Search

Vegetation composition has been greatly modified by human activity since Neolithic times, providing valuable insights into the evolution of human-landscape relationships. In this paper, we integrated 26 pollen records from the Zhejiang Province of China where a Neolithic culture of rice farming existed at an early date, to examine the dynamics of agricultural development and its impact on vegetation. Firstly, we synthesized the relative abundance of Oryza pollen and charcoal (Cpeak) using generalized additive models, to produce a record of agricultural development and the intensity of human activities. We found that changes in Oryza abundance and Cpeak were positively correlated, and identified three phases as follows: agricultural initiation before 8000 cal yr BP, agricultural development between 8000 and 6000 cal yr BP and the onset of intensive rice farming after 6000 cal yr BP. Pearson correlation between each pollen taxon and Oryza indicates that arboreal taxa exhibit an overall negative correlation with Oryza , but terrestrial herbs and ferns show a positive correlation, indicating that deforestation accompanied agricultural development. Rosaceae, Castanea , Fagus and Typha display positive correlation with Oryza during the earliest stage dominated by hunter-gathering, reflecting the protection and cultivation of food-producing vegetation. During the intensive farming stage, the Liangzhu ancestors reclaimed more farmland and began to pay attention on farmland management including clearing the fields of weeds. This is the main reason for the enhanced negative correlation between Artemisia , Chenopodiaceae, Brassicaceae, Asteraceae and Lamiaceae with Oryza at 6000–5000 cal yr BP. Finally, we confirm the potential of integrated Oryza abundance in pollen records as a human-impact index in the Zhejiang region, and emphasize that temporal dynamics in vegetation and human activities should be critically pre-examined when applying relevant human-impact indices. • Integrated charcoal and Oryza pollen reveal Neolithic human intensity and rice farming history. • Food-providing plants were protected during the hunter-gatherer stage. • During the intensive agriculture phase, weed taxa exhibited a strengthened negative correlation with Oryza correlation. • The application of anthropogenic pollen necessitates a critical evaluation of its temporal dynamics. [ABSTRACT FROM AUTHOR]

Understanding human impact on the vegetation of the Tibetan Plateau through the Holocene is important for developing strategies for sustainable ecosystem management in the region. In this paper, 53 pairs of surface-soil samples from inside and outside livestock enclosures were obtained from across the Tibetan Plateau to investigate the differences in pollen assemblages between grazed and ungrazed sites. This modern dataset was then applied to palynological records from four lakes in the northeast Tibetan Plateau region to investigate middle to late Holocene grazing history. Results show that modern grazing activities have a limited impact on the vegetation, although grazing activity leads to an increase in the pollen proportion of Cyperaceae, Artemisia , Ranunculaceae, Brassicaceae, Taraxacum -type, Fabaceae, and Saxifrageceae while representatives of Poaceae, Chenopodiaceae, and Aster -type pollen decrease. Application of these grazing indicators to the pollen spectra obtained from the four lake sites, together with other proxies, reveals that grazing activity only commenced during the last few hundred years in the northeast marginal areas of the Tibetan Plateau at c. 3000 m a.s.l, while there is no grazing signal in pollen records from above 4000 m a.s.l. Our study emphasises the importance of using multi-proxy methods in estimating signals of past human activity. • Pollen assemblage should be insensitive to grazing activities on the Tibetan Plateau. • Human impacts on vegetation at ∼3400 m a.s.l are limited to within a few centuries. • No significant pollen signal of grazing is revealed for the high-elevation areas. [ABSTRACT FROM AUTHOR]

The vegetation history of the central Tibetan Plateau over the last two millennia provides an important baseline for exploring future vegetation evolution. In this paper, we analyze high-resolution records of pollen, grain-size, total organic carbon (TOC) and total nitrogen (TN) for a 66.5 cm deep sediment core collected from Beilei Co on the central Tibetan Plateau. Between ca. 210 CE and 1988 CE, pollen spectra together with other proxies show that the Beilei Co region was covered by alpine steppe and experienced a relatively stable environment, with only slight changes in vegetation composition and minor climatic variations. However, since 1988 CE, abundances of Artemisia and Cyperaceae have begun to increase, while those of Chenopodiaceae (current accepted Latin name is Amaranthaceae) and Asteraceae have decreased sharply. Both the pollen assemblages and other proxies show that the study area is currently undergoing a major change and that the period of vegetation stability that has characterized the past two millenia has now ended. We argue that the recent changes in the vegetation may be caused by increasing precipitation and/or thawing permafrost due to global warming. In the future, the alpine steppe around Beilei Co may be replaced by alpine meadow. • High-resolution pollen spectra covering last two millennia completed for the central Tibetan Plateau. • Vegetation of the central Tibetan Plateau is stable for most of the time until the last few decades. • The central Tibetan Plateau is experiencing an unprecedented phase of wetting. [ABSTRACT FROM AUTHOR]

In this paper, we undertake a high-resolution palynological analysis of a sediment core covering the last 1500 years obtained from Lake Ayakum in the northern Tibetan Plateau, to improve the understanding of regional climate fluctuations and their driving mechanisms. The pollen spectra are dominated by herbaceous species such as Artemisia , Chenopodiaceae, Cyperaceae and Poaceae, which grew in various alpine desert settings. Four pollen assemblage zones are identified using stratigraphically constrained cluster analysis, representing climate history at different stages. The Artemisia /Chenopodiaceae (A/C) ratio and axis score of the first principal component are used to infer regional moisture conditions and reveal a temporal pattern that is consistent with various records from central Asia. The source of Cyperaceae pollen is mainly from marsh wetlands distributed around the lake, which responded sensitively to the lake level fluctuations. In contrast, arboreal pollen is mainly a long-distance transported component, reflecting changes in regional vegetation. Our findings show that the northern Tibetan Plateau experienced relatively wet conditions during the Dark Age Cold Period and the Little Ice Age, while relatively dry conditions occurred during the Medieval Warm Period and the last two centuries. Fluctuations in moisture levels are broadly consistent with moisture records elsewhere in western China, and show a good correlation with phase changes of the North Atlantic Oscillation. The climate changes in the northern Tibetan Plateau are supposed to be primarily triggered by the NAO phases through south-north migrations of the mid-latitude westerlies during the late Holocene. • Fossil pollen based 1500-year vegetation and climate changes on the northern Tibetan Plateau. • Major pollen species were analyzed and interpreted in terms of regional moisture variations. • Four vegetation and climate stages during the late Holocene were determined accordingly. • NAO phases affected northern TP climate through south-north migrations of the westerlies. [ABSTRACT FROM AUTHOR]

Driselase-digestion of cell walls from suspension-cultures of spinach (Spinacia oleracea L.), followed by anion-exchange chromatography, gel-permeation chromatography, preparative paper chromatography and preparative paper electrophoresis, yielded ten uronic acid-containing products in addition to free galacturonic acid (GalA). These included 4-O-methylglucuronic acid, α-l-rhamnopyranosyl-(1→4)-d-glucuronic acid and several oligosaccharides containing GalA residues. The structures were unambiguously determined by a combination of 1- and 2-dimensional NMR spectroscopic techniques. Five of the six homogalacturonan-derived oligosaccharides purified contained 3-O-acetyl-GalA residues; however, methyl-esterified GalA residues occurred adjacent to both 2-O-acetyl-GalA and 3-O-acetyl-GalA residues. An acetylated, rhamnogalacturonan-I-derived oligosaccharide that was purified also contained 3-O-acetyl-GalA residues. Taken together with published data, our findings indicate considerable diversity in the patterns of pectin esterification. The implications for the action of pectin esterases are discussed. [Copyright &y& Elsevier]

Steppe and grassland ecosystems constitute important biomes that are influenced by multiple factors such as climate, human activity, and fire. Yet how these factors have influenced the plant composition of these biomes through time continues to be understudied. This paper investigates how these mechanisms have transformed the steppe landscape recorded at the mire site of Shenkani, Armenia. This highland site, located in the South Caucasus, has a long human history of permanent settlements near the core site starting at 5500 cal. BP. A variety of biological and geochemical proxies, including pollen, non-pollen palynomorphs, macro-charcoal, 14C age model, X-ray fluorescence, loss-of-ignition, magnetic susceptibility, and a quantitative climate reconstruction inferred from pollen, are utilized in this paper. We find that this area has remained a steppe with small stands of trees throughout the duration of the Holocene. Changes in steppe plant composition primarily occur between semi-desert steppes (Chenopodiaceae), grassland steppes (or Poaceae dominated meadow-steppes), and mixed steppes with forest patches. In this record, two phases of local grassland expansion occurred between 9500 and 7000 cal. BP and 2500–1000 cal. BP, which covaried with local fire events. These grassland steppes were sustained until tree encroachment led to a more mixed steppe landscape around 7000 cal. BP and again at 1000 cal. BP. Climate, primarily precipitation, is the main driver of this persistent steppe landscape and the plant compositional shifts within it. However, fire and human activities contributed to steppe maintenance. • A 10,240 year-old sequence from Shenkani, Armenia documents a persistent Holocene steppe. • Changes in steppe plant composition occur between semi-desert, grassland, and mixed steppes with forest patches. • Poaceae dominated grasslands covary with fires that limit tree and shrub encroachment. • The mid- to late Holocene transition is characterized by drops in Betula and declines in distant arboreal pollen. [ABSTRACT FROM AUTHOR]

Artemisia and Chenopodiaceae are the two main pollen taxa in studies of lake sediments on the central and western Tibetan Plateau (TP). In this paper, we present Artemisia /Chenopodiaceae (A/C) ratios in pollen assemblages of surface sediments from 42 lakes on the central and western TP. Relationships between vegetation, climate and A/C ratio are investigated. The results show that the A/C ratio in the study region can distinguish desert from steppe vegetation. As a whole, the A/C ratio was higher than 1.2 in the steppe vegetation and lower than 1.2 in the desert vegetation zone. Statistical analysis revealed that the A/C ratio can be used as a moisture indicator on the TP. Based on the A/C ratio in pollen assemblages of sediment core TAN12-2 from Lake Tangra Yumco, we reconstructed the vegetation and climate history of the southern TP during the transitional period from the late glacial to the Holocene (17.5–10 cal kyr BP). From 17.5 to 16 cal kyr BP, desert vegetation occurred and climate was extremely dry. During 16–15 cal kyr BP, desert was replaced by steppe vegetation and climate became wetter. From 15 to 10 cal kyr BP, the lake basin of Tangra Yumco was covered by the steppe vegetation and climate tended to be more humid. Comparing our results with other lacustrine records on the TP, we found that the Indian summer monsoon (ISM) significantly affected the southern TP earlier than the northeastern TP. [ABSTRACT FROM AUTHOR]

This paper presents the results of pollen trapping studies designed to quantify the pollen assemblages carried in the winds of the Loess Plateau in Luochuan and Hunyuan. The one-year-collection samples analysis results show that pollen assemblages can be more sensitive to the change of climate than the vegetation composition, because of the change of pollen production. The analysis results of pollen traps in different weather regimes indicate that the pollen influx coming from dust weather contribute more to the total pollen influx than that coming from non-dust weather. The wind speed is the most important influenced factor to pollen assemblages, then the mean temperature and the mean relative humidity, the wind direction also contributes some. Strong wind coming from dust direction can make the percent and influx of Artemisia and Chenopodiaceae increase obviously with averagely higher than over 2.7 times in dust weather than in non-dust samples. The influences of wind speed and wind direction are not serious to some arboreal pollen such as Rosaceae, Quercus , Betula , Pinus and Ostryopsis , which are mainly influenced by temperature or the relative humidity such as Salix , Hippophae , Carpinus , Brassicaceae, Cupressaceae, Fabaceae. [ABSTRACT FROM AUTHOR]

Abstract: Studies of vegetation successions related to climate changes during previous interglacial periods provide important insights into the mechanisms of climate change during the current interglacial and enable predictions of future climate impacts on ecosystems. The Chinese Loess Plateau (CLP), which is particularly sensitive to climate warming, presents an excellent site for such studies. However, few detailed records exist of vegetation and climate variations during interglacial periods on the CLP. This study obtained a series high resolution pollen records from the Luochuan loess-paleosol section on the CLP, and the paper discusses the vegetation and climate histories during three previous interglacial periods (MIS 9, MIS 7 and MIS 5). The Artemisia-Chenopodiaceae steppe vegetation that covered this area between 342 ka and 312 ka changed to Humulus-Chenopodiaceae steppe between 312 ka and 302 ka, and then reverted to Artemisia-Chenopodiaceae steppe after 302 ka. From 250 ka to 237 ka, the vegetation type remained Artemisia-Chenopodiaceae steppe, and then changed to Artemisia-Humulus steppe between 237 ka and 227 ka. Between 227 ka and 195 ka, the vegetation returned to Artemisia-Chenopodiaceae steppe. During MIS 5, vegetation of the study area changed from Pinus-Rosaceae-Chenopodiaceae forest-steppe between 129 ka and 117 ka, to Artemisia-Humulus-Ranunculaceae steppe from 117 ka to 96 ka. After 96 ka, the vegetation types changed to Pinus-Betula-Chenopodiaceae forest-steppe. Comparing these pollen records with other climatic proxies from the CLP and the oxygen isotope records from the Pacific Ocean suggests that vegetation and climate change features around the study site were synchronous with East Asian monsoon variations near 65°N. The regional tectonic uplift probably provided only a subordinate influence on vegetation and climate variation on the CLP during MIS 5. [Copyright &y& Elsevier]

In the presence of metal stress, plants can resort to a series of tolerance mechanisms. Therefore field studies should be undertaken in order to evaluate the real role of these mechanisms in stress coping. The aim of this paper was to clarify the biochemical processes behind mercury tolerance in Halimione portulacoides (L.) Aellen (Caryophyllales: Chenopodiaceae) collected in a mercury contaminated salt marsh. Different fractions of mercury were separated: buffer-soluble (mainly cytosolic) and insoluble mercury (mainly associated with membranes and cell walls). The amounts in each fraction of metal were compared and related to metal distribution within plant organs. Protein–mercury complexes were isolated and analysed for their thiol content in order to assess wether the tolerance of this salt marsh plant was associated with the induction of metal chelation by phytochelatins. Overall, the mercury tolerance strategies of the plant are likely to involve root cell wall immobilization as a major mechanism of metal resistance, rather than metal chelation in the cytosolic fraction. Nevertheless, phytochelatins were demonstrated to chelate mercury under environmental exposure. [Copyright &y& Elsevier]

Abstract: Atriplex tatarica is a heterocarpic annual native to a wide area of Middle and western Central Asia, Asia Minor, North Africa, and Eastern Europe. It is an early successional species of disturbed habitats, in Central Europe mostly occupying road margins and waste places. This paper deals with taxonomic status, morphology, distribution, ecology, and population biology of this species with special emphasis on its population genetics. [Copyright &y& Elsevier]

• Identify ancient flood events, which may be the reason for decline of the culture. • Pollen and heavy metals can be used to reflect the strength of human activities. • Pollen and heavy metals revealed the process of culture from prosperity to decline. • This paper defined the chronology from prosperity to decline of Shijiahe culture. • Climate change has been revealed by pollen and heavy metals since 4800 cal. yr BP. The Shijiahe Culture (ca. 4800–4100 yr BP), which originated in the middle Yangtze Basin, was a milestone of prehistoric Chinese civilization. To reveal the interactions between climatic changes and human activities during this time interval, the geochronology and multiple proxies (pollen and heavy metals) of samples from a 220-cm-deep outer wall at the Sanfangwan Site (a typical site of the Shijiahe Culture) were analyzed. Radiocarbon dating indicates that the age range of the Sanfangwan Site is ca. 4800 to 4100 cal. yr BP. From ca. 4800 to 4600 cal. yr BP (the early Shijiahe Culture), pollen assemblages were dominated by Gramineae and an anthropogenic plant community (e.g. Ranunculaceae, Chenopodiaceae, Labiatae, and Cruciferae), indicating an expansion in rice agriculture during this interval. High metal concentrations in the same interval indicate a large flux of metals from smelting and farming activities. Between ca. 4600 and 4100 cal. yr BP (the middle and late Shijiahe Culture), decreases in Gramineae and anthropogenic pollen mirrored the recession of farming. Concurrent decreases in heavy metals may be attributable to a decline in the smelting industry. Three episodes of high pollen concentrations and visible increases in hygrophyte pollen, Pinus pollen, and fern spores at 4600–4550, 4450–4350, and 4200–4100 cal. yr BP probably indicate the occurrence of several flooding events during the middle and late Shijiahe Culture, resulting in the migration of local inhabitants. This study highlights the driving effect of flood events on the collapse of the Shijiahe Culture. [ABSTRACT FROM AUTHOR]

Abstract: The importance of density dependence, aggregation and background density of seeds on intensity of seed predation in cereal fields were examined in central Netherlands. Four sequential 1-week trials were conducted from 9 July to 8 August 2001 and lamb''s quarters (Chenopodium album) was used as the test species. C. album was offered to potential predators by lightly adhering seeds to small strips of sand paper. The interaction between spatial scale and density dependence was tested at a large (varying seed density/block) and a small (varying seed density/card) spatial scale. Three distributions (random, even, aggregated) and two background (seed cards presented in plots with none versus many C. album seeds added to the soil) treatments were tested, all experiments being conducted simultaneously but in different fields. There was no large spatial scale density effect but in Week 4, a higher proportion of seeds was removed from the low-density seed cards. In the distribution study, significantly more seeds were removed from the aggregated distribution treatment in Week 2. In the background density study, predation was highest in Week 2 of the high background density treatment. In all experiments, there was considerable temporal and spatial variation in the intensity of seed predation. The importance of seed in the diet of seed predators declined with time, whereas the presence or the absence of density dependent predation was likely to be a function of the spatial scale at which densities were enhanced. [Copyright &y& Elsevier]

Improved studies of past vegetation change are required to better understand the variation of alpine ecosystems on the Qinghai-Tibetan Plateau (QTP) in response to future climate change. Spatial and temporal variations of past vegetation can be traced by fossil pollen data mapping. In this paper, we synthesized 57 continuous pollen records on the QTP covering the past 15 kyr to depict large-scale vegetation change and its response to climate variations. In order to minimize potential chronological biases, age-depth models were revised using a state-of-the-art and consistent method for all the records. The spatial and temporal variation of major pollen taxa were examined based on interpolated pollen maps at 1000-year intervals. The arboreal pollen (AP, mainly of Pinus , Betula and Abies / Picea) content expressed significant climate signals over a broad spatial and temporal gradient. During the late glacial period, high proportions of AP widely occurred in regions that are presently unforested owing to the sparse local vegetation coverage. For the Holocene period, AP showed relatively high contributions in records from the southeastern margin of the QTP, with a decreasing gradient in abundance towards the northwest. The transportation of AP to unforested regions corresponds closely to the intensity of monsoon wind, which can be used to track the Holocene evolution of the summer monsoon. The dominant shrub and herbaceous taxa (including Artemisia , Chenopodiaceae, Cyperaceae, Poaceae and Ephedra) generally represent developments of local vegetation responding to climate variations. In addition, the persistent increase in Poaceae pollen during the mid to late Holocene correlates possibly to regional human activities. The inferred spatial and temporal patterns of major pollen types on the QTP provide significant knowledge about long-term vegetation change and its potential response to climate variations. • An initial plateau-scale examination of fossil pollen records on the Tibetan Plateau. • Spatial and temporal patterns of major pollen types were mapped at 1000-year interval. • Arboreal pollen from unforested plateau surface represents intensity of summer monsoon. • Herbaceous pollen reveals local vegetation development in response to climate change. [ABSTRACT FROM AUTHOR]

This paper analyzes the distribution patterns of pollen and spore assemblages in modern surface sediments recovered from the bottom of the San Jorge Gulf (SJG) and from offshore sites, in relation to the location of different phytogeographic provinces surrounding the SJG, including the distant forest from southwestern Patagonia. Results reveal that pollen spectra are dominated by Chenopodiaceae-Amaranthaceae, Poaceae, Asteraceae subf. Asteroideae, Colliguaja integerrima and Ephedra sp.; which represents the vegetation adjacent to the SJG. Overall, the pollen distribution in surface sediments reflects the location of the different phytogeographic provinces and will be used as modern-analogues to document vegetation history around the SJG. Pollen assemblages also reveal the latitudinal variation of vegetation taxa in the Patagonian steppe, which is characterized by a slight increase in herbaceous pollen and a decrease in high shrubs (e.g. Colliguaja integerrima) towards the southern-central part of the SJG. Furthermore, we identified two pollen taxa from the southwestern Patagonian forest, Nothofagus and Podocarpus that could be used as indicators of past dynamics and variations of the Southern Westerly Wind Belt (SWWB) in the SJG during the Late Pleistocene and Holocene. High pollen concentrations are recorded at the central part of the SJG (480–8080 grains/g), while low concentrations are measured in the northern and southern parts of the Gulf, as well as at offshore sites (26–1806 grains/g). The pollen distribution in the study area is most likely governed by the SWWB in combination with the marine sediment composition and surface currents flowing through the SJG. • Pollen and spore surface distribution patterns from the San Jorge Gulf. • Pollen assemblages echo different phytogeographic provinces surrounding the gulf. • Nothofagus and Podocarpus reflect long distance transport by westerly winds. • Pollen distribution results from transport by westerly winds and surface currents. [ABSTRACT FROM AUTHOR]

The synthesis of few-layer graphene from graphite typically uses N, N methyl pyrrolidone (NMP) or dimethylformamide (DMF) due to the strong affinity of both solvents for graphite. However, NMP and DMF are known as carcinogens and a long-time exposure to these substances may subject users to potential risk of major health issue later. Therefore, a replacement with dispersing solvent that is not only harmless but also able to exfoliate graphite at an excellent concentration yield must be outlined for a sustainable mass-production of graphene. In this work, we have successfully exfoliated graphite to few-layer graphene with a recorded yield concentration of up to 0.75°mg/ml (2.5°h) just by using extracted red spinach/water mixture as an exfoliating medium. The prepared graphene was found to possess less structural defect (I D /I G : 0.5) and high C/O ratio (6.8) and can be used further as an electrical conductive ink for smart "Sticky Note" sensor. The fabricated device was able to detect strain and temperature with gauge factor and temperature coefficient resistance of 23.5 and −32.14 × 10-4°Ω/°;C, respectively. We believe that this study would be useful for the preparation of environmental-friendly graphene that is not only strain and thermally sensitive but also producible at low -cost. Image 1 [ABSTRACT FROM AUTHOR]

In this work, natural extraction (NE) from spinach leaves is used as modifier for ZnO based electron transporting layer (ETL) in polymer solar cells (PSCs). And NE modifying decreased the work function of ZnO film, smoothed the surface of ZnO and enhanced the charge carrier extraction, resulting in much improved devices performance. The device founded on ZnO/NE ETL with PCE-10:PC 71 BM as the photoactive layer attained PCE (power conversion efficiency) = 9.41% (18.51% enhancement compared with that for device based on pure ZnO ETL), suggesting that NE is an interesting candidate as efficient modifier for ETL in PSCs. Image 1 • Natural extraction (NE) from spinach leaves is used as Zno modifier in polymer solar cells. • The ZnO/NE co-interlayer shows increased electron mobility compared to the pure ZnO interlayer. • The PCE of devices based on ZnO/NE interlayer showing 18.51% enhancement compared to that for device based on pure ZnO interlayer. [ABSTRACT FROM AUTHOR]