SPORE MORPHOLOGY IN THE CYATHEACEAE. I. THE PERINE AND SPORANGIAL CAPACITY: GENERAL CONSIDERATIONS

The literature on cyatheaceous spore morphology relative to the presence of a perine layer is reviewed, and evidence based on a sodium-hydroxide assay is presented indicating that the outer scultpine layer in certain cyatheaceous spores is perine. Perine so defined characterizes Metaxya, paleotropical and certain neotropical species of Sphaeropteris, nearly all species of Alsophila, all species of Nephelea, and certain species of Trichipteris and Cyathea. It is lacking in Lophosoria, many species of Trichipteris and Cyathea, and all species of Cnemidaria. Two major patterns of spore number per sporangium in the family are reported. Lophosoria, Sphaeropteris, Trichipteris, Cyathea, Cnemidaria, and probably Metaxya are characterized by 64-spored sporangia, whereas most species of Alsophila and all species of Nephelea are characterized by 16-spored sporangia. The congruence of this generic distribution of sporangial-capacity types with Tryon's phyletic arrangement of cyatheaceous genera supports the naturalness of his system. The intrasporangial germination of spores retained in dehisced and dispersed sporangia supports the suggestion that decreased spore number per sporangium in Alsophila and Nephelea may relate to the role of the sporangia as dispersal units. The decreased number of spores per sporangium is associated with a trend toward increase in the number of sporangia per sores, with the highest known count approaching 1000 sporangia per sorus. The Alsophila-Nephelea evolutionary line has probably not been ancestral in the phylogeny of the more advanced groups of ferns.     

SPORE MORPHOLOGY IN THE CYATHEACEAE. II. THE GENERA LOPHOSORIA,METAXYA, SPHAEROPTERIS,ALSOPHILA, AND NEPHELEA

Scanning electron microscopy and transmitted light microscopy are used in a palynological study of Lophosoria, Metaxya, Sphaeropteris, Alsophila, and Nephelea of the tree fern family Cyatheaceae. The monotypic American genera Lophosoria and Metaxya each have a unique spore morphology which reinforces the taxonomic distinctness of these genera as indicated by their other characters. All investigated paleotropical species of Sphaeropteris develop a single type of perine characterized by coarse, pointed projections. In the neotropics, the Sphaeropteris horrida group shares this perine type, whereas all other neotropical Sphaeropteris species appear to have a different kind of perine with fine hair-like processes. The exine in paleotropical Sphaeropteris appears uniformly unsculptured, whereas in the neotropics several exine morphologies are found. In Alsophila all investigated neotropical species and the vast majority of the paleotropical species are characterized by a basically ridged perine morphology and an unsculptured exine. In several paleotropical Alsophila species, however, a perine with hair-like processes similar to those in neotropical Sphaeropteris is found, and the exine in several species is variously pitted. In at least one paleotropical Alsophila species, the porate exine morphology is indistinguishable from that in the neotropical genus Cnemidaria. The spores of the American genus Nephelea are similar to those of the majority of Alsophila species in ridged perine morphology and unsculptured exine. Several new instances of atypical spore numbers per sporangium are reported in Sphaeropteris and Alsophila. These and the palynological data are discussed in a taxonomic framework. The spore morphology in these genera is consistent with Tryon's recent generic revision of the family.     

环境因子对中华双扇蕨孢子萌发的影响

为了解珍稀濒危植物中华双扇蕨(Dipteris chinensis)濒危原因,研究了温度和湿度对其孢子萌发的影响.结果表明,中华双扇蕨孢子萌发能力较强,萌发方式为Vittaria型,配子体萌发为Marattia型.中华双扇蕨孢子繁殖不受温度影响,而湿度显著影响孢子繁殖过程,湿润环境中孢子正常萌发,并形成心形配子体,顺利...     

Gametophyte development and reproduction of the Asian fern Polystichum polyblepharum (Roem. ex Kunze) C. Presl (Dryopteridaceae,Polypodiopsida)

Abstract

The gametophytic generation of Polystichum polyblepharum (Dryopteridaceae), including spore germination, morphological development of the gametophytes, major vegetative features and reproduction strategies, was studied. Spore germination was of the Vittaria model and the developmental pattern was of the Aspidium model. Adult gametophytes were cordate and hairy, with unicellular hairs located at the margins and at the prothallus surface. The marginal ones were secretory. The gametophytes produced archegonia located in the central area between the notch and the rhizoids, but antheridia were never detected. Archegonia were of the normal type described for leptosporangiate ferns. Apogamous sporophytes appeared from a cellular outgrowth developed just under the apical notch. Initially, the outgrowth appeared completely surrounded by glandular hairs and scales, which persisted throughout the subsequent stages of leaf development.     

COMPARATIVE ONTOGENETIC STUDIES IN YOUNG SPOROPHYTES OF TREE FERNS. I. A PRIMITIVE AND AN ADVANCED TAXON

Ontogenetic studies of young sporophytes were undertaken to determine anatomical and morphological differences between a primitive (Lophosoria quadripinnata) and an advanced (Sphaeropteris elongata) tree fern. In both species the first leaf is simple, fanshaped, and possesses dichotomous venation. Later-formed leaves exhibit either a pinnate or bipinnate pattern of laminar dissection. As the sporophyte matures, the stelar pattern changes from a protostele to an amphiphloic siphonostele, and finally to a dictyostele in Sphaeropteris. Medullation of the protostele occurs either prior to or after the formation of the first leaf trace in both species. Differentiation of xylem in the shoot is acropetal and the appearance of mature protoxylem occurs closer to the apical meristem in Sphaeropteris. The nodal pattern varies within each species with a no gap 1-trace pattern characteristic for the first two or three leaves, depending upon the taxon. In Lophosoria subsequent leaves possess a unilacunar 1-trace nodal pattern, whereas a complete nodal series (1 gap 1-trace to 1 gap 6-trace) occurs in Sphaeropteris. Fusiform leaf gaps are noted in both species. The shoot apical meristem is dominated by a single apical cell, with an organized apical cell first found in P₂. Stem, root, and petiole anatomy are discussed.     

Attack density and breeding success of bark beetles (Coleoptera, Scolytidae) at different distances from forest-clearcut edge

1 Attack density and breeding success of bark beetles (Coleoptera: Scolytidae) and the abundance of their predators were studied at forest-clearcut edges in southern Finland on Norway spruce, Picea abies, bolts placed at different distances from a forest-clearcut edge. 2 Attack densities of two species, Hylurgops palliatus and H. glabratus, increased markedly towards the forest interior. The breeding success of H. palliatus was increased with increasing distance from the stand edge. None of the recorded 10 bark beetle species was distinctly abundant near the edge, but Pityogenes chalcographus appeared to prefer this zone. 3 There were no significant differences in numbers of bark beetle predators between the forest interior and the edge. Forest-clearcut edge had a significant effect on the desiccation of sample bolts. 4 Thus, forest edge is likely to affect the colonization behaviour and breeding success of bark beetles via host material properties.     

A methodology for large-scale Athyrium sheareri gametophyte proliferation and sporophyte production using tissue culture

Tissue culture methods using gametophytes are considered the easiest ways to mass-produce fern sporophytes. The aim of this study was to develop a practical propagation method for the ornamental fern, Athyrium sheareri. The gametophytes obtained from in vitro spore germination were used as experimental materials. We used the chopping method to investigate the culturing conditions for proliferating gametophytes and the blending method for evaluating the mass production of sporophytes in mixed soil. Gametophyte proliferation was determined via Knop medium, various concentrations of Murashige and Skoog (MS) basal medium (1, 1/2, 1/4), and media components (sucrose, nitrogen source, and activated charcoal). The fresh weight of the gametophytes increased by more than 24-fold in 1/2 MS medium. In addition, 1 g of gametophyte could produce a maximum of 255.3 sporophytes in a mixed soil of 7.5 cm² area. Treating gametophytes with exogenous plant growth regulators promoted the formation and growth of sporophytes. The cultivated young sporophytes were acclimated and successfully grown in greenhouses. We developed a mass production protocol for A. sheareri sporophytes suitable for field application, which is expected to have commercial value.

     

Antheridiogen,dark spore germination,and outcrossing mechanisms in Bommeria (Adiantaceae)

Isozymic analyses of the patterns of genetic variability in sporophyte populations have demonstrated that most fern species have outcrossing breeding systems. However, because fertilization takes place during the ephemeral, diminutive gametophyte generation, direct observation of breeding systems in nature has not been possible. Recent discoveries of soil-bound spore banks suggested that genetic diversity could be stored beneath the surface and subsequently released by appropriate chemical cues. Previous studies demonstrated that Bommeria sporophytes are the product of outcrossing, that their gametophytes carry high levels of genetic load, and that they produce and respond to antheridiogen. Research reported here demonstrated that Bommeria spores can survive long-term storage but will not germinate in the dark. Antheridiogen, however, will release spores from this light requirement and stimulate germination. Higher concentrations of antheridiogen result in higher germination rates. Gametophytes grown in the dark on antheridiogen-enriched agar form antheridia and release actively swimming sperms. Thus, spores housed beneath the soil surface could remain dormant until stimulated to germinate by antheridiogen secreted by surface-dwelling, archegoniate gametophytes. Sperm released from these subterranean gametophytes could fertilize eggs on the surface. Because spores housed in the soil are likely to be genetically different than those at the surface, heterozygous sporophytes would be more likely to result. Discovering that Bommeria species contain all of the prerequisites for this proposed outcrossing mechanism provides an explanation for the maintenance of genetic diversity in some fern populations.     

<Emphasis Type="Italic">In vitro</Emphasis> culture of <Emphasis Type="Italic">Drynaria fortunei</Emphasis>, a fern species source of Chinese medicine “Gu-Sui-Bu”

This study reports spore germination, early gametophyte development and change in the reproductive phase of Drynaria fortunei, a medicinal fern, in response to changes in pH and light spectra. Germination of D. fortunei spores occurred on a wide range of pH from 3.7 to 9.7. The highest germination (63.3%) occurred on ½ strength Murashige and Skoog basal medium supplemented with 2% sucrose at pH 7.7 under white light condition. Among the different light spectra tested, red, far-red, blue, and white light resulted in 71.3, 42.3, 52.7, and 71.0% spore germination, respectively. There were no morphological differences among gametophytes grown under white and blue light. Elongated or filamentous but multiseriate gametophytes developed under red light, whereas under far-red light gametophytes grew as uniseriate filaments consisting of mostly elongated cells. Different light spectra influenced development of antheridia and archegonia in the gametophytes. Gametophytes gave rise to new gametophytes and developed antheridia and archegonia after they were transferred to culture flasks. After these gametophytes were transferred to plastic tray cells with potting mix of tree fern trunk fiber mix (TFTF mix) and peatmoss the highest number of sporophytes was found. Sporophytes grown in pots developed rhizomes.     

Effect of temperature and photon fluence rate on gametophytes and young sporophytes of Laminaria ochroleuca Pylaie

We analysed the effects of temperature and photon fluence rate on meiospore germination, growth and fertility of gametophytes, and growth of young sporophytes of Laminaria ochroleuca. Maximum percentages of germination (91–98%) were obtained at 15°C and 18°C, independent of photon fluence rate. Optimal development of female gametophyte and maximum fecundity and reproductive success of gametophytes occurred at 15°C and 18°C and at 20 and 40 μmol m^–2 s^–1. Maximum relative growth rate of young sporophytes after 2 weeks of culture was achieved under the same conditions. L. ochroleuca gametophytes cannot reproduce and growth of its sporophytes is not competitive at temperatures close to 10°C. Received in revised form: 31 August 2001 Electronic Publication     

Gap phase regeneration of tree species of differing successional status in a humid tropical forest of Kerala,India

Germination, establishment and growth of seedlings of tree speciesPalaquium ellipticum (primary),Actinodaphne malabarica (late secondary) andMacaranga peltata (early secondary) were studied in a humid tropical forest at Nelliampathy, in the Western Ghats of Kerala. While the primary species completed its germination within a brief period of 1.5 months, at the other extreme, early secondary species showed slow germination extending for about 5 months, the late secondary species falling in between. Although, all the species studied showed higher establishment and growth under gaps, the early secondary species were more responsive compared to the primary species. Primary species showed better establishment in undisturbed sites and natural gaps than under selection felled gaps; the reverse was true for late and early secondary species. Survival of seedlings increased with gap size, but sharply declined with gap age. Shoot/root ratio was consistently higher in the early secondary species than in the primary species.     

CONTROL OF SEX RATIOS IN HAPLOID POPULATIONS OF THE MOSS,CERATODON PURPUREUS

Female biased sex ratios occur in a number of unrelated mosses. Such ratios refer to the relative numbers of male and female gametophytes in moss populations and are therefore more comparable to the numbers of pollen grains and ovules in populations of seed plants than to the numbers of male (microsporangiate) and female (megasporangiate) sporophytes. A survey of 11 populations of the moss, Ceratodon purpureus, showed that sex ratios are heterogeneous, but that female biases occur in more than half the populations. One hundred and sixty single spore isolates representing 40 sporophytes from one population demonstrated that female gametophytes outnumbered males by a ratio of 3:2 at the time of germination. Female gametophytic clones formed significantly more biomass than male clones, and individual female shoots were more robust. Male clones, however, produced more numerous stems. These sexually dimorphic traits may be related to life history differences between male and female gametophytes since females must provide nutritional support to the “parasitic” sporophyte generation, a burden that males do not share.     

Resistance of Island Rainforest to Invasion by Alien Plants: Influence of Microhabitat and Herbivory on Seedling Performance

Experiments have promise in determining mechanisms by which communities resist invasion. Growth and survivorship of transplanted seedlings of introduced tree species (Leucaena leucocephala, Muntingia calabura, Adenanthera pavonia, and Clausena excavata) were used to assess abiotic (light regime) and biotic resistance (herbivory) to invasion of rainforest on Christmas Island (Indian Ocean). At four sites, seedlings were transplanted into the forest edge along roadside verges and into adjacent intact forest; half were caged to prevent access by the dominant seedling consumer, the red land crab (Gecarcoidea natalis). Red crab densities did not differ between roadside and forest plots. Red crabs initially reduced survivorship of Leucaena in both edge and interior plots but virtually all seedlings in the forest interior were dead after 41 weeks. Survivorship of Muntingia was also initially reduced by crabs in the forest edge, but again, all but one seedling died by the end of the experiment. Seedlings of Adenanthera and Clausena fared much better overall, surviving well in both locations. Red crabs had no overall effect on Adenanthera survival but significantly reduced survival of Clausena in forest plots. For both species, seedling performance was greater in the forest edge than in the forest interior. Red crabs had no effect on height increment for either species; however, for Clausena, red crabs reduced seedling mass in the forest interior. Both Adenanthera and Clausena were able to persist in the intact forest. Clausena is now actively invading intact rainforest, but Adenanthera appears dispersal-limited. Resistance factors in intact forest appear hierarchical: biotic resistance afforded by land crabs can impede establishment of some plant invaders but seedling responses to abiotic factors (e.g., the light regime) largely overwhelm its effect. Together, these two community attributes are likely to restrict the range of plant invaders to a small suite of species that can successfully establish in intact rainforest on the island. However, increased propagule pressure from a variety of shade-tolerant species and further declines in the abundance of the dominant seedling consumer may lead to increasing invasion success in this island rainforest. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of temperature and nutrients on microscopic stages of the bull kelp (Nereocystis luetkeana,Phaeophyceae)

Warming ocean temperatures have been linked to kelp forest declines worldwide, and elevated temperatures can act synergistically with other local stressors to exacerbate kelp loss. The bull kelp Nereocystis luetkeana is the primary canopy-forming kelp species in the Salish Sea, where it is declining in areas with elevated summer water temperatures and low nutrient concentrations. To determine the interactive effects of these two stressors on microscopic stages of N. luetkeana, we cultured gametophytes and microscopic sporophytes from seven different Salish Sea populations across seven different temperatures (10–22°C) and two nitrogen concentrations. The thermal tolerance of microscopic gametophytes and sporophytes was similar across populations, and high temperatures were more stressful than low nitrogen levels. Additional nitrogen did not improve gametophyte or sporophyte survival at high temperatures. Gametophyte densities were highest between 10 and 16°C and declined sharply at 18°C, and temperatures of 20 and 22°C were lethal. The window for successful sporophyte production was narrower, peaking at 10–14°C. Across all populations, the warmest temperature at which sporophytes were produced was 16 or 18°C, but sporophyte densities were 78% lower at 16°C and 95% lower at 18°C compared to cooler temperatures. In the field, bottom temperatures revealed that the thermal limits of gametophyte growth (18°C) and sporophyte production (16–18°C) were reached during the summer at multiple sites. Prolonged exposure of bull kelp gametophytes to temperatures of 16°C and above could limit reproduction, and therefore recruitment, of adult kelp sporophytes.     

Peculiarities of development in the marine brown alga <Emphasis Type="Italic">Alaria angusta</Emphasis> Kjellman, 1889 (Alariaceae: Ochrophyta) under laboratory-controlled conditions

This paper describes the formation of gametophytes and the early stages of the development of sporophytes in the kelp seaweed Alaria angusta from Kamchatka. To establish laboratory cultures we used zoospores obtained from A. angusta sporophytes collected on October 29, 2014. The gametophytes were grown under different conditions: at 6–7°С and natural light and at 10°С and illumination with cool white fluorescent bulbs, 30 μmol photon m^–2 s^–1, 12: 12 h L: D cycle. In the first case (natural light, 6–7°С), the vegetative growth of male and female gametophytes lasted for more than 4 months; maturation of sexual products occurred 144 days after germination of the embryospores. In the second case (artificial light, 10°С), rapid development of the gametophytes occurred; the first juvenile sporophytes appeared on the 10th day after the zoospores settled onto the substrate. Our data contribute to understanding of the regulatory effect of temperature and light on the peculiarities of species vegetation in the natural environment and formation of the age structure of the species population, one particular feature of this process is the continuous appearance of juvenile sporophytes in the warm period of the year.     

Natural soil spore banks — can they be used to retrieve lost ferns?

Some fern species form spore banks — reservoirs in the soil of viable spores which remain dormant while buried but germinate in light if brought to the surface. The recently discovered characteristics of these spore banks are described. Enough is now known to suggest that they might have a role in the conservation of endangered fern species as alternatives toex situ collections of sporophytes, gametophytes and spores, the relative merits of which are also considered. Mature sporophytes of several British species have now been raised from natural spore banks in soil samples; if this proves to be possible also for endangered species, some interesting options become available. The possibilities are discussed of augmenting surviving populations and increasing their genetic diversity, even perhaps of retrieving lost populations, by reintroduction of spore bank-derived plants or by stimulating regeneration from spore banksin situ. Botanic gardens are well placed to provide the further research, the regular monitoring of endangered populations, and the taxonomic and horticultural support required to realise these possiblities.     

Urchin grazing of kelp gametophytes in warming oceans

Sea urchins can cause extensive damage to kelp forests, and their overgrazing can create extensive barren areas, leading to a loss of biodiversity. Barrens may persist when the recruitment of kelp, which occurs through the microscopic haploid gametophyte stage, is suppressed. However, the ecology of kelp gametophytes is poorly understood, and here we investigate if grazing by juvenile urchins on kelp gametophytes can suppress kelp recruitment and if this is exacerbated by climate change. We compared grazing of Ecklonia radiata gametophytes by two species of juvenile urchins, the tropical Tripneustes gratilla and the temperate Centrostephanus rodgersii, at winter (19°C), summer (23°C), and ocean warming (26°C) temperatures for the low-latitude range edge of E. radiata, which is vulnerable to ocean warming. We examined the rate of recovery of gametophytes following grazing and determined whether they survived and formed sporophytes after ingestion by sea urchins. Both T. gratilla and C. rodgersii grazed E. radiata gametophytes, reducing their abundance compared to no grazing controls. Surprisingly, temperature did not influence grazing rates, but gametophytes did not recover from grazing in the ocean warming (26°C) treatment. Gametophytes survived ingestion by both species of sea urchin and formed sporophytes after ingestion by T. gratilla, but not C. rodgersii. These results suggest complex grazer–gametophyte interactions, in which both negative (reduced abundance and poor recovery with warming) and positive (facilitated recruitment) effects are possible. Small grazers may play a more important role in kelp ecosystem function than previously thought and should be considered in our understanding of alternate stable states.     

Seeds and seedlings of two neotropical montane understory shrubs respond differently to anthropogenic edges and treefall gaps

Edges resulting from forest clear-cutting and treefall gaps can affect plant populations and consequently the distribution of species across landscapes. These two types of disturbance might interact to exacerbate or ameliorate “edge effects”, a rarely tested possibility. We focused on the effects of distance from forest edge (0–10, 30–40, 60–70, and 190–200 m) and habitat within forest fragments (treefall gaps and intact forest) on the early stages of development of Palicourea gibbosa and Faramea affinis, two common shrubs of montane forests in southwest Colombia. Seed germination and seedling growth did not change with distance from forest edge. Within forest fragments, however, seed germination and seedling growth were higher in treefall gaps than in intact forest understory for both species. In contrast, seed predation was influenced by distance from forest edge and in P gibbosa it depended on habitat. Seed predation was highest in the forest interior (190–200 m from forest edge) and in P. gibbosa this was true only in treefall gap habitats. These results suggest that animal mediated processes such as post-dispersal seed predation are more likely than physiological processes to be affected by anthropogenic edges. Our results provide some evidence that treefall gaps may interact with “edge effects”, however, they are inconclusive as to whether they exacerbate or ameliorate them. Received: 31 August 1998 / Accepted: 18 February 1999     

Reproductive Output,Synchrony across Depth and Influence of Source Depth in the Development of Early Life stages of Kelp

Ecklonia radiata is the main foundation species in Australian temperate reefs, yet little has been published on its reproduction and how this may change across its depth range (1–50+ m). In this study, we examined differences in sporophyte morphology and zoospore production during a reproductive season and across four depths (7, 15, 25, and 40 m). Additionally, we examined differences in germination rate, survival, and morphological traits of gametophytes obtained from these four depths, cultured under the same light and temperature conditions. Multivariate morphology of sporophytes differed significantly between deep (~40 m) and shallow sites (7 and 15 m), but individual morphological traits were not significantly different across depths. Total spore production was similar across depths but the peak of zoospore release was observed in February at 15 m of depth (6,154 zoospores · mm^?2 of tissue) and the minimum observed in January at 7, 25, and 40 m (1,141, 987, and 214 zoospores · mm^?2 of tissue, respectively). The source depth of zoospores did not have an influence in the germination rate or the survival of gametophytes, and only gametophytes sourced from 40 m sites presented significantly less surface area and number of branches. Overall, these results indicate that E. radiata’s reproductive performance does not change across its depth range and that kelp beds reproducing in deeper areas may contribute to the replenishment of their shallow counterparts. We propose that deep kelps may constitute a mechanism of resilience against climate change and anthropogenic disturbances.     

Practical methodology for gametophyte proliferation and sporophyte production in green penny fern (Lemmaphyllum microphyllum C. Presl) using mechanical fragmentation

Propagation of gametophytes and sporophytes using mechanical fragmentation has been considered a suitable method for mass production of ferns. This study aimed to develop a practical propagation method for Lemmaphyllum microphyllum C. Presl, which is a fern of significant ornamental and medicinal value. Gametophytes were obtained through in vitro spore germination and used for propagation experiments. The gametophyte was mechanically fragmented using a scalpel into small fragments, which were then used to investigate gametophyte proliferation. In addition, the gametophyte was fragmented using a blender and then used to study sporophyte formation. Optimal proliferation conditions of the gametophyte were determined using Murashige and Skoog (MS) basal medium (double-, full-, half-, quarter-strength), Knop medium, and medium components (sucrose, nitrogen sources, activated charcoal), at various concentrations. The fresh weight of the gametophyte was 14-fold higher than that of gametophytes (300 mg) used as culture material, when cultured on double-strength MS. Moreover, 1 g of the gametophyte fragmented in 25 mL of distilled water formed more than 430 sporophytes in a soil mixture in an area of 7.5 cm². The sporophytes were successfully cultivated in the greenhouse after acclimation. A large-scale production method for L. microphyllum that can be easily implemented in a fern production farm is outlined.