Silica Phytoliths Research Articles

Chemical composition of plant silica phytoliths

Silica phytoliths are a subgroup of biogenic opal. Silica phytoliths are formed in many plant species and remain preserved in soil and sediments after plant decay. The chemical composition of fossil phytoliths may reveal ancient plant taxa, soil composition and climate. However, actually detailed knowledge on silica phytolith composition is scarce. Here we present result of instrumental neutron activation analysis of barley awns, stems and leaves, and barley phytoliths. The elements of interest were Na, Mg, Al, Si, Cl, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Zn, As, Br, Rb, Sb, Cs, Ba, La, Ce, Sm, Eu, Tb, Dy, Yb, Hf, Ta, W, Th, and U. We compared three phytolith extraction methods: dry ashing, acid digestion, and acid digestion followed by incineration. We found that sole acid digestion is inefficient to remove organic matter. By contrast both dry ashing and acid digestion followed by incineration are suitable for phytolith analysis. Comparison of phytoliths with their source plant material shows that phytoliths are enriched in terrigenous elements such as Al, Sc, Ti, V, Cs, Fe, rare earth elements, and depleted in the major inorganic constituents of plants such as K, Ca, Mg, Mn, Cl and Br.

Detecting ancient wild rice (Zizania spp. L.) using phytoliths: a taphonomic study of modern wild rice in Minnesota (USA) lake sediments

Wild rice (Zizania spp. L.) is a North American native grain with spiritual and dietary significance to many native people. Wild rice is also an important aquatic plant that provides critical habitat to wetland and aquatic wildlife. Past distribution of wild rice in North America is poorly understood, largely because of the limited taxonomic resolution of Poaceae pollen. A novel technique for detecting diagnostic Zizania silica phytoliths allows unambiguous identification of this taxon in lake sediments. We need to better understand modern depositional patterns of phytoliths in lake sediments, however, before attempting detailed paleoreconstructions. We analyzed distributions of diagnostic Zizania and other Poaceae phytoliths in modern sediments from three lakes with variable percent cover of wild rice and a non-wild rice control lake in central Minnesota. Absolute counts of phytoliths per gram sediment were achieved using an exotic diatom marker. Non-Zizania short-cell phytoliths, i.e. phytoliths from wetland grasses Phragmites australis and Muhlenbergia glomerata, dominate the assemblages in all lakes. Most Poaceae short-cell phytoliths appear to be derived locally, with little evidence for regional inheritance from eolian or alluvial processes. Because of anatomical differences in decay of plant debris and other taphonomic issues, Zizania inflorescence rondel phytoliths were most abundant, with morphotypes from other parts rarely encountered. Even in sediments under the densest wild rice stands, Zizania phytoliths contributed a maximum of 9 % to total Poaceae phytolith abundance. Lake morphology also affects the depositional pattern of phytoliths in modern sediments, so coring locations should be considered carefully. At least 500 phytoliths should be counted to detect a sufficient number of wild rice phytolith morphotypes. Diagnostic Zizania phytoliths are a reliable tool for wild rice detection in paleolake sediments.

Anatomía de las hojas y biomineralización en Empetrum rubrum Valh ex Willd. (Ericaceae).

Fil: Fernandez Pepi, Maria Gabriela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

Typological and Frequency Based Study of Opaline Silica (Phytolith) Deposition in Two Common Indian Sorghum L. Species

Sorghum of the family Poaceae is one of the important cereal crops of India which accumulate silica in the form of phytoliths. Silica which forms phytoliths has manifold role in the crop plants. It enhances the crop quality, yield, growth and protects the plant from various biotic and abiotic hurdles. Present paper provides brief observations of the morphology, diversity and frequency of opal phytoliths in leaves of Sorghum bicolor and Sorghum halepense. Among all the morphotypes, bilobate phytoliths showed the highest frequency in both species while other forms like trapezoids, prickle hair, micro hair, long micro hair, epidermal long cells, stomata, bulliform and parallelepipedal phytoliths are present in minimal range. Some phytoliths like micro hair and polylobate phytoliths are not present in S. bicolor while they are present in S. halepense. The frequency of all the phytoliths of both the species is remarkably varied whereas the morphometry of these phytoliths is slightly varied. Therefore, these results could contribute in evaluating their taxonomic demarcation as well as will help to investigate their history of cultivation.

Experimental investigation of pathogenic stress on phytolith formation in Cucurbita pepo var. texana (wild gourd)

Silica phytoliths that form in plant tissues are useful to archaeologists because of their diagnostic value and longevity in ancient deposits. Palaeoecology, site formation processes, plant domestication, and other topics are routinely addressed using phytolith assemblages, especially when macrobotanical remains are not well preserved. However, little research has been conducted to document the effects of ecological variables on phytolith formation. Here, we investigate the effects of mosaic virus and bacterial wilt disease on diagnostic scalloped phytoliths in the rind of a wild-type Cucurbita pepo var texana (gourd). We observe a minimal change in phytolith size distribution between control plants and individuals with mosaic virus. However, we observe a notable difference between plants with bacterial wilt disease and control plants, with diseased individuals carrying a greater proportion of large-diameter scalloped phytoliths. This and similar phenomena could potentially confound archaeological interpretations of phytolith assemblages, and we suggest that the effects of this and other ecological variables should be studied in a diverse range of taxa.

Abrasive, silica phytoliths and the evolution of thick molar enamel in primates, with implications for the diet of Paranthropus boisei.

BackgroundPrimates—including fossil species of apes and hominins—show variation in their degree of molar enamel thickness, a trait long thought to reflect a diet of hard or tough foods. The early hominins demonstrated molar enamel thickness of moderate to extreme degrees, which suggested to most researchers that they ate hard foods obtained on or near the ground, such as nuts, seeds, tubers, and roots. We propose an alternative hypothesis—that the amount of phytoliths in foods correlates with the evolution of thick molar enamel in primates, although this effect is constrained by a species' degree of folivory.Methodology/Principal FindingsFrom a combination of dietary data and evidence for the levels of phytoliths in plant families in the literature, we calculated the percentage of plant foods rich in phytoliths in the diets of twelve extant primates with wide variation in their molar enamel thickness. Additional dietary data from the literature provided the percentage of each primate's diet made up of plants and of leaves. A statistical analysis of these variables showed that the amount of abrasive silica phytoliths in the diets of our sample primates correlated positively with the thickness of their molar enamel, constrained by the amount of leaves in their diet (R2 = 0.875; p<.0006).Conclusions/SignificanceThe need to resist abrasion from phytoliths appears to be a key selective force behind the evolution of thick molar enamel in primates. The extreme molar enamel thickness of the teeth of the East African hominin Paranthropus boisei, long thought to suggest a diet comprising predominantly hard objects, instead appears to indicate a diet with plants high in abrasive silica phytoliths.

Locally diagnostic phytoliths of wild rice (Z izania palustris L.) from Minnesota, USA: comparison to other wetland grasses and usefulness for archaeobotany and paleoecological reconstructions

Wild rice ( Zizania spp.) is an important native grain of north-central North America, with spiritual and subsistence significance to many native peoples. Due to lack of suitable proxies, its past distribution and pattern of use are poorly known. This study demonstrates the diagnostic value of silica phytoliths from Z. palustris as a proxy tool to detect its past occurrence in a variety of paleoenvironmental and archaeological contexts. Our main findings are: 1) Dominant wetland grass species in Minnesota produce phytoliths distinct from Zizania phytoliths; 2) Closely related Leersia oryzoides produces a few Zizania-like phytolith morphotypes; however, these potential confusers can be identified based on 2-D and 3-D morphologies; 3) Z. palustris produces a wide variety of phytolith morphotypes, many of which are only found in certain parts of the plant (e.g., Inflorescence Type 1 from the spikelet); 4) Z. palustris produces 23 locally diagnostic phytolith morphotypes that can be used to determine the presence and abundance of wild rice in modern and paleo lake sediments; and 5) Wild rice phytolith Inflorescence Type 1 is the morphotype most likely to be observed in archaeological contexts, and may be unequivocally diagnostic for the genera Zizania.

Phytolith occluded carbon and silica variability in wheat cultivars

Phytolith Occluded Carbon (PhytOC) has recently been demonstrated to be an important long-term terrestrial carbon fraction. The aim of this study was to examine the rates of silica accumulation and carbon bio-sequestered within the silica phytoliths of the leaf and stem material of wheat (Triticum sp.) cultivars. The phytolith content of 53 wheat cultivars sourced from 25 countries around the world and grown on a single trial site was first isolated and the PhytOC content then determined. The data shows that the phytolith occluded carbon content of the wheat cultivars ranged from 0.06% to 0.60% of dry leaf and stem biomass: a range of 1,000%. The data also demonstrates that it is the efficiency by which carbon is encapsulated within silica rather than the quantity of silica accumulated by the plant that is the most important factor in determining the relative PhytOC yields. The potential phytolith carbon bio-sequestration rates in the leaf and stem components of these wheat cultivars ranged up to 0.246 t-e-CO2 ha−1y−1. These phytolith carbon bio-sequestration rates indicate a substantial potential (~50 million t-e-CO2 y−1) exists for increasing the rate of secure carbon bio-sequestration in wheat crops using existing cultivars.

Carbon bio‐sequestration within the phytoliths of economic bamboo species

AbstractThe rates of carbon bio‐sequestration within silica phytoliths of the leaf litter of 10 economically important bamboo species indicates that (a) there is considerable variation in the content of carbon occluded within the phytoliths (PhytOC) of the leaves between different bamboo species, (b) this variation does not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by the silica. The PhytOC content of the species under the experimental conditions ranged from 1.6% to 4% of the leaf silica weight. The potential phytolith carbon bio‐sequestration rates in the leaf‐litter component for the bamboos ranged up to 0.7 tonnes of carbon dioxide (CO2) equivalents (t‐e‐CO2) ha−1 yr−1 for these species. Assuming a median phytolith carbon bio‐sequestration yield of 0.36 t‐e‐CO2 ha−1 yr−1, the global potential for bio‐sequestration via phytolith carbon (from bamboo and/or other similar grass crops) is estimated to be ∼1.5 billion t‐e‐CO2 yr−1, equivalent to 11% of the current increase in atmospheric CO2. The data indicate that the management of vegetation such as bamboo forests to maximize the production of PhytOC has the potential to result in considerable quantities of securely bio‐sequestered carbon.

Ancient agriculture and domestic activities: a contextual approach studying silica phytoliths and other microfossils in soils

Based on microfossil and soil data, we discuss a different methodological approach to agricultural and domestic archaeological studies, taking two Formative sites in the north-west Argentinian high valleys (province of Catamarca) as case studies, independently of traditional datasets and historical analogies. As a result of our investigations we not only recognised the vegetal species cultivated in ancient fields (dated to c. AD 800) but also distinguished some of the agricultural practices, such as crop rotation and alternation, use of animal fertilisers and irrigation resources, as well as the abandonment of the site. From this perspective, corral episodes could also be distinguished. In residential enclosures, we obtained results concerning activity areas, the definition of floors and the identification of reoccupations.

Limitations on the climatic and ecological signals provided by the δ13C values of phytoliths from a C4 North American prairie grass

Abstract Silica phytoliths, which are deposits of opal-A that precipitate in the intra- and intercellular spaces of plant tissues during transpiration, commonly contain small amounts of occluded organic matter. In this paper, we investigate whether the δ13C values of phytoliths from a C4 grass, Calamovilfa longifolia, vary in response to climatic variables that can affect the carbon-isotope composition of plant tissues. There is no significant correlation (r2

Plant ontogeny and chemical defence: older seedlings are better defended

Although patterns of seedling selection by herbivores are strongly influenced by plant age and the expression of anti‐herbivore defence, it is unclear how these characteristics interact to influence seedling susceptibility to herbivory. We tracked ontogenetic changes in a range of secondary metabolites (total phenolics, alkaloids and cyanogenic glycosides) commonly associated with seedling defence for nine sympatric British grassland species. Although there was marked variation in concentrations of secondary metabolites between different species, we found a consistent increase in the deployment of phenolics, alkaloids and cyanogenics with seedling age for six of the seven dicotyledonous species examined. The two grass species by contrast exhibited low levels of secondary metabolites across all developmental stages, possibly due to an investment in structural (silica phytoliths) defence. Our results corroborate species‐specific patterns of seedling herbivory observed in field studies, and offer some explanation for the relatively high sensitivity to herbivore attack frequently observed for relatively young seedlings compared with their older conspecifics. Our results also support predictions made by the growth–differentiation balance hypothesis regarding ontogenetic changes in resource allocation to anti‐herbivore defence for a range of potential chemical defences and across a range of sympatric plant species presumably subject to broadly similar selective pressures at the regeneration stage.

A simulated bird gastric mill and its implications for fossil gastrolith authenticity

<strong class="journal-contentHeaderColor">Abstract.</strong> A rock tumbler, stones, water, plant material, hydrochloric acid, and pepsin were used to simulate a bird gizzard in order to study abrasion rate and influence of stomach juices and foodstuff on gastrolith surface development. The experiment lasted for six months. Each week, the "stomach" was supplied with fresh grass and stomach juices. After the end of the experiment, the set of stones had a combined weight loss of 22.4%, with softer rock types showing higher abrasion rates. The combination of stomach juices and silica phytoliths within the grass had no visible effect on stone surface development: polish or pitting did not occur. A second experiment combined only pebbles with water in the tumbler. Results indicate that rock abrasion is mainly caused by contacts between moving stones. A comparison with authentic ostrich gastroliths showed that abrasion in the artificial stomach must have been lower than in a real gizzard, but still too high to maintain or develop surface polish. If high polish occasionally seen on sauropodomorph dinosaur gastroliths was indeed caused in a stomach environment, it implies digestive processes different from those of extant birds and the "artificial gizzard". Geologic origins of polish, such as transport in hyperconcentrated flows, wind blasting, or tectonic movements must be considered for polished fossil gastroliths and isolated clasts in fine-grained sediments (exoliths). <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.200800013" target="_blank">10.1002/mmng.200800013</a>

A simulated bird gastric mill and its implications for fossil gastrolith authenticity

A rock tumbler, stones, water, plant material, hydrochloric acid, and pepsin were used to simulate a bird gizzard in order to study abrasion rate and influence of stomach juices and foodstuff on gastrolith surface development. The experiment lasted for six months. Each week, the "stomach" was supplied with fresh grass and stomach juices. After the end of the experiment, the set of stones had a combined weight loss of 22.4%, with softer rock types showing higher abrasion rates. The combination of stomach juices and silica phytoliths within the grass had no visible effect on stone surface development: polish or pitting did not occur. A second experiment combined only pebbles with water in the tumbler. Results indicate that rock abrasion is mainly caused by contacts between moving stones. A comparison with authentic ostrich gastroliths showed that abrasion in the artificial stomach must have been lower than in a real gizzard, but still too high to maintain or develop surface polish. If high polish occasionally seen on sauropodomorph dinosaur gastroliths was indeed caused in a stomach environment, it implies digestive processes different from those of extant birds and the "artificial gizzard". Geologic origins of polish, such as transport in hyperconcentrated flows, wind blasting, or tectonic movements must be considered for polished fossil gastroliths and isolated clasts in fine-grained sediments (exoliths). &lt;br&gt;&lt;br&gt; doi:&lt;a href="http://dx.doi.org/10.1002/mmng.200800013" target="_blank"&gt;10.1002/mmng.200800013&lt;/a&gt;

Dental microwear analysis of notoungulates (Mammalia) from Salla (Late Oligocene, Bolivia) and discussion on their precocious hypsodonty

The extinct endemic South American notoungulates are remarkable for their early evolution of hypsodonty in the Late Eocene/Early Oligocene. Due to this ‘precocious hypsodonty’ they have been considered to be the earliest grazers, suggesting an early spread of grassland in South America (at least 10 Myr earlier than in North America). This hypothesis is based on the idea that the abrasion of their hypsodont cheek teeth might have been caused by silica phytoliths which are abundant in a rich-in-grass diet. The analysis of the dental microwear pattern (using an optical stereomicroscope connected to a tri-CCD camera) of hypsodont notoungulates from the Late Oligocene Salla Beds of Bolivia revealed the preponderance of thin parallel scratches on the fossil teeth of most of the taxa analyzed, like extant grazers. This microwear pattern above all indicates predominant sub-horizontal jaw movements in the chewing behaviour of notoungulates with “precocious” hypsodonty. This signals shearing movements as in a diet rich in tough plants. This peculiar chewing pattern and/or a larger ingested proportion of grass phytoliths or exogenous grit are further discussed as hypothetical causes of increasing wear on notoungulate teeth during middle Cenozoic times. We particularly argue that the putative precocious spread of grasslands in South America traditionally linked with notoungulate hypsodonty is still far from being supported. Many questions arise concerning the development of hypsodonty within notoungulates and this case perfectly illustrates that the relations between high-crowned mammals and the source of tooth wear in the fossil record may not be straightforward.

Sugarcane phytoliths: Encapsulation and sequestration of a long-lived carbon fraction

The potential to reduce emissions from agriculture and increase the amount of carbon captured in soils is currently being examined by researchers in a number of countries. This paper describes a process of carbon capture and long-term storage using silica phytoliths and, provides the results of a study of this process on newly planted and ratooned sugarcane varieties. Our results indicate that a) there was significant variation in the phytolith occluded carbon (PhytOC) content of different varieties, b) this did not appear to be directly related to the quantity of silica in the plant but rather the efficiency of carbon encapsulation by individual varieties and c) it was possible to accurately quantify this carbon fraction prior to its incorporation into soil. The carbon content of the varieties tested under the particular suite of environmental conditions for which they were grown ranged from 0.12 te-CO2 ha-y−1 to 0.36 te-CO2 ha-y−1. This PhytOC process provides an approach which reduces emissions from agriculture for the long-term (millennia), as opposed to many other soil organic carbon fractions that may decompose over a much shorter time. Moreover, the ability to quantify PhytOC prior to its incorporation into the soil will provide a distinct practical advantage for the quantification of this carbon form over other soil carbon fractions in emerging emissions trading and offset markets.

Fire in prehistory: An experimental approach to combustion processes and phytolith remains

Albert, R.M. and Cabanes, D. 2007. Fire in prehistory: An experimental ap proach to combustion processes and phytolith remains. Isr. J. Earth sci. 56: 175–189. Silica phytoliths are commonly found in hearths as a result of the combustion of plants. Their study in prehistoric hearths has enabled the identification of fire remains not visible to the naked eye due to the postdepositional processes. It has also enabled determination of the type of fuel used for the fires, and a better understanding of the functionality of hearths. However, little work has been done on understanding the combustion properties of fires and their relationship to the amount, distribution, and preservation of burned phytolith remains. We present here results of experiments carried out to shed more light on these questions. These results indicate that there are important differences in the combustion properties of fires. The remaining burned residues of the combustion depend on the use of naturally-dried or fresh fuel. These differences are related to the relationship between the presence of ash and charcoal fragments, the proportion of the acid-insoluble fraction, the amount and morphological distribution of phytoliths in the different fractions, and the refractive indices of the phytoliths. To recognize these properties it is essential to sieve the samples into different size fractions prior to the phytolith and mineralogical study. Postdepositional processes need to be taken into account as well when analyzing archaeological fire remains. The preference of one type of fuel over the other may have important implications related to the collection strategies and the proximity of available resources, as well as to the various possible uses of caves.

Taphonomical aspects of silica phytoliths in the loess sediments of the Argentinean Pampas

Although Pampean loess and pedostratigraphy processes in the Pampas have been widely studied, phytoliths observed in these sediments have been only mentioned without further quantitative or qualitative studies. The present work is a first step towards an understanding of the environmental significance of loess phytolith datasets and their validity for palaeoenvironmental reconstructions, and to comprehend the environmental conditions of loess formation. The research focused on the taphonomy of loess phytoliths investigating the loess morphological and sedimentological characteristics, variability in the qualitative and quantitative assemblage composition, the phytolith frequency and were also phytolith extraction techniques. The results highlight that the phytolith pool of loess deposits still retains information about the past vegetation and phytolith analysis from these deposits can be a useful exercise to further comprehend past climatic and environmental conditions under which loess–palaeosol sequences formed.

Do silica phytoliths really wear mammalian teeth?

There is considerable literature suggesting that silica (opal) phytoliths cause dental enamel microwear in mammals. Much of this literature cites a single study from 1959 as evidence that silica phytoliths are harder than mammalian tooth enamel and so have the potential to cause dental microwear. No other studies using similar methodology have actually confirmed whether phytoliths are harder than dental enamel. The hardness of silica phytoliths from four species of grass and mammalian tooth enamel from sheep was tested using a modern nanoindentation tool. We found that silica phytoliths are considerably softer (51–211 Vickers Hardness, HV) than tooth enamel (257–397 HV) and therefore must be re-evaluated as a major source of dental microwear. The hardness results indicate that silica phytoliths do not contribute as much to mammalian dental microwear as previously reported and that exogenous grit and dust are a more likely cause. This premise has implications for interpretations of the causal agents of microwear phenomena in areas such as the evolution of high-crowned teeth in grazing mammals during the Miocene, and the inference of diet from fossilized mammal teeth as reported by some studies in physical anthropology and archaeology.

Identifying the δ 18O signature of precipitation in grass cellulose and phytoliths: Refining the paleoclimate model

Cellulose and silica phytoliths were extracted from the leaves and stems of Calamovilfa longifolia, a C 4 grass, grown under varying climatic conditions across the North American prairies. The oxygen-isotope compositions of both cellulose and silica record a complex signal of the isotopic composition of the soil water that feeds the plants and the relative humidity conditions that influence transpiration rates, stomatal conductance, and ultimately the 18O-enrichment of leaf water. As the initial stages of cellulose formation occur in the leaves, cellulose in both the leaves and stems forms primarily from leaf water and does not differ greatly in its oxygen-isotope composition between these locations. In contrast, the δ 18O values of leaf phytoliths are significantly enriched in 18O relative to stem phytoliths, reflecting the varying isotopic composition of the water in these tissues. The oxygen-isotope compositions of leaf cellulose may be used as a proxy for the isotopic composition of water involved in leaf phytolith formation, while the δ 18O values of stem phytoliths can be used to determine the δ 18O values of stem water involved in partial exchange reactions during the transport of carbohydrates through the plant. A comparison of the isotopic compositions of phytoliths with cellulose allows for the deduction of soil and leaf water δ 18O values as well as temperature and relative humidity conditions during plant growth. This approach has application in paleoclimate studies that traditionally have required estimations of one or more of these variables because direct measurements were unavailable.