Seed rain,seedling establishment and clonal growth strategies on a glacier foreland

Abstract. Seed production, composition of the seed rain, germination, and seedling mortality, as well as vegetative growth characteristics of common pioneer plant species were studied on the foreland of the retreating Morteratsch glacier in the Swiss Alps. The frequency of diaspores trapped in different successional stages was related to their dispersal mode and was highly skewed towards a few species. Plenty of diaspores well adapted for dispersal by wind are a precondition for the most important pioneer species. Seeds from all pioneer species investigated had a good germination success, provided that the moisture content of the soil was high enough. However, requirement for seedling establishment differed among sites of increasing terrain age and among species. Only specialized pioneers such as Cerastium pedunulatum, Linaria alpina, Oxyria digyna and Saxifraga aizoides tolerate the cold and moist conditions near the glacier. However, these species are restricted to early successional stages. Seedlings of Epilobium fleischeri are affected not only by the cold and moist conditions near the glacier but also by moderately dry conditions on older sites. Availability of safe sites becomes crucial for most species with increasing age of sites and with drier conditions. Most species playing a dominant role during early succession and persisting during later successional stages have a distinctive ability to spread clonally and have a growth form with more or less widely spaced ramets: Achillea moschata. Cerastium pedunculatum. Epilobium fleischeri and Hieraium staticifolium. The growth strategy and demography of the clonal E. fleischeri is presented as an example. The life cycle of this species is characterized in succession by (1) the colonization of safe sites by small seeds adapted for wind dispersal, (2) horizontal spread by clonal growth, and (3) the persistence through phenotypic morphological plasticity in later successional stages. Seedling establishment and clonal growth are thus complementary mechanisms in plant succession on recently deglaciated terrain.     

Weichselian interstadial pollen stratigraphy from Härjedalen,central Sweden

Weichselian interstadial vegetation history has been studied by means of pollen analysis of organic bearing fine-grained sediments at Dörrsvålen and Brovalltjärnen in a low mountain area in Härjedalen. The composition of the pollen flora suggests treeless vegetation consisting of shrubs and herbs. The interstadial vegetation consisted of Betula nana, Ericaceae, Juniperus and Salix spp. mixed with herbaceous plant communities including Gramineae, Cyperaceae, Caryophyllaceae, Saxifraga, Rumex/Oxyria and Polygonum. Betula and Pinus are represented by long distance-transported pollen. During the interstadial the climatic conditions seem to have been very harsh and continental as (cold) steppe plants reach high frequencies, e.g. Artemisia and Chenopodiaceae. The sediments are thought to have been deposited during an early Weichselian interstadial tentatively correlated with Tärendö in Norrbotten province, northern Sweden, and Odderade in Denmark and north-western Germany. Comparisons are made with other interstadial sites in central and northern Sweden, and in south-eastern Norway.     

Eight microsatellite markers for sympatric alpine shrubs,Phyllodoce aleutica and P. caerulea (Ericaceae)

Phyllodoce aleutica and Phyllodoce caerulea are sympatric alpine‐snowbed plants in northern Japan. They compete for pollinators (bumblebees) each other and the competitive situation varies depending on snow conditions. We isolated and characterized eight microsatellite loci in these species. Additionally, one of 13 primers developed for Rhododendron metternichii was available in these species. The expected heterozygosity of these nine markers ranged from 0.06 to 0.93 in P. aleutica and from 0.09 to 0.96 in P. caerulea. These markers may be useful to reveal the mating system evolution, patterns of pollen flow and the process of natural hybridization in these Phyllodoce species.     

Contrasting primary successional trajectories of fungi and bacteria in retreating glacier soils

Early community assembly of soil microbial communities is essential for pedogenesis and development of organic legacies. We examined fungal and bacterial successions along a well‐established temperate glacier forefront chronosequence representing ~70 years of deglaciation to determine community assembly. As microbial communities may be heavily structured by establishing vegetation, we included nonvegetated soils as well as soils from underneath four plant species with differing mycorrhizal ecologies (Abies lasiocarpa, ectomycorrhizal; Luetkea pectinata, arbuscular mycorrhizal; Phyllodoce empetriformis, ericoid mycorrhizal; Saxifraga ferruginea, nonmycorrhizal). Our main objectives were to contrast fungal and bacterial successional dynamics and community assembly as well as to decouple the effects of plant establishment and time since deglaciation on microbial trajectories using high‐throughput sequencing. Our data indicate that distance from glacier terminus has large effects on biomass accumulation, community membership, and distribution for both fungi and bacteria. Surprisingly, presence of plants rather than their identity was more important in structuring bacterial communities along the chronosequence and played only a very minor role in structuring the fungal communities. Further, our analyses suggest that bacterial communities may converge during assembly supporting determinism, whereas fungal communities show no such patterns. Although fungal communities provided little evidence of convergence in community structure, many taxa were nonrandomly distributed across the glacier foreland; similar taxon‐level responses were observed in bacterial communities. Overall, our data highlight differing drivers for fungal and bacterial trajectories during early primary succession in recently deglaciated soils.     

Alpine species seed longevity in the soil in relation to seed size and shape – A 5-year burial experiment in the Central Alps

Long-term persistent seeds are generally expected to be small and spherically shaped. In contrast, transient seeds are often large, flattened and elongated. We hypothesized that alpine species follow these trends, and that most species of unstable alpine habitats have the potential to form long-term persistent seed banks. The latter would enable them to delay germination until favourable conditions are present in their environment thereby increasing the likelihood for establishment of seedlings. We selected nine alpine species of more or less unstable habitats (i.e. Achillea moschata, Artemisia genipi, Anthyllis vulneraria ssp. alpicola, Geum reptans, Linaria alpina, Oxyria digyna, Saxifraga aizoides, Saxifraga oppositifolia, and Trifolium pallescens) for this study. Seed longevity was estimated by a 5-year burial experiment in the field with seed excavations after 1 winter, 2 years and 5 years. Germination experiments in the growth chamber and viability tests were performed after each excavation. We detected longevity patterns ranging from transient to long-term persistent. Two species were classified as transient. All other species have the potential to form persistent seed banks, with almost half of the investigated species showing a trend for long-term persistence. Despite contradictory reports, long-term persistent seed banks are an important life history trait of species of unstable alpine habitats. We found that seed shape and hard-seededness are good predictors of seed persistence of alpine species. Seed size seems to be less important. The data from this study support the general hypotheses describing the relationship among seed size, seed shape and seed persistence in the soil.     

Kurztag-Einflüsse auf arktische Pflanzen während der arktischen Langtage

Zusammenfassung Kurztagbehandlung im sommerlichen 24 Std-Langtag führt bei arktischen Pflanzen am natürlichen Standort schon nach 10 Tagen zu einer Erhöhung der Hitzeresistenz um 2–8° C. Betula nana zeigt zudem unter Kurztagbedingungen eine um l1/2 Monate verfrüht eintretende herbstliche Rotfärbung der Blätter. Es wird daraus geschlossen, daß die gegen Herbst und Winter zu eintretenden physiologischen Veränderungen bei Pflanzen der kalten und gemäßigten Zone primär auf die Verkürzung der Tageslänge und erst in zweiter Linie auf die abnehmende Temperatur zurückzuführen sind.

---

Influence of short-days on arctic plants during the arctic long-days

Summary In Godhavn (Disko Island, West Greenland) Salix glauca ssp. callicarpaea, Betula nana, Vaccinium uliginosum and Empetrum hermaphroditum in their natural habitat were darkened from 5 p.m. to 9 a.m. daily. The experiment started July 2. At this time the plants were already flowering. After 10 days of this 8-hour short-day treatment the plants showed significant physiological changes compared with the plants in the normal 24-hour long-day: the leaflets of Betula nana showed an autumnal red coloring and the heat resistance (1/2 hours heating, observation 3 days later) of all 4 plants increased by 2–8° C. The frost resistance (24 hours freezing, observation 3 days later) increased significantly in the case of Betula nana. —These experiments seem to indicate that towards the fall the seasonal increase of temperature resistance and other physiological changes in plants are due primarily to the shortening of the day length and only secondarily to the decrease of temperature.

     

Importance of demographic history for phylogeographic inference on the arctic–alpine plant Phyllodoce caerulea in East Asia

Arctic–alpine plants have enormous ranges in the Northern Hemisphere. Phylogeographic studies have provided insights into their glacial survival as well as their postglacial colonization history. However, our understanding of the population dynamics of disjunct alpine populations in temperate regions remains limited. During Pleistocene cold periods, alpine populations of arctic–alpine species in East Asia were either connected to an ice-free Beringia refugium or they persisted with prolonged isolation after their establishment. To estimate which of these scenarios is more likely, we elucidated the genetic structure of Phyllodoce caerulea (Ericaceae) in Beringia and northern Japan, East Asia. Sequence variation in multiple nuclear loci revealed that P. caerulea can be distinguished into northern and southern groups. A demographic analysis demonstrated that the north–south divergence did not predate the last glacial period and detected introgression from Phyllodoce aleutica, relative widely distributed in East Asia, exclusively into the southern group. Therefore, although there has been genetic divergence between northern Japan and Beringia in P. caerulea, the divergence is unlikely to have resulted from their prolonged geographic separation throughout several cycles of glacial and interglacial periods. Instead, our study suggests that the introgression contributed to the genetic divergence of P. caerulea and that the range of P. caerulea was plausibly connected between northern Japan and Beringia during the last glacial period. Overall, our study not only provides a biogeographic insight into alpine populations of arctic–alpine plants in East Asia but also emphasizes the importance of careful interpretation of genetic structure for inferring phylogeographic history.     

The impact on the senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

During high run-off events the river Sakasagawa carries extremely large quantities of alluvial materials which are deposited in the north east corner of the Senjogahara moor. This study was initiated to examine the effects, both recent and historic, that this periodic and catastrophic inundation has had on the ecology of this area. It also questions the potential importance of alluvial deposition on the conservation of the moor as a whole. From the data presented it is clear that the present day vegetation of the north east corner of the moor represents a mosaic of vegetation reflecting differential levels of damage to the plants, deposition of alluvial material and the establishment of erosion channels in a space-time continum. The results indicate thatMalus Toringo andSalix integra can survive in the areas outside the heaviest flood damage, whereasUlmus Davidiana var.japonica, Betula platyphylla var.japonica andLarix Kaempferi are quite sensitive to flooding. SimilarlySasa nipponica var.nana is intolerant of even light alluvial deposition in contrast toLonicera caerulea var.emphyllocalyx andSpiraea salicifolia which are also still dominant beyond the zone of major alluvial deposition.     

Airborne pollen and spores on the Arctic island of Jan Mayen

A survey of airspora collected on Jan Mayen, an isolated North Atlantic island (71°N, 8°30′W), using a Burkard seven-day volumetric trap from 24th April to 31th August, 1988, revealed only very small concentrations. A total of 10 different pollen types were recorded, constituting a seasonal sum of 29 pollen grains. The local pollen season was confined to July, with Oxyria digna and Salix as the most numerous pollen types recorded. Exotic pollen grains, namely Betula, Pinus and Castanea type, were recorded in three periods during June and July. Studies of back trajectories indicate North America and/or Iceland and Greenland as possible source areas for the Betula pollen. There were more diatoms than pollen in the local airspora. Fungal spores mainly occurred in late July and August. Cladosporium constituted less than 5% of the total seasonal sum of fungal spores, while basidiospores contributed nearly 12%. The highest diurnal average of Cladosporium was 27 spores m^?3 air. The seasonal maximum of unidentified fungal spores reached a diurnal average of 639 spores m^?1 air on 27th August.     

Ellagitannins: defences of Betula nana against Epirrita autumnata folivory?

• 1 The induced resistance of the subarctic mountain birch Betula pubescens ssp. czerepanovii is a well‐characterized phenomenon, whereas the induced responses of Betula nana L., one of the parental species of mountain birch, have not yet been characterized. Betula nana is more resistant to several classes of insectivorous herbivores than the mountain birch, although the mechanisms responsible for the better ability to resist herbivores are not known.
• 2 The present study aimed to determine the metabolic changes that are induced by early season herbivory in B. nana leaves and to study the effects of rapidly induced resistance on the growth of Epirrita autumnata larvae.
• 3 Defoliation of B. nana was accomplished by E. autumnata larvae and leaf samples for chemical analyses were collected when the defoliating larvae were at their third and fifth instar. At the same time, laboratory assays for the growth and consumption rates of E. autumnata larvae were conducted.
• 4 The wounding of leaves by E. autumna larvae induced the production of ellagitannins (ETs) in B. nana. Intriguingly, the concentrations of protein‐bound amino acids were also induced by herbivory; however, an increase in proteins was not mirrored in the growth rate of larvae, which was less on the induced foliage. The decreased growth rate of larvae was apparently linked to the increased concentrations of oxidatively‐active ETs and the high concentration of ETs may explain the better resistance of this parental species compared with the hybrid mountain birch with its lower levels of ETs.

     

The influence of hybridization on epidermal properties of birch species and the consequences for palaeoclimatic interpretations

The Fennoscandian birch population primarily consists of Betula nana, B. pendula and B. pubescens ssp. czerepanovii, the Mountain birch. Frequent hybridization between the Mountain birch and B. nana generates a wide range of genotypic and phenotypic plasticity in the subarctic birch zone of Fennoscandia. Phases of subarctic conditions prevailed during the Late Glacial in large parts of NW Europe, and palynological as well as macrofossil analysis provide some evidence for the occurrence of birch hybrids during these intervals. Leaves from genetically controlled specimens of Betula pendula, B. pubescens ssp. czerepanovii, B. nana and the hybrids B. pubescens ssp. czerepanovii × nana and B. nana × pubescens ssp. czerepanovii are investigated for their specific characteristics of the epidermis morphology. Frequency and size of epidermal cells and stomata reveal a close affinity of both hybrids to B. nana and allow a differentiation of the intermediate forms between B. nana and the Mountain birch. With respect to palaeoatmospheric CO₂ reconstructions based on stomatal index, epidermal analysis shows that a possible occurrence of hybrids in fossil leaf assemblages has no profound consequences for combined species records. However, the significant differences observed in B. nana demand the separation of this species. A comparison of the cuticle properties of B. pendula and B. pubescens from Finnish Lapland and leaf material from The Netherlands reveals a divergence of the stomatal index that may be due to differences in day light length.     

The role of summer precipitation and summer temperature in establishment and growth of dwarf shrub <Emphasis Type="Italic">Betula nana</Emphasis> in northeast Siberian tundra

It is widely believed that deciduous tundra-shrub dominance is increasing in the pan-Arctic region, mainly due to rising temperature. We sampled dwarf birch (Betula nana L.) at a northeastern Siberian tundra site and used dendrochronological methods to explore the relationship between climatic variables and local shrub dominance. We found that establishment of shrub ramets was positively related to summer precipitation, which implies that the current high dominance of B. nana at our study site could be related to high summer precipitation in the period from 1960 to 1990. The results confirmed that early summer temperature is most influential to annual growth rates of B. nana. In addition, summer precipitation stimulated shrub growth in years with warm summers, suggesting that B. nana growth may be co-limited by summer moisture supply. The dual controlling role of temperature and summer precipitation on B. nana growth and establishment is important to predict future climate-driven vegetation dynamics in the Arctic tundra.     

Litter of the hemiparasite<Emphasis Type="Italic"> Bartsia alpina</Emphasis> enhances plant growth: evidence for a functional role in nutrient cycling

Hemiparasitic angiosperms concentrate nutrients in their leaves and also produce high quality litter, which can decompose faster and release more nutrients than that of surrounding species. The impact of these litters on plant growth may be particularly important in nutrient-poor communities where hemiparisites can be abundant, such as the sub-Arctic. We tested the hypothesis that plant growth is enhanced by the litter of the hemiparasite Bartsia alpina, in comparison with litter of co-occurring dwarf shrub species, using a pot based bioassay approach. Growth of Betula nana and Poa alpina was up to 51% and 41% greater, respectively, in the presence of Bartsia alpina litter than when grown with dwarf shrub litter (Vaccinium uliginosum, Betula nana and Empetrum nigrum subsp. hermaphroditum). The nutrient concentrations of Betula nana plants grown with Bartsia alpina litter were almost double those of plants grown with dwarf shrub litter, and a significantly greater proportion of biomass was allocated to shoots rather than roots, strongly suggesting that nutrient availability was higher where Bartsia alpina litter was present. The presence of litter from dwarf shrubs, or the moss Hylocomium splendens, did not reduce the positive effect of Bartsia alpina litter on plant growth. E. nigrum litter did not appear to affect plant growth substantially differently from litter of other dwarf shrub species, despite earlier reports of its allelopathic action. The enhanced nutrient uptake and growth of plants in the presence of Bartsia alpina (and potentially other hemiparasitic species) litter could have important implications for communities in which it occurs, including enhanced survival of seedlings of co-occurring species and increased resource patchiness.     

Floral morphogenesis in choripetalous and sympetalous members of Ericaceae s.l. (Ericales)

Choripetaly of Rhododendron tomentosum is the result of secondary reduction. Our data support earlier observations of P. Leins [4] that a rudimentary corolla tube occurs during early stages of floral development. Choripetaly of Empetrum may be a plesiomorphic condition, because no vestiges of corolla tube were detected throughout all stages of flower development. However, a complete loss of corolla tube cannot be excluded. The type of congenital petal fusion varies within a group of closely related taxa of Ericaceae: Phyllodoce caerulea has late sympetaly while Loiseleuria procumbens has early sympetaly. In contrast, in euasterids, the type of sympetaly appears to characterize taxa of higher rank.     

Pioneer vegetation on glacier forelands in southern Norway: emerging communities?

Question: How variable is the pioneer plant community on glacier forelands in southern Norway, both in terms of species composition and geographical distribution? Location: The Jotunheim and Jostedalsbreen regions of southern Norway (61°‐62°N, 6°‐9°E). Methods: The relative frequencies of vascular plant species were recorded in the pioneer zones of 43 glacier forelands, with an altitudinal range of 80‐1860 m (boreal to high alpine) and an east‐west range of 100 km. Classification and ordination techniques were used to search for evidence of consistently recurring communities, variability along a continuum or stochasticity. Results: Mean variability in species composition between all glacier forelands sampled was 65% (Sørensen dissimilarity). Poa alpina, Oxyria digyna, Deschampsia alpina and Festuca ovina had the highest frequency, occurring on over 80% of forelands. Non‐metric multidimensional scaling did not reveal clear divisions between groups of sites, but cluster analysis, multi‐response permutation procedures and indicator species analysis suggested two sub‐communities: the Saxifraga cespitosa‐Trisetum spicatum sub‐community is restricted to forelands above 1100 m in the Jotunheim region; whereas the D. alpina‐O. digyna sub‐community has a wider altitudinal range of 80‐1780 m. Variance partitioning indicated that altitude alone accounts for 24%, distance east for 18%, and the component shared by altitude and distance east for 17% of the variance in species composition. Conclusions: At the broadest scale, pioneer vegetation on the glacier forelands can be viewed as a single P. alpina‐O. digyna community of predominantly wind‐ and water‐dispersed perennials. However, this community shows a high degree of variability, with dominant species missing from a number of sites, and is poorly structured, suggesting a degree of stochasticity. Furthermore, the pioneer vegetation can be dissected within a continuum of variation to produce two emerging sub‐communities, reflecting the influence of environmental factors and, possibly, early successional development within the pioneer zone. Variance partitioning indicates that altitudinal and continentality gradients are important in accounting for a significant proportion of the variability within this dataset.     

Systematics and evolution of arctic-alpine Arabis alpina (Brassicaceae) and its closest relatives in the eastern Mediterranean

? Premise of the study: The high mountains in southern Anatolia and the eastern Mediterranean are assumed to play a major role as a primary center of genetic diversity and species richness in Eurasia. We tested this hypothesis by focusing on the widespread perennial arctic-alpine Arabis alpina and its sympatrically distributed closest relatives in the eastern Mediterranean. ? Methods: Plastid (trnL intron, trnL-F intergenic spacer) and nuclear (ITS) DNA sequence analysis was used for phylogenetic reconstruction. Broad-scale plastid haplotype analyses were conducted to infer ancestral biogeographic patterns. ? Key results: Five Arabis species, identified from the eastern Mediterranean (Turkey mainland and Cyprus), evolved directly and independently from A. alpina, leaving Arabis alpina as a paraphyletic taxon. These species are not affected by hybridization or introgression, and species divergence took place at the diploid level during the Pleistocene. ? Conclusions: Pleistocene climate fluctuations produced local altitudinal range-shifts among mountain glacial survival areas, resulting not only in the accumulation of intraspecific genotype diversity but also in the formation of five local species. We also show that the closest sister group of Arabis alpina consists exclusively of annuals/winter annuals and diverged prior to Pleistocene climatic fluctuations during the colonization of the lowland Mediterranean landscape. These findings highlight that Anatolia is not only a center of species richness but also a center for life-history diversification.     

A Race for Space? How Sphagnum fuscum stabilizes vegetation composition during long‐term climate manipulations

Strong climate warming is predicted at higher latitudes this century, with potentially major consequences for productivity and carbon sequestration. Although northern peatlands contain one‐third of the world's soil organic carbon, little is known about the long‐term responses to experimental climate change of vascular plant communities in these Sphagnum‐dominated ecosystems. We aimed to see how long‐term experimental climate manipulations, relevant to different predicted future climate scenarios, affect total vascular plant abundance and species composition when the community is dominated by mosses. During 8 years, we investigated how the vascular plant community of a Sphagnum fuscum‐dominated subarctic peat bog responded to six experimental climate regimes, including factorial combinations of summer as well as spring warming and a thicker snow cover. Vascular plant species composition in our peat bog was more stable than is typically observed in (sub)arctic experiments: neither changes in total vascular plant abundance, nor in individual species abundances, Shannon's diversity or evenness were found in response to the climate manipulations. For three key species (Empetrum hermaphroditum, Betula nana and S. fuscum) we also measured whether the treatments had a sustained effect on plant length growth responses and how these responses interacted. Contrasting with the stability at the community level, both key shrubs and the peatmoss showed sustained positive growth responses at the plant level to the climate treatments. However, a higher percentage of moss‐encroached E. hermaphroditum shoots and a lack of change in B. nana net shrub height indicated encroachment by S. fuscum, resulting in long‐term stability of the vascular community composition: in a warmer world, vascular species of subarctic peat bogs appear to just keep pace with growing Sphagnum in their race for space. Our findings contribute to general ecological theory by demonstrating that community resistance to environmental changes does not necessarily mean inertia in vegetation response.     

Shrub expansion may reduce summer permafrost thaw in Siberian tundra

Climate change is expected to cause extensive vegetation changes in the Arctic: deciduous shrubs are already expanding, in response to climate warming. The results from transect studies suggest that increasing shrub cover will impact significantly on the surface energy balance. However, little is known about the direct effects of shrub cover on permafrost thaw during summer. We experimentally quantified the influence of Betula nana cover on permafrost thaw in a moist tundra site in northeast Siberia with continuous permafrost. We measured the thaw depth of the soil, also called the active layer thickness (ALT), ground heat flux and net radiation in 10 m diameter plots with natural B. nana cover (control plots) and in plots in which B. nana was removed (removal plots). Removal of B. nana increased ALT by 9% on average late in the growing season, compared with control plots. Differences in ALT correlated well with differences in ground heat flux between the control plots and B. nana removal plots. In the undisturbed control plots, we found an inverse correlation between B. nana cover and late growing season ALT. These results suggest that the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw. Increased shrub growth may thus partially offset further permafrost degradation by future temperature increases. Permafrost models need to include a dynamic vegetation component to accurately predict future permafrost thaw.     

Development patterns in young conifer-hardwood forests of interior Alaska

Abstract. The age structure and growth patterns of 53 young conifer-hardwood stands on upland, south-facing sites of interior Alaska were analyzed to determine the length of time for stand establishment after disturbance, the composition of early-successional stands compared to existing stands, and the potential for late-successional stands dominated by conifers. Mixed stands of Picea glauca, Populus tremuloides and Betula papyrifera represented five plant community types and developed as single cohorts after stand-replacement fires. In the Populus tremuloides/Arctostaphylos uva-ursi and Populus tremuloides/Shepherdia canadensis community types, hardwoods established rapidly and Picea glauca established slowly. In contrast, stands in the Betula papyrifera-Populus tremuloides/Viburnum edule, Betula papyrifera-Populus tremuloides/Alnus crispa, and Picea glauca-Betula papyrifera/Hylocomium splendens community types generally developed as a result of rapid, concurrent establishment of conifers and hardwoods. These single-cohort, mixed species development patterns are not consistent with continual establishment of conifers and are likely the result of unique life-history traits and frequent stand-replacement fires.     

Holocene chloroplast genetic variation of shrubs (Alnus alnobetula,Betula nana,Salix sp.) at the siberian tundra‐taiga ecotone inferred from modern chloroplast genome assembly and sedimentary ancient DNA analyses

Climate warming alters plant composition and population dynamics of arctic ecosystems. In particular, an increase in relative abundance and cover of deciduous shrub species (shrubification) has been recorded. We inferred genetic variation of common shrub species (Alnus alnobetula, Betula nana, Salix sp.) through time. Chloroplast genomes were assembled from modern plants (n = 15) from the Siberian forest‐tundra ecotone. Sedimentary ancient DNA (sedaDNA; n = 4) was retrieved from a lake on the southern Taymyr Peninsula and analyzed by metagenomics shotgun sequencing and a hybridization capture approach. For A. alnobetula, analyses of modern DNA showed low intraspecies genetic variability and a clear geographical structure in haplotype distribution. In contrast, B. nana showed high intraspecies genetic diversity and weak geographical structure. Analyses of sedaDNA revealed a decreasing relative abundance of Alnus since 5,400 cal yr BP, whereas Betula and Salix increased. A comparison between genetic variations identified in modern DNA and sedaDNA showed that Alnus variants were maintained over the last 6,700 years in the Taymyr region. In accordance with modern individuals, the variants retrieved from Betula and Salix sedaDNA showed higher genetic diversity. The success of the hybridization capture in retrieving diverged sequences demonstrates the high potential for future studies of plant biodiversity as well as specific genetic variation on ancient DNA from lake sediments. Overall, our results suggest that shrubification has species‐specific trajectories. The low genetic diversity in A. alnobetula suggests a local population recruitment and growth response of the already present communities, whereas the higher genetic variability and lack of geographical structure in B. nana may indicate a recruitment from different populations due to more efficient seed dispersal, increasing the genetic connectivity over long distances.