Silica Phytoliths Research Articles

Phytoliths in plants and soils of the interior Pacific Northwest, USA

Phytoliths are a useful paleoproxy in the arid environments. This modern analog study assessed variability of silica phytoliths in 38 species of plants and 58 modern soil samples from 24 locations in the interior Pacific Northwest. Phytoliths were grouped into 20 broadly defined morphotypes based on their 3D shapes under light microscope and presumed anatomical origin within the plant. Grasses (all C 3) have most diverse forms. Most examined conifers, sedges and some shrubs produce identifiable phytoliths as well. Eight different community types can be distinguished based on their modern phytolith record in soils, including shrublands, four regional grassland types, and three forest types. Low percentages of grass phytoliths and high incidence of non-grass forms correspond to forest vegetation in the region today, while certain grass phytoliths allow further differentiation among different grasslands. Phytolith assemblages were further compared to 5 environmental variables, including elevation, mean annual temperature, mean annual precipitation, a moisture index and a growing-degree days index. Some morphotypes tend to occur within relatively narrow environmental windows, which could enable direct paleoenvironmental inferences from phytoliths in geological sediments from the region.

Pervasiveness of phytoliths in prehistoric southwestern diet and implications for regional and temporal trends for dental microwear

Our previous analysis of phytolith content of coprolites showed that calcium oxalate phytoliths from desert food plants caused dental microwear among prehistoric Texas hunter-gatherers. We demonstrated that phytoliths from desert succulents were ubiquitous and abundant in hunter-gatherer coprolites. We found that calcium oxalate phytoliths were harder than human dental enamel. We concluded that phytoliths from desert succulent plants caused dental microwear and hypothesized that such dental microwear would be common in other desert hunter-gatherer and horticultural peoples. Presented here are further analyses of phytoliths from coprolites. Two additional hunter-gatherer sites and three Ancestral Pueblo (Anasazi) horticultural sites are included in this study. Calcium oxalate phytoliths are ubiquitous in coprolites from hunter-gatherer sites in the Mojave Desert and the Colorado Plateau. For the three Ancestral Pueblo sites, calcium oxalate phytoliths from desert succulents (agave family and cactus family) are the most common types of phytoliths encountered. However, silica phytoliths are also present in Ancestral Pueblo coprolites. The data demonstrate that phytoliths from non-cultivated desert plants were a source of dental microwear for the pre-maize Archaic hunter-gatherer bands and maize-reliant Ancestral Pueblo villages.

Evidence for the control of phytolith formation in Cucurbita fruits by the hard rind (Hr) genetic locus: Archaeological and ecological implications.

Many angiosperms, both monocotyledons and dicotyledons, heavily impregnate their vegetative and reproductive organs with solid particles of silicon dioxide (SiO(2)) known as opaline phytoliths. The underlying mechanisms accounting for the formation of phytoliths in plants are poorly understood, however. Using wild and domesticated species in the genus Cucurbita along with their F(1) and F(2) progeny, we have demonstrated that the production of large diagnostic phytoliths in fruit rinds exhibits a one-to-one correspondence to the lignification of these structures. We propose that phytolith formation in Cucurbita fruits is primarily determined by a dominant genetic locus, called hard rind (Hr), previously shown to code for lignin deposition. If true, this evidence represents a demonstration of genetic control over phytolith production in a dicotyledon and provides considerable support to hypotheses that silica phytoliths constitute another important system of mechanical defense in plants. Our research also identifies Hr as another single locus controlling more than one important phenotypic difference between wild and domesticated plants, and establishes rind tissue cell structure and hardness under the effects of Hr as an important determinant of phytolith morphology. When recovered from pre-Columbian archaeological sites, Cucurbita phytoliths represent genetically controlled fossil markers of exploitation and domestication in this important economic genus.

Reconstruction of the late Pleistocene grassland of the Columbia basin, Washington, USA, based on phytolith records in loess

Silica phytoliths preserved in three loess sections in southeastern Washington State revealed a 100 000-year history of the Columbia Basin grassland. Changes in the proportion of different morphotypes indicate large shifts in vegetation composition during the last 100 ka. A low-elevation section (677 m asl) near the center of the basin provided a record of alternating xeric Festuca–Poa and mesic Festuca–Koeleria grassland. The middle-slope section (1095 m asl) supported Picea–Abies or Pinus ponderosa forest or non-analog parkland at different times. Some trees were present at or near the site even during the Last Glacial Maximum. The highest site (1220 m asl) supported Stipa-, Festuca- and Poa-dominated grassland with some Artemisia shrub during most of the late Pleistocene, but supports a coniferous forest today. Variations in vegetation can be explained as a response to changes in large-scale climatic controls. Grasslands and shrub steppe were apparently more widespread and forests more restricted than today during the marine isotope stages 2 and 4, probably as a result of cooler and drier conditions. The three new records are well correlated with previously published paleo-reconstructions based on phytolith, cicada burrow and stable isotope data from a nearby KP-1 loess section, Carp Lake pollen record, and global ice volume variations.

The oxygen isotopic compositions of silica phytoliths and plant water in grasses: implications for the study of paleoclimate

Information about climatic conditions during plant growth is preserved by the oxygen-isotope composition of biogenic silica (phytoliths) deposited in grasses. The oxygen-isotope composition of phytolith silica is dependent on soil-water δ 18O values, relative humidity and evapotranspiration, and temperature during plant growth. Phytolith and plant-water δ 18O values for C3 ( A. breviligulata) and C4 ( C. longifolia) grasses from natural and greenhouse sites in southwestern Ontario were used to compare the isotopic fractionation between biogenic silica and water in various parts of these living plants. For non or weakly transpiring tissues (rhizomes, stems, sheaths) in both grass species, the Δ 18O silica-plant water remained constant at ∼34‰, and the δ 18O and δD values of plant water collected from pre-dawn and mid-day samplings showed little variation. These plant waters were only slightly enriched in 18O and D relative to water provided to the grasses. Isotopic temperatures calculated from the silica and plant-water isotopic data matched measured growing temperatures for the region. By comparison, the upper leaf water was extremely enriched in oxygen-18 and deuterium at maximum rates of transpiration relative to water from non-transpiring tissues, as were the calculated, steady-state values for leaf-water δ 18O and δD. Silica produced in the transpiring tissues (leaf, inflorescence) has higher δ 18O values than silica from non-transpiring tissues, but the enrichment is modest compared to upper leaf water under mid-day conditions. Leaf phytoliths have formed from plant water typical of average conditions in the lower leaf, where the extreme 18O-enrichment is not encountered. C. longifolia was also collected from Alberta and Nebraska, where growing conditions are different from southwestern Ontario. Phytoliths at all three sites have a similar pattern of δ 18O values within the plants, but the isotopic separation between leaf and stem silica increases from 4 to 8‰ as average relative humidity decreases. The difference between actual growing temperature and that calculated using measured δ 18O values for stem silica and local meteoric water became progressively larger as relative humidity decreased, likely because of evaporative 18O-enrichment of soil water. Such effects are most pronounced in arid environments and pertinent in grasslands where much of the active rooting zone can be situated at the shallower depths most affected by the 18O-enrichment of soil water.

Identifying inflorescence phytoliths from selected species of wheat (Triticum monococcum, T. dicoccon, T. dicoccoides, and T. aestivum) and barley (Hordeum vulgare and H. spontaneum) (Gramineae)

Analysis of microfossil silica phytoliths is becoming an increasingly important research tool for taxonomists, archaeobotanists, and paleoecologists. Expanded use of phytolith analysis by researchers is dependent upon development of phytolith systematics. In this study phytoliths produced by the inflorescence bracts from four species of wheat, Triticum monoccocum, T. dicoccon, T. dicoccoides, and T. aestivum, and two species of barley, Hordeum vulgare, and H. spontaneum, were analyzed using computer-assisted image and statistical analysis with the intent to develop taxonomic tools to distinguish among the taxa. A classification key based on significant differences among the mean morphometries of the inflorescence phytoliths produced by each species was created and tested. Discriminant analysis of the morphometries of several morphotypes of phytoliths was also conducted to determine whether this computer-assisted statistical procedure could be used as another method to classify the taxa and to determine which morphotypes have measurements that can best be used in discriminant functions. Test results indicated that, at the genus level, both the classification key and discriminant analysis of certain morphotypes of phytoliths were relatively reliable tools for distinguishing among phytoliths produced in the inflorescence bracts of the taxa considered. For distinguishing among the taxa at the species level, the classification key was most reliable. Of the discriminant analyses tested, that based on all the phytolith morphotypes combined was more reliable than those based on only one morphotype.

Human dental microwear caused by calcium oxalate phytoliths in prehistoric diet of the lower Pecos region, Texas.

Recent research demonstrates that silica phytoliths of dietary origin are associated with microwear of human teeth. Previous research has shown that severe enamel microwear and dental wear characterizes Archaic hunter-gatherers in the lower Pecos region of west Texas. Calcium oxalate crystals are especially common in Archaic coprolites. The vast majority are derived from prickly pear and agave, which were the dietary staples in west Texas for 6,000 years. The calcium oxalate phytoliths are harder than enamel. Therefore, calcium oxalate crystals are the most likely source of previously documented dental microwear and wear in the lower Pecos region.

Drainage-line silcretes of the Middle Kalahari: an analogue for Cenozoic sarsen trains?

This paper describes models put forward to explain the development of silcretes within drainage lines at the distal end of the Okavango Delta system in the Middle Kalahari of Botswana, and proposes that they provide an analogue for the formation of sarsen stones within sarsen trains. The models describe silcrete formation in shallow pans situated within river valleys, with silicification resulting from the accumulation of fluvial inputs of clastic material, silica from groundwater and additions of silica phytoliths from aquatic vegetation in seasonal pools. It is suggested, on the basis of macro- and micromorphological comparisons, that sarsens in the Clatford Bottom area of Wiltshire formed by this mechanism. The sarsens would have originally formed a spatially-limited linear silcrete body and would have then accumulated within contemporary valleys during the course of landscape evolution. The implications of this model for the environmental conditions associated with sarsen formation and the likely timing of silicification are subsequently discussed. It is concluded that the geomorphological setting of sarsen formation may have been more important than climatic conditions at the time(s) of silicification.

Actividad antrópica en el Neolítico antiguo catalán a través del análisis micromorfológico

On the basis ofmicromorphological analysis of the sediment of an archaelogical site, this study aims to show that it is possible to extract data referring to human activity. We focus on three sites with sequences corresponding to the early Neolithic in Catalonia, Parco, Guineu and Vidre caves. These analyses demonstrate there was a great increase in elements of human origin: charcoal and ash, silica phytoliths, coprolites, fragments of bone and pottery, and fragments of mud with plant impressions. The diagnostic elements of this period are the long silica phytoliths (gramineae) and the coprolites of herbivorous animals (in general ovicaprines). On the basis of this evidence we hypothesis that these occupations reflect the early practice of animal stabling.

Phytolith analysis on dental calculus, enamel surface, and burial soil: Information about diet and paleoenvironment

Silica phytoliths (microscopic remains originating in plant tissues) have been identified on the enamel surface and dental calculus of a sample of teeth selected from well preserved skeletons from a Late Roman necropolis in Tarragona (Spain). Phytoliths were observed by scanning electron microscopy (SEM) and their siliceous nature was confirmed by X-ray microanalysis. The phytoliths were compared to those of soil samples from both the areas of the tombs corresponding to the abdomen and the periphery of the skeletons, and were classified taxonomically by comparison with a large collection of silica particles from modern plants in the Mediterranean area. Most of the phytoliths identified on the enamel and the dental calculus belong to the family of Poaceae, while the phytoliths from the abdominal area belong to Poaceae, Leguminosae, Cyperaceae, and Chenopodiaceae. Results are concordant with archaeological, ecological, and historical data from the same site, and with the human Mediterranean diet. If done properly, the study of phytoliths can provide direct information about the vegetable diet of past human populations, and could be applied to the study of human fossils. © 1996 Wiley-Liss, Inc.

Phytolith analysis on dental calculus, enamel surface, and burial soil: information about diet and paleoenvironment.

Silica phytoliths (microscopic remains originating in plant tissues) have been identified on the enamel surface and dental calculus of a sample of teeth selected from well preserved skeletons from a Late Roman necropolis in Tarragona (Spain). Phytoliths were observed by scanning electron microscopy (SEM) and their siliceous nature was confirmed by X-ray microanalysis. The phytoliths were compared to those of soil samples from both the areas of the tombs corresponding to the abdomen and the periphery of the skeletons, and were classified taxonomically by comparison with a large collection of silica particles from modern plants in the Mediterranean area. Most of the phytoliths identified on the enamel and the dental calculus belong to the family of Poaceae, while the phytoliths from the abdominal area belong to Poaceae, Leguminosae, Cyperaceae, and Chenopodiaceae. Results are concordant with archaeological, ecological, and historical data from the same site, and with the human Mediterranean diet. If done properly, the study of phytoliths can provide direct information about the vegetable diet of past human populations, and could be applied to the study of human fossils.

Phytolith analysis of olive oil and wine sediments for possible identification in archaeology

Phytoliths are microscopic, amorphous silica or crystalline, inclusions of plant origin that can be of diagnostic value in an archaeological context. This study demonstrated that distinct phytoliths can be extracted from two major extant and ancient crop species: olive (Olea europaea L.) and grape (Vitis vinifera L.). Nonacid digestion of leaves and fruits of two Greek olive cultivars (Megareitiki and Kothreiki) and a Greek grape cultivar (Agiorgitiko) showed that olive and grape contained distinctly different calcium phytoliths and that olive fruit flesh and stone contained sclereids. Olive oil sediment from traditionally produced oil from Greece and Turkey and barrel sediment from traditional Greek red wine were found to contain phytoliths and (or) sclereids corresponding to their fruit of origin. Olive oil could therefore be distinguished from wine, making the nonacid phytolith extraction method a potentially useful alternative to chemical analysis of ancient storage jar residues. Key words: calcium and silica phytoliths, olive, grape, sediment analysis.

Soils and Mineral Weathering on Phyllite Colluvium and Serpentinite in Northwestern California

AbstractHaplohumults and Argixerolls have formed in close proximity on phyllite colluvium and serpentinite residuum, respectively, in the Klamath Mountains of northwestern California. This study was conducted to compare their contrasting properties and to investigate soil mineral weathering. Thick, dark A horizons containing 20 to 50 g kg−1 organic C have formed in the Argixeroll under the influence of perennial grass cover with sparse conifers and shrubs. The Haplohumult, under dense Douglas fir [Pseudotsuga menziesii (Mirbel) Franco] forest, has a thin A horizon containing 10 to 20 g kg−1 organic C. Soil pH is in the range of 5.6 to 5.8 in the A horizons of both soils. In the Haplohumult, pH decreases slightly with depth, whereas pH increases to 6.5 in the Crt horizon of the Argixeroll. The mineralogy of the Haplohumult is relatively uniform throughout its 260‐cm depth. Chlorite, the dominant mineral in the phyllite parent rock, has altered to interstratified chlorite/vermiculite and poorly crystalline kaolin in the soil fine‐sand fraction. Chlorite/vermiculite and kaolin dominate the clay fraction, accompanied by gibbsite, talc, and Fe oxides. Serpentine weathering prevails in the Argixeroll. The serpentine content of the fine‐sand fraction decreases upward in the profile, whereas magnetite and chlorite resist weathering and are concentrated. Serpentine is the most abundant mineral in the clay fraction. Clay‐size smectite, a product of serpentine weathering, is absent from A horizons, but increases with depth to a maximum in the fine‐earth material from cracks in the Crt horizon. Chlorite in the clay fraction is inherited from the parent rock. Both soils have experienced minor surficial additions of amorphous silica phytoliths and volcanic glass shards.

Characterization of Grass Phytoliths for Archaeological Analysis

The word phytolith means “plant rocks.” Phytoliths are mineral deposits that form in and between plant cells. Any mineral deposit may be considered a phytolith, although most recent research has focused on opaline silica. Silica seems to be widespread in at least some plant families and is resistant to dissolution in a pH less than 9. Silica phytoliths therefore have the potential to be useful microfossils that can be helpful in the documentation of prehistoric environment and economy.Identifiable shapes rather than amorphous deposits are a necessary characteristic for useful microfossils. Several plant families have long been known to be consistent accumulators of identifiable silica bodies: Gramineae (grass), Cyperaceae (sedge), and Equisetaceae (horsetail). Phytoliths from the Gramineae are especially well known; specialized silica-accumulating cells produce distinctively shaped phytoliths. However, other families have also been shown to produce significant amounts of identifiable phytoliths. Ulmaceae (elm), Fabaceae (bean), Cucurbitaceae (squash), and Compositae (sunflower) are a few examples of dicotyledonous families that commonly produce phytoliths. Some families, such as the Labiatae (mint), have yielded little or no identifiable phytoliths to date. However, further study may indicate phytolith production in particular species.

Completeness of the rock and fossil record: some estimates using fossil soils

Surprisingly, there is a relationship between rates of sediment accumulation and the time spans for which they have been calculated. This relationship can be used to estimate expected rates for specific sedimentary environments and time spans. The most probable completeness of a given sedimentary section at a given short time span can be calculated by the ratio of the measured long-term rate of sediment accumulation to the expected short-term rate. Although the measured time span is usually based on radiometric and paleomagnetic data, the cumulative time of formation estimated from fossil soils in a sequence may also be used to calculate rates and may be useful in comparing the completeness and rate of accumulation of different sequences. By both kinds of estimates, terrestrial sedimentary successions are disappointingly incomplete. Some reasons for incompleteness are illustrated with a simple model of episodic flooding, exceeding a threshold for destruction and sedimentation over a particular kind of vegetation, and thus initiating a new cycle of soil formation. In such a model, rock record is lost to erosion during cutting and filling cycles, to overprinting of weakly developed soils by later, better-developed soils, and to continued development, near steady state, of the soils preserved.Because fossil soils are evidence of ancient environments and ecosystems independent of the fossil record, they may provide evidence of expected kinds of fossils, such as silica phytoliths, calcareous phytoliths, pollen, leaves, fruits, seeds, charcoal, land snails, coprolites, and bones. The degree to which the kinds of fossils actually found fail to meet these expectations is a crude measure of the completeness of representation of a former ecosystem in the fossil record. Some of the discrepancy between expected and actual occurrence of fossils can be related to the original Eh and pH of a fossil soil, as approximated by the oxidation state of iron in its minerals (for Eh) and by carbonate or zeolite content (for pH). Different kinds of fossils can be envisaged as having a characteristic Eh-pH stability field within which they can be expected to have been preserved if originally present. Even under ideal conditions of preservation, it takes some time for fossils to accumulate in soils to levels at which representative collections can be made. Estimates of this temporal control on preservation can be gained by comparing fossil occurrences with the degree of development of fossil soils. Neither these chemical nor temporal factors account fully for the degree of incompleteness observed because original abundance, trampling, predation and many other factors are also important determinants of fossil occurrence.These considerations can be used as guidelines for choosing stratigraphic sections appropriate for particular paleobiological and geological problems. For example, a study of speciation of terrestrial vertebrates would best be in a sequence of weakly developed, calcareous fossil soils (Entisols and Inceptisols), of near-uniform texture and yellow to brown color, formed under an extraordinarily high long-term rate of sediment accumulation. On the other hand, a study of coevolution of vertebrates and plants would best be based on a sequence of weakly to moderately developed, calcareous fossil soils of predominantly drab (gray, green, and blue) color, with interbedded carbonaceous shales.