25 C were grown in chambers at 15/10 C, 25/20 C and 35/30 C. Growth of seedlings was greatest at 25/20 C. The data suggest that the seed germination and seedling growth ofC. doenitzii occur only under limited conditions in the field.     

Seed weight increases with altitude in the Swiss Alps between related species but not among populations of individual species

Seed weight is a crucial plant life history trait, determining establishment success and dispersal ability. Especially in stressful environments, larger seeds may be selected at the expense of seed number, because larger seeds have a better chance of giving rise to an established offspring. We tested the hypotheses that between related species-pairs and among populations of single species a similar trend for increasing seed weight with increasing altitude should be present. Firstly, we measured seed weights from 29 species-pairs, with one species occurring in lowland areas and a congeneric species from high altitudes. Seeds of the alpine species were 28±8% larger than seeds from lowland species (P<0.01). Compared to the related lowland species, 55% of the alpine species had heavier seeds, 3% (one species) had lighter, and 41% had seeds of approximately equal weight. Secondly, we compared seed weights among populations of four species from different habitats and with different life histories. Seeds from between 11 and 34 populations per species were sampled along altitudinal gradients of 800–1,500 m (ca. 800 m in Scabiosa lucida, ca. 1,000 m in Saxifraga oppositifolia, ca. 1,000 m in Epilobium fleischeri, and ca. 1,500 m in Carex flacca). In all the four species, we found no indication for heavier seeds at higher altitudes. Our results indicate a selection pressure for species with heavier seeds at higher altitude, but the trend does not seem to operate across all cases. Phylogenetic constraints may limit the correlation among altitude and seed weight, operating particularly against selection for larger seed size, the closer populations and species are related to each other.     

Altitudinal zonation of human-disturbed vegetation on Mt. Tianmu,eastern China

Much of the primary vegetation at low altitudes has been greatly altered or destroyed by a long history of human activities. This is particularly true in eastern China, where low-altitude areas are now dominated by secondary forests or plantations. Altitudinal vegetation zonation of this region is often based on these secondary forests, resulting in seral vegetation with an obscure zonal sequence. Here, we deduced the potential climax vegetation according to the regeneration patterns of the dominant species of the secondary forests at low altitudes (below 1,000 m a.s.l.) on Mt. Tianmu (1,506 m a.s.l., 30°18′30″–30°21′37″N, 119°24′11″–119°27′11″E). Based on the potential climax vegetation combined with the floristic composition and community structure, three vegetation zones were identified, viz: (1) evergreen broad-leaved forest zone (400–950 m a.s.l.); (2) evergreen and deciduous broad-leaved mixed forest zone (950–1,100 m a.s.l.); (3) deciduous broad-leaved forest zone (1,100–1,506 m a.s.l.). The altitudinal vegetation zones identified in this study correspond with the thermal conditions on Mt. Tianmu. The distribution of vegetation on Mt. Tianmu was limited by lower temperatures in winter, and the altitudinal thermal vegetation zones on this mountain were more similar to the thermal vegetation of Japan than to that of China. The vertical distributions and roles of conifers were different between the eastern and the western regions along 30°N latitude in humid East Asia. Cryptomeria fortunei formed the emergent layer, towering above the broad-leaved canopy at middle altitudes as C. japonica on Yakushima, but disappeared at high altitudes with hydrothermal limitation on Mt. Tianmu.     

Low genetic differentiation among populations ofArabis serrata (Brassicaceae) along an altitudinal gradient

We investigated the extent of genetic differentiation among populations of fujihatazao,Arabis serrata along an altitudinal gradient at Mt. Fuji in Shizuoka Prefecture. This species is a perennial plant, widely distributed in Japan forming small isolated populations. However, at Mt. Fuji, this species constitutes a large population distributed from 1440 to 2400 m altitude. A total of 411 individuals were sampled from ten subpopulations. Eighteen loci were detected on eleven enzyme systems. Eleven loci were monomorphic and seven loci were polymorphic with a mean of 2.11 alleles per loci. Nei's genetic distance (mean 0.01) and genetic identity (mean 0.968) were very similar among populations indicating a low genetic differentiation. The total genetic diversity (H _T ) estimated for the polymorphic loci was, in average, 0.396. The mean gene differentiation (G_ST=0.091) was very low. Gene frequency of seven polymorphic loci was analyzed by spatial autocorrelation methods based on Moran's indexes. Only Pgi-3 exhibited a significant negative autocorrelation (−0.160;P<0.05); other loci values ranged from −0.134 to 0.027. Gene flow estimated by indirect methods varied between genes but most of the values were high (meanNm=20.8) suggesting that subpopulations at different altitudes are probably connected. Despite plants at different altitudes present different ecological traits (e.g., differences in phenology, growth and reproductive traits), subpopulations ofA. serrata are still low differentiated, at least for the loci studied. This may be explained by the recent origin of some habitats (e.g., second crater and surrounded areas) in this locality.     

Homogeneous genetic structure and variation in tree architecture of <Emphasis Type="Italic">Larix kaempferi</Emphasis> along altitudinal gradients on Mt. Fuji

Variations in tree architecture and in the genetic structure of Larix kaempferi on Mt. Fuji were surveyed along altitudinal gradients using 11 nSSR loci. In total, 249 individuals from six populations along three trails at altitudes ranging from approximately 1,300 to 2,700 m were investigated. Gradual changes in tree architecture with increasing elevation, from erect trees to flag trees and krummholz mats, were observed in the high-altitude populations (>2,000 m) on all trails. These findings suggest that tree architecture is correlated with the severe environmental conditions associated with increasing elevation, such as strong winds. In contrast to obvious variations in tree architecture, the genetic diversity of populations along the trails was almost uniform (H _E = 0.717–0.762) across the altitudinal range. The results of the AMOVA and STRUCTURE analyses, and the analysis for isolation by distance pattern, suggest homogeneous genetic structuring across all populations on Mt. Fuji, while the pairwise F _ST showed barriers to gene flow between altitudinal populations that were demarcated as high- or low-altitude populations by Abies-Tsuga forest. Although the evergreen coniferous forests on the mountainside may hinder gene flow, this may be explained by the long-distance seed dispersal of the Japanese larch and/or a short population history resulting from eruptions or slush avalanches, although evergreen coniferous forests on the mountainside may hinder gene flow.     

Reproductive attributes of <Emphasis Type="Italic">Campanula</Emphasis> populations from Mt Olympos,Greece

We studied five reproductive attributes (fruit production and volume, seed content and weight, and seed germination) of different populations of Campanula species occurring along the elevation gradient of Mt Olympos, the highest mountain of Greece (2917 m), in order to examine whether and how they change with elevation, and if there are trade-offs among them. We also studied flower and fruit (reproductive) losses and population features in order to estimate whether there might be a threat to the survival of Campanula species on Mt Olympos. The genus is represented by nine species, ranging from cosmopolitan to steno-endemic. All species were found non-autogamous, and hence they depend on pollinators for their sexual reproduction. At the genus level, there is a trade-off between seed content per fruit and seed weight. At the species level, this is manifested only for C. glomerata, which produces the heaviest seeds, far exceeding all other species, and for C. spatulata, represented on Mt Olympos by two elevation distinct subspecies. Changes of the reproductive attributes are not continuous all along the elevation gradient at the genus level nor are they monotonic at the species level. Nevertheless, upland Campanula populations (≥1500 m) produce fewer fruits per individual, containing fewer but heavier seeds than lowland populations. This indicates a transition from ‘r’ to ‘K’ strategies, from low to high elevations, respectively. The patterns of change of reproductive attributes indicate prevalence of phylogenetic over environmental constraints. Laboratory tests showed that for many populations germinability is high at 15 °C, but there are both inter- and intraspecific differences regarding temperature optima. Ecotypic variation among populations of the same species at different elevations was evident; populations from higher elevations had lower optima and vice versa. Reproductive losses, ranging from zero to over 90%, occurred mainly at the stage of fruit maturation; grazing by sheep and goats was the usual cause. Though such losses might affect the short-lived species (the annual C. sparsa and the biennial C. lingulata), which depend entirely on fruit maturation and seed dispersal for their reproduction, there does not seem to be a serious threat to the survival of Campanula species on the mountain.     

Seed traits and germination behaviour of four Sardinian populations of Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) along an altitudinal gradient

• Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) is an endemic taxon of Sardinia and Corsica, where it grows at different altitudes. The objective of this study was to investigate the seed traits and germination behaviour of four Sardinian populations of this taxon located at different altitudes.
• Seed traits were evaluated, and germination tests were carried out by incubating seeds at a range of constant (5–30 °C) and alternating (25/10 °C) temperatures. The dry after‐ripening (DAR) pre‐treatment was also applied by storing seed in dry conditions for 3 months at 25 °C. Seed traits and germination behaviour data were statistically analysed to identify if there was a correlation with altitude.
• Differences in seed size, area and mass among populations were recorded, however, no relationship was found with altitude. High germination percentages were obtained in all populations, both in untreated and DAR seeds, and were positively affected by alternating temperatures. The final germination percentage and time required to reach 50% final germination (T₅₀) showed no relationship with altitude.
• The differences in seed traits and germination detected among the studied populations of H. microphyllum subsp. tyrrhenicum were not correlated with altitude. This study provides new and important knowledge for this taxon. H. microphyllum subsp. tyrrhenicum is characterised by high germination percentages and low T₅₀ values and does not seem to require any dormancy‐breaking treatment. This species represents a high‐potential native plant species that should be considered within environmental management plans.

     

Germination and seedling frost tolerance differ between the native and invasive range in common ragweed

Germination characteristics and frost tolerance of seedlings are crucial parameters for establishment and invasion success of plants. The characterization of differences between populations in native and invasive ranges may improve our understanding of range expansion and adaptation. Here, we investigated germination characteristics of Ambrosia artemisiifolia L., a successful invader in Europe, under a temperature gradient between 5 and 25 °C. Besides rate and speed of germination we determined optimal, minimal and maximal temperature for germination of ten North American and 17 European populations that were sampled along major latitudinal and longitudinal gradients. We furthermore investigated the frost tolerance of seedlings. Germination rate was highest at 15 °C and germination speed was highest at 25 °C. Germination rate, germination speed, frost tolerance of seedlings, and the temperature niche width for germination were significantly higher and broader, respectively, for European populations. This was partly due to a higher seed mass of these populations. Germination traits lacked evidence for adaptation to climatic variables at the point of origin for both provenances. Instead, in the native range, seedling frost tolerance was positively correlated with the risk of frosts which supports the assumption of local adaptation. The increased frost tolerance of European populations may allow germination earlier in the year which may subsequently lead to higher biomass allocation—due to a longer growing period—and result in higher pollen and seed production. The increase in germination rates, germination speed and seedling frost tolerance might result in a higher fitness of the European populations which may facilitate further successful invasion and enhance the existing public health problems associated with this species.     

Germination ecology of <Emphasis Type="Italic">Scorpiurus subvillosus</Emphasis> L. seeds: the role of temperature and storage time

Scorpiurus subvillosus L., wide spread in pastures of Mediterranean basin, is disappearing in the native pastures of the Hyblean plateau (Sicily, southern Italy), because of overgrazing and intensive management techniques. Moreover, it exhibits seed coat dormancy, which delays and reduces germination preventing its diffusion. This paper represents a first attempt in order to investigate changing in germination determined by storage time and temperature on seeds of two populations of S. subvillosus. Germination of S.␣subvillosus seeds was tested in relation to four storage time (30, 130, 200 and 360 days after harvest (DAH)), eight constant temperatures (5, 10, 15, 20, 25, 30, 35 and 40°C) and two populations of different provenience (30 and 600 m above mean sea level). The experiments were conducted either on scarified and unscarified seeds. In S. subvillosus the failure of germination under favourable conditions must be attributed␣only to seed coat, since seed scarification enhanced germination percentage with values up to 100% at almost all tested temperatures. In both treatments, but with a grater incidence in unscarified, seed germination increased gradually as temperature raised, peaking at 20–25°C, then declined with further increases of temperatures. At 40°C no germination occurred. Storage time induced a softening effect, which is somewhat limited by the natural ageing of seeds occurring from about 6 months after harvest.     

Altitudinal distribution of chytrid (Batrachochytrium dendrobatidis) infection in subtropical Australian frogs

The disappearance of amphibian populations from seemingly pristine upland areas worldwide has become a major focus of conservation efforts in the last two decades, and a parasitic chytrid fungus, Batrachochytrium dendrobatidis, is thought to be the causative agent of the population declines. We examined the altitudinal distribution of chytrid infections in three stream‐dwelling frog species (Litoria wilcoxii, L. pearsoniana and L. chloris) in southeast Queensland, Australia, and hypothesized that if B. dendrobatidis were responsible for the disappearance of high‐altitude frog populations, infection prevalence and intensity would be greatest at higher altitudes. Overall, 37.7% of the 798 adult frogs we sampled were infected with B. dendrobatidis, and infections were found in all the populations we examined. Contrary to our initial hypothesis, we found no consistent evidence that high‐altitude frogs were more likely to be infected than were lowland frogs. Further, the intensity of fungal infections (number of zoospores) on high‐altitude frogs did not differ significantly from that of lowland frogs. Batrachochytrium dendrobatidis appears to be capable of infecting frogs at all altitudes in the subtropics, suggesting that all populations are at risk of decline when conditions favour disease outbreaks. We did find evidence, however, that chytrid infections persist longer into summer in upland as compared with lowland areas, suggesting that montane amphibian populations remain susceptible to disease outbreaks for longer periods than do lowland populations. Further, we found that at high altitudes, temperatures optimal for chytrid growth and reproduction coincide with frog metamorphosis, the life‐stage at which frogs are most susceptible to chytrid infections. While these altitudinal differences may account for the differential population‐level responses to the presence of B. dendrobatidis, the reason why many of southeast Queensland's montane frog populations declined precipitously while lowland populations remained stable has yet to be resolved.     

Effects of altitude and livestock on the regeneration of two tree line forming <Emphasis Type="Italic">Polylepis</Emphasis> species in Ecuador

Regeneration is known to be limited at many temperate tree lines, but very little data is available on the impacts of altitude and anthropogenic disturbance on regeneration patterns along tropical tree lines. The study focused on the reproductive traits of two Polylepis species in the Páramo de Papallacta in Ecuador along an altitudinal gradient, and involved different intensities of cattle trampling within subsequent altitudinal ranges. We analyzed flowering, fruit set, seed viability, germination, and seedling establishment as well as stand structure of Polylepis incana and P. pauta. The numbers of P. incana inflorescences and seedlings per m2 showed a marginally significant decrease with increasing altitude. Mean tree height was significantly lower at higher altitudes, while stem number increased. The number of P. pauta inflorescences also decreased significantly upslope. In both forest types, trampling was found to have a positive impact on seedling abundance, presumably due to the removal of the litter layer. Thus, there was no evidence of negative effects of moderate cattle grazing on both tree line species. However, sapling establishment was minimal inside the forest stands at all altitudes and grazing levels, and we consequently observed a low proportion of narrow stems within all investigated forests. Our results show that, along with vegetative growth limitations of adult trees, important regeneration traits such as seedling and inflorescence numbers are also influenced by altitude, which might contribute to the formation of the upper tree line. Nevertheless, recruitment in the forest interior was low overall indicating that further factors, such as light conditions, affect regeneration of the studied species.     

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

Seedling establishment ofPolygonum cuspidatum andPolygonum weyrichii var.alpinum at high altitudes of Mt Fuji

Seedling establishment ofPolygonum cuspidatum (Seib. et Zucc.) andPolygonum weyrichii (F. Schmit) var.alpinum (Maxim.), dominant early-successional species in a volcanic gravel area on Mt Fuji, Japan, was compared for current-year seedlings at 2500 m a.s.l. The rate of survival in the first winter after germination at 2500 m was 2% and 24% forP. cuspidatum andP. weyrichii seedlings, respectively, and correlated with the upper distribution limit of each (2500–2600 m forP. cuspidatum; 3200–3300 m forP. weyrichii). The critical size for survival was 12 mg dry weight for overwintering current-year seedlings of both species. At 2500 m, the percentage of seedlings that attained the critical size for survival at the end of the first growing season was 19% and 85% forP. cuspidatum andP. weyrichii, respectively. Growth curves indicated that the larger-seeded characteristic ofP. weyrichii contributed to larger end-of-season size and resulted in higher rate of seedling survival at 2500 m, compared with smaller-seededP. cuspidatum. Current-year seedlings ofP. weyrichii, at least up to 3250 m, attained the first year annual growth critical for overwintering and therefore for successful seedling establishment, due to the large-seeded characteristic. At the top (3770 m) beyond the upper distribution limit ofP. weyrichii, most seedlings raised artificially failed to attain the critical size for survival in the first growing period due to the reduced growing period. Failure of seedling establishment would thus appear to restrict the distribution of the species at altitudes higher than 3300 m.     

A butenolide, isolated from smoke, can overcome the detrimental effects of extreme temperatures during tomato seed germination

The butenolide, 3-methyl-2H-furo[2, 3-c]pyran-2-one, is an highly active compound isolated from plant-derived smoke. This compound is known to stimulate seed germination in a wide range of plants akin to smoke or aqueous extracts of smoke. The present study attempted to elucidate the role of the butenolide in overcoming detrimental effects of low and high temperatures on tomato seed germination and seedling growth. The germination percentage followed a parabolic curve for temperatures ranging from 10 to 40°C, with 25°C being the optimum for all treatments. Control seeds showed radicle emergence at two extreme temperatures (10 and 40°C) and seedlings failed to develop further, even upon prolonged incubation. By comparison the butenolide-treated seeds grew into phenotypically normal seedlings at these non-optimum temperatures. The smoke–water-treated seeds had an intermediate response as only a fraction of germinated seed developed into normal seedlings. Seedling vigour indices as well as seedling weight were significantly higher (p ≤ 0.05) for butenolide-treated seeds at all temperatures. Furthermore, seedlings developed in the presence of the butenolide had about a 1:1 correspondence between root and shoot length. Butenolide-treated seeds grew better than the control seeds in the temperature shift experiments. A gradual decline in the vigour index values was recorded with an increased duration of incubation at the extreme temperatures. Results of the present study are very important from an horticultural point of view as they indicate the potential use of the butenolide compound in restoring normal seed germination and seedling establishment in tomato below and above optimum temperatures.     

Adaptation to habitat in Aquilegia species endemic to Sardinia (Italy): Seed dispersal,germination and persistence in the soil

Abstract

The autecology of the Sardinian endemics Aquilegia barbaricina Arrigoni et Nardi and A. nugorensis Arrigoni et Nardi were investigated. Peaks of anthesis and seed dispersal were recorded for five populations occurring in two distinct habitats, one riparian and one rupicolous. Germination tests were carried out on seed lots belonging to each population by sowing seeds at 10, 15, 20, 25 and 25/15°C. In addition, seeds were incubated for 2 months at either 25°C (summer), 5°C (winter) or 25°C for 2 months plus 2 months at 5°C (summer followed by winter–SW), and then moved to the germination temperatures. Embryo measurements were taken during pre-treatments and germination. Experimental seed burials were carried out for two populations of each species. Both species dispersed in summer. The population of A. nugorensis occurring on rocky outcrops differed in phenology from both the other A. nugorensis population from riparian vegetation and from A. barbaricina. Both species showed morphophysiological seed dormancy, with <50% germination under laboratory conditions. All riparian populations germinated only after the SW pre-treatment, while the rupicolous population germinated at 25°C, without any pre-treatment. Low germination percentages were observed in the experimental seed burials, suggesting the ability for both species to form a persistent soil seed bank.     

Altitudinal patterns for longevity, fecundity and senescence in Drosophila buzzatii

We tested for variation in longevity, senescence rate and early fecundity of Drosophila buzzatii along an elevational transect in Argentina, using laboratory-reared flies in laboratory tests performed to avoid extrinsic mortality. At 25 °C, females from lowland populations lived longer and had a lower demographic rate of senescence than females from highland populations. Minimal instead of maximal temperature at the sites of origin of population best predicted this cline. A very different pattern was found at higher test temperature. At 29.5 °C, longevity of males increased with altitude of origin of population. No clinal trend was apparent for longevity of females at 29.5 °C. There was evidence for a trade-off between early fecundity and longevity at non-stressful temperature (25 °C) along the altitudinal gradient. This trait association is consistent with evolutionary theories of aging. Population-by-temperature and sex-by-temperature interactions indicate that senescence patterns are expressed in environment specific ways.     

Exogenous selection shapes germination behaviour and seedling traits of populations at different altitudes in a Senecio hybrid zone

Background and Aims

The Senecio hybrid zone on Mt Etna, Sicily, is characterized by steep altitudinal clines in quantitative traits and genetic variation. Such clines are thought to be maintained by a combination of ‘endogenous’ selection arising from genetic incompatibilities and environment-dependent ‘exogenous’ selection leading to local adaptation. Here, the hypothesis was tested that local adaptation to the altitudinal temperature gradient contributes to maintaining divergence between the parental species, S. chrysanthemifolius and S. aethnensis.

Methods

Intra- and inter-population crosses were performed between five populations from across the hybrid zone and the germination and early seedling growth of the progeny were assessed.

Key Results

Seedlings from higher-altitude populations germinated better under low temperatures (9–13 °C) than those from lower altitude populations. Seedlings from higher-altitude populations had lower survival rates under warm conditions (25/15 °C) than those from lower altitude populations, but also attained greater biomass. There was no altitudinal variation in growth or survival under cold conditions (15/5 °C). Population-level plasticity increased with altitude. Germination, growth and survival of natural hybrids and experimentally generated F₁s generally exceeded the worse-performing parent.

Conclusions

Limited evidence was found for endogenous selection against hybrids but relatively clear evidence was found for divergence in seed and seedling traits, which is probably adaptive. The combination of low-temperature germination and faster growth in warm conditions might enable high-altitude S. aethnensis to maximize its growth during a shorter growing season, while the slower growth of S. chrysanthemifolius may be an adaptation to drought stress at low altitudes. This study indicates that temperature gradients are likely to be an important environmental factor generating and maintaining adaptive divergence across the Senecio hybrid zone on Mt Etna.     

Comparative <Emphasis Type="Italic">in vitro</Emphasis> germination ecology of <Emphasis Type="Italic">Calopogon tuberosus</Emphasis> var. <Emphasis Type="Italic">tuberosus</Emphasis> (Orchidaceae) across its geographic range

Seed responses to temperature are often essential to the study of germination ecology, but the ecological role of temperature in orchid seed germination remains uncertain. The response of orchid seeds to cold stratification have been studied, but the exact physiological role remains unclear. No studies exist that compare the effects of either cold stratification or temperature on germination among distant populations of the same species. In two separate experiments, the role of temperature (25, 22/11, 27/15, 29/19, 33/24°C) and chilling at 10°C on in vitro seed germination were investigated using distant populations of Calopogon tuberosus var. tuberosus. Cooler temperatures promoted germination of Michigan seeds; warmer temperatures promoted germination of South Carolina and north central Florida seeds. South Florida seed germination was highest under both warm and cool temperatures. More advanced seedling development generally occurred at higher temperatures with the exception of south Florida seedlings, in which the warmest temperature suppressed development. Fluctuating diurnal temperatures were more beneficial for germination compared to constant temperatures. Cold stratification had a positive effect on germination among all populations, but South Carolina seeds required the longest chilling treatments to obtain maximum germination. Results from the cold stratification experiment indicate that a physiological dormancy is present, but the degree of dormancy varies across the species range. The variable responses among populations may indicate ecotypic differentiation.     

The performance of Polylepis australis trees along their entire altitudinal range: implications of climate change for their conservation

Altitudinal gradients are expected to heavily influence the general performance of mountain tree species. For this study we evaluated vitality, radial growth and reproductive efficiency in Polylepis australis (Rosaceae) throughout its complete altitudinal range in central Argentina. We selected seven forest fragments ranging from 900 to 2700 m a.s.l. In the field, we subjectively assigned vitality and seed productivity indexes to 12 P. australis trees per fragment. In addition, we cored and assessed for radial growth 10–18 trees per altitudinal level. In the laboratory, we individually weighed seeds from four or five trees from each altitudinal level and divided into two seed mass classes (light and heavy). We then tested for germination and monitored their seedlings for survival. Seedlings of three trees per altitudinal level were harvested after 40 days and assessed for dry mass. Seedlings of one to two trees per altitudinal level were monitored for survival until both leaves and roots had died. Our main results showed two types of responses to altitude: a unimodal relationship with an optimum at intermediate altitudes of around 1800 m a.s.l. for tree vitality, radial growth, seed productivity and seed mass; and an increase with altitude for in-vitro seed germination and seedling survival. A rise in temperature due to climate change could restrict P. australis to the upper most altitudes, where conservation of these forests will be a priority.