Bai-Nian Sun

Variation in Ginkgo biloba L. leaf characters across a climatic gradient in China

Fossil leaves assigned to the genus Ginkgo are increasingly being used to reconstruct Mesozoic and Tertiary environments based on their stomatal and carbon isotopic characteristics. We sought to provide a more secure basis for understanding variations seen in the plant fossil record by determining the natural variability of these properties of sun and shade leaf morphotypes of Ginkgo biloba trees under the present atmospheric CO2 concentration and a range of contemporary climates in three Chinese locations (Lanzhou, Beijing, and Nanjing). Climate had no major effects on leaf stomatal index (proportion of leaf surface cells that are stomata) but did result in more variable stomatal densities. The effects of climate and leaf morphotype on stomatal index were rather conserved (<1%) and much less than the response of trees to recent CO2 increases. Leaf carbon isotope discrimination (Δ) was highest for trees in Nanjing, which experience a warm, moist climate, whereas trees in the most arid site (Lanzhou) had the lowest Δ values. Interestingly, the variation in Δ shown by leaf populations of trees from China and the United Kingdom was very similar to that of fossil Ginkgo cuticles dating to the Mesozoic and Tertiary, which suggests to us that the physiology of leaf carbon uptake and regulation of water loss in Ginkgo has remained highly conserved despite the potential for evolutionary change over millions of years.

Paliurus Fruits from the Oligocene of South China and Their Phytogeographic Implications

Paliurus favonii Unger is recognized and described based on fruits from the Oligocene Ningming flora of Guangxi, South China. Characteristics of the present specimens include circular winged fruits that are 10.0–11.5 mm in diameter with a central endocarp at 3.0 to 4.0 mm in diameter. The specimens fall into the morphological range of the fossil species P. favonii, which has been observed in other Cenozoic sites in the Northern Hemisphere. The present discovery represents the lowest latitude distribution of P. favonii in the world, and we are presenting the first P. favonii fossil described with detailed cuticular characteristics from China. Further, this finding demonstrates that the genus existed in the Oligocene Ningming region, South China, and provides new information for understanding the fossil history. The dispersal mode for winged fossils demonstrates that wind dispersal is well-represented in the Oligocene Ningming flora.

A new species of Meliolinites associated with Buxus leaves from the Oligocene of Guangxi, southern China

A new species of Meliolinites (fossil Meliolaceae), M. buxi sp. nov., is reported from the Oligocene Ningming Formation of Guangxi, South China. The fungus has hyphopodia characteristics of extant Meliolaceae, such as thick-walled, branching hyphae with appressoria and phialides. However, these fossils entirely lack mycelial or perithecial setae and have only a few phialides, thereby distinguishing the new species from most known species. The fungus was discovered on the adaxial and abaxial cuticles of several fossilized Buxus leaves. Thickening and twisting of cell walls in the Buxus leaf cuticle, along with the parasitic feeding strategy of the extant Meliolaceae, suggest that a parasitic interaction between Buxus and M. buxi seems feasible. The distribution of modern Meliolaceae suggests that they live in warm, humid subtropical-tropical climates. It is possible that the presence of M. buxi indicates a similar climatic condition. The co-occurrence of large-leaf Buxus and floristic comparisons of the Ningming assemblage also corroborate this conclusion.

Variations in leaf characteristics of three species of angiosperms with changing of altitude in Qilian Mountains and their inland high-altitude pattern

In this study, 39 leaf samples of three angiosperms (Betula albo-sinensis, tree species; and Caragana jubata and Berberis diaphana, shrub species) were collected in the middle-east parts at 2300–3640 m asl of the Qilian Mountains to study the variations of leaf characteristics of angiosperms with altitude change in inland high-altitude regions of China. Five leaf indexes, viz. epidermal cell density (ED), stomatal density (SD), stomatal index (SI), leaf vein density (VD) and carbon isotopic ratio (δ13C), were analyzed in laboratory. The results show that there are significant or even very significant linear correlations between the five indexes and altitude, of which SD, SI and VD exhibit a negative correlation with altitude, while ED and δ13C exhibit a positive correlation with altitude. Such a correlation assemblage is quite different from the situation in the low-altitude humid environment. Generally, only an assemblage of positive correlations can be observed between the indexes (viz. SD, SI and δ13C, etc.) and the altitude in the low-altitude humid environment, which were caused mainly by the plants’ responses to the change of atmospheric CO2 concentration (Ca). However, an assemblage of the negative and positive correlations found here may be attributed mainly to the plants’ responses to the change of physiological drought caused by change of low temperature, and here it is preliminarily called the inland high-altitude pattern of plant leaf variations.

Evidence of Oil Sources and Migration in Triassic-Jurassic Reservoirs in the South Tianhuan Depression of the Ordos Basin, China Based on Analysis of Biomarkers and Nitrogen-Bearing Compounds

The Ordos Basin is an important intracontinental sedimentary basin in western China for its abundant Mesozoic crude oil resources. The southern part of the Tianhuan Depression is located in the southwestern marginal area of this Basin, in which the Jurassic and Triassic Chang-3 are the main oil-bearing strata. Currently, no consensus has been reached regarding oil source and oil migration in the area, and an assessment of oil accumulation patterns is thus challenging. In this paper, the oil source, migration direction, charging site and migration pathways are investigated through analysis of pyrrolic nitrogen compounds and hydrocarbon biomarkers. Oil source correlations show that the oils trapped in the Jurassic and Chang-3 reservoirs were derived from the Triassic Chang-7 source rocks. The Jurassic and Chang-3 crude oils both underwent distinct vertical migration from deep to shallow strata, indicating that the oils generated by Chang-7 source rocks may have migrated upward to the shallower Chang-3 and Jurassic strata under abnormally high pressures, to accumulate along the sand bodies of the ancient rivers and the unconformity surface. The charging direction of the Jurassic and Chang-3 crude oils is primarily derived from Mubo, Chenhao, and Shangliyuan, which are located northeast of the southern Tianhuan Depression, with oils moving toward the west, southwest, and south. The results show that an integration of biomarker and nitrogen-bearing compound analyses can provide useful information about oil source, migration, and accumulation.

Quercus yangyiensis sp nov from the Late Pliocene of Baoshan, Yunnan and Its Paleoclimatic Significance

A new Quercus (Fagaceae) morphospecies is described based on well-preserved fossil leaves. The fossils were collected from Yangyi Formation of the Upper Pliocene at the Yangyi coalmine, Baoshan, western Yunnan, China. Details of the microstructure of mesophyll tissue are preserved because lithification of the fossils was not complete. The fossil laminas possess typical characteristics of Quercus sect Heterobalanus: quite thick and coriaceous cuticle; secondary veins bifurcating near the margin in the middle and top of the leaf; and upper epidermis with adaxial hypodermis. Based on a detailed morphological and anatomical comparison with all living and fossil species of Quercus sect Heterobalanus, the fossil leaves prove to be different in their sparse and garland-shaped multicellular trichomes on the lower epidermis, and so it is described as a new species Quercus yangyiensis He, Li et Sun sp. nov. The much sparser trichomes of our fossils compare well with those of living Quercus sect. Heterobalanus and indicate a more humid climate during the deposition of the Yangyi Formation in the Late Pliocene.

Citrus linczangensis sp. n., a Leaf Fossil of Rutaceae from the Late Miocene of Yunnan, China

Premise of research. The origin and phytogeographic history of Citrus (Rutaceae) is poorly known, partly because of the very limited fossil record of this genus. Our newly discovered fossil materials confirm the existence of Citrus in the late Miocene in Asia. Methodology. Fossil leaves were collected from the field, carefully exposed in the laboratory, and investigated through comparison of architectural characters with extant leaves. Pivotal results. A new species, Citrus linczangensis sp. n., from the late Miocene of Lincang, Yunnan, China, is characterized by unifoliolate compound leaf morphology, an articulated and broadly winged petiole, and an entire margined leaflet with basal intramarginal veins. Conclusions. The unique morphological characters of this fossil provide definitive evidence of Citrus in the fossil record of Asia and expand the geological history of the genus back to the late Miocene. The new fossil material gives some clues for the origin of modern Citrus species and supplements knowledge of the Lincang fossil flora.

A new species of Zelkova (Ulmaceae, Ulmoideae) with leaves and fruits from the Oligocene of South China and its biogeographical implications

A new fossil species of Zelkova is described from the Oligocene Ningming Formation of Guangxi, South China. Zelkova ningmingensis sp. nov. is characterized by leaves with craspedodromous venation pattern and drupaceous fruit type. The new species possesses elliptical to ovate leaves, bearing 7–12 pairs of secondary and simple toothed margin, as well as epidermal cells with straight or rounded anticlinal walls. The species is compared with extant and other fossil species hitherto reported of the genus. It is most similar to the living Zelkova schneideriana in the leaf gross morphology and epidermal characters, which may be suggested to be the ancestral type of Zelkova schneideriana. The discovery of Zelkova ningmingensis sp. nov. in Guangxi indicates that Zelkova has already existed in southern China as early as the Oligocene. In combination with Zelkova material from the Oligocene of Europe, it can be inferred that Eurasian Zelkova had begun to diversify by at least the Oligocene. Because China is the biodiversity centre of modern Zelkova, the fossil herein provides new insights into Zelkova biogeography.

First megafossil record of Neolepisorus (Polypodiaceae) from the late Miocene of Yunnan, Southwest China

The first megafossil record of the genus Neolepisorus Ching from the late Miocene of Yunnan Province, SW China, is reported. Neolepisoruschingii sp. nov. is represented by a simple fertile frond with one line exindusiate, elliptic-fusiform sori along the lower part of the midrib, and a basal contractive sterile frond with a sinuolate margin. The venation is characterized by a strong midrib, prominent zigzagging lateral veins, and reticulate higher order veins with free-ending veinlets (simple or forked once). The combination of these characters confirms the genus Neolepisorus (Polypodiaceae), now distributed in subtropical Southeast Asia, except for one species, which inhabits Madagascar of tropical Africa. It has a distribution center south of the Yangtze River in China. So far, no megafossil assigned to Neolepisorus has been reported, and the occurrence of Neolepisoruschingii in SW China associated with other types of fern occurrence adds increased evidence of fern radiation during the Neogene in Yunnan Province in response to the uplift of the Tibetan Plateau.KurzfassungDas erste Makrofossil der Gattung Neolepisorus Ching wird aus dem späten Miozän der Provinz Yunnan in SW-China beschrieben. Neolepisorus chingii sp. nov. ist durch einen einfachen fertilen Wedel mit einzeiligen exindusiaten, elliptisch-spindelförmigen Sori entlang dem unteren Teil der Mittelrippe und einem basalen kontraktiven sterilen Wedel mit sinuolaten Rand charakterisiert. Die Äderung wird von einer starken Mittelrippe, prominenten zickzackförmigen Seitenrippen sowie netzförmigen Adern höherer Ordnung, mit frei endenden Äderchen (einfach oder einmal gegabelt), gekennzeichnet. Die Kombination dieser Merkmale bestätigt für unser Taxon eine Zugehörigkeit zur Gattung Neolepisorus (Polypodiaceae). Deren Vertreter sind heute, mit einer Ausnahme (Madagaskar), im subtropischen Südostasien verbreitet, wobei ein Verbreitungszentrum in China, südlich des Jangtse, liegt. Bisher fehlten Nachweise von Neolepisorus-Makrofossilien, so dass das südwestchinesische Vorkommen von Neolepisorus chingii sp. nov. (zusammen mit dort assoziiert vorkommenden anderen Farnarten) einen weiteren Beleg einer neogenen Radiation der Farne in Yunnan liefert, welche als Reaktion auf die Hebung des Tibet-Plateaus interpretiert werden kann.

First Occurrence of Platycladus from the Upper Miocene of Southwest China and Its Phytogeographic Implications

Platycladus Spach is native to Central China, but its natural occurrences are very difficult to establish. According to molecular phylogenetic data, this genus might have originated since the Oligocene, but no fossil record has been reported. Here, we describe eight foliage branches from the upper Miocene in western Yunnan, Southwest China as a new species, P. yunnanensis sp. nov., which is characterized by foliage branches spread in flattened sprays, and leaves decussate, imbricate, scale-like and dimorphic. The leaves are amphistomatic, and the stomata are elliptical or oblong, haplocheilic, and monocyclic type. Based on a detailed comparison with the extant genera of Cupressaceae sensu lato, our fossils are classified into the genus Platycladus. The occurrence of P. yunnanensis sp. nov. indicates that this genus had a more southernly natural distribution in the late Miocene than at present. Molecular phylogeny and fossil records support a pre-Oligocene common ancestor for the genera Platycladus, Microbiota and Calocedrus. The separation of the three taxa was most likely caused by the arid belt across Central China during the Oligocene. In addition, the cooling down of the global temperature and the strengthening of Asian monsoon since the Miocene will further promote the migration of these genera.