Search

Abstract A new method for reconstructing paleoenvironments using the pavement cell characteristics of Middle Jurassic ginkgoalean fossils from the Yaojie and Baojishan basins, Gansu Province, China, is presented. Specifically, we use present-day relationships between the length-to-width (L/W) ratio of leaf pavement cells of Ginkgo biloba and mean annual temperature (MAT), mean annual precipitation (MAP), and relative humidity (RH). Primary analyses indicate that the L/W ratio of Ginkgo biloba pavement cells is negatively correlated with MAT, MAP, and RH, and linear regression equations can be established. Based on these equations, paleoclimatic parameters were inferred using the ginkgoalean fossil data. The estimated paleotemperatures in the Yaojie and Baojishan basins during the Middle Jurassic are approximately 6 °C higher than those of the present day, which is consistent with the results of the currently used stomata ratio method and the global CO 2 prediction model. We deduce that paleoprecipitation in the basins was approximately 460 mm higher and paleohumidity approximately 20% higher than current conditions and thus the two basins exhibited humid subtropical conditions during the Middle Jurassic. Fossil flora and spore-pollen assemblage data from the study areas corroborate the new observations. [ABSTRACT FROM AUTHOR]

Background: At the end of the Pliocene and the beginning of Pleistocene glaciation and deglaciation cycles Ginkgo biloba went extinct all over the world, and only few populations remained in China in relict areas serving as sanctuary for Tertiary relict trees. Yet the status of these regions as refuge areas with naturally existing populations has been proven not earlier than one decade ago. Herein we elaborated the hypothesis that during the Pleistocene cooling periods G. biloba expanded its distribution range in China repeatedly. Whole plastid genomes were sequenced, assembled and annotated, and sequence data was analyzed in a phylogenetic framework of the entire gymnosperms to establish a robust spatio-temporal framework for gymnosperms and in particular for G. biloba Pleistocene evolutionary history. Results: Using a phylogenetic approach, we identified that Ginkgoatae stem group age is about 325 million years, whereas crown group radiation of extant Ginkgo started not earlier than 390,000 years ago. During repeated warming phases, Gingko populations were separated and isolated by contraction of distribution range and retreated into mountainous regions serving as refuge for warm-temperate deciduous forests. Diversification and phylogenetic splits correlate with the onset of cooling phases when Ginkgo expanded its distribution range and gene pools merged. Conclusions: Analysis of whole plastid genome sequence data representing the entire spatio-temporal genetic variation of wild extant Ginkgo populations revealed the deepest temporal footprint dating back to approximately 390,000 years ago. Present-day directional West-East admixture of genetic diversity is shown to be the result of pronounced effects of the last cooling period. Our evolutionary framework will serve as a conceptual roadmap for forthcoming genomic sequence data, which can then provide deep insights into the demographic history of Ginkgo. [ABSTRACT FROM AUTHOR]

Background: Ginkgo biloba L. (Ginkgoaceae) is one of the most distinctive plants. It possesses a suite of fascinating characteristics including a large genome, outstanding resistance/tolerance to abiotic and biotic stresses, and dioecious reproduction, making it an ideal model species for biological studies. However, the lack of a high-quality genome sequence has been an impediment to our understanding of its biology and evolution. Findings: The 10.61 Gb genome sequence containing 41,840 annotated genes was assembled in the present study. Repetitive sequences account for 76.58% of the assembled sequence, and long terminal repeat retrotransposons (LTR-RTs) are particularly prevalent. The diversity and abundance of LTR-RTs is due to their gradual accumulation and a remarkable amplification between 16 and 24 million years ago, and they contribute to the long introns and large genome. Whole genome duplication (WGD) may have occurred twice, with an ancient WGD consistent with that shown to occur in other seed plants, and a more recent event specific to ginkgo. Abundant gene clusters from tandem duplication were also evident, and enrichment of expanded gene families indicates a remarkable array of chemical and antibacterial defense pathways. Conclusions: The ginkgo genome consists mainly of LTR-RTs resulting from ancient gradual accumulation and two WGD events. The multiple defense mechanisms underlying the characteristic resilience of ginkgo are fostered by a remarkable enrichment in ancient duplicated and ginkgo-specific gene clusters. The present study sheds light on sequencing large genomes, and opens an avenue for further genetic and evolutionary research. [ABSTRACT FROM AUTHOR]

Stomatal properties of fossil Ginkgo have been used widely to infer the atmospheric concentration of CO 2 in the geological past (paleo- p CO 2 ). Many of these estimates of paleo- p CO 2 have relied on the inverse correlation between p CO 2 and stomatal index ( SI – the proportion of epidermal cells that are stomata) observed in recent Ginkgo biloba , and therefore depend on the accuracy of this relationship. The SI - p CO 2 relationship in G. biloba has not been well documented, however. Here we present new measurements of SI for leaves of G. biloba that grew under p CO 2 from 290 to 430 ppm. We prepared and imaged all specimens using a consistent procedure and photo-documented each count. As in prior studies, we found a significant inverse relationship between SI and p CO 2 , however, the relationship is more linear, has a shallower slope, and a lower correlation coefficient than previously reported. We examined leaves of G. biloba grown under p CO 2 of 1500 ppm, but found they had highly variable SI and a large proportion of malformed stomata. We also measured stomatal dimensions, stomatal density, and the carbon isotope composition of G. biloba leaves in order to test a mechanistic model for inferring p CO 2 . This model overestimated observed p CO 2 , performing less well than the SI method between 290 and 430 ppm. We used our revised SI- p CO 2 response curve, and new observations of selected fossils, to estimate late Cretaceous and Cenozoic p CO 2 from fossil Ginkgo adiantoides . All but one of the new estimates is below 800 ppm, and together they show little long-term change in p CO 2 or relation to global temperature. The low Paleogene p CO 2 levels indicated by the Ginkgo SI proxy are not consistent with the high p CO 2 inferred by some climate and carbon cycle models. We cannot currently resolve the discrepancy, but greater agreement between proxy data and models may come from a better understanding of the stomatal response of G. biloba to elevated p CO 2 , better counts and measurements of fossil Ginkgo , or models that can simulate greenhouse climates at lower p CO 2 . [ABSTRACT FROM AUTHOR]

Background: Fossil evidence of ginkgophyte ontogeny is exceedingly rare. Early development in the extant Ginkgo biloba is characterized by a series of distinct ontogenetic stages. Fossils providing insights into the early ontogeny of ancient ginkgophytes may be significant in assessing the degree of relatedness between fossil ginkgophytes and G. biloba. Results: An assemblage of seedlings from the early Middle Triassic of France is assigned to the ginkgophytes based on leaf morphology. The specimens represent an ontogenetic sequence consisting of four stages: (I) formation of the cotyledons in the seed and germination; (II) development of primary leaves and taproot; (III) thickening of the taproot and appearance of secondary roots; and (IV) development of the first differentiated leaves and absence of the seed remnants. Conclusions: The fossil seedlings provide a rare opportunity to examine the early ontogeny of a Triassic ginkgophyte. Germination and seedling development in the fossil are nearly identical to that of the extant gymnosperm G. biloba. We hypothesize that the fossil may be closely related biologically to G. biloba, and that certain developmental processes in seedling development were in place by the Middle Triassic. [ABSTRACT FROM AUTHOR]

The general morphology, surface sculpturing, and exine ultrastructure have been studied in dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia. The pollen grains dominate the palynological assemblage extracted from coal deposits of the Khilok Formation in the Buryat Republic, which also contain ginkgoalean leaves of Baierella averianovii as the only constituent of the assemblage of plant megafossils. The relationship between the pollen grains and ginkgoalean leaves from this autochthonous burial is hypothesised on the basis of taphonomical analysis and palaeobiogeographical data. It is shown that the ectexine of the pollen grains includes a thick solid tectum, a thin granular infratectum and a thin foot layer; the endexine is fine-grained, slightly more electron-dense than the ectexine, and is preserved only in places. The distal aperture is formed by a thinning of the exine. No analogous ultrastructure has been described so far in fossil pollen grains of this morphotype studied ultrastructurally from in situ material. For comparison, we also studied the exine ultrastructure of pollen grains Ginkgo biloba. The fossil pollen is not identical to pollen of extant G. biloba, but shows several significant similarities in the exine ultrastructure, which does not contradict the presumable ginkgoalean affinity of the fossil pollen. [ABSTRACT FROM AUTHOR]

Abstract: The morphology and epidermal structure of the type material of Ginkgoites obrutschewii (Seward) Seward (1911, 1919), a species established for isolated leaves from the Jurassic of Northwestern China, have been revised based on the type material and recent findings from a geographically close, coeval locality. A diagnosis, missing in the original publication, is provided and a lectotype is designated. Numerous specimens of Ginkgoites/Ginkgo leaves without epidermal structure, that were ascribed to this species over the last century solely on the basis of the leaf morphology, have to be classified as Ginkgoites sp. This change restricts the known distribution of G. obrutschewii to the Middle Jurassic of the Xinjiang Uygur Autonomous Region in Northwestern China. [Copyright &y& Elsevier]

Abstract: A new taxon of ginkgophyte affinity Palaeoginkgoxylon zhoui gen. nov. et sp. nov. is described from the Guadalupian Lower Shihhotse Formation of the Hulstai coalfield, Inner Mongolia Autonomous Region (Nei Mongol), northern China, on the basis of the anatomical structures of the broad eustele and pycnoxylic secondary xylem. The anatomical structure of the new woody tree trunk resembles both the early gymnosperms of Eristophyton–Pitus types and the modern Ginkgo. Therefore, the new tree trunk is interpreted as representing a transitional stage in the evolution of Ginkgo from early arborescent lignophytes since the Early Carboniferous. [Copyright &y& Elsevier]

Abstract: Estimates of pCO2 for the early Paleogene vary widely, from near modern-day levels to an order of magnitude greater, based on various proxy measures. Resolving the relationship between climate and pCO2 during this globally warm period is a key task in understanding climate dynamics in a warmer world. Here, we use the stomatal frequency of fossil Ginkgo adiantoides from the Okanagan Highlands of British Columbia, Canada to estimate pCO2 during the Early Eocene Climatic Optimum (EECO), the interval of peak warmth in the Cenozoic. We also examine a dataset of modern Ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of pCO2. Early Eocene fossil G. adiantoides has significantly lower stomatal frequency than modern G. biloba, suggesting pCO2 levels >2× modern pre-industrial values. This result is in contrast to earlier studies using stomatal frequency of Ginkgo that indicated near modern-day levels of pCO2 in the early Paleogene, though not including samples from the EECO. We also find that levels of pCO2 as indicated by stomatal frequency are correlated with trends in climate (mean annual temperature) over time at the Falkland fossil locality, suggesting that climate and pCO2 were coupled during the EECO hyperthermal. [Copyright &y& Elsevier]

UV-B absorbing compounds (UACs) in present-day and fossil pollen, spores, cuticles, seed coats and wood have been evaluated as a proxy for past UV. This proxy may not only provide information on variation of stratospheric ozone and solar UV in the period preceding and during the Antarctic ozone hole (1974–present day), but also on the development and variation of the stratospheric ozone layer and solar surface UV during the evolution of life on Earth. Sporopollenin and cutin are highly resistant biopolymers, preserving well in the geological record and contain the phenolic acids p-coumaric (pCA) and ferulic acid (FA). pCA and FA represent a good perspective for a plant-based proxy for past surface UV radiation since they are induced by solar UV-B viathe phenylpropanoid pathway (PPP). UV-B absorption by these monomers in the wall of pollen and spores and in cuticles may prevent damage to the cellular metabolism. Increased pCA and FA in pollen of Vicia fabaexposed to enhanced UV-B was found in greenhouse experiments. Further correlative evidence comes from UV-absorbing compounds in spores from 1960–2000 comparing exposure of land plants (Lycopodiumspecies) to solar UV before and during ozone depletion and comparing plants from Antarctica (severe ozone depletion), Arctic, and other latitudes with less or negligible ozone depletion. Wood-derived compounds guaiacyl (G), syringyl (S), and p-hydroxyphenyl (P) are produced viathe PPP. The proportions of P, G, and S in the lignin differ between various plant groups (e.g.dicotyledons/monocotyledons, gymnosperms/angiosperms). It is hypothesized that this lignin composition and derived physiological and physical properties of lignin (such as tree-ring wood density) has potential as a proxy for palaeo-UV climate. However validation by exposure of trees to enhanced UV is lacking. pCA and FA also form part of cutin polymers and are found in extant and fossil Ginkgoleaf cuticles as shown by thermally-assisted hydrolysis and methylation (THM)-pyrolysis-GC-MS. Potentially, the time scale for reconstruction of ozone column thickness and UV-B based on the UAC UV proxy may be decadal, centennial, millennial and possibly billenial. For further development of the UACs and pCA and FA-based UV proxy, it is necessary to obtain the UV dose–response (content of UACs, pCA and FA in sporopollenin and cutin) relationships for validation, based on outdoor UV radiation manipulations experiments with plants, and comparative analysis of stored plants (herbaria) or fossil material of the same or related plant species. [ABSTRACT FROM AUTHOR]

Abstract: Ginkgoalean ovulate organs Yimaia, detached seeds and the associated Baiera-type leaves are described from a paper coal at the uppermost part of the Middle Jurassic Shimengou Formation in the northern border of the Qaidam Basin, Qinghai Province, Northwest China. The organ bears a cluster of at least 3 orthotropous ovules at the apex of a peduncle. The seeds (ovules) are sessile, nearly rounded or broadly ovate to oblong, about 7mm long and 5.7mm wide, with an obtusely acute, acute or mucronate apex. Despite a general resemblance in gross morphology, the new Yimaia organ is distinguished from other species of the genus in the stomatal structure of the integument. Associated leaf segments of Baiera bear a resemblance to the Yorkshire Middle Jurassic species B. furcata, but are somewhat different in cuticular structure. Selected Mesozoic leaves with well-preserved cuticle and other Baiera type leaves that are known to have been associated with the Yimaia-type ovulate organs from China and other parts of the world are found to be different either in gross morphology and/or in cuticular structure from the present associated leaf segments. Yimaia ovulate organs and vegetative leaves dominantly of the Baiera-type appear to form a regular combination in the Mesozoic ginkgoaleans. They represented a rather small, but coherent plant group (Yimaiaceae) that was widely distributed in the Jurassic of Eurasia. [Copyright &y& Elsevier]

Investigation of the Mesozoic seed plant Leptostrobus Heer from the Yangcaogou Formation of the Late Triassic and the Yixian Formation of the Early Cretaceous, Liaoning Province, China, provides new insight into its general morphology and geographical distribution. The materials of L. cancer from the Yixian Formation described herein are later than all the past findings of this species and add to the record of L. cancer during the Early Cretaceous. Based on well-preserved specimens, the specific diagnosis is slightly emended and the reconstruction of L. cancer is perfected. The materials from the Yangcaogou Formation of the Late Triassic are placed in L. sphaericus. In addition, we review the history of investigation of the genus Leptostrobus since its establishment in 1876 and discuss the main characteristics of each species. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

During the Mesozoic Era, gingkoaleans comprised a diverse and widespread group. Here we describe ginkgoalean fossils in their facies context from the Late Cretaceous (Cenomanian) Peruc-Korycany Formation of the Czech Republic and present a reconstruction of tree architecture and ecology. Newly described in this study is the ovuliferous reproductive structure, Nehvizdyella bipartita gen. et sp. nov. (Ginkgoales). This ovuliferous organ consists of a bifurcating axis, terminated by large cupule-like structures, probably homologous to the collar of the recent Ginkgo. Each cupule encloses an orthotropous ovule. In specimens with the early developmental stages preserved, the entire ovule and young seed, with the exception of the micropylar area, is embedded in the cupule. Mature seeds consist of sclerotesta and sarcotesta. Monosulcate pollen grains of Cycadopites-type are found adhering to the seeds. Although similar to Ginkgo in terms of its large size and reduced number of seeds, N. bipartita differs from the extant genus in having ovules completely enclosed in a cupule-like structure. The co-occurrence of N. bipartita with ginkgoalean leaves of Eretmophyllum obtusum (Velenovský) Kvaček, J., ginkgoalean short shoots of Pecinovicladus kvacekii Falcon-Lang, and ginkgoalean trunk wood of Ginkgoxylon gruettii Pons and Vozenin-Serra in monodominant taphocoenoses at four geographically distant localities suggests that these remains all belong to one plant. This is supported by the close morphological and anatomical similarity between the different organs. Facies analysis of plant assemblages indicates that our Cretaceous tree occupied a water-stressed coastal salt marsh environment. It therefore represents the first unequivocal halophyte among the Ginkgoales. [ABSTRACT FROM AUTHOR]

Tertiary leaf compressions of a Ginkgo plant with cuticle displaying all taxonomically important epidermal features are reported for the first time from Greece, and for the Mediterranean area as a whole. The fossils are from Upper Miocene sediments of Vegora, north-western Greece, and assigned to Ginkgo adiantoides (Unger) Heer. The most conspicuous cuticle characteristics are prominent papillae on the subsidiary cells that sometimes completely cover the stomatal apertures. Such papillae also occur in leaves of G. adiantoides from the Pliocene of eastern Central Europe, but are absent in leaves from the Pliocene of Germany also assigned to this species. We observed a high variability in the degree of papillosity of subsidiary cells of stomata in leaves of living Ginkgo biloba that exhibited prominent papillae in mature sun leaves and a total lack of papillae in shade leaves of a potted plant. This may suggest that differences in epidermal characters between the fossil leaves from Greece and Germany are due to ecotypical/intraspecific variability and not to genetically fixed specific differences. It also suggests that a number of Tertiary Ginkgo species from Eurasia that were distinguished from G. adiantoides by having papillate epidermis cells and subsidiary cells of the abaxial cuticle should be included within G. adiantoides. Two lineages of Ginkgo can be distinguished for the Tertiary of the Northern Hemisphere. From the Palaeogene high latitudes leaves were reported that exhibit upper epidermis cells with prominent papillae similar to those of older Mesozoic Ginkgo, whereas G. adiantoides lacks the papillae of the upper epidermis, a feature which is shared with the living G. biloba. In general, the size of stomata is larger in extant Ginkgo leaves than in those of the fossils. [Copyright &y& Elsevier]