Anatomy and development of the fern sporophyte

Recent research on the developmental anatomy and morphology of the fern sporophyte is reviewed. Detailed histological and experimental studies of the organization of the fern shoot apical meristem have reconfirmed the recently controversial role of the shoot apical cell as the single apical initial of the meristem. The shoot apical meristem is nevertheless an anatomically and functionally complex structure with a strongly zoned cytohistological organization. Fern shoot apex organization can be compared with that of seed plants. The control of leaf initiation and phyllotaxy remains poorly understood. Studies differ as to whether leaf initiation in ferns involves one leaf mother cell or a multicellular region of the shoot apex. The concept of non-appendicular fronds is refuted for living ferns. The later developmental changes in the determinate leaf apical and marginal meristems of the leaf primordium form an area that is still largely unexplored but could be investigated by methods similar to those used to study shoot and root apices. Branching in ferns is morphologiclaly and developmentally diverse. There is apparently more than one developmental mode of dichotomous branching, and several modes of lateral bud formation have been described, including the phyllogenous initiation of branches at the base of leaf primordia. Developmental changes in bud meristems related to apical dominance, inhibition, and bud activation is another major area for continued study. The traditional concept of the role of the root apical cell has been reestablished by studies similar to those made of the shoot apex. Detailed ultrastructural investigations of the root ofAzolla have given a sophisticated new picture of developmental processes in that organ. Fern roots show remarkably precise patterns of histogenesis in relation to apical segmentation. The formation of secondary vascular tissue inBotrychium suggests that the Ophioglossales may be related to the seed plants. The causal relationship of leaf (and branch and root) formation and the initiation of vascular tissue in the shoot needs more study. Although still poorly understood, protoxylem systems in ferns are variable and may have morphological and systematic significance. Recent investigations of hydraulic conductance in fern stems have found possible correlations of conductance levels with growth forms. The anatomical diversity of ferns makes comparative functional anatomy a promising field for future study.     

Protoplast induction from sporophyte tissues of the heterosporous fern Azolla

We have developed a method for producing protoplasts from the heterosporous water fern Azolla using a combination of Cellulysin (4.0%) and Pectolyase (0.025%) in 0.6 M mannitol containing 6 mM CaCl₂ 2H₂O. These protoplasts regenerate new cell walls within 48 hours when cultured on modified Gamborg B-5 medium.     

Vegetative reproduction of trees in some European natural forests

Various means of vegetative reproduction in unexploited forests in western Europe are illustrated with examples. Root suckers are sometimes almost the only method of forest regeneration near the limits of tree growth on the Wadden islands and they can play an important role in forest gaps and riverine forests. Trunk suckers finally replacing their parent trees occur in Alnus, Tilia and Ulmus. Partial uprooting of trees, favoured by special soil conditions, was shown to be an important condition for vegetative reproduction. Temporary survival after uprooting gives opportunity for development of reiterative sprouts, that can replace the vertical axis of a fallen tree. Contact of living branches or even whole stems with soil or mouldering logs favours the growth of adventitious roots. Thus vegetatively reproduced individual trees establish before the uprooted parent tree finally dies. Examples of the clonal spreading of trees are given and a special strategy of layering its branches in pasture woods has been described for beech. Modern forestry rigorously eliminates conditions suitable for the vegetative reproduction of forest trees so their abilities in this respect are often underestimated. Vegetative reproduction seems to be particularly important under circumstances where natural growth is difficult e.g. near the limits of tree growth, on dynamic sites and under heavy shade.     

Vegetative reproduction as a stabilizing feature of the population dynamics of Yucca glauca

Summary The life history of Yucca glauca in the Great Plains was the subject of a four year field study. Data were incorporated in a stage transition model (based on rosette size) to explain how populations are maintained in spite of large regional and temporal variation in sexual reproductive success. Rosette size was found to be a good predictor of flowering effort, but a poor predictor of fruit set. Large rosettes that failed to set fruit, however, exhibited an increased capacity for vegetative reproduction. Asexual reproduction contributes to population stability by reducing the variance in annual recruitment, and perhaps by damping oscillations caused by departures from a stable stage distribution.     

Vegetative reproduction by species with different adaptations to shallow-flooded habitats

In shallow flooded parts of rich fens Mentha aquatica might thrive in deeper water than Epilobium hirsutum but previous experiments have provided no clear indication that the flooding tolerance of these species differs. In this study we investigated, by measuring growth, biomass allocation and vegetative reproduction, whether the impact of water level on vegetative reproduction might produce different lower boundaries on water level gradients. There was a striking contrast between biomass production at high water levels and the field distribution of both species. After 18 wk, the mean biomass of E. hirsutum grown in waterlogged and flooded conditions was 82% and 54%, respectively, of the mean biomass production of drained plants. Biomass of waterlogged and flooded M. aquatica was reduced to 57% and 37% in drained conditions. Waterlogged and flooded E. hirsutum had swollen stem bases and invested a high proportion of biomass in adventitious roots. Stems of M. aquatica did not swell, formed few adventitious roots and maintained an equal proportion of below-ground roots at all water levels. The effect of water level on vegetative reproduction corresponded well with the lower hydrological boundaries of both species. When waterlogged and flooded, most rhizomes of E. hirsutum emerged from above-ground parts of the stem base and were oriented in an upward direction. Plants in flooded soil allocated less biomass to rhizomes and also reduced the number and size of rhizomes. Rhizome formation of M. aquatica on the other hand was not directly affected by water level and only depended on plant size. These differences in vegetative reproduction are discussed in relation to the different abilities of both species to oxygenate their below-ground roots. It was concluded that the mode of adaptation to soil flooding might also affect vegetative reproduction and, therefore, a species' ability for long-term persistence in soil-flooded habitats.     

Vegetative reproduction in the octocoral Briareumasbestinum (Pallas)

Briareum asbestinum (Pallas), a common octocoral of Caribbean reefs, produces runner-like branches which are capable of attaching to the substratum and establishing new colonies. The subsequent death of the intervening runner leaves groups of genetically identical but physiologically distinct colonies. The origin of these colonies can be deduced by the presence or absence of runners. Analysis of colonies at Marsarkantupo in the San Blas Islands, Panama and at Carrie Bow Cay, Belize indicate that 23–56% and 18–67%, respectively, of the colonies at these sites originate from vegetative runners. In both areas the distribution of colonies of larval origin is not uniform. Colonies originating from larvae are patchily distributed within habitats and are over-represented in shallow habitats. The ability of B. asbestinum to reproduce vegetatively results in the spread and development of large populations of this species in many habitats where it might otherwise be rare.     

Vegetative reproduction capacities of floodplain willows--cutting response to competition and biomass loss

While several studies on regeneration in Salicaceae have focused on seedling recruitment, little is known about factors controlling their vegetative reproduction. In two greenhouse experiments, we studied the response of floodplain willows (Salix fragilis, S. viminalis, S. triandra) to competition with Poa trivialis, and to shoot and root removal when planted as vegetative cuttings. In the first experiment, growth performance variables were analysed in relation to full competition, shoot competition, root competition and control, taking into account two different water levels. After 9 weeks, shoots were removed and the resprouting capacity of the bare cuttings was recorded. In the second experiment, the cutting performance of the three floodplain and an additional two fen willow species (S. cinerea, S. aurita) was compared when grown in three different soil compositions and with two different water levels. After 9 weeks, shoot and root biomass was removed and the bare cuttings were replanted to test their ability to resprout. Cutting performance and secondary resprouting were negatively affected by full and shoot competition while root competition had no or weak effects. The floodplain species performed better than the fen species in all soil types and water levels. Secondary resprouting capacity was also higher in the floodplain species, which showed an additional strong positive response to the previous waterlogging treatment. The results contribute to understanding of the vegetative regeneration ecology of floodplain willows, and suggest that the use of vegetative plantings in restoration plantings could be an effective strategy for recovering floodplain forests.     

Vegetative propagation and sexual reproduction in the woodland understorey pseudo-annual Circaea lutetiana L.

On the forest floor of deciduous woodlands, relative light intensity gradually declines during the early growing season. The woodland understorey pseudo-annual Circaea lutetiana L. completes its life-cycle at the end of summer. These pseudo-annuals are clonal plants which survive the winter only as seeds and as hibernacles produced by the rhizome apices. In this paper, we asked several questions related to the life-history of C. lutetiana. It was found that shoot formation in early spring did not exhaust the old hibernacle. A trade-off between rhizome + hibernacle number and weight might be expected when plants grow under resource limitation. It was hypothesised that both number and weight of rhizomes and hibernacles will be affected by light availability. Since the effect of resource supply on the size number trade-off will depend on the developmental pattern of the rhizome system, rhizome development was studied as well. Soon after the shoots emerged, 1st order rhizomes were formed in May on the nodes of the old hibernacle. First-order rhizomes branched in June and 2nd order rhizomes (side-branches) were continuously produced throughout the growing season. The phenology and developmental rate of plants growing in different light treatments were plastic. On average 30% of rhizome biomass was formed during the vegetative phase, and rhizome and fruit production were only partly separated in time. The ratio of total rhizome biomass to total fruit biomass was not affected by light. Also flower bud removal did not lead to an increase in rhizome production, which suggests that division of biomass to both reproductive modes is rather rigid. The number of 1st order rhizomes was not affected by the light treatments. Under light limitation, both rhizome number and weight of single rhizomes were reduced. In contrast, fruit number, but not weight of single fruits, was limited.     

Comparison of gametophyte growth, sex determination and reproduction in three fern species from the tropics

The gametophytes of Athyrium boryanurn, Thelypteris subpubescens and Pteridium aquilinum (vars. aquilinum, esculentum and wightianum) were grown as isolates, pairs and groups, and they were found to differ in their life histories: A. boryanum is a selfer which is sensitive to competition, while T. subpubescens is an ineffective selfer which is sensitive to competition, and P. aquilinurn is generally ineffective at sexual reproduction. A relationship between the level of gametophyte reproduction and the sporophyte viability was detected. The interactions between neighbours (competition or antheridiogen effects) appeared to influence gametophyte growth and reproductive success. In general, hermaphroditic gametophytes were considerably larger than males in all species, and those hermaphrodites which formed sporophytes were often smaller than other hermaphrodites.     

The cuticle of the Buxbaumia viridis sporophyte

The sporophytes of Buxbaumia viridis are covered with a cuticle-like skin, which is peeling off when the capsules are ripe. Scanning electron microscopy (SEM) analysis showed that the supposed peeling of the cuticle of ripe capsules is not restricted to the cuticle, but to the complete epidermis. Additionally the SEM investigations showed that the capsule epidermis is covered by epicuticular wax crystals in different morphologies. Wax crystal morphologies indicate the presence of massive wax layers with small embedded and superimposed platelets and granules on top. For bryophytes such wax crystals were so far reported only from the Polytrichales, but they are common wax types of various groups of several phanerogams. Based on these micro-morphological markers the phylogenetic relationship between the cuticles of moss sporophytes and tracheophytes is discussed here.     

The cost of realized sexual reproduction: assessing patterns of reproductive allocation and sporophyte abortion in a desert moss

The desert moss Syntrichia caninervis exhibits one of the most skewed sex ratios in the plant kingdom, with female individuals far outnumbering male individuals (exceeding 14♀:1♂). The "cost of sex hypothesis" derives from allocational theory and predicts that the sex which is most expensive should be the rarer sex. This hypothesis, which, as considered here represents the realized cost of sexual reproduction, is contingent upon two assumptions that are explored: (1) that male sex expression is more expensive than female sex expression, and (2) that sexual reproduction is resource limited. Using inflorescence biomass and discounting sperm, male sex expression was found to be in the neighborhood of one order of magnitude more expensive than female sex expression, and this difference is reflected in higher numbers of gametangia per male inflorescence, presence of paraphyses in male inflorescences, and a much longer developmental time for male inflorescences. The realized cost of female reproduction from two communities dominated by S. caninervis was found to be lower than the realized cost of male sexual reproduction. Resource-limited reproduction was assessed by determining the frequency of sporophyte abortion, the age distribution of sporophyte abortions, and patterns of sporophyte abortion that may be density dependent. Among ten sexually reproducing populations, abortive sporophytes occurred at a frequency of 0.64. Abortive sporophytes averaged 8% the mass of mature sporophytes, and cohort sporophytes from the same individual female were found to abort in a density-dependent pattern. We conclude that the two assumptions, upon which the cost of sex hypothesis depends, are supported.     

Morpho-ecological studies on geophilic plants: Vegetative reproduction inIris vartani (Iridaceae)

Structure and behaviour of the underground organs ofIris vartani were investigated in connection with the vegetative reproduction of this species. Under favourable conditions, well developed mature plants give rise to two replacement bulbs and to several propagation bulblets each year. In spite of this considerable vegetative propagation, no crowding occurs at the natural habitat. Controlled experiments show that as soon as a small group is formed, each bulb produces only one replacement bulb and not two as before. Moreover, the bulblets do not sprout while they are attached to the respective mother bulbs, but rather die and disintegrate, remaining as empty peels. In contrast, detached bulblets, sown individually in separate pots, germinate readily. Consequently, the aggregates ofI. vartani do not increase to any great extent and thus ensure their survival “in situ” for many years.     

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.

     

松嫩平原异质生境羊草种群营养繁殖特征

多年生无性系禾草主要依靠营养繁殖实现种群的持续更新,而各类芽和由芽形成的苗为其种群进行营养繁殖的潜在种群。通过单位面积挖掘取样,利用营养繁殖世代数划分分株、根茎和各类型芽和苗的龄级,对松嫩平原封育草甸、长期割草草甸、封育积沙草甸和林间草地的羊草潜在种群组成和大小进行了比较研究。结果表明: 在生长季末期,羊草的潜在种群均由根茎芽和各龄级分蘖节向上生长的芽以及根茎苗和分蘖节苗组成。在4种生境条件下,羊草分株潜在种群由3～4个龄级组成,1～4龄级根茎均可形成潜在种群,其中,根茎潜在种群占整个羊草潜在种群数量比例为68.3%,占绝对优势。1龄分株和根茎产生的潜在种群占总体的60.2%,是潜在种群组成的主要部分,是种群更新的主要来源。分株潜在种群数量以长期割草草甸最高,根茎潜在种群数量以封育积沙草甸最高。营养繁殖力均以年轻龄级分株和根茎最高,根茎的营养繁殖力是分株的10.0倍,在羊草种群营养繁殖过程中始终占据优势。羊草的潜在种群构成在不同生境条件下变异较大,但体现出对生境差异的趋异适应。     

Vegetative reproduction and chemical control with post-emergent herbicides of field bindweed (Convolvulus arvensis L.)

It is clearly seen from data that roots of Convolvulus arvensis L. have more and less intensive regenerative period during growing season. The more intensive period is in autumn, because in that time roots culminate nutrients, carbohydrate as starch and sugar. The less intensive regenerative or shoot-growing period is in spring, called "late spring bud dormancy". Experiments were conducted to get more information and further details about the regenerative capacity of roots close to and far from the collar of Convolvulus arvensis L. Root segments closer to collar have an intensive regenerative capacity than those ones further to collar. By data of Bakke et al. (1939) is well known, roots exhumed from deep soil layers are able to create shoots with low intensity. So finally we can exclaim that regenerative capacity is decreasing further to collar. Using mechanical weed control it is sufficient to till the upper layer of soil, but many times. Chemical treatments are most effective in the integrated weed control. It is clearly seen that auxin-type herbicide such as 2,4-D, fluroxipir, MCPA. dicamba give the best result. They gave 95% weed control effect used them separately or in combination with other herbicides. Combination of Banvel 480 S (dicamba) and Logran 75 WG (triasulfuron) introduced 95% weed control effect. Only one time got absolutely 100% weed control effect, in the case of Glyphosate active substance. Caused total plant destruction. Excellent result was given with the application of Pledge 50WP (flumioxazin). Herbicides mentioned above are absolutely allowed to take an important and significant part in chemical plant protection against Convolvulus arvensis L. Other herbicides like Granstar 75DF (tribenuron-methyl), Basis 75DF (rimsulfuron + tifensulfuron-methyl) and Huszár (jodosulfuron-methyl-sodium + mefenpir-diethyl) are not so effective against Convolvulus arvensis L., as compared to the previous ones.