Diurnal patterns of CO2 and H2O exchange of the Arctic sedges Eriophorum angustifolium and E. vaginatum (Cyperaceae)

Eriophorum vaginatum and E. angustifolium are dominant arctic sedges of the well-drained tussock tundra and the permanently flooded wet-sedge tundra, respectively. We determined diurnal courses of gas exchange and water relations of the two species in their natural habitat and compared their responses to changes in light, air temperature, and humidity. Mean photosynthetic response to light was similar between E. angustifolium and E. vaginatum and carbon gain in both species was light limited during most of the growing season. On sunny and dry days, both species closed stomata in response to high leaf-to-air vapor pressure deficits. Even though E. angustifolium was growing in standing water, it exhibited a tighter control of transpirational water loss and had lower hydraulic conductivity in the soil-root-shoot pathway than E. vaginatum. The different response pattern between the two species is discussed in the context of differences in habitat conditions.     

Exsertion, elongation, and senescence of leaves of Eriophorum vaginatum and Carex bigelowii in Northern Alaska

The seasonal patterns of leaf exsertion, elongation, and senescence were described and compared for two of the most abundant graminoid species of Alaskan moist tussock tundra, Eriophorum vaginatum and Carex bigelowii . In addition the responses of both species to NPK fertilizer and to variation in site fertility (water track vs. non-track areas) were also assayed and compared. The research was done over two full growing seasons at two sites near Toolik Lake, Alaska, where other aspects of the ecology of both species have been the subject of intensive and ongoing research.
Both species showed the typical graminoid pattern of sequential leaf growth, in which the exsertion and elongation of new leaves is coincident with the senescence of old leaves. However, the rates of these processes were much slower and steadier in Eriophorum than in Carex , with much greater overlap in the life histories of individual leaf cohorts. The total and green leaf lengths of whole tillers in Eriophorum were also less variable over the entire year than in Carex . The conclusion is that leaf growth in Carex should depend more on external storage of carbon and nutrients than Eriophorum , with a much greater seasonal variation in demands on storage and retranslocation to and from leaves.
The effects of fertilizer and the water track on leaf growth dynamics and turnover rates were largely nonsignificant, despite major effects on total tiller size and productivity. This is in contrast to previous research on evergreen leaf dynamics, but similar to results of previous research on overall production and biomass regulation in Eriophorum . It is concluded that the graminoid response to increased nutrient availability in the Arctic is to dilute the greater amounts of nutrient uptake by greater growth, so that nearly the same metabolic homeostasis is achieved as under low nutrient availability, but at a higher biomass.     

Seasonal dynamics and standing crops of biomass and nutrients in a subarctic tundra vegetation

Standing crops of biomass and nutrients were measured in Eriophorum vaginatum tussock tundra and on a north-facing slope, called the camp site, with similar species composition during the summer of 1976 at Eagle Creek, Alaska. These data were then compared to similar data collected at Meade River, Alaska in 1975. Four species are compared: Ledum palustre, Salix pulchra, Betula nana , and Eriophorum vaginatum . The density of aboveground individuals was greater at the tussock site than at the camp site. The total late season above- and belowground standing crop of organic matter and of biomass was greater at the camp site. The nitrogen and calcium contents of new leaves usually increased during the season while phosphorus and potassium contents decreased. Most of the nutrients were in the mosses and lichen compartments rather than in vascular plants.     

Intraspecific variations in seedling emergence and survival of Potentilla matsumurae (Rosaceae) between alpine fellfield and snowbed habitats

Potentilla matsumurae has a wide distribution from wind-blown fellfields to snowbeds in alpine regions of Japan. The environmental factors influencing seedling establishment differ between the fellfield and snowbed habitats; plants growing in each habitat may therefore have different germination strategies. Using a reciprocal sowing experiment, patterns of seedling emergence and survivorship were examined in both habitat types in the Taisetsu Mountains, Japan. Seeds derived from a fellfield population germinated earlier than did those derived from a snowbed population at both habitats, and the germination of fellfield seeds continued throughout the growing season. The timing of seedling emergence greatly affected subsequent survival at the fellfield. Seedlings that emerged in the first half of the growing season had low survivorship during the first year because of frost and drought damage, but the remaining seedlings had high survivorship during the winter; seedlings that emerged in the latter half of the growing season showed the opposite trend. At the snowbed, seedling survival was high throughout the growing season. Germination experiments in the laboratory highlighted a difference in the sensitivity of seeds from the fellfield and snowbed populations to fluctuating temperatures. These results indicate that intraspecific variation in emergence and survivorship may occur over a small scale in an alpine environment.     

Size-dependent perennation bud formation and its effect on seedling establishment inVeronicastrum sibiricum ssp.japonicum

Seedling establishment of a perennial,Veronicastrum sibiricum ssp.japonicum colonizing at 1,600 m altitude in Nikko National Park was studied for two years. About half of the first-year seedlings died during the growing season and 45–74 per cent of the seedlings surviving the first summer died during the following winter season. This winter mortality depended on the end-of-season size of the seedling in the previous autumn and was caused mainly by the absence of perennation buds. Seedlings which had emerged on bare ground attained larger size and had higher winter survival than seedlings in a mat of moss. Seedlings germinating in early season attained larger size and had higher probability of winter survival than seedlings germinating in later season.     

Early emergence increases survival of tree seedlings in Central European temperate forests despite severe late frost

Global warming is expected to result in earlier emergence of tree seedlings that may experience higher damages and mortality due to late frost in spring. We monitored emergence, characteristics, and survival of seedlings across ten tree species in temperate mixed deciduous forests of Central Europe over one and a half year. We tested whether the timing of emergence represents a trade‐off for seedling survival between minimizing frost risk and maximizing the length of the growing period. Almost two‐thirds of the seedlings died during the first growing period. The timing of emergence was decisive for seedling survival. Although seedlings that emerged early faced a severe late frost event, they benefited from a longer growing period resulting in increased overall survival. Larger seedling height and higher number of leaves positively influenced survival. Seedlings growing on moss had higher survival compared to mineral soil, litter, or herbaceous vegetation. Synthesis. Our findings demonstrate the importance of emergence time for survival of tree seedlings, with early‐emerging seedlings more likely surviving the first growing period.     

Effect of Acorn Burying Depth on Germination,Seedling Emergence and Development of Quercus aliena var. acuteserrata

Acorns of Quercus aliena var. acuteserrata Maxim. are often predated by small mammals and birds in natural forests. These animals not only eat the acorns during the acorn ripening season, but also cache and hoard most of the remaining acorns on the forest floor in the soil for their future use. These buried acorns form the main seed resource for regeneration. Burying depth is potentially important for germination and for seedling development. The effects of burying depth on germination and seedling development in relation to acorn size were studied in an experiment, in which acorns were planted at 6 cm-, 12 cm- and 18 cm-depth. The experimental results showed that fewer acorns germinated as burying depth increased. From the deeply buried acorns fewer seedlings emerged at later time than from those acorns buried less deeply. They appeared to have more difficulties to emerge above-ground than the seedlings from shallowly buried acorns. The deeply buried acorns and their seedlings also appeared to be more susceptible to rot. Acorn size did not significantly affect germination and emergence of the seedlings. As early emerged seedlings had longer developmental periods in their first growing season, and therefore grew better than the late emerged seedlings, seedlings from the shallowly buried acorns took the advantage.     

Survivorship and Spatial Development of Spartina alterniflora Loisel. (Gramineae) Seedlings in a New England Salt Marsh

Patterns of survival and spatial arrangement of tillers of Spartinaalterniflora were examined in natural and in artificially producedbare areas, and in pure stands of adult S. alterniflora in aNew England salt marsh. Seedling growth and survival were highin naturally occurring bare patches and in artificial patches,whether created by continual clipping of adult plants to groundlevel throughout the growing season or by providing bare substrateafter removal of adult plants. Seedling growth and survivorshipincreased with increasing size of bare area. S. alternifloraseedlings were also common in areas dominated by adult plants,but no seedlings survived a whole first growing season underthe mature canopy, probably because of competition from adultplants. In large bare areas, S. alterniflora seedlings grew non-directionally,reaching heights of 0.5 m, and producing as many as 36 tillersin one growing season. Examination of leaf area ratios suggestedthat the production of tillers increased photosynthetic capacityin seedlings with several tillers in contrast to seedlings withouttillers. Thus, seedlings can apparently tiller and colonizefree space radially without a loss of photosynthetic capacity. These results suggest that while seedling success is generallylimited by adult plants in monocultures of S. alterniflora,in disturbed spaces seedling success is high and results ina rapid non-directional proliferation of sexually generatedclones that ultimately preclude the successful invasion of futureseedlings. Clones, directional growth, leaf area ratio, salt marsh cordgrass, seedling survivorship, Spartina alterniflora Loisel     

锐齿槲栎橡子埋藏深度对发芽、幼苗出土和发育的影响

锐齿槲栎（Quercus aliena var.acuteserrata Maxim.)林内活动的许多型哺乳动物和鸟类不仅采食橡子,而且还常窖贮或在土壤大量的橡 子以便季后利用。这些埋藏的橡子构成了发育有效更新苗的主要种子来源。橡子被埋藏的深度和橡子的大小对幼苗的发育有潜在的影响。把橡子埋藏在6、12和18cm3个土层深度的实验结果显示：随着埋藏深度的增加,橡子的发芽率和发芽橡子的幼苗出土率都有明显下降,由深埋橡胶子发育的幼苗出土比较困难,所需时间较长,也更易腐烂,橡子的大小对发芽和幼苗出土没有明显的影响,早出土幼苗在第一个生长季内由于有较长的生长发育期,季末发育得较好,所以,由浅埋橡子发育的幼苗在更新成功方面有优势。     

Reproductive effort in cotton grass tussock tundra

Eriophorum vaginatum ssp. spissum is a dominant plant species of undisturbed cotton grass tussock tundra in Alaska. It also quickly invades and dominates recently disturbed sites. The hypothesis tested in this research was that the success of E. vaginatum on disturbed sites might be achieved through a higher allocation of biomass to reproductive structures relative to other tundra species. Reproductive allocation of tundra plants in general also was compared with plants of the temperate zone. The results indicate that E. vaginatum is about average among the common tundra species in terms of total reproductive allocation, allocation to seeds, and the proportion of total reproductive allocation that is accounted for by viable seeds. Tundra species, on a relative basis, allocate less biomass to all reproductive structures than temperate species but not necessarily less biomass to the output of viable seeds.     

Phenology and life cycle of the annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations in Japan

The phenology of germination, vegetative growth and sexual reproduction in the annual Chamaesyce maculata (L.) Small (Euphorbiaceae) were investigated in a natural population in western Japan. Seedlings emerged from mid-June to early October, with three peaks: mid-June, late July and late August. Plants that emerged in June commenced sexual reproduction from late July, and thereafter both vegetative growth and sexual reproduction occurred together until early November, the plants showing no switching from vegetative growth to sexual reproduction. Seedlings that emerged in June and July suffered high mortality, but most seedlings that emerged from August onward survived until the reproductive stage. The minimum size for reproduction was largest for plants that emerged early in the season, and it decreased with a delay in seedling emergence. The late emergence of seedlings that resulted in low reproductive output may be to some extent compensated for by the increased probability of survival in the seedling stage. A transplant experiment clarified that C. maculata can repeat a maximum of three overlapping generations within a year. Multiple generations per year were attained by non-dormant seeds produced in the first and second generations and clearly resulted in an increased reproductive output per year. The life cycle with multiple overlapping generations may have been acquired in habitats where unpredictable disturbance results in temporally unsuitable conditions for germination, vegetative growth and sexual reproduction of annual plants, but where suitable conditions frequently continue over a period longer than the single generation time of annual plants.     

Fire,canopy cover and seedling dynamics in Mediterranean shrubland of northeastern Spain

Abstract. Seedling establishment and survival of the main woody species of early-successional shrubland in northeastern Spain were studied from 1992 to 1995 with emphasis on the importance of vegetation cover (existence of open areas and the situation beneath the plant canopy) and microhabitat (occurrence of stones, litter and bare soil). In the absence of fire, vegetation cover (measured at a scale of 30cm × 30 cm) was not correlated with seedling emergence of most species, nor with growth and survival of seedlings up to one year old. Seedlings older than one year showed a similar pattern: their density was not significantly different in both kinds of habitats. The emergence of seedlings was mainly associated with the presence of mature plants – which can provide seeds – and with the absence of unsuitable microhabitats (large stones, deep litter and bare soil). In April 1994 a wildfire burned the study area. This enabled a study of the pattern of post-fire establishment. After the wildfire, seedling emergence of several species increased and most species produced seedlings with higher survival and growth rates than in the period before the fire. Pre-fire cover, however, did not show significant effects on post-fire seedling dynamics in most cases.     

Advantage of early seedling emergence in <Emphasis Type="Italic">Fagus crenata</Emphasis>: importance of cotyledon stage for predator escape and pathogen avoidance

To examine how early-emerging seedlings take advantage of establishment in a deciduous forest, we explored the relationships among the emergence date, growth stage and major causes of mortality (damping-off by fungi and predation by rodents) in seedlings of Fagus crenata. The emergence of current-year seedlings and their survival and damage were followed at short (3–7 days in early spring) intervals for a growing season. The growth stage was divided into two stages, with only cotyledons (CT stage) and with true leaves (TL stage). The survival rate was negatively correlated with the emergence date, indicating the advantage of early seedling emergence. This advantage was largely explained by the lower occurrence of damping-off. In contrast, seedling predation occurred independently of the emergence date, but depended strongly on the developmental stage. Rodents consumed a considerable number of seeds during the early period after emergence, and strongly preferred CT-stage over TL-stage seedlings throughout the growing season. Therefore, seedling predation was inferred to be concentrated in a relatively short period while the remaining seeds were depleted and CT-stage seedlings were abundant. The seedling stage synchronously shifted from the CT to TL stage. This growth-stage transition was independent of the emergence date and appeared to correspond with the timing of seed depletion. Delayed stage transition resulted in a disproportionately high risk of damping-off later in the season. Our results indicate that early seedling emergence is advantageous for F. crenata for resistance to pathogens and that the timing of growth-stage progression of seedlings appears important to escape predation because of the distinct food preference of predators.     

Ecophysiological analysis of two arctic sedges under reduced root temperatures

Shoot physiological activity in arctic vascular plants may be controlled by low soil temperatures. While leaves may be exposed to moderate temperatures during the growing season, root temperatures often remain near freezing. In this study, two tundra sedges, Eriophorum vaginatum and Carex bigellowii , were subjected to reduced soil temperatures, and photosynthetic parameters (light saturated photosynthesis A _max, variable to maximal fluorescence and F _v/ F _m stomatal conductance) and abscisic acid concentrations were determined. Stomatal conductance and A _max for both E. vaginatum and C. bigellowii strongly decreased with declining soil temperatures. Decreasing soil temperature, however, impacted F _v/ F _m to a much lesser degree. Root and leaf ABA concentrations increased with decreasing root temperature. These observations support the contention that soil temperature is a significant photosynthetic driving factor in arctic sedges exposed to variable root and shoot temperatures. Because these two species comprise approximately 30% of the vascular ground cover of wet tussock tundra, the soil temperature responses of these sedges potentially scale up to significant effects on ecosystem carbon exchange.     

Neighbor effects on germination, survival, and growth in two arctic tundra plant communities

In relatively harsh environments such as arctic tundra, abiotic factors have traditionally been considered the primary determinants of community structure, overwhelming any effects of biotic interactions such as competition. Two common low arctic tundra types that differ in soil properties, moist acidic and moist non-acidic tussock tundra (MAT and MNT, respectively), occur in close proximity in northern Alaska. Several plant species occur in both communities with different relative abundance, while others are restricted to one. This study experimentally examined how neighboring vegetation affects germination, survival, and growth of species in these two communities that differ in soil pH, cation availability, and other characteristics. Germination of sown seeds was greater than background levels suggesting seed limitation may restrict recruitment of these clonal, perennial species. Germination of sown seeds was greater at both sites when both mosses and vascular plants had been removed compared to plots with intact vegetation. However, neighbors had almost no effect on survival and growth of adult transplants. Patterns of germination, survival and growth of several species differed depending on the community of origin and the community of destination of the seeds or transplanted adults. For example, transplants of the sedge Eriophorum vaginatum grew better if they were from MAT, and this species germinated better when sown at MNT. Although of relatively short duration (three growing seasons), this study suggests that biotic interactions may affect local species composition by restricting germination and establishment in these two communities, but have less of an effect on adult plants. Not surprisingly, site-specific abiotic conditions also exhibit control over species occurrence and relative abundance. Without disturbance to clear bare ground for recruitment of new individuals, these populations for the most part must rely on clonal growth to persist.     

Effects of bryophytes and lichens on seedling emergence of alvar plants: evidence from greenhouse experiments

Emergence of seedlings of four alvar grassland species ( Arenaria serpyllifolia , Festuca ovina , Filipendula vulgaris and Veronica spicata ) in bryophyte and lichen carpets was analysed in a series of greenhouse experiments. The aspects investigated were: the influence of thickness of moss mats, both in dry and moist conditions, the effects of thick Cladonia spp. clumps, and of living vs dead moss shoots and lichen podetia. Overall, Festuca seedlings emerged best whereas the small-seeded species, Arenaria and Veronica , had the lowest emergence. Moisture had a significant effect only on the emergence of Festuca seedlings, which emerged better in the dry treatment than in the moist. A thick moss cover negatively affected seedling emergence of Arenaria and Veronica but did not affect the emergence of Festuca . Filipendula showed lower seedling emergence in both thick and thin moss than on bare soil only in the dry treatment, whereas in the moist treatment emergence did not differ among the three substrates. Arenaria seedlings emerged less in thick and thin moss than on bare soil in the dry treatment, whereas in the moist treatment emergence in the thin moss was not different from bare soil. Thus, in relatively dry environments even a thin moss cover may inhibit rather than facilitate seedling emergence. The lichen clumps inhibited only the emergence of the forbs. Both living moss shoots and lichen podetia inhibited emergence of Veronica seedlings but did not affect Festuca . In contrast, emergence in the presence of dead mosses and lichens did not differ from emergence in their absence for both species. Hence, inhibition of seedling emergence by bryophytes and lichens of at least some vascular plant species may be mediated by some biotic factor. However, the effect of differences in substrate properties on germination cannot be excluded     

Phosphate absorption and root respiration of different plant growth forms from northern Alaska

Rate of phosphate absorption measured on field-collected, excised roots of eight species from a tundra site and a taiga forest was more strongly correlated with growth form traits than with type of community. In the taiga forest phosphate absorption rate ranged tenfold among species and was higher in graminoids than in shrubs. In both sites deciduous shrubs tended to have higher rates than evergreens. Phosphate absorption rate was not strongly reduced at low temperature in any species examined and there was a temperature optimum of about 20°C in Eriophorum vaginatum . Phosphate absorption rates were higher in lateral than primary roots, although both root types had substantial respiration rates. At one tundra site, calculations suggest that roots of E. vaginatum require 30–40 d to absorb a quantity of phosphorus equivalent to that required to synthesize the root and another 5–6 d to provide the net phosphorus requirements for the remainder of the plant.     

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

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

Vertical distribution of organic matter in eight vegetation types near Eagle Summit, Alaska

The amount and distribution of organic matter was measured in different categories in six montane tundra vegetation types in a snow accumulation area and in tussock and intertussock areas in Eriophorum vaginatum tussock tundra in central Alaska. In root properties, the tussock and intertussock areas were more similar to the fellfield zone than to the vegetation zones below the snow accumulation area. Root density apparently increased as soil nutrients decreased, but this increase may be caused by higher soil moisture and higher root relative water content. The tussock tundra has accumulated more dead soil organic matter than any of the montane zones.     

Conifer seedling recruitment across a gradient from forest to alpine tundra: effects of species,provenance, and site

Background: Seedling germination and survival is a critical control on forest ecosystem boundaries, such as at the alpine–treeline ecotone. In addition, while it is known that species respond individualistically to the same suite of environmental drivers, the potential additional effect of local adaptation on seedling success has not been evaluated.

Aims: To determine whether local adaptation may influence the position and movement of forest ecosystem boundaries, we quantified conifer seedling recruitment in common gardens across a subalpine forest to alpine tundra gradient at Niwot Ridge, Colorado, USA.

Methods: We studied Pinus flexilis and Picea engelmannii grown from seed collected locally at High (3400 m a.s.l.) and Low (3060 m a.s.l.) elevations. We monitored emergence and survival of seeds sown directly into plots and survival of seedlings germinated indoors and transplanted after snowmelt.

Results: Emergence and survival through the first growing season was greater for P. flexilis than P. engelmannii and for Low compared with High provenances. Yet survival through the second growing season was similar for both species and provenances. Seedling emergence and survival tended to be greatest in the subalpine forest and lowest in the alpine tundra. Survival was greater for transplants than for field-germinated seedlings.

Conclusions: These results suggest that survival through the first few weeks is critical to the establishment of natural germinants. In addition, even small distances between seed sources can have a significant effect on early demographic performance – a factor that has rarely been considered in previous studies of tree recruitment and species range shifts.