Late Silurian trilete spores from northern Jiangsu, China

The Late Silurian is generally considered to a particular significant key period in the study of early land vascular plants. A trilete spore assemblage of the Upper Silurian is described from northern Jiangsu, China. This assemblage comprises 11 genera and 20 species of trilete spores (including laevigate, apiculate, perinotrilite, patinate, rarely distally murornate and equatorially crassitate, and three indeterminate trilete miospores forms). It has similarities to those described from coeval assemblages from around the world (e.g., England and South Wales; Tripolitania, Libya; Cornwallis Island, Canadian Arctic; Northwest Spain). The rare cryptospore, only one specimen (Tetrahedraletes sp.) had been found to be associated with the Chinese trilete spore assemblage. The discovery of the trilete spores from Late Silurian rocks indicates the existence of early land plants, some possibly vascular, at that time in northern Jiangsu, China.     

Microstructures of possible early land plants from tripolitania, North Africa

Palynological preparations of spores and microplankton from the Silurian and Early Devonian (Gedinnian) of the Ghadames Basin, Libya, revealed also sheets of cells (or cuticles) and tubes. Nine types of sheets of possible land plant origin and four tubes of tracheid, sclerites and algae have been described. Their affinities and occurrence were also determined.     

Miospore assemblages from the Silurian–Devonian boundary,in borehole A1-61, Ghadamis Basin,Libya

Well preserved and diversified miospore assemblages have been recorded from a relatively continuous sequence in borehole A1-61 which spans the Silurian–Devonian boundary in the northwestern part of the Ghadamis Basin, Libya. The sequence is represented by early Devonian Lochkovian beds of the Tadrart Formation that transgress onto the Silurian Ludlow-Pridoli beds of the upper part of the ‘Alternances Argilo-gréseuses’ Formation. The present work demonstrates a succession of miospore assemblages from closely sampled layers that have been stratigraphically dated as Ludlow–middle Pridoli and early Lochkovian by chitinozoans and acritarchs. Over 80 species of cryptospores and trilete spores have been identified. Modified detailed morphological interpretations are given. The miospore assemblages are correlated with miospore zonation schemes established for the type sequences of the Welsh Borderland, and those previously described from Libya. Early occurrences of some species as Streelispora newportensis on the western Gondwana plate, are put forward by comparison with the Old Red Sandstone continent. Phytogeographic and palaeobotanic implications based on these observations are discussed.     

Devonian spore assemblages of China

Data available show that there are many genera and species of Devonian spores in China (together with acritarchs, chitinozoans and scolecodonts) which are commonly well-preserved, especially in South China where they are also better studied. This permits their use for correlation in detailed stratigraphical studies.On the basis of the study on Devonian spores for the past twenty years it is suggested that eight Devonian spore assemblage zones may be recognised in China, with four zones for the Lower Devonian, two zones for the Middle Devonian and two zones for the Upper Devonian. Each zone is characterised by a distinctive suite of miospores.The spore assemblages of China may be correlated basically with those in Great Britain, Federal Germany, Spitsbergen, U.S.S.R., and North America.     

Germination and infectivity of ectomycorrhizal fungal spores in relation to their ecological traits during primary succession

The spores of ectomycorrhizal fungi (EMF) play critical roles in the population and community development of EMF. Here, the germination and infectivity of EMF spores are examined with reference to the ecological traits of the EMF species. Spores were collected from 12 EMF species, whose successional patterns have been studied in the volcanic desert on Mount Fuji, Japan. Spore germination experiments were conducted with host plants (Salix reinii), with nonhost plants (Polygonum cuspidatum), and without plants. The mycorrhizal formation ability of spores was also examined in seven EMF using spore inoculation experiments. To determine the effects of the spore preservation period, both experiments were repeated up to 1 yr after spore collection. Spore germination was very low in the absence of host plants. In the presence of hosts, even 30 d after spore collection, spore germination was significantly enhanced in all pioneer EMF (c. 20%) but less so in late-stage EMF (< 5%), except in Hebeloma species. Mycorrhizal formation from spores was also greater in pioneer EMF but was significantly reduced by 1 yr of spore preservation. High spore germination and infectivity of pioneer EMF should enable these species to colonize disturbed and isolated areas in accordance with their ecological traits.     

Size distribution in some Middle Devonian dispersed spores and its bearing on the problem of the evolution of heterospory

Some Middle Devonian dispersed spore species have been studied whose size range embraces the arbitrary demarcation line of 200 μm in diameter generally accepted for the identification of a megaspore. The spore size distribution for one species is unimodal while those for other three species are bimodal. The spores of the smaller size classes (the presumed microspores) are relatively large, the means being 90 μm, 100 μm and 207 μm. The morphological features of the spores imply their progymnospermous affinity. It is suggested that in progymnosperms, in the course of heterospory evolution, the increase in spore size occurred before size differentiation and, presumably, before sex determination. The cause of the size increase might have been endospory, which may thus have occurred previous to the last two events.     

Deux Lycophytesavec structures conservées du dÉvonien supérieur D'Ukraine (U.R.S.S.)

A revision of fossil plants, with preserved structures, collected in the Upper Devonian of the Donetz Basin (Ukrainia) allows us to describe 2 Lycophyta. One of them is a new species: Colpodexylon (?) schopfii nov. sp.     

ULTRASTRUCTURE OF DISPERSED AND IN SITU SPECIMENS OF THE DEVONIAN SPORE RHABDOSPORITES LANGII: EVIDENCE FOR THE EVOLUTIONARY RELATIONSHIPS OF PROGYMNOSPERMS

Abstract: The spore Rhabdosporites (Triletes) langii (Eisenack) Richardson, 1960 is abundant and well preserved in Middle Devonian (Eifelian) ‘Middle Old Red Sandstone’ deposits from the Orcadian Basin, Scotland. Here it occurs as dispersed individual spores and in situ in isolated sporangia. This paper reports on a detailed light microscope (LM), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis of both dispersed and in situ spores. The dispersed spores are pseudosaccate with a thick walled inner body enclosed within an outer layer that was originally attached only over the proximal face. The inner body has lamellate/laminate ultrastructure consisting of fine lamellae that are continuous around the spore and parallel stacked. Towards the outer part of the inner body these group to form thicker laminate structures that are also continuous and parallel stacked. The outer layer has spongy ultrastructure. In situ spores preserved in the isolated sporangia are identical to the dispersed forms in terms of morphology, gross structure and wall ultrastructure. The sporangium wall is two‐layered. A thick coalified outer layer is cellular and represents the main sporangium wall. This layer is readily lost if oxidation is applied during processing. A thin inner layer is interpreted as a peritapetal membrane. This layer survives oxidation as a tightly adherent membranous covering of the spore mass. Ultrastructurally it consists of three layers, with the innermost layer composed of material similar to that comprising the outer layer of the spores. Based on the new LM, SEM and TEM information, consideration is given to spore wall formation. The inner body of the spores is interpreted as developing by centripetal accumulation of lamellae at the plasma membrane. The outer layer is interpreted as forming by accretion of sporopollenin units derived from a tapetum. The inner layer of the sporangium wall is considered to represent a peritapetal membrane formed from the remnants of this tapetum. The spore R. langii derives from aneurophytalean progymnosperms. In light of the new evidence on spore/sporangium characters, and hypotheses of spore wall development based on interpretation of these, the evolutionary relationships of the progymnosperms are considered in terms of their origins and relationship to the seed plants. It is concluded that there is a smooth evolutionary transition between Apiculiretusispora‐type spores of certain basal euphyllophytes, Rhabdosporites‐type spores of aneurophytalean progymnosperms and Geminospora‐/Contagisporites‐type spores of heterosporous archaeopteridalean progymnosperms. Prepollen of basal seed plants (hydrasperman, medullosan and callistophytalean pteridosperms) are easily derived from the spores of either homosporous or heterosporous progymnosperms. The proposed evolutionary transition was sequential with increasing complexity of the spore/pollen wall probably reflecting increasing sophistication of reproductive strategy. The pollen wall of crown group seed plants appears to incorporate a completely new developmental mechanism: tectum and infratectum initiation within a glycocalyx‐like Microspore Surface Coat. It is unclear when this feature evolved, but it appears likely that it was not present in the most basal stem group seed plants.     

Spore wall ultrastructure in the early lycopsid Leclercqia (Protolepidodendrales) from the Lower Devonian of North America: Evidence for a fundamental division in the lycopsids

Documenting the morphology and ultrastructure of spores from known Silurian-Devonian plants clarifies organization and probable affinities of dispersed spores and contributes to analyses of evolutionary changes and phylogenetic relationships in early plants. In this study of fossil in situ spores from the early protolepidodendralean lycopsid Leclercqia, we identified new characters including an additional synapomorphy of the ligulate lycopsid clade. A detailed light (LM), scanning electron (SEM), and transmission electron microscope (TEM) analysis of spores from two species of Leclercqia from the Lower Devonian (Emsian) of New Brunswick, eastern Canada, L. andrewsii and L. complexa, shows both are homosporous, yielding spores belonging to the dispersed spore form taxon Acinosporites lindlarensis. Important features of wall ultrastructure include the presence of a paraexospore, peculiar exospore-derived, peg-like structures located in the gap between the outer exospore/inner paraexospore, and multilamellate regions in the interradial areas of the proximal surface. Similar interradial multilamellate regions occur in other ligulate lycopsids (fossil and extant). This character is probably a further synapomorphy for the ligulate lycopsid clade, within which heterosporous lycopods form a monophyletic group. These data suggest the ligule and interradial multilamellate region appeared prior to heterospory.     

New insights into early land ecosystems: a glimpse of a lilliputian world

Small, relatively uncompressed, very fragmentary plant remains (mesofossils) are described from a Silurian (P ídolí) and a Lower Devonian (Lochkovian) locality in the Welsh Borderland. Excellent cellular preservation provides characters leading to the demonstration of diversity in plants of simple gross morphology and allows deliberations on functional anatomy (e.g. of stomata), and reproductive biology (including development and dehiscence of sporangia). A survey of in-situ spores is presented, and preliminary comparisons made with dispersed spore assemblages especially in relation to reconstruction of vegetation on local and regional scales. The earliest body fossils of unequivocal terrestrial arthropods isolated from the same locality as the P ídolí plants suggest that the decomposer/microherbivore/predator soil and litter communities found in the Lower and Middle Devonian extend back at least into the Silurian. Evidence for plant—animal interaction in the Lower Devonian comes from spore-dominated coprolites believed to have been produced by litter-feeding myriapods.     

Sporangia containing Scylaspora from the Lower Devonian of the Welsh Borderland

ABSTRACT. Bulk maceration of Early Devonian (Lochkovian) deposits from the Welsh Borderland has yielded eight specimens of a new type of sporangium characterized by its elongate shape and distinctive spores. The specimens have been examined using scanning electron, transmission electron and light microscopy. The elongate sporangia occur isolated and are fragmented to varying degrees. They contain trilete spores that possess a proximal surface with shallow murornate ornament and a distal surface that is laevigate. The spores belong to the dispersed spore genus Scylaspora , and this is the first report of such spores in situ . Ultrastructural studies demonstrate that the spore walls are bilayered with a lamellate inner layer overlain by an essentially homogeneous outer layer. There is little or no associated extra-exosporal material. To date this is the earliest reported example of lamellate wall ultrastructure in trilete spores. Models of spore wall development are suggested in the light of evidence provided by spore wall ultrastructure. Detailed comparisons of the characters preserved in the fossils (morphological, anatomical and ultrastructural), with those in other fossil and extant plants, currently shed little light on the phylogenetic relationships of these specimens, primarily due to the paucity of comparable data. It is proposed that the plant is probably of vascular status, but in the absence of evidence for vascular tissue, it must be classified as rhyniophytoid.     

Fern and lycopod spores rain in a cloud forest of Hidalgo,Mexico

The aim of this study was to determine the composition of the “spore rain” of ferns and lycopods in a cloud forest. We tested whether the canopy impedes spore dispersal to surrounding areas and how spore dispersal is affected by rainfall. The spores were captured with a modified Bush–Gosling trap placed at 30 cm above ground level in forested and non-forested sites from March 2009 to February 2010. We collected 2462 fern spores from 158 morphospecies of which 76 were identified to species level. Thirty-seven species were found exclusively in the spore rain, and 39 were found as sporophytes as well (local component). Mean daily spore density (spores m^?2) was calculated to find the sporulation period for each species. Twenty species showed seasonal patterns of sporulation. The highest spore density was found at the forested site (70 morphospecies and 1856 spores), of which 39 morphospecies (1482 spores) corresponded to the local vegetation. Fifty-five taxa were shared between the forested and non-forested site. In the non-forested site, 605 spores were captured belonging to 64 species. The density of spore rain between sites was significantly different. The rainfall amount was the same at both sites, with a dry period in March, April, and July 2009, and February 2010. There was a negative effect of rainfall on spore rain. The main sporulation occurred in the dry season with strong winds. Although the canopy inhibits airborne dispersal of fern spores, a small amount of spores can disperse beyond the canopy and reach surrounding areas. The rainfall might wash spores to ground and favor the colonization and the establishment of new populations.     

Substructure in exines of Artemisia vulgaris (Asteraceae)

Of the Silurian and Devonian macroplant genera described in the literature, about half have been recorded with spores. These in situ spores can be compared at generic level with only about a quarter of the dispersed spore genera described for the same period. Emphasis is here placed on the structure and sculpture of in situ and dispersed Silurian, Gedinnian and Siegenian spores, where records of macroplants with in situ spores are high compared with the Middle and Upper Devonian.A comparative study of the structure and sculpture of the in situ and dispersed spores, together with information from the macroplants recorded, suggests a fairly simple Silurian and Gedinnian flora, with the evolution of a more advanced upland flora during Siegenian times.     

感染羽茅的香柱菌属内生真菌对丛枝菌根真菌孢子萌发的影响

内生真菌与丛枝菌根(AM)真菌是构成草原生态系统的重要组成部分.内生真菌会抑制其宿主植物的AM真菌侵染率.本研究以感染2种香柱菌属内生真菌[Epichloё gansuensis(Eg)和E. sibirica(Es)]的天然禾草羽茅为供试材料,进行体外纯培养的内生真菌培养滤液、感染内生真菌的羽茅叶片(包括鲜叶和枯叶)浸提液,以及根系分泌物对摩西球囊霉(Gm)和幼套球囊霉(Ge)2种AM真菌孢子萌发影响试验.结果表明: 香柱菌属内生真菌的培养滤液会显著抑制2种AM真菌孢子的萌发,而感染香柱菌属内生真菌的羽茅根系分泌物只对Ge孢子萌发有显著抑制作用,且上述抑制作用与内生真菌种类无关;鲜叶浸提液对Gm和Ge的孢子萌发率均无显著影响,而枯叶浸提液对Ge的孢子萌发有显著抑制作用.在自然生态系统中,香柱菌属内生真菌通常存在于宿主植物体内,可能通过影响宿主植物的根系分泌物来影响AM真菌孢子的萌发.     

Spore assemblages from the Lower Devonian Xujiachong Formation from Qujing,Yunnan, China

Abstract: The Lower Devonian Xujiachong Formation from the vicinity of Qujing City, Yunnan, China is interpreted as a terrestrial‐fluviatile‐lacustrine sequence. It contains important nonmarine biotas including plants, fish and invertebrates. The plants are particularly interesting as they include many endemic taxa. Dispersed spore assemblages have been recovered from the upper part of this formation. The spores are well preserved and of moderate thermal maturity. They are systematically described and four new species erected: Aneurospora xujiachongensis sp. nov., Chelinospora ouyangii sp. nov., Camptozonotriletes? luii sp. nov. and Leiozonospora xichongensis sp. nov. One new combination is proposed: Aneurospora conica (Ouyang and Lu) comb. nov. This is a rare report of a Lower Devonian dispersed spore assemblage from the South China Plate. Indeed, few dispersed spore assemblages of this age are known outside of Euramerica and Northern Gondwana. It is suggested that the Xujiachong Formation spore assemblages can all be equated to the polygonalis‐emsiensis Spore Assemblages Biozone (PE SAB) of Richardson and McGregor (1986) indicating an early (but not earliest) Pragian to ?earliest Emsian age. However, caution is urged, because biostratigraphical interpretation is difficult owing to distinct differences between dispersed spore assemblages from South China and Euramerica/Northern Gondwana. This almost certainly reflects palaeophytogeographical variation and regional endemism among early land plant floras on widely separated land masses. Palynofacies analysis supports a nonmarine origin for the deposits of the Xujiachong Formation, with the very rare marine palynomorphs that were encountered interpreted as reworked.     

Spores and the middle-upper Devonian boundary

The stratigraphic levels most favoured for the Middle-Upper Devonian boundary fall approximately within the range of the ammonoid Pharciceras lunulicosta Zone, i.e. from the Middle varcus Subzone to the base of the Lower asymmetricus Zone of the conodont scale. Spore data that are potentially useful for recognition of the boundary within this range have been correlated with conodont zones in marine facies in the Boulonnais region of France. A vast amount of information on spores from Middle-Upper Devonian boundary strata has accumulated in the European U.S.S.R., where the boundary is taken at a somewhat lower level. Late Givetian and early Frasnian continental strata of Melville Island in the Canadian Arctic contain species present in the Boulonnais or the European U.S.S.R., as well as species common to both regions. Diatomozonotriletes spp., Rhabdosporites langii, Samarisporites triangulatus, Contagisporites optivus, Archaeoperisaccus timanicus, Chelinospora concinna and Ancyrospora langii, among others, may be useful for correlating the boundary as eventually defined. The stratigraphic ranges of most of these taxa show only limited agreement interregionally at present, probably owing at least in part to problems of spore nomenclature and taxonomy, and an insufficiency of spore reference sequences keyed to faunal zones. Nevertheless, individual species of spores, and especially assemblages of species, have much potential for delimiting and correlating the Middle-Upper Devonian boundary in both marine and continental facies.     

The Potential of Stagonospora sp. as a Mycoherbicide for Field Bindweed

Field bindweed ( Convolvulus arvensis L.) is one of the 12 most important weeds worldwide. Stagonospora sp. Isolate LA39 was isolated from diseased field bindweed plants collected in Europe. No crop tested was susceptible to the fungus, but disease symptoms were observed on other Convolvulaceae species. On field bindweed, the fungus induces disease symptoms (i.e. lesions) mainly on leaves and less severely on stems. The application of spores in an oil emulsion (10% oil in water) enhanced the disease on field bindweed plants compared with spores suspended in a 0.1% aqueous solution of the surfactant agent, Tween 80. The necrotic leaf area of inoculated plants increased as the length of exposure to 100% relative humidity (RH) and the spore density applied increased. Severe disease developed on plants inoculated with 1 107 spores/ml in oil emulsion, even in the absence of exposure to 100% RH. A delay of exposure to 100% RH (up to 8 h) did not have a significant eVect on disease severity. Field bindweed was susceptible to the fungus at all growth stages tested, but older plants were more susceptible than younger ones. It was concluded that isolate LA39 has potential as a biocontrol agent of field bindweed, especially when applied in an oil emulsion. The oil emulsion maintains the aggressiveness of the pathogen during a dew-free period and provides a favourable microenvironment during the infection process.     

Interaction of vascular plants and vesicular-arbuscular mycorrhizal fungi across a soil moisture-nutrient gradient

Summary Abundance and distribution of vascular plants and vesicular-arbuscular mycorrhizal (VAM) fungi across a soil moisture-nutrient gradient were studied at a single site. Vegetation on the site varied from a dry mesic paririe dominated by little bluestem (Schizachyrium scoparium) to emergent aquatic vegetation dominated by cattail (Typha latifolia) and water smartweed (Polygonum hydropiperoides). Plant cover, VAM spore abundance, plant species richness, and number of VAM fungi represented as spores, had significant positive correlations with each other and with percent organic matter. The plant and VAM spore variables had significant negative correlations with soil pH and available Ca, Mg, P and gravimetric soil moisture. Using stepwise multiple regression, Ca was found to be the best predictor of spore abundance. Test for association between plant species and VAM fungal spores indicated that the spores of Glomus caledonium are associated with plants from dry, nutrient poor sites and spores of gigaspora gigantea are positively associated with plants occurring on the wet, relatively nutrient rich sites. Glomus fasciculatum was the most abundant and widely distributed VAM fungus and it had more positive associations with endophyte hosts than the other VAM fungi. We found no relationship between beta niche breadth of plant species and the presence or absence of mycorrhizal infection. However, our data suggest that some plant species may vary with respect to their infection status depending upon soil moisture conditions that may fluctuate seasonally or annually to favor or hinder VAM associations.     

SPORE TETRAD STRUCTURES OF POSSIBLE HEPATIC AFFINITY FROM THE AUSTRALIAN LOWER CARBONIFEROUS

Palynological studies of Early Carboniferous (Viséan) sediments of the Bonaparte Gulf Basin, northwestern Australia, reveal the presence of intact tetrahedral spore tetrads (here described as Sagenotetradites gen. nov.) and, more usually, of their disjunct spore portions which had previously been interpreted as dispersed whole-miospore species. Two species of the new tetrad genus are recognized: S. bonapartensis (Playford) comb, nov., as type species; and S. spiritensis (Playford) comb. nov. The species are distinguished, as originally, on the basis of sculptural attributes of their distal exoexines. When intact, both species share a common internal “binding” element (“Cadiospora abrupta” Playford, 1971) composed of the fused proximal exoexinal faces of all four spores of a given tetrad. Morphological comparisons with modern hepatic spores suggest an alliance of the microfossils with the order Sphaerocarpales. The occurrence of Sagenotetradites in exclusively marine sediments suggests that its parent plants grew in close proximity to the marine depositional basin. Moreover, the morphological attributes of the tetrads would appear to have facilitated dissemination by water.     

Effect of the spatial and seasonal soil heterogeneity over arbuscular mycorrhizal fungal spore abundance in the semi-arid valley of Tehuacán-Cuicatlán, Mexico

Recent studies have shown that some species of Mimosa (Leguminosae-Mimosoideae) create resource islands (RI), rich in soil organic matter and nutrients, as well as in arbuscular mycorrhyzal fungal (AMF) spores, in the semi-arid Valley of Tehuacán-Cuicatlán. The relevance of this fact is that arid and semi-arid regions are characterized by low fertility soils and scarce precipitation, limiting plant species growth and development; this explains why the presence of AM fungi may be advantageous for mycorrhizal desert plants. Fluctuations in AMF spore numbers could be related to environmental, seasonal and soil factors which affect AMF sporulation, in addition to the life history of the host plant. The aim of this study was to asses the impact of spatial (resource islands vs open areas, OA) and seasonal (wet season vs start of dry season vs dry season) soil heterogeneity in the distribution and abundance of AMF spores in four different study sites within the Valley. We registered AMF spores in the 120 soil samples examined. Significant differences in the number of AMF spores were reported in the soil below the canopy of Mimosa species (RI) comparing with OA (RI > OA), and between Mimosa RI themselves when comparing along a soil gradient within the RI (soil near the trunk > soil below the middle of the canopy > soil in the margin of the canopy > OA); however, there were no significant differences between the soil closest to the trunk vs middle, and margin 's OA. Finally, more spores were reported in the soil collected during the wet season than during the dry season (wet > start of dry > dry). Therefore, the distribution of AMF spores is affected by spatial and seasonal soil heterogeneity. This study points out the relevance of Mimosa RI as AMF spore reservoirs and the potential importance of AM fungi for plant species survivorship and establishment in semi-arid regions. AM fungi have recently been recognized as an important factor determining plant species diversity in arid and temperate ecosystems.