Phytolith Assemblages Research Articles

REGISTRO PALEOBOTÁNICO DEL PLIO–PLEISTOCENO INFERIOR EN EL VALLE DEL RÍO URUGUAY. CARACTERIZACIÓN FITOLÍTICA DE LA FORMACIÓN SAN SALVADOR, ESTE DE LA PROVINCIA DE ENTRE RÍOS, ARGENTINA.

The San Salvador Formation is one of the few deposits from the Pliocene–Lower Pleistocene in the east of Entre Rios Province, which from a palaeontological point of view has been described exclusively through its phytolith content. This contribution includes the synthesis and expansion of this knowledge through the results of the phytolith study of the Jose Etchepare Hijo profile (Colon Department, Entre Rios). For this, an ad-hoc methodology has been used, adapted to obtain phytoliths in fluvial deposits. The sedimentary sequences were characterized by a succession of conglomerate supported matrix strata, fine to coarse sandy facies and fine facies (represented by clays and silts). The results allowed to observe a greater abundance and variability of phytoliths in layers with sandy texture; and proportionally more scarce and even absent in the gravel texture layers. Non-diagnostic grass phytoliths were common in all the samples with microremain materials, while among those of smaller size and diagnostic ones, their presence was manifested only in certain sectors of the profile. The phytolith assemblages were made up of elements from the Arecaceae, Poaceae (Bambusoideae, Panicoideae, Danthonioideae, Chloridoideae and Pooideae), and Podostemaceae families; and they have allowed inferring palaeocommunities of stratified hygrophilous forests, palm groves and riparian forests, which indicate a humid tropical-subtropical climate, with great water availability.

Possibilities of Speciation in the Central Sandy Steppe, Woody Steppe Area of the Carpathian Basin through the Example of Festuca Taxa

Research Highlights: We examined the vegetation appearing in forest-steppes in the Pannon region. In the present survey taxonomical relations of the dominant Festuca species were examined. Background and Objectives: After deforestation and shrubcutting bare soil patches exposed to anthropogenous effects provided an opportunity for new vegetation to form. Materials and Methods: Inflorescence parameters and micromorphological characters of the leaves were examined in a new taxon and compared with two, presumably closely related, species of the genus Festuca L. Festuca tomanii Korneck & T.Gregor, with silvery leaf surface, Festuca vaginata W. K. and Festuca pseudovaginata Penksza were compared based on 24 traits of the inflorescence and their leaf anatomy studied on leaf cross-sections. Moreover, leaf micromorphological features were compared using a stereomicroscope, a scanning electron microscope completed with Energy Dispersive X-Ray Spectroscopy measurements and phytolith analysis method to establish the taxonomic applications of the micromorphological characters of the epidermis. Results: The awns of the lemma of Festuca tomanii were shown to be longer than those of the two other species. Festuca vaginata and Festuca pseudovaginata specimen showed low variability in inflorescence parameters but inflorescence characters were not uniform because the panicle of Festuca tomanii individuals was found to be bigger in the northern part than the panicles originating from the southern part of the sampled area. The phytolith assemblages of the Festuca pseudovaginata and Festuca tomanii differ from the Festuca vaginata in the abundance of ELONGATE SINUATE phytolith morphotype. Conclusions: we confirmed the appearance of F. vaginata in natural grasslands and discovered new occurrences of F. pseudovaginata and F. tomanii. F. pseudovaginata inhabits only the Pannon region, we found endemic and natural stands of it, but in its secondary habitats it was confirmed as a completely new species. Furthermore, taxa of disturbed vegetations are currently being examined. These habitats are potential hotspots of speciation.

Phytolith records of flourishing early Holocene Pooideae linked to an 8.2 ka cold event in subtropical China

The grass subfamily Pooideae originated in a temperate niche during the late Cretaceous; it is the largest Poaceae subfamily, consisting of almost 4,000 species, which are distributed worldwide. Pooideae responses to climate changes at different time scales, and different ecological zones are thus important in understanding Poaceae evolutionary processes and their relationship with climate change. In the study described in this article, we reconstructed Pooideae variability during the early Holocene, as inferred by a phytolith sequence from the Lower Yangtze in subtropical China. The phytolith assemblage was marked by three increases in Pooideae phytoliths, dated to ca 8.4–8.0, 7.8–7.6, and 7.4–7.2 ka BP (before present, 1950 AD), with each representing pronounced increases in Pooideae extent and distribution. All these increases were within age ranges that agreed well with the timing of weak Asian Monsoon events, at 8.2, 7.7, and 7.3 ka BP. The first Pooideae flourishing period in subtropical China was the most significant, lasting for approximately four centuries and being characterized by a double peak, which equated with an event at 8.2 ka. This suggested that cold and/or dry conditions—which occurred over a period of several hundred years and were linked to weakening of the Asian monsoon—probably caused Pooideae to flourish in the Lower Yangtze region. Comparison of two diagnostic trapezoid phytolith types—namely wavy and wavy narrow—which showed different changes between ca 8.4 and 8.0 ka BP, suggested that they responded differently to the climate change represented by the 8.2 ka event. Our phytolith records have provided not only new data clarifying the detailed Pooideae response to the 8.2 ka event but also a reliable index for past cold climates in subtropical China.

Olduvai's oldest Oldowan

Previously, Olduvai Bed I excavations revealed Oldowan assemblages <1.85 Ma, mainly in the eastern gorge. New western gorge excavations locate a much older ∼2.0 Ma assemblage between the Coarse Feldspar Crystal Tuff (∼2.015 Ma) and Tuff IA (∼1.98 Ma) of Lower Bed I, predating the oldest eastern gorge DK assemblage below Tuff IB by ∼150 kyr. We characterize this newly discovered fossil and artifact assemblage, adding information on landscape and hominin resource use during the ∼2.3–2.0 Ma period, scarce in Oldowan sites. Assemblage lithics and bones, lithofacies boundaries, and phytolith samples were surveyed and mapped. Sedimentological facies analysis, tephrostratigraphic and sequence stratigraphic principles were applied to reconstruct paleoenvironments and sedimentary processes of sandy claystone (lake), sandstone (fluvial), and sandy diamictite (debris flow) as principal lithofacies. Artifacts, sized, weighed, categorized, were examined for petrography, retouch, and flake scar size. Taxonomic classifications and taphonomic descriptions of faunal remains were made, and phytoliths were categorized based on reference collections. Lithics are dominantly quartzite, mainly debitage and less frequently simple cores, retouched pieces, and percussors. Well-rounded spheroids and retouched flakes are rare. Identifiable taxa, Ceratotherium cf. simum (white rhinoceros) and Equus cf. oldowayensis (extinct zebra), accord with nearby open savanna grasslands, inferred from C3 grass, mixed and/or alternating with C4 grass-dominated phytolith assemblages. Palms, sedges, and dicots were also identified from phytoliths. Diatoms and sponge spicules imply nearby freshwater. The assemblage accumulated at the toe of a Ngorongoro Volcano-sourced fan-delta apron of stacked debris flows, fluvials, and tuffs, preserving fossil tree stumps and wooded grassland phytoliths farther upfan. It formed after the climax of Ngorongoro volcanic activity during a Paleolake Olduvai lowstand and was then buried and preserved by lacustrine clays, marking the first of two lake transgressions, signifying wetter climates. Orbital precessional lake cycles were superposed upon multimillennial (∼4.9 kyr) lake fluctuations.

Application of soil phytoliths to the quantitative characterization of temperate grassland ecosystems: a case study in Northeast China

Although phytolith analysis is a promising tool for reconstructing the palaeovegetation in grassland ecosystems, no phytolith study has yet attempted to quantitatively reconstruct the corresponding plant community characteristics. Questions remain regarding whether or not soil phytoliths can quantitatively reflect various aspects of grassland physiognomy, and how well modern phytoliths represent the quantitative characteristics of grassland ecosystems. These are important scientific issues in the field of phytolith analysis, which require further research on the modern phytoliths of grassland ecosystems. In order to explore the potential of phytolith analysis in the temperate grassland region, we have for the first time established a modern soil phytolith reference dataset by exploring the relationships between soil phytoliths and plant species inventory data from 77 sites in the Songnen grassland in Northeast China. The results show that phytolith assemblages can clearly distinguish Leymus chinensis grassland, Stipa grassland and mesophytic herb grassland. In addition, we found that the Ic phytolith index could discriminate samples of L. chinensis grassland from the other samples, while the Iph phytolith index proved to be less reliable in the region. In addition, in terms of quantitative plant community characteristics, the soil phytoliths showed a good correspondence with plant community cover and species richness, but not with biomass and diversity index. The transfer functions established in this study can provide reliable estimates of community cover and species richness in the Songnen grassland. In addition, phytoliths are shown to have the potential to reconstruct the taxonomic abundance of the aboveground plant community. This study is a major advance in the application of phytolith analysis to the quantitative estimation of plant community characteristics, and it provides a modern phytolith reference for the quantitative reconstruction of the paleovegetation of grassland ecosystems.

Spatial patterns of soil phytoliths in a wet vs. dry neotropical forest: Implications for paleoecology

To improve paleoenvironmental reconstruction based on fossil phytoliths, it is vital to establish modern calibrations that explicitly consider important functional aspects of vegetation, such as structure, composition, diversity, and spatial heterogeneity. No such studies currently exist for Central- and South America. To begin to solve this problem, we address two questions: 1) do phytolith assemblages reflect the overall differences in structure, composition, and diversity between rainforest and dry forest? and 2) do phytolith assemblages from lateral transects capture variation in structure and composition typical of these vegetation types? At La Selva (rainforest) and Palo Verde (dry forest) biological stations (Costa Rica), we collected soil phytolith samples from, respectively, fourteen and eleven quadrats along vegetation transects. Along each transect, we measured gradients in canopy openness (LAI), elevation, and moisture. Statistical analyses were used to characterize and compare vegetation structure, composition, and diversity to soil phytolith assemblage composition, and to test for correlation with environmental gradients at each site. The two sites were then compared using multivariate statistical methods. Results indicate that rainforest and dry forest vegetation can be distinguished by analyzing multiple phytolith samples collected within sites. Within each vegetation type, the comparison of phytolith assemblages along transects allows reconstruction of important structural (canopy openness and patchiness) and compositional (dominant plant functional types) aspects of the vegetation. Thus, the analysis of phytolith samples collected along temporally constrained stratigraphic levels is a viable and vital tool for inferring heterogeneity in canopy cover and gross vegetation composition in the deep-time fossil record.

Landscape change and occupation history in the Central Russian Upland from Upper Palaeolithic to medieval: Paleopedological record from Zaraysk Kremlin

Paleosol-sedimentary sequences encountered in the settlements with long occupation history could provide a unique insight into the trends of landscape development and human-environment interaction over long time scales. We studied paleosols exposed by the excavations in the Kremlin of Zaraysk (Central European Russia) which were formed during the late Pleistocene and the Holocene and contain archaeological materials spanning from Upper Palaeolithic till late Medieval. Archaeological findings and numerous radiocarbon dates provide a reliable time frame for paleopedological record which we extracted from paleosols using macro- and micromorphological observations as well as physical and chemical properties and paleobotanical indicators (phytolith assemblages). The basal layer without archaeological materials presents signs of soil formation which resemble Bryansk fossil soil developed in the second half of Marine Isotope Stage (MIS) 3. The overlying archaeological stratum - one of the Gravettian cultural layers is linked to the paleosol level known as Zaraysk soil. Its age is estimated at 16 ka BP. Macro- and micromorphological features point to moderate dark humus accumulation, anthropogenic compaction and cryogenic processes at the final stages of paleopedogenesis. Poorly sorted heterogeneous composition of the mineral material with a large proportion of sand grains indicates colluvial origin of the paleosol parent material. The overlying sorted silty deposit supposes contribution of windblown material to its formation. We associate cryogenic and eolian processes at the end and after Zaraysk soil development with the cold intervals at the end MIS 2, presumably with the Oldest and Younger Dryas. The complete profile of Luvisol/Grey Forest Soil with eluvial and illuvial horizons and relict dark humus morphons is developed within the silty unit. This soil indicates long-term natural pedogenesis under first steppe and then deciduous forest vegetation during major part of the Holocene. The topsoil however is formed by clear plough horizon which points to cultivation started in the Middle Ages. Sharp boundary separates the buried Luvisol from the overlying cultural layer-Technosol developed after building of Zaraysk Kremlin in the 16th century. Technosol presents a mixture of natural soil with construction materials, especially limestone fragments. Soil units, both natural and affected by humans, are not separated one from another by an unaltered C horizon, so soil-forming processes from the upper soils penetrate into the underlying ones forming a multistory pedocomplex.

An evaluation of soil phytoliths for reconstructing plant communities and palaeoclimate in the northern temperate region

AbstractPhytoliths can act as efficient carriers of information about palaeovegetation and palaeoclimatic conditions, but the representativeness of soil phytoliths from palaeoecological sediments has not been fully understood. In this study, phytolith assemblages in topsoils and associated plant communities at 55 sites in Northeast China were compared. The results indicate that samples from herbaceous and woody communities could be reliably differentiated by topsoil phytoliths. Notably, different phytolith types exhibit varying degrees of representational bias in terms of the aboveground plant community. Some morphotypes (e.g., bilobate, rondel and lanceolate) over‐represent the richness of the corresponding plant; some morphotypes, including microhair, conical epidermal, silicified stomata and epidermal phytoliths, under‐represent the parent plant abundance; additional morphotypes (e.g., elongate, saddle and trapeziform sinuate) are consistent with the changes of associated plants. Based on the representational bias, we calibrated the percentages of topsoil phytoliths and established a phytolith‐based transfer function for precipitation in Northeast China. A palaeoclimate reconstruction in the Changbai Mountains (in the eastern part of Northeast China) based on the above phytolith‐based transfer function for precipitation shows that the region has gone through continuous climatic changes since the late glacial period: from cold and dry conditions to warm and dry conditions, then to warm and wet conditions, and finally to cool and dry conditions. The phytolith‐based reconstructed climate changes since the late glacial period correspond well to those reconstructed by other records from the same stratigraphic profile, and our phytolith‐based climatic reconstruction also confirms the reliability of abrupt cold climatic shifts at 8.2, 6.8, 5.6, 4.6 and 4.2 ka. In conclusion, our results provide the basis for the reliability of phytoliths for reconstructing climatic changes in the northern temperate region.Highlights Calibrating soil phytolith assemblages for any quantitative palaeovegetation reconstruction using phytoliths is necessary. Phytolith morphotypes in topsoils may over‐ or under‐represent or agree with the abundance of modern plant taxa. Phytolith‐based climatic reconstruction corresponds well with the abrupt climate changes evident since the Late Glacial period and other proxy records.

Translocation and preservation of soil phytoliths in temperate regions and its implications for palaeoenvironment reconstruction

The reliability of soil phytoliths within representatives of past phytolith assemblages in archaeological and palaeoecological contexts needs to be improved. In this study, we investigated soil phytolith representation by comparing phytoliths from plant communities with those from paired topsoils and those subjected to vertical translocation at 54 sites in Northeast China. With respect to soil phytolith preservation in the soil-plant system, there is a reasonable correspondence between phytolith morphotypes from forested topsoil (or grassland topsoil) and those from the associated communities. But the comparison and contrast between phytoliths from topsoil and communities indicates that different phytolith morphotypes also exhibit different degrees of representational bias (R values). Additionally, for the vertical translocation of soil phytoliths, together with a phytolith translocation index (T), ~31% and 19% of the phytoliths are transported below the surface of the studied soil profiles in the forested and grassland regions, respectively. The translocation rates of different phytolith morphotypes in the forested samples are all larger than those in the grassland samples. Based on R and T values, the changes of revised topsoil phytolith indices are moderately in accord with actual plant richness and climatic changes. These results we show that the R and T values are effective parameters indicating the degree of soil phytolith preservation and can be used in future studies for developing training sets of modern phytolith assemblages. The results of our study provide a methodological template to investigate the extent to which phytolith assemblages in palaeoenvironmental contexts satisfy the criteria necessary to justify their use as a meaningful proxy of past ecological and climatic change.

Assessing past water availability using phytoliths from the C4 plant Sorghum bicolor: An experimental approach

Water availability and water management systems were critical for the success of past agricultural societies. One way to determine past water availability is through phytolith ratios as demonstrated by research conducted on modern C3 plants. In order to determine if phytolith ratios in C4 plants are similarly affected by plant water availability, the C4 plant Sorghum bicolor was experimentally grown at three different crop growing stations over a two year period in Jordan. The husks, leaves and stems of the plants grown under the 0% and 100% irrigation regimes were processed and analysed for their sensitive to fixed form phytolith ratio. These results were then compared to results of those conducted using C3 plants. Our results showed that while there were differences in ratios between growing years and the crop growing site, the greatest difference in the ratios was in irrigation regime. Our results also showed, however, that the ratio of sensitive to fixed forms for the samples taken from the husks was far higher than the ratios found in the leaves and stems and far higher than those found in previous studies on C3 grasses. We suggest that if this method is to be used to interpret archaeological phytolith assemblages, an assessment of the likely taxa and plant part composition of the assemblage should first be undertaken through phytolith and macro-botanical analysis.

Preservation of common soil phytoliths in the northern temperate region: a case study from northeast China

We investigated the phytolith assemblage characteristics and preservation of soil phytoliths in nine soil types at 83 sites in northeast China. The results indicate that the phytolith assemblages from the nine soils are similar, particularly in terms of the content of the dominant short cell phytoliths, and elongate and lanceolate phytoliths. The phytolith indexes of aridity and water stress (Iph and Fs, respectively) have been proven to be effective in the temperate zone, and we find that values of Iph and Fs higher than 0.45 and 0.24, respectively, are characteristic of meadow steppe. However, there are differences in phytolith indexes amongst the different soil types. In addition, the preservation characteristics of phytoliths in different soil types are different, with phytolith preservation in zonal soils being better than in azonal soils. Morphotypes such as rondel, bilobate, lanceolate, blocky, tabular and bulliform are well preserved in the studied soils; however, other morphotypes, such as microhair, conical epidermal, silicified stomata and epidermal, are poorly preserved. Morphotypes such as saddle, trapeziform sinuate and elongate are moderately well preserved in the soils. The preservation characteristics of the same type of phytolith differ between the soil types. Thus, there are differences in the preservation of soil phytoliths amongst different soil types, which needs to be considered when soil phytoliths are used to produce quantitative palaeoenvironmental reconstructions.

Pen management and livestock activities based on phytoliths, dung spherulites, and minerals from Cova Gran de Santa Linya (Southeastern pre-Pyrenees)

The archaeological evidence from Cova Gran de Santa Linya suggests that during the Late Neolithic and Early Bronze Age, the site was used as a livestock enclosure where the accumulated excrements were burned, generating a sequence known by the term fumier. Here we present the results of an integrated study of silica phytoliths, dung spherulites, and mineral composition of sedimentary matrix from the remaining Holocene sequence. The use of fire to sanitize the space had important consequences for the preservation of dung spherulites and the accumulation of phytoliths. Phytolith assemblages indicate that the animals enclosed in the cave were mostly sheep that exploited the pastures nearby the site during the year. In this sense, the results from our modern plant reference collection challenge the assumption that grass inflorescence phytolith can be used as a seasonality indicator.

Phytolith evidence of water management for rice growing and processing between 8,500 and 7,500 cal years bp in the middle Huai river valley, China

The archaeological sites of Shunshanji and Hanjing are recorded as the earliest Neolithic sites in the middle Huai river valley, China, which were occupied between 8,500 and 7,500 cal bp, and provide crucial evidence of rice growing. However, the water availability and management of arable land systems for rice cultivation and the main stages of rice processing at the two sites have not been studied before. In this paper, phytolith analyses are discussed in 66 samples from the Shunshanji site and 32 samples from the Hanjing site, with three phases of occupation at each. The ratios of sensitive to fixed forms in the phytolith assemblages over three phases reveal that in Phase I these ratios are relatively low, and they become significantly higher in Phases II and III at both sites. These results suggest that rice was grown probably only using natural water supplies in the lowlands during Phase I, but changed to growing on highly controlled and regularly flooded and drained wetlands in Phase II at the two sites. In addition, seen from the distribution and concentrations of phytoliths from rice, weeds and their by-products, as well as the proportions of each, both double peaked glume cells (DPG) and rice cuneiform bulliform cells (RCB) were found together with some rice paddy weed phytoliths. The concentrations of DPG were much higher than those of RCB in most samples from the Shunshanji and Hanjing sites over the three phases. The findings imply that rice ears together with the stems and leaves were probably stored after the harvest, then threshed and de-husked simultaneously, and the straw and chaff by-products were discarded together at the sites between 8,500 and 7,500 cal bp. The study in this paper aims towards a better understanding of past human behaviour and social organization in rice growing communities during the middle Neolithic in eastern China.

Quantitative reconstruction of Holocene millennial-scale precipitation in the Asian monsoon margin of northwest China, revealed by phytolith assemblages from calcareous root tubes in the Tengger Desert

The spatio-temporal characteristics and driving mechanisms of the Asian summer monsoon (ASM) during the early and middle Holocene remain unclear. Moreover, the timing of maximum monsoon precipitation in the Asian monsoon margin of northwest China during this period is also a subject of considerable debate. Herein, we analyzed phytolith assemblages within 55 calcareous root tube (CRT) samples from the hinterland of the Tengger Desert to quantitatively reconstruct Holocene millennial-scale precipitation changes and discuss the potential forcing mechanisms. Our results revealed that the mean annual precipitation (MAP) was 138 ± 53 to 149 ± 18 mm during 10.0–7.0 cal kyr BP, 179 ± 26 to 192 ± 26 mm during 7.0–5.0 cal kyr BP, and 129 ± 20 to 161 ± 13 mm during 5.0–1.0 cal kyr BP. The quantitative reconstruction results suggested that precipitation in this area was low in the early Holocene, then increased to a maximum in the middle Holocene (30% higher precipitation than present), and gradually decreased in the late Holocene. Maximum monsoon precipitation did not occur until the middle Holocene in this area because the northernmost margin of the ASM reached its northernmost latitude lagging behind its maximum monsoon intensity suppressed by high-northern latitude ice volume forcing during the early Holocene despite high summer insolation. In addition to quantifying the Holocene millennial-scale precipitation changes in the northwestern margin of the ASM, this study also provides new evidence for spatial and temporal variations of the ASM during the Holocene.

Phytoliths as paleopedological records of an histosol-cambisol-ferralsol sequence in Southeastern Brazil

Soils can preserve numerous proxies that provide highly useful data on ancient climates or environments. In this study we hypothesized that analysis of the pedological cover combining soil phytolith assemblages and pedological, geochemical and isotopic analyses (δ13C and 14C) allows the reconstruction of events associated with the soil-landscape relationship at a toposequence scale. Soil profiles were collected from a toposequence in the upper montane environment of Mantiqueira Range, Espírito Santo State, in the Southeastern region of Brazil. Samples were collected by horizon/layer for pedological and geochemical analysis, and by depth, at 10-cm intervals, for phytolith and carbon (C) isotope (14C and δ13C) analysis. The soils are characterized by high organic matter contents, favored by the cold and humid climate, which is typical of the upland mountainous environments of Mantiqueira Range. The multiproxy approach provided important information about the paleoenvironmental conditions during the pedogenesis process, allowing to establish pedochronostratigraphic correlations, that improved the understanding of soil-landscape relationships in these environments. Soil-preserved phytolith assemblages, isotopic composition (δ13C) and organic matter dating (14C) indicated variations in the type of plant communities in the studied soils, suggesting climatic changes that influenced the soil formation and evolution. The soils experienced different pedogenesis conditions during the Late Holocene, and are, therefore, considered polygenetic soils. In summary, 3 environmental moments were identified by multiproxy analysis: Phase I (before −2330 cal. yr BP), hotter and drier than the current period; Phase II (from −2330 to −2063 cal. yr BP), colder and wetter than the current period; Phase III (after −2063 cal. yr BP), during which the current climate conditions were established.

Phytoliths from native plants and surface soils from the Upper Madeira river, SW Amazonia, and their potential for paleoecological reconstruction

Phytolith reference collections of plants and surface soils are a critical part of studies that use these microbotanical remains for archaeological and paleoecological reconstruction. In the archaeologically-rich region of the Upper Madeira river in Rondônia, Brazil, phytolith analysis is being applied in both on- and off-site contexts in order to shed light on human-environment interactions over a period that extends almost the entire Holocene. The present study brings together data on phytolith production patterns among 90 native species, representing 36 plant families, as well as 56 surface soil samples taken from underneath 11 monitored forest plots. Our discussion focuses on the comparison between the surface soil phytolith records and the above-ground floristic inventories, scrutinized considering the plant reference collection results. We found that the phytoliths of several species which produce diagnostic or potentially-diagnostic morphotypes were under-represented in the surface soils, including several understory herbs. While the phytolith assemblages from three forest types (palm, sororoca and dense forest) presented considerable overlap, in accordance with similarities in the floristic inventories, bamboo forest and different types of campinaranas were able to be distinguished based on their phytolith signatures.

Continuous aridification since the mid‐Holocene as the main cause of C3/C4 dynamics in the grasslands of northeastern China

AbstractEcological responses to past climate change as determined from palaeorecords offer insights into responses that may accompany future climate change. In arid and semi‐arid lands, the interactions between regional vegetation and climate change are not yet well understood, partly due to a lack of suitable palaeovegetation proxies that can provide accurate and continuous tracers for past vegetation dynamics. To gain a better understanding of long‐term vegetation dynamics, this study employs a multiproxy approach applied to sand‐palaeosol sediments of northeastern China's Songnen grasslands. Phytolith analyses and data on the stable carbon isotope composition (δ13C) of organic matter are used to reconstruct palaeovegetation composition, namely, the changing abundance of C3 and C4 species, whereas a geochemical weathering index (Fed/Fet ratios) tracks past East Asian summer monsoon (EASM) intensity. The phytolith assemblages and indices and δ13C of the soil indicate that C4 species' abundance has been increasing in the Songnen grasslands since the mid‐Holocene, although C3 vegetation is still dominant. Statistically significant negative correlations between the δ13C data and Fet/Fed ratios suggest that continuous weakening of the EASM since the mid‐Holocene may be responsible for the 13C‐enrichment of the sediments in the Songnen grasslands. Field vegetation surveys, modern topsoil phytoliths and δ13C calibration data indicate that the expansion of C4 species since the mid‐Holocene is mainly due to their ability to cope with aridity when growing season temperature is not undergoing a significant decrease. Future precipitation decreases in arid and semi‐arid lands should make C4 species more competitive in the grasslands of northeastern China.Highlights A continuous grassland landscape history is reconstructed from a sand‐palaeosol sequence via phytolith analysis. Multiple independent approaches were used to reconstruct past EASM intensity and palaeovegetation patterns. Phytolith and δ13C analyses indicate an increase in C4 species since the mid‐Holocene. Aridification drives the increase in C4 species within the grassland ecosystem.

Phytolith analysis in Quaternary fluvial deposits (El Palmar Formation-Late Pleistocene) of the Uruguay River valley, Entre Ríos province, Argentina

The phytolith assemblages of the El Palmar Formation (Late Pleistocene) are presented together with general stratigraphic and sedimentological data. The El Palmar Formation represents a channel system of the Uruguay river (South America) with longitudinal sandy gravel and gravelly sand bedforms, and associated floodplain deposits. The phytolith content of the unit was analyzed along the profiles on the right bank of the river in the middle reach (eastern Entre Ríos province, Argentina). Four outcropping profiles of the El Palmar Fm. were selected for detailed analyses: Santa Ana (Federación department), La Chola quarry, El Palmar National Park and Nueva Escocia (Colón department) localities. The herbaceous palaeoflora of the El Palmar Fm. is represented by mixed environments, such as meso-megathermic grassland with the presence of palm trees in a savanna ecosystem and micro-environments with aquatic plants and bamboo grasses that characterized a stratified forest in humid environments with high water availability. The reconstructed vegetation pattern is composed of a stratified gallery forest changing to temperate savanna, extended along the upper basin of the Uruguay river and occupying the river valley in the middle reach of the basin. The data contribute to the palaeobiodiversity knowledge of Quaternary fluvial sedimentary units of South America. In addition, the results give a better understanding of the evolutionary history of some vegetal communities, and especially the present palm trees of the El Palmar National Park reserve, as part of a relict flora that has inhabited the area since, at least, the Upper Pleistocene. The geological and micro-paleobotanical records of the El Palmar Fm. lead to the inference of general warm and humid conditions during most of the deposition of the formation, probably covering part of the last major interglacial period before the present (MIS 5).

Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies

BackgroundGrass phytoliths are the most common phytoliths in sediments; recognizing grass phytolith types is important when using phytoliths as a tool to reconstruct paleoenvironments. Grass bulliform cells may be silicified to large size parallelepipedal or cuneiform shaped phytoliths, which were often regarded as of no taxonomic value. However, studies in eastern Asia had identified several forms of grass bulliform phytoliths, including rice bulliform phytolith, a phytolith type frequently used to track the history of rice domestication. Identification with a higher level of taxonomic resolution is possible, yet a systematic investigation on morphology of Poaceae bulliform phytoliths is lacking. We aimed at providing a morphological description of bulliform phytoliths of Poaceae from Taiwan based on morphometric measurements in anatomical aspect. The results are important references for paleo-ecological studies.ResultThe morphology of grass bulliform phytoliths is usually consistent within a subfamily; the end profile is relatively rectangular in Panicoideae and Micrairoideae, whereas cuneiform to nearly circular in Oryzoideae, Bambusoideae, Arundinoideae, and Chloridoideae. Bulliform phytoliths were seldom observed in Pooideae. Certain morphotypes are limited to plants growing in specific environments. For example, large, thin, and pointed bulliform phytoliths are associated with wet habitat; Chloridoideae types are mostly from C4 plants occupying open arid places.ConclusionGrass bulliform phytoliths can be identified at least to the subfamily level, and several forms were distinguished within large subfamilies. Previously un-reported silicified cell types, i.e., arm cells and fusoids, and two special trichome phytolith types associated with bulliform phytoliths, were described. Morphometric methods were great tools for delimiting morphotypes; with refined morphological classification the association between forms and habit/habitats was revealed. The knowledge provides new ways to interpret phytolith assemblage data, and it is especially useful when the sediments are enriched in large blocky phytoliths.

Phytoliths indicate environmental changes correlated with facies analysis in a paleo island-lake, Upper Paraná River, Brazil

Phytolith analysis has become a useful tool for paleoenvironmental studies. Phytoliths are produced by plants and are composed of biogenic silica, giving them higher resistance to diagenetic and oxidation processes that commonly occur in tropical sediments. Here, we analyzed the preserved phytolith assemblages in a sedimentary core recovered from an island in the Upper Paraná River. Deposition and preservation of distinctive phytoliths of different vegetation types in the sedimentary facies have provided evidence of the formation of the fluvial island and the floral succession since the Late Pleistocene. Three distinctive phases were described in the island formation. The sandy base (Sr facies) of the core (240 cm) was dated to 14,620 cal yr BP. Most phytoliths in this phase were characteristic of the Podostemaceae family -- aquatic plants adapted to intense water flow. At 97 cm depth, organic sedimentary facies (Fm facies) were dated to 7382 cal yr BP. At this phase, the phytolith assemblage is composed mainly of parallelepipedal bulliform, cuneiform bulliform, and elongate psilate; such morphotypes are primarily produced by grasses. Towards the core top is a layer of massive fine sediments (Vm facies) with greater abundance of plant fragments. The assemblage is composed of short cells, predominantly the bilobate morphotype, which is characteristic of the Panicoideae subfamily (Poaceae) and indicative of soil humidity.