Grass Silica Short Cells Research Articles

Phytolith spectra of the monotypic grass Danthonidium gammiei (Bhide) Hubb in Hook (Danthonioideae) from Northern Western Ghats, India: Taxonomic and environmental significance of its distinctive Bilobates

Grass Silica Short Cell Phytoliths (GSSCPs) are regarded as a potential adjunctive tool for grass subfamily identification owing to their definite morphology and affinity towards certain grass subfamilies. In the present study phytolith spectra of the monotypic genus Danthonidium gammiei (Bhide) Hubb in Hook, collected from northern Western Ghats, Maharashtra is studied in detail for the first time. This grass profusely produces Bilobates along with other GSSCPs and Elongate types. A thorough study is undertaken to find out potential of the Danthonidium gammiei Bilobates in distinguishing this grass from other major Bilobate producing grass sub-families like Panicoideae and Aristidoideae. The possible relationship between Bilobates specific for Danthonidium gammiei and the intensity of rainfall in northern Western Ghats is also discussed here. Statistical analyses (PCA, CA, and CCA) also establish the potential of Bilobate phytoliths in identifying Danthonioideae subfamily and discriminating different rainfall zones of the region.

Phytoliths in bamboos from eastern and north-eastern India: Implications in distinguishing different ecoclimatic conditions and in deciphering Late Holocene climate variability

To develop a phytolith (biogenic silica) reference and to understand the eco-climatic indicative values of some grass silica short cells (GSSCs) occurring in the bamboos (Bambusoideae grasses), one of the chief floral components of eastern and north-eastern parts of India, we studied 44 modern bambusoid grasses and 26 surface soils from different eco-climatic zones covering both the plains and mountainous regions. Of the diverse phytoliths retrieved from the bamboos, Saddle tall and Saddle collapsed were the most abundant types (except in Yushania maling) and these types were also common in surface soil phytolith assemblages of the eastern and north-eastern parts of India. To assess the environmental sensitivity of most consistent morphotypes, we categorized two commonly occurring GSSC morphotypes namely Saddle tall into three groups based on their length and Saddle collapsed into two groups based on their length to width ratio respectively. Pearson’s correlation analysis, principal component analysis (PCA), and redundancy analysis (RDA) were used to understand if these morphotypes could distinguish different eco-climatic conditions. Variability of Saddle tall and Saddle collapsed types (both morphometric and abundance) in bamboos growing in these parts of India is a function of mean precipitation of the wettest quarter (MPWeQ) and mean temperature of the driest quarter (MTDQ). The present results served as a baseline for reevaluating the interpretations of a Late-Holocene fossil phytolith record from the eastern Himalaya further validating the potential of Saddle tall and Saddle collapsed types in reconstructing past climate variability in a wide geographical region.

Taxonomic and environmental significance of Poaceae and Cyperaceae phytoliths from the Northern Territory, Australia

Phytoliths are a valuable tool for reconstructing past grassy ecosystems. However, they are not commonly utilised as a palaeoecological proxy in Australia due to a lack of modern reference material from plants, particularly grasses. This study analyses phytolith reference material from 49 grass and 4 sedge species from the Northern Territory, Australia. This is used to develop a detailed classification scheme and multivariate morphospace analysis to examine taxonomic and ecological patterns of grass silica short cell phytolith (GSSCP) production within the Poaceae (grass) family. The results of detrended correspondence analysis show that grass subfamilies, tribes, and genera in this region can be differentiated through phytolith assemblages, and that these assemblages reflect the environmental conditions associated with various grass taxa. The developed detailed classification system and examination of co-occurrence patterns reduces redundancy of phytolith morphotypes across subfamilies, improving taxonomic and palaeoecological resolution of phytolith assemblages. Finally, based on the results of this study, a detailed scheme is presented for palaeoecological reconstructions in grassy ecosystems of northern Australia.

Chloridoideae grass phytoliths can distinguish two different rainfall zones: A case study from northern parts of Western Ghats, India

Grass silica short cell phytoliths (GSSCPs), which are profusely produced within the grasses are often subfamily-specific and hence may act as one of the reliable plant proxies in deciphering eco-climatic conditions of an area. To assess how reliably grass phytolith morphs can capture the signal of rainfall variations of an area and to overcome the bias caused due to the redundancy and the multiplicity of GSSCPs, some Chloridoid grasses and soil samples from Maharashtra part of the Western Ghats along the west-east rainfall gradient are studied. The study reveals that Saddle are the dominant morphotype produced by the members of this grass subfamily irrespective of the rainfall variations. Surface soil phytolith assemblage revealed that Saddle morphs are inversely proportional to rainfall i.e., they increase with decrease in rainfall and vice versa. Based on this data, regions with MAP >2000 mm and <2000 mm could be separated in the northern Western Ghats. The results of the CCA and PCA also corroborated these observations.

Soil surface grass phytolith morphotypes across bioclimatic gradients and biomes at about latitude 29°S in South Africa

This study examines the distribution patterns of grass subfamilies and their diagnostic silica phytoliths along a transect running approximately at latitude 28° S in South Africa. The transect encompasses 77 surface samples collected along moisture and temperature gradients, across 6 biomes and 39 ecozones, and spanning elevations between near-sea level and over 2253 m. This study tests the relation between the distribution and density of grass subfamilies and the proportions of their diagnostic grass silica short cell phytoliths (GSSCP) representing them, and how these proportions correlate with five climatic variables (mean temperature of the wettest quarter, annual precipitation, precipitation of the wettest quarter, precipitation variability, and the aridity index). The results suggest that C3-grass diagnostic GSSCP morphotypes increase with a decline in temperature in the wettest quarter, occurring in areas receiving mostly winter rain or at high elevations in areas of summer rain. Of the C4 grass subfamilies, the Panicoideae increase with summer precipitation and low precipitation variability, while the Aristidoideae-Stipagrostis the opposite. The distribution of Chloridoideae depends on complex changes in all climatic variables, suggesting aridity gradients only in the eastern half of the transect. In view of the data, this study reviews the usefulness of the phytolith humidity-aridity index (Iph) and the water stress index (Fs) and proposes the Panicoideae index (PI) and Stipagrostis index (SI) as indicator of aridity and high precipitation variability in southern Africa.

First record of phytolith assemblages from the Salto Ander Egg Formation (Late Pleistocene). Palaeoenvironment inferences in the Last Interglacial Stage in southwestern Mesopotamia (Entre Ríos, Argentina)

This contribution aims to describe the first palaeobotanical record of the Late Pleistocene in the Salto Ander Egg Formation (SAEF) through the analysis of phytolith assemblages. The microremains association allowed us to characterise the palaeoenvironmental conditions for these deposits and to complete the palaeobotanical record for the stratigraphic sequence of the Late Pleistocene in southwestern Entre Ríos province, Argentina. The Salto Ander Egg Formation is composed of fluvial deposits with a well-defined floodplain and channel facies dated at ages ranging from 120 to 60 ky. The phytolith content of the unit was analysed along two stratigraphic sections in outcrops exposed on the cliffs of the fluvial valleys located in the drainage basin of La Ensenada creek. The vegetation composition was interpreted principally from the proportions of very frequent and frequent morphotypes in the phytolith assemblages and was grouped in plant functional group affinities: “non-GSSCPs” (diagnostic grass phytoliths); “GSSCPs” (grass silica short cell phytoliths); “Woody dicots” and “Palms”. The phytolith assemblages describe a palaeoflora composed of a continuous herbaceous stratum of C3/C4 grasses, although C3 might have been more significant accompanied by isolated trees and palms in an open savanna physiognomy, probably with a temperate/warm climate with low rainfall and average to high temperatures.

Phytolith Assemblages as a Promising Tool for Quantitative Canopy Coverage Reconstruction in Subtropical Forests, China.

This study investigates the reliability of phytolith assemblage analysis for characterizing subtropical vegetation and explores the potential for using these modern phytolith–vegetation relationships for paleoenvironmental interpretation in southeastern China. The samples were collected from five common subtropical vegetation communities in the Daiyun Mountains, southeastern China, with the above-ground vegetation recorded at each plot. Constrained ordination analysis was used to determine the most important factor governing the variations in phytolith assemblages that could be quantitatively reconstructed with weighted averaging partial least squares regression (WAPLS). The relationship between modern phytolith assemblages and the parent vegetation, as well as production, dispersal, and taphonomic processes, was discussed. Results demonstrated that the main subtropical biomes in southeastern China could be well distinguished by soil phytolith assemblages. In particular, the overall amount of tree coverage was well represented by topsoil phytolith assemblages. Grass silica short cell phytoliths (GSSCP) tended to occur in higher proportions in open habitats (shrub-meadow) at higher elevations, whereas non-grass phytolith morphotypes attained higher frequencies under mixed and broadleaf forests at lower elevations. Human-induced deforestation might increase the frequency of GSSCP within the bulk phytolith assemblage. Our results constitute the primary phytolith reference data for the subtropical zone in southeastern Asia where vegetation change during the Holocene period, particularly forest shifts, anthropogenic deforestation, and early agriculture are poorly documented.

Characterising Dutch forests, wetlands and cultivated lands on the basis of phytolith assemblages

Abstract Palaeoecological reconstructions in the Netherlands are commonly based on pollen and macrofossil analysis, but can be limited if the preservation of organic material is poor. Phytoliths, biogenic silica, do not have this limitation and preserve in settings where other macro- and microfossils do not. Little is known about how phytolith assemblages preserved in soils and sediments reflect the parent vegetation in north-western European systems, so it is currently difficult to contextualise past environments. Here, we characterise phytolith assemblages for soil samples recovered from three major vegetation types in the Netherlands to provide reference data for future reconstructions of past vegetation change. We collected 42 soil surface samples from forests, wetlands and agricultural fields across the Netherlands and characterised the phytolith assemblages they contained. We identified the different phytolith morphotypes and quantified the percentages and concentrations (#phytoliths/cm3 soil) in each sample. We used non-metric multidimensional scaling to assess the variation in phytolith assemblage composition within, and between, the three vegetation types. The phytolith assemblages analysed from the forests, wetlands and agricultural fields were clearly distinguishable from each other. Agricultural fields were dominated by four phytolith morphotypes of grass silica short cells (GSSCs): rondel (tabular), cross type 1 (&gt;15 µm), rondel (elongated) and disturbance or crop phytoliths. Forests settings had significantly higher amounts of different arboreal phytoliths (large and small spheroid rugose) compared with other vegetation types. Wetlands could be identified by significantly higher amounts of Cyperaceae phytoliths (papillate) and other GSSCs (saddle and bilobates with thick castula). Phytolith assemblages could distinguish different subtypes of vegetation within forest and wetland areas, while differences between agricultural systems could not be identified. Our study demonstrates that phytoliths preserved in soils or sediments can be used to separate major vegetation types across the Netherlands. Thus, these results support the hypothesis that phytoliths can be used to infer past environmental conditions in palaeoecological reconstructions. We suggest that future work should: (1) focus on characterising which phytolith types are produced by the commonest tree, wetland, shrub and herb species in the Netherlands and (2) characterise phytolith assemblages across a wider array of vegetation types in north-western European systems to increase the capability for quantitative reconstructions using phytolith assemblages.

3D shape analysis of grass silica short cell phytoliths: a new method for fossil classification and analysis of shape evolution.

Fossil grass silica short cell phytoliths (GSSCP) have been used to reconstruct the biogeography of Poaceae, untangle crop domestication history and detect past vegetation shifts. These inferences depend on accurately identifying the clade to which the fossils belong. Patterns of GSSCP shape and size variation across the family have not been established and current classification methods are subjective or based on a 2D view that ignores important 3D shape variation. Focusing on Poaceae subfamilies Anomochlooideae, Pharoideae, Pueliodieae, Bambusoideae and Oryzoideae, we observed in situ GSSCP to establish their orientation and imaged isolated GSSCP using confocal microscopy to produce 3D models. 3D geometric morphometrics was used to analyze GSSCP shape and size. Classification models were applied to GSSCP from Eocene sediments from Nebraska, USA, and Anatolia, Turkey. There were significant shape differences between nearly all recognized GSSCP morphotypes and between clades with shared morphotypes. Most of the Eocene GSSCP were classified as woody bamboos with some distinctive Nebraska GSSCP classified as herbaceous bamboos. 3D morphometrics hold great promise for GSSCP classification. It accounts for the complete GSSCP shape, automates size measurements and accommodates the complete range of morphotypes within a single analytical framework.

Bilobate phytolith size matters for taxonomical and ecological identification of Chad grasses: A case study on 15 species

The Poaceae family produces diagnostic phytoliths commonly called Grass Silica Short Cell Phytoliths (GSSCP), of which shapes and sizes are very distinguishable from those produced by other plant families. Grass Silica Short Cell Phytoliths are usually classified into four main categories: the rondels, bilobates, crosses, and saddles. Among them, the bilobates have in common a general "dumbbell" shape consisting of two lobes inter-connected by a shank. They represent the dominant morphotypes observed in the leaf tissues of many Panicoideae grass species. Besides, they tend to often be related to this subfamily in the fossil record, especially when they occur in large amounts. Several studies based on modern African grasses have however demonstrated that bilobates were also abundantly produced by a few members of the Aristidoideae, Chloridoideae, and Oryzoideae grass subfamilies which, like Panicoideae, are today mainly distributed in tropical low-altitude areas. The relationship between bilobates and Panicoideae is thus not so direct in the tropics. As a result, it can lead to significant misinterpretations when applied to paleoenvironmental and archaeological surveys.This study investigates variations in the size of bilobate phytoliths in 15 African grass species, including eight Panicoideae, three Aristidoideae, two Chloridoideae, and two Oryzoideae, with the intention to explore new alternatives for refining their identification in the past deposits of tropical Africa. Different statistical analyses (Principal Component Analysis, Mann–Whitney tests, decisional trees) applied to the previous dataset allowed testing whether: (i) bilobate length and width significantly vary between grass species; (ii) these variations (if so) have the potential to be used as taxonomical and/or ecological proxies.Our analyses confirm that bilobate length is significant in discriminating dry-adapted Aristidoideae and Chloridoideae species from the other sub-families. In particular, a bilobate base longer than 25 μm is almost exclusively observed for Aristidoideae and Chloridoideae, which is in agreement with previous studies. Although subject to less variations, the length/width of bilobate shanks and the average length of their lobes appear significantly useful to refine grass taxonomical identification and discriminate <120 cm-high grasses from taller grasses. Yet, it seems that the key towards a robust identification of bilobate phytoliths involves considering the size parameters.

Phytoliths in modern plants and soils from Klasies River, Cape Region (South Africa)

The archaeological site of Klasies River is famous for the richness of its Middle Stone Age deposits, which offer the opportunity to document behaviors of early modern humans in Africa, as well as the paleoenvironmental context of their occupation of the area during the late Pleistocene. The Main Site deposits (dated to ca. 115 to 55 ka) include botanical remains such as seeds and charcoal, which suggests that micro-plant particles like phytoliths could also have been deposited. Yet, no phytolith reference collection based on both modern plant and soil material has been produced for Klasies River, which complicates attempts of phytolith analysis of the site's deposits. One of our challenges was therefore to initiate a new and comprehensive phytolith reference collection of modern plants and soils occurring today in the vicinity of Klasies. For this purpose, we processed phytoliths from 24 modern plant specimens and 16 soil samples from different vegetation patches, all located today in a perimeter <5 km2 around the Main Site. Our analyses indicate that ovate/orbicular and/or tabular polygonal phytoliths are the most recurrent and abundant morphotypes (>53% and up to 94%) produced in the leaf tissues of the Anacardiaceae, Asteraceae, Celastraceae, Ericaceae, Proteaceae, and Vitaceae species we studied, which are all eudicotyledoneous taxa. Regarding the Cyperaceae, Restionaceae, and one of the Proteaceae species (Leucadendron spissifolium, a fynbos shrub), they each produce distinct phytolith assemblages: the Restionaceae leaf/culm assemblage is dominated by psilate and decorated globular/spheroid phytoliths (94%), whereas the Cyperaceae leaf/culm content and the Proteaceae leaf content are both dominated by silicified papillae (-like) bodies (54% and 63%, respectively). Besides, both globular/spheroid and papillae (-like) phytoliths account for 34% and 8% in the fynbos soil collected. Our analyses also show that ovate/orbicular and/or polygonal phytoliths occur in very small amounts (<2%) in modern soils of the area although they are numerous in most of the eudicotyledoneous leaf tissues we analyzed. Conversely, grass silica short cell phytoliths are found abundantly in the soils collected in close proximity to the Main Site (>66%), where grasses do however occur sparsely in the current vegetation.

Paleovegetation changes accompanying the evolution of a riverine system at the BK paleoanthropological site (Upper Bed II, Olduvai Gorge, Tanzania)

Paleovegetation studies are essential to ecologically frame hominin evolution. The analysis of the phytolith content of 22 paleosol samples collected along the vertical sequence of the channel containing the BK (Bell's Korongo) archaeological levels, provided evidence of the paleovegetation that accompanied the evolution of the riverine system that formed this site 1.353millionyears ago, when climate was particularly arid. The analysis reveals the abundance of forest indicator phytoliths (46% to 92% of the assemblages), rare grass silica short cells and sedges phytoliths (up to 15% of assemblages), and palms (up to 10% of the phytolith assemblages). The vegetation of the BK fluvial system was therefore characterized by abundant woody plants. It did not vary significantly diachronically in the period of time under scrutiny. The alluvial paleovegetation corresponds well to the fluvial dynamic that formed BK, including the presence of sterile samples recovered in areas where the water traction changed the soils frequently. This spot of dense paleovegetation together with the fluvial watercourse (in a paleolandscape likely dominated by sparse/open vegetation) could have been attractive, seasonally, for animals and hominins.

An Early Pleistocene Phytolith Record from Wonderwerk Cave, Northern Cape, South Africa

Grass silica short cell phytoliths were sampled from the four lowermost archaeological strata in excavation 1 at Wonderwerk Cave and offer an independent record of climatic change during an episode of Early Stone Age hominin occupation at the cave. Linked to differences in growing season temperature and the geographic distribution of C3 and C4 grasses in southern Africa, fossil grass phytoliths were used to trace palaeoenvironmental shifts at the site. The results suggest that Early Pleistocene environmental conditions at the cave fluctuated: between wetter and drier summer–rainfall growing conditions (C4) towards the end of the Olduvai subchron and the beginning of the subsequent interval of reversed polarity, to mostly dry and cooler winter–rainfall growing conditions (C3), that continued throughout the interval. It ended with a shift towards increased summer rainfall aridity at around one million years ago. The fluctuation between markedly wetter and drier C4 conditions at the cave (NADP-me grass types vs. NAD-me grass types) does not support the premise that the expansion of C4 grasslands was always coupled with increased aridity.

Modern soil phytolith assemblages used as proxies for Paleoscape reconstruction on the south coast of South Africa

South Africa continues to receive substantial attention from scholars researching modern human origins. The importance of this region lies in the many caves and rock shelters containing well preserved evidence of human activity, cultural material complexity and a growing number of early modern human fossils dating to the Middle Stone Age (MSA). South Africa also hosts the world's smallest floral kingdom, now called the Greater Cape Floristic Region (GCFR), with high species richness and endemism. In paleoanthropological research, improving our capacity to reconstruct past climatic and environmental conditions can help us to shed light on survival strategies of hunter–gatherers. To do this, one must use actualistic studies of modern assemblages from extant habitats to develop analogies for the past and improve paleoenvironmental reconstructions. Here, we present a phytolith study of modern surface soil samples from different GCFR vegetation types of the south coast of South Africa. In this study, the phytolith concentration and morphological distribution are related to the physicochemical properties of soils, the environmental conditions and the characterization of the vegetation for the different study areas. Our results show that phytolith concentration relates mostly to vegetation types and the dominant vegetation rather than to the type of soils. More abundant phytoliths from Restionaceae and woody/shrubby vegetation are also noted from fynbos vegetation and grass phytoliths are a recurrent component in all the vegetation types in spite of being a minor component in the modern vegetation. The grass silica short cells from these plants, however, suggest a mix of C3 and C4 grasses in most of the vegetation types with a major presence of the rondels ascribed to C3 grasses. The exceptions are riparian, coastal thicket and coastal forest vegetation, which are characterized by the dominance of C4 grass phytoliths.

Diatom, phytolith, and pollen records from a 10Be/9Be dated lacustrine succession in the Chad basin: Insight on the Miocene–Pliocene paleoenvironmental changes in Central Africa

Abstract A discontinuous 200 m-long borehole drilled in the Bol Archipelago (13°N, Lake Chad) provided 25 samples, which were dated using the 10 Be/ 9 Be method and analyzed for their micro-biological content. The dating provided ages ranging from 6.3 ± 0.1 to 2.6 ± 0.1 Ma, a period contemporaneous with the Pliocene fossil localities located in the current Djurab desert of Chad (16–17°N). Well-preserved diatom assemblages first occurred at 4.7 ± 0.1 Ma and were dominated by the freshwater planktonic genera Aulacoseira and Stephanodiscus until the end of the Pliocene. This supports the recurrence of lacustrine conditions at Bol during all the Pliocene. The presence of pelite and argillaceous deposits in the core before 4.7 ± 0.1 Ma, however, suggests that the lake settled earlier, at least since 6.3 ± 0.1 Ma. The abundance of Afromontane pollen taxa at 4.2 ± 0.1 Ma and the occurrence of trapeziform polylobate phytoliths throughout the sequence suggest significant vegetation inputs from the southern highlands, while the importance of kaolinite in the clay sediments indicates a water supply predominantly from the south during the Pliocene. Phytolith assemblages are all dominated by lobate grass silica short cells and by blocky and elongate types, which attest to the presence of herbaceous-dominated vegetation around Bol and/or in the southern drainage basin during the Pliocene. This result is also supported by the pollen assemblage described at 4.2 ± 0.1 Ma, which shows highest affinity for the savanna biome. Moreover, low values for the Xerophytic grass phytolith index indicate the presence of humid-loving (mesophytic and aquatic) grass communities in this vegetation. At last, significant variations in the abundance of blocky and elongate phytoliths are indicative of local alternations of fully lacustrine and marshy conditions at Bol. Particularly between 3.6 and 2.7 Ma, the abundance of silicified bulliform cells combined with the absence of diatoms support a significant lacustrine reduction at Bol favoring the increasing of local marshy vegetation.

Grass inflorescence phytoliths of useful species and wild cereals from sub-Saharan Africa

Dendritic phytoliths that precipitate in grass inflorescences are often used in archaeology to trace the use of cereals (i.e. grasses harvested for their edible grain) and their domestication by early human societies. High amounts of these morphotypes are sometimes interpreted in terms of cereal accumulation in archaeological contexts. In sub-Saharan Africa, few cereals were domesticated during the mid-Holocene, but many wild grasses are still largely harvested by modern societies for food. The harvesting of wild cereals is also considered as one of the first stages toward early grass domestication. To evaluate how well dendritic phytoliths and/or other phytoliths produced in the grass inflorescences could help trace the use of wild cereal grains in sub-Saharan Africa, we analyzed the phytolith content of 67 African species (including 20 wild cereals), and 56 modern soils. We used test-value analysis and ANOVA to evaluate how well grass inflorescences could be distinguished from leaf/culm parts based on their phytolith content. We also measured the abundances of these phytoliths in natural soils from sub-Saharan Africa to provide a benchmark percentage abundance above which anthropogenic accumulation may be suspected in archaeological deposits. Our results confirm that, although rondel type phytoliths are abundant, only the dendritic phytolith morphotype is exclusive to the grass inflorescences. Yet, dendritic phytoliths do not occur in all species. They happen to be most frequent and found in greatest abundance (>34% relative to total phytolith count) in Panicoideae grasses (Sehima ischaemoides, Sorghastrum stipoides, and Sorghum purpureo-sericeum), and in one Eragrostideae species (Eragrostis squamata), which are not considered cereals. Inflorescences of the wild African cereals studied here do not happen to be particularly rich in dendritics (<7% in average). Finally, dendritics are rare in modern natural soils (<1% relative to total phytolith count, <3% relative to sum of grass silica short cells plus dendritics), even under stands of rich dendritic producers. We conclude that dendritic phytoliths may be used for tracing remarkable deposits of grass inflorescences at archaeological sites in sub-Saharan Africa, but are not exclusive to domesticated or wild cereals. Abundances of dendritics >>3% relative to sum of grass silica short cell phytoliths plus dendritics are likely to indicate anthropogenic accumulation of grass inflorescences. Yet, the absence or low abundance of dendritic phytoliths in archaeological deposits may not always indicate the absence of anthropogenic accumulation of grass inflorescence material.

Estimating phytolith influx in lake sediments

So far, no phytolith extraction protocols have been tested for accuracy and repeatability. Here we aim to display a phytolith extraction method combining the strengths of two widely used protocols, supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations. Phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age–depth models make it possible to calculate phytolith influxes (phytolith numbers per cm2per yr). Analysis of replicates confirmed the statistical robustness, the repeatability and the very few biases of our extraction technique for small phytoliths, since the relationship between grass silica short cells and microspheres was kept stable. Furthermore, we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations. The minimum number of items (i.e., phytoliths plus silica microspheres) that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres (R) and is minimized when R=1. Nevertheless, we recommend using ratios R≤1 in order to avoid having the counting process become excessively time-consuming, because microspheres are easier to identify and count than phytoliths.

C3 Poaceae and Restionaceae phytoliths as potential proxies for reconstructing winter rainfall in South Africa

The main objective of this research is to identify graminoid phytolith morphotypes with potential as proxies for reconstructing past winter rainfall in South Africa. The main argument of this study is that phytolith proxies for winter-rainfall maxima should be found among native graminoids abundant in the Cape Region, where most of the precipitation occurs in the cooler part of the year. Vegetation surveys indicate that C3 Poaceae (cool-season grasses) and Restionaceae (restios) are abundant graminoids in the winter rainfall zone (WRZ). Therefore, the frequencies of diagnostic graminoid morphotypes of each of these two groups are correlated independently with both percent and amount of winter rainfall (defined here as the sum of April-September precipitation). The phytolith assemblages used for this study were collected from soils along two transects across the winter (WRZ), all-year (ARZ), and summer (SRZ) rainfall zones of South Africa.The study shows that the highest frequencies of the diagnostic C3 grass silica short-cell (GSSC) morphotypes increase with winter rainfall. Although considerable numbers of C3-GSSC morphotypes occur in samples at elevation above 1500m in the SRZ, their frequencies are lower than in the samples of the WRZ and ARZ. Correlation is noteworthy only when all the C3-GSSC morphotypes are grouped. Individual C3-GSSC morphotypes and groups of GSSC morphotypes linked to particular C3 grass subfamilies (Pooideae, Ehrhartoideae and Danthonioideae) correlate poorly with winter rainfall incidence. The results of this study also suggest that Restionaceae phytoliths are good indicators of winter rainfall, but because Restionaceae occur mainly in oligotrophic soils in association with fynbos vegetation, the use of their phytoliths in paleorainfall reconstruction should be taken with care. Despite certain limitations, this research shows that the use of C3-GSSC and Restionaceae phytolith has a strong potential for reconstructing the extent of winter rainfall during the colder stages of the Pleistocene. However, to achieve this objective a study with a larger number of reference material and tighter geographical sampling is needed.

Phytolith signal of aquatic plants and soils in Chad, Central Africa

To identify the phytolith signal of lacustrine environments, which are prone to preserving faunal remains including hominins, we analyzed the phytolith content of 46 grass and sedge species, and of 26 soil and mud samples. The samples were collected in Chad (Central Africa), in the Sudanian and Sahelian phytogeographical zones, near temporary and permanent water-bodies (including Lake Chad) and in grass-dominated biomes on well-drained soils. Altogether, we observed and counted separately 80 different phytolith types, including 38 grass silica short cells (GSSCs). Phytolith type diversity and relative abundances were analyzed in the botanical specimens to improve the phytolith taxonomic resolution. For the Poaceae, we used a value-test analysis to identify significant cohorts of phytoliths to characterize aquatic, mesophytic, and xerophytic species. Our results show that the abundance of Cyperaceae in swampy areas may be deduced from the combined abundance of blocky and elongate phytolith types, but not by the typical silicified Papillae phytoliths, which were barely found preserved in the soil/mud. The abundance of aquatic Poaceae near water-bodies is inferred from the presence and abundance of a cohort of eight GSSC types (including notably several trapeziform GSSCs within the bilobate, cross, and saddle categories), which averages 42% in the mud samples, but only 23% and 14% in the samples from the Sudanian and Sahelian zones, respectively. The characterization is unclear for mesophytic grasses, but obvious for xerophytic grasses whose abundance in the Sahelian grasslands is inferred from the presence and abundance of a cohort of five GSSC types (mainly tabular saddles), which averages 50% in the soil samples from the arid Sahelian zone, and <19% in the more humid Sudanian and swamp samples. In conclusion, considering the full morphological diversity of grass silica short cell phytoliths (rather than just the broad morphological categories) allows greater discrimination of the aquatic environments. Such approach is therefore required for analyzing vegetation distribution at a local scale.

The spread of grass-dominated habitats in Turkey and surrounding areas during the Cenozoic: Phytolith evidence

The arrival of hipparionine horses in the eastern Mediterranean region around 11 Ma was traditionally thought to mark the simultaneous westward expansion of savanna vegetation across Eurasia. However, recent paleoecological reconstructions based on tooth wear, carbon isotopes, and functional morphology indicate that grasses played a minor role in Late Miocene ecosystems of the eastern Mediterranean, which were more likely dry woodlands or forests. The scarcity of grass macrofossils and pollen in Miocene floras of Europe and Asia Minor has been used to support this interpretation. Based on the combined evidence, it has therefore been suggested that Late Miocene ungulate faunal change in the eastern Mediterranean signals increased aridity and landscape openness, but not necessarily the development of grass-dominated habitats. To shed new light on the Miocene evolution of eastern Mediterranean ecosystems, we used phytolith assemblages preserved in direct association with faunas as a proxy for paleovegetation structure (grassland vs. forest). We extracted phytoliths and other biogenic silica from sediment samples from well-known Early to Late Miocene (∼ 20–7 Ma) faunal localities in Greece, Turkey, and Iran. In addition, a Middle Eocene sample from Turkey yielded phytoliths and served as a baseline comparison for vegetation inference. Phytolith analysis showed that the Middle Eocene assemblage consists of abundant grass phytoliths (grass silica short cells) interpreted as deriving from bambusoid grasses, as well as diverse forest indicator phytoliths from dicotyledonous angiosperms and palms, pointing to the presence of a woodland or forest with abundant bamboos. In contrast, the Miocene assemblages are dominated by diverse silica short cells typical of pooid open-habitat grasses. Forest indicator phytoliths are also present, but are rare in the Late Miocene (9–7 Ma) assemblages. Our analysis of the Miocene grass community composition is consistent with evidence from stable carbon isotopes from paleosols and ungulate tooth enamel, showing that C 4 grasses were rare in the Mediterranean throughout the Miocene. These data indicate that relatively open habitats had become common in Turkey and surrounding areas by at least the Early Miocene (∼ 20 Ma), > 7 million years before hipparionine horses reached Europe and arid conditions ensued, as judged by faunal data.