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Phytoliths (siliceous structures) present in the plants have been employed in the fields of taxonomy and archaeology for many decades. Rostraria cristata is an economically important grass species (Poaceae) which accumulates silica in its different organs in the form of phytoliths. In order to understand the pattern of phytolith production and biochemical architecture of silica in R. cristata, leaf epidermis (blade) using the clearing solution method and different organs using the dry ashing method, X-ray diffraction and Fourier-transform infrared spectroscopy techniques were analyzed. Both abaxial and adaxial leaf epidermis showed the presence of acute bulbosus, rectangular sinuate and stomata phytolith morphotypes. Leaf including sheath and blade had the highest silica content. Characteristic phytolith morphotypes were present in different organs. A total of 34 phytolith morphotypes were present among which nine (9) were articulated and 25 were isolated forms. The most abundant were elongate scrobiculate (48.20%) in root and rectangular sinuate (26.16%) in leaf part. Other common phytolith morphotypes present in different organs of R. cristata were articulated elongate irregular, articulated elongate scrobiculate, acute bulbosus, and polygonal rondel etc. Leaf and synflorescence had the highest similarity based on presence/absence of phytolith morphotypes (Jaccard's similarity index). XRD studies revealed the presence of cristobalite, quartz, tridymite, zeolite etc. forms of silica in different organs. FTIR spectra showed that inplane stretching vibration of Si–C was unique to root, anti-symmetric stretching vibration of C–H was unique to leaf and Al2O3.SiO2 was found in synflorescence only. Our results show the characteristic pattern of phytoliths production in R. cristata. [ABSTRACT FROM AUTHOR]

Dinosaurs were the dominant megaherbivores during the Cretaceous when angiosperms, the flowering plants, emerged and diversified. How herbivorous dinosaurs responded to the increasing diversity of angiosperms is largely unknown due to the lack of methods that can reconstruct diet directly from body fossils. We applied dental microwear texture analysis (DMTA), an approach that quantifies microtopography of diet‐induced wear marks on tooth surfaces, to ornithopods, the dinosaur clade that includes taxa with the most sophisticated masticatory system. We found that Late Cretaceous ornithopods have significantly rougher dental microwear texture (DMT) compared to pre‐Late Cretaceous ornithopods, and DMT variation increased in hadrosaurids, a derived Late Cretaceous ornithopod clade. These changes indicate a likely temporal dietary shift towards more abrasive foodstuffs within ornithopods, probably due to the increased ingestion of phytoliths (amorphous silica bodies in plants). Phytoliths are a main source of rough DMT in modern herbivores, along with exogenous dust and grit, and were generally more concentrated in Late Cretaceous angiosperms than in other major plant groups. Our results show that DMTA of the occlusal enamel surface can be used to reconstruct the diets of herbivorous dinosaurs, with a resolution superior to conventional methods. [ABSTRACT FROM AUTHOR]

Silicon-based defenses deter insect herbivores in many cultivated and wild grass species. Furthermore, in some of these species, silicon (Si) uptake and defense can be induced by herbivory. Tropical trees also take up Si and leaf Si concentrations vary greatly across and within species. As herbivory is a major driver of seedling mortality and niche differentiation of tropical tree species, understanding antiherbivore defenses is pivotal. Yet, whether silicon is a constitutive and inducible herbivory defense in tropical forest tree species remains unknown. We grew seedlings of eight tropical tree species in a full factorial experiment, including two levels of plant-available soil Si concentrations (-Si/+Si) and a simulated herbivory treatment (-H/+H). The simulated herbivory treatment was a combination of clipping and application of methyl jasmonate. We then carried out multiplechoice feeding trials, separately for each tree species, in which leaves of each treatment combination were offered to a generalist caterpillar (Spodoptera frugiperda). Leaf damage was assessed. Three species showed a significant decrease in leaf damage under high compared to low Si conditions (by up to 72%), consistent with our expectation of Si-based defenses acting in tropical tree species. In one species, leaf damage was increased by increasing soil Si and in four species, no effect of soil Si on leaf damage was observed. Opposite to our expectation of Si uptake and defense being inducible by herbivory damage, simulated herbivory increased leaf damage in two species. Furthermore, simulated herbivory reduced Si concentrations in one species. Our results showed that tropical tree seedlings can be better defended when growing in Si-rich compared to Si-poor soils, and that the effects of Si on plant defense vary strongly across species. Furthermore, Si-based defenses may not be inducible in tropical tree species. Overall, constitutive Si-based defense should be considered part of the vast array of anti-herbivore defenses of tropical tree species. Our finding that Si-based defenses are highly species-specific combined with the fact that herbivory is a major driver of mortality in tropical tree seedling, suggests that variation in soil Si concentrations may have pervasive consequences for regeneration and performance across tropical tree species. [ABSTRACT FROM AUTHOR]

Summary: Phytoliths, microscopic deposits of hydrated silica within plants, play a myriad of functional roles in extant tracheophytes – yet their evolutionary origins and the original selective pressures leading to their deposition remain poorly understood. To gain new insights into the ancestral condition of tracheophyte phytolith production and function, phytolith content was intensively assayed in a basal, morphologically conserved tracheophyte: the foxtail clubmoss Lycopodiella alopecuroides.Wet ashing was employed to perform phytolith extractions from every major anatomical region of L. alopecuroides. Phytolith occurrence was recorded, alongside abundance, morphometric information, and morphological descriptions.Phytoliths were recovered exclusively from the microphylls, which were apicodistally silicified into multiphytolith aggregates. Phytolith aggregates were larger and more numerous in anatomical regions engaging in greater evapotranspirational activity.The tissue distribution of L. alopecuroides phytoliths is inconsistent with the expectations of proposed adaptive hypotheses of phytolith evolutionary origin. Instead, it is hypothesized that phytoliths may have arisen incidentally in the L. alopecuroides‐like ancestral plant, polymerizing from intraplant silicon accumulations arising via bulk flow and 'leaky' cellular micronutrient channels. This basal, nonadaptive phytolith formation model would provide the evolutionary 'raw material' for later modification into the useful, adaptative, phytolith deposits seen in later‐diverging plant clades. [ABSTRACT FROM AUTHOR]

Background Silicon and aluminium oxides make the bulk of agricultural soils. Plants absorb dissolved silicon as silicic acid into their bodies through their roots. The silicic acid moves with transpiration to target tissues in the plant body, where it polymerizes into biogenic silica. Mostly, the mineral forms on a matrix of cell wall polymers to create a composite material. Historically, silica deposition (silicification) was supposed to occur once water evaporated from the plant surface, leaving behind an increased concentration of silicic acid within plant tissues. However, recent publications indicate that certain cell wall polymers and proteins initiate and control the extent of plant silicification. Scope Here we review recent publications on the polymers that scaffold the formation of biogenic plant silica, and propose a paradigm shift from spontaneous polymerization of silicic acid to dedicated active metabolic processes that control both the location and the extent of the mineralization. Conclusion Protein activity concentrates silicic acid beyond its saturation level. Polymeric structures at the cell wall stabilize the supersaturated silicic acid and allow its flow with the transpiration stream, or bind it and allow its initial condensation. Silica nucleation and further polymerization are enabled on a polymeric scaffold, which is embedded within the mineral. Deposition is terminated once free silicic acid is consumed or the chemical moieties for its binding are saturated. [ABSTRACT FROM AUTHOR]

Grasses are hyper-accumulators of silicon (Si), which is known to alleviate diverse environmental stresses, prompting speculation that Si accumulation evolved in response to unfavourable climatic conditions, including seasonally arid environments. We conducted a common garden experiment using 57 accessions of the model grass Brachypodium distachyon, sourced from different Mediterranean locations, to test relationships between Si accumulation and 19 bioclimatic variables. Plants were grown in soil with either low or high (Si supplemented) levels of bioavailable Si. Si accumulation was negatively correlated with temperature variables (annual mean diurnal temperature range, temperature seasonality, annual temperature range) and precipitation seasonality. Si accumulation was positively correlated with precipitation variables (annual precipitation, precipitation of the driest month and quarter, and precipitation of the warmest quarter). These relationships, however, were only observed in low-Si soils and not in Si-supplemented soils. Our hypothesis that accessions of B. distachyon from seasonally arid conditions have higher Si accumulation was not supported. On the contrary, higher temperatures and lower precipitation regimes were associated with lower Si accumulation. These relationships were decoupled in high-Si soils. These exploratory results suggest that geographical origin and prevailing climatic conditions may play a role in predicting patterns of Si accumulation in grasses. [ABSTRACT FROM AUTHOR]

Phytoliths form in plant tissues as fine, silt-sized amorphous silica particles. Once deposited in soils by plant debris, they can dissolve and feed silicon (Si) fluxes to the biosphere and hydrosphere, enhancing the positive effects of Si on plant health and carbon fixation by marine diatoms. In soils, microaggregates (<250 μm) may entrap phytoliths and protect them from dissolution. Here we aimed at analyzing the role of aggregation in protecting phytoliths and delaying the release of bioavailable Si. Synthetic 32-days aged aggregates were composed of (g kg−1): organic matter (50), aluminosilicate mineral (370), iron (Fe) oxide (60), quartz (500) and rice phytolith (20). Models with either amorphous (Am) or crystalline (Cryst) aluminosilicates and Fe-oxides were tested. The Am model included allophane and ferrihydrite while the Cryst model included kaolinite and goethite. Aggregates were visualized by Scanning and Transmission Electron Microscopy. They were compared to individual compounds and unaggregated mixtures through kinetic Na 2 CO 3 and CaCl 2 extraction assessing the pools of phytoliths and bioavailable Si, respectively. Aluminum (Al) and germanium (Ge) concentrations, and pH were measured in the CaCl 2 extracts. CaCl 2 extractable Si decreased in the order (g kg−1): Am mixture (3.72) > Am aggregate (0.95) > Cryst mixture (0.48) > Cryst aggregate (0.39). Aggregation thus reduced Si release by 3.9- and 1.2- fold in the amorphous and crystalline model, respectively. The Si/Al and Ge/Si atomic ratios showed that allophane and phytolith were the main sources of bioavailable Si in the amorphous and crystalline model, respectively. In contrast to the crystalline model (pH 5.0–7.8), the acidic medium in the amorphous model (pH 3.7–4.9) enhanced allophane dissolution. Aggregation thus protected both allophane and phytolith from dissolution, and reduced the release of bioavailable Si, the source of which depended on the component stability and pH. [ABSTRACT FROM AUTHOR]

Grasses are hyper-accumulators of silicon (Si), which is known to alleviate diverse environmental stresses, prompting speculation that Si accumulation evolved in response to unfavourable climatic conditions, including seasonally arid environments. We conducted a common garden experiment using 57 accessions of the model grass Brachypodium distachyon, sourced from different Mediterranean locations, to test relationships between Si accumulation and 19 bioclimatic variables. Plants were grown in soil with either low or high (Si supplemented) levels of bioavailable Si. Si accumulation was negatively correlated with temperature variables (annual mean diurnal temperature range, temperature seasonality, annual temperature range) and precipitation seasonality. Si accumulation was positively correlated with precipitation variables (annual precipitation, precipitation of the driest month and quarter, and precipitation of the warmest quarter). These relationships, however, were only observed in low-Si soils and not in Si-supplemented soils. Our hypothesis that accessions of B. distachyon from seasonally arid conditions have higher Si accumulation was not supported. On the contrary, higher temperatures and lower precipitation regimes were associated with lower Si accumulation. These relationships were decoupled in high-Si soils. These exploratory results suggest that geographical origin and prevailing climatic conditions may play a role in predicting patterns of Si accumulation in grasses.

The article analyzed main phytolith morphotypes produced and anatomical microscopic structure of grass leaf epidermis in dominant species in the south of West Siberia. Phytoliths are silica microfossils formed inside plant cells that allow identification of plants in paleobotanical studies. The choice of objects in the study was based on presence of strong silicification in selected dominant grasses. For the first time in our region, phytolith assemblage from a plant (% of morphotypes) was compared to the anatomical structure of leaf epidermis in Poaceae. We studied seven Poaceae species that together produced all major morphotypes found in soils of the region: Achnatherum sibiricum, Agrostis gigantea, Elymus dahuricus, Festuca pseudovina, Festuca pratensis, Koeleria cristata, Phalaroides arundinacea. Because all of these species were regionally important dominants, their phytoliths would help diagnose specific plant communities. We showed localization of main phytoliths in the leaves of these species and compared short cell and trichome distribution in a plant with its silicification. The results allowed to better visualize 3D shapes of epidermal cells. Most common phytoliths were formed as cell wall casts that repeat the shape of the cell in question. Some short cells, for example rondels and bilobates, did not match the shape of the cell, indicating active shaping process present inside the cells. An interesting result was a lack of silicification of trichomes in some grasses despite heavy trichome presence. This study will help researchers to avoid mistakes in identifying common dominant plants based on their phytolith record in paleosediments, within West Siberia and across all of Northern Eurasia.

Date fruits are special representative of hard fruits and one of the richest sources of dietary silica and edible lignin, which are believed to have several health benefits. In this study, we used optical and scanning electron microscopy (SEM) to investigate the presence of associations between silicification and lignification in date fruits (Phoenix dactylifera, L.). Phloroglucinol staining was employed to observe lignification in date fruits, while silicification was studied by SEM of whole fruits and their acid digesta. This work revealed the presence of heterogeneity and complexity in the silica phytoliths and the lignified structures in date fruits. It was found that lignin exists independently of silica in the secondary cell walls of parenchymal and sclereid cells and that silica exists independently of lignin in the spheroid phytoliths that surround the sclereid cells. Interestingly, a small proportion of lignin and silica seemed to co-exist as partners in the spiral coils of the tracheid phytoliths.

Date fruits are special representative of hard fruits and one of the richest sources of dietary silica and edible lignin, which are believed to have several health benefits. In this study, we used optical and scanning electron microscopy (SEM) to investigate the presence of associations between silicification and lignification in date fruits (Phoenix dactylifera, L.). Phloroglucinol staining was employed to observe lignification in date fruits, while silicification was studied by SEM of whole fruits and their acid digesta. This work revealed the presence of heterogeneity and complexity in the silica phytoliths and the lignified structures in date fruits. It was found that lignin exists independently of silica in the secondary cell walls of parenchymal and sclereid cells and that silica exists independently of lignin in the spheroid phytoliths that surround the sclereid cells. Interestingly, a small proportion of lignin and silica seemed to co-exist as partners in the spiral coils of the tracheid phytoliths. [ABSTRACT FROM AUTHOR]

Purpose: Phytolith-occluded carbon (PhytOC) is mainly derived from the products of photosynthesis, which can be preserved in soils and sediments for hundreds-to-thousands of years due to the resilient nature of the amorphous phytolith silica. Therefore, stable and radioactive carbon (C) isotopes of phytoliths can be effectively utilized in paleoecological and archeological research. However, there still exists debate about the applicability of C isotopes of phytoliths, as a "two-pool" hypothesis to characterize PhytOC sources has been proposed, whereby a component of the PhytOC is derived from soil organic matter (SOM) absorbed through plant roots. Therefore, it is necessary to review this topic to better understand the source of PhytOC. Materials and method: We introduce the stable and radioactive C isotopic compositions of PhytOC, present the impacts of different extraction methods on the study of PhytOC, and discuss the implications of these factors for determining the sources of PhytOC. Results and discussion: Based on this review, we suggest that organic matter synthesized by photosynthesis is the main source of PhytOC. However, it is important to make clear whether and how SOM-derived C present in phytoliths influence the controversial "too-old" skew and isotopic fractionation. Conclusions: Though the two-pool hypothesis has been proved by many researches, the carbon isotopes of phytoliths still have potential in paleoecology and archeology, because the main source is photosynthesis and many previous studies put forward the availability of these parameters. This review also shows that phytolith C isotopes may vary with different organic C compounds within phytoliths, which needs further study at the molecular scale. Different phytolith extraction methods can influence 14C dating results. [ABSTRACT FROM AUTHOR]

Grasses accumulate silicon in the form of silicic acid, which is precipitated as amorphous silica in microscopic particles termed phytoliths. These particles comprise a variety of morphologies according to the cell type in which the silica was deposited. Despite the evident morphological differences, phytolith chemistry has mostly been analysed in bulk samples, neglecting differences between the varied types formed in the same species. In this work, we extracted leaf phytoliths from mature plants of Sorghum bicolor (L.) Moench. Using solid state NMR and thermogravimetric analysis, we show that the extraction methods alter greatly the silica molecular structure, its condensation degree and the trapped organic matter. Measurements of individual phytoliths by Raman and synchrotron FTIR microspectroscopies in combination with multivariate analysis separated bilobate silica cells from prickles and long cells, based on the silica molecular structures and the fraction and composition of occluded organic matter. The variations in structure and composition of sorghum phytoliths suggest that the biological pathways leading to silica deposition vary between these cell types. [ABSTRACT FROM AUTHOR]

Biological cycling of silica plays an important role in terrestrial primary production. Soil warming stemming from climate change can alter the cycling of elements, such as carbon and nitrogen, in forested ecosystems. However, the effects of soil warming on the biogeochemical cycle of silica in forested ecosystems remain unexplored. Here we examine long-term forest silica cycling under ambient and warmed conditions over a 15-year period of experimental soil warming at Harvard Forest (Petersham, MA). Specifically, we measured silica concentrations in organic and mineral soils, and in the foliage and litter of two dominant species (Acer rubrum and Quercus rubra), in a large (30 × 30 m) heated plot and an adjacent control plot (30 × 30 m). In 2016, we also examined effects of heating on dissolved silica in the soil solution, and conducted a litter decomposition experiment using four tree species (Acer rubrum, Quercus rubra, Betula lenta, Tsuga canadensis) to examine effects of warming on the release of biogenic silica (BSi) from plants to soils. We find that tree foliage maintained constant silica concentrations in the control and warmed plots, which, coupled with productivity enhancements under warming, led to an increase in total plant silica uptake. We also find that warming drove an acceleration in the release of silica from decaying litter in three of the four species we examined, and a substantial increase in the silica dissolved in soil solution. However, we observe no changes in soil BSi stocks with warming. Together, our data indicate that warming increases the magnitude of silica uptake by vegetation and accelerates the internal cycling of silica in in temperate forests, with possible, and yet unresolved, effects on the delivery of silica from terrestrial to marine systems.

Biological cycling of silica plays an important role in terrestrial primary production. Soil warming stemming from climate change can alter the cycling of elements, such as carbon and nitrogen, in forested ecosystems. However, the effects of soil warming on the biogeochemical cycle of silica in forested ecosystems remain unexplored. Here we examine long-term forest silica cycling under ambient and warmed conditions over a 15-year period of experimental soil warming at Harvard Forest (Petersham, MA). Specifically, we measured silica concentrations in organic and mineral soils, and in the foliage and litter of two dominant species (Acer rubrum and Quercus rubra), in a large (30 × 30 m) heated plot and an adjacent control plot (30 × 30 m). In 2016, we also examined effects of heating on dissolved silica in the soil solution, and conducted a litter decomposition experiment using four tree species (Acer rubrum, Quercus rubra, Betula lenta, Tsuga canadensis) to examine effects of warming on the release of biogenic silica (BSi) from plants to soils. We find that tree foliage maintained constant silica concentrations in the control and warmed plots, which, coupled with productivity enhancements under warming, led to an increase in total plant silica uptake. We also find that warming drove an acceleration in the release of silica from decaying litter in three of the four species we examined, and a substantial increase in the silica dissolved in soil solution. However, we observe no changes in soil BSi stocks with warming. Together, our data indicate that warming increases the magnitude of silica uptake by vegetation and accelerates the internal cycling of silica in in temperate forests, with possible, and yet unresolved, effects on the delivery of silica from terrestrial to marine systems. [ABSTRACT FROM AUTHOR]

Phytoliths are silica casts of plant cells, created within and between living tissues across almost all plant clades. Because they are abundant, durable and distinctive, phytoliths are used to deduce historic vegetation patterns and human uses across the fields of archeology, paleoethnobotany, paleoecology, and historical ecology, particularly at sites where preservation of larger plant-derived samples is poor. Nonetheless, phytolith research has recently contributed to advances in biogeochemical cycling and carbon sequestration. Although much progress has been made over the past few decades, some basic methodological concerns in phytolith systematics and Si cycling still hamper the overall development of this emerging field of science. Here, we first review basic scenarios of phytolith studies across different disciplines of science and then advocate interdisciplinary phytolith research to overcome the challenges of phytolith systematics, inform the representation of Si and C cycling in biogeochemical models, and improve the utility of phytoliths as proxies in archeology and paleontology. [ABSTRACT FROM AUTHOR]

Summary: Anecdotal evidence indicating substantial silica accumulation in tissues of bryophytes suggests that silica (phytolith) deposition evolved early on in embryophytes. To test this hypothesis, we conducted the first survey of phytolith content representing the major liverwort, moss and hornwort clades. We also assessed the diagnostic value of bryophyte phytoliths.Silica extracted from bryophyte material through wet‐ashing was described, focusing on abundance, classifying taxa as nonproducers, light producers and higher producers; and phytolith morphotypes. Ancestral state reconstruction of these characters was performed for mosses and liverworts using published phylogenies.Phytoliths are present in multiple subclades within liverworts, mosses and hornworts, but these phyla were not ancestrally high silica‐producers. Higher deposition occurs in liverworts and mosses with specialized water‐conducting cells.We hypothesize that active, high silica accumulation was not ancestral for embryophytes, but became possible in clades with increased water conductance. Phytoliths of diagnostic structures (e.g. pegged rhizoids) could help track bryophyte clades or water conductance evolution in the fossil record. [ABSTRACT FROM AUTHOR]

Certain areas in North China have the highest incidence of esophageal squamous cell carcinoma (ESCC) in the world, which has not seen convincing explanation by any risk factor yet. Biogenic silica in millet bran was linked to ESCC in the early 1980s but the hypothesis was largely dismissed because of the lack of geographic correlation between millet consumption and ESCC. Later epidemiological studies disclosed the linkage of wheat consumption in North China to ESCC instead. Now, we hypothesize silica phytoliths (silicified bodies that have definite shapes) from wheat chaff are a major etiologic factor of ESCC in this region. This hypothesis is supported by the potentially high abundance of silica phytoliths on the bracts of wheat (Triticum aestivum) in North China due to favorable Si-accumulation genotype, arid climate, and siallitic soil with bioavailable Si. These silica phytoliths can contaminate wheat flour and cause repeated local injuries in the esophagus and stimulate proliferation by providing anchorage. [ABSTRACT FROM AUTHOR]

Scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction were successfully used to observe the location and morphology of the silica phytoliths in biomass-derived carbons and their transformation into SiC and SiO2 particles at high heat treatment temperatures (HTT). The analyses were conducted in chars derived from the endocarp of babassu coconut (EBC), which naturally contains 1.6 wt% of silica in its mineral matter. It was observed that EBC chars with 500-1200 °C HTT present globular echinate SiO2 phytoliths with sizes of 12-16 μm; these phytoliths are mostly concentrated around the surface of the submillimeter char fibers and also in the carbonaceous char matrix. No phytoliths are found in the interior of the char fibers. At 1200 °C HTT, the phytoliths begin to be rounded, and above 1300 °C HTT, most phytoliths decompose and silicon reacts with carbon-forming nanocrystalline β-SiC particles (~ 35 nm crystallite size). Numerous (tens to hundreds) micro- and sub-micro-amorphous or nanostructured SiO2 particles (with sizes predominantly below 2 µm) are then observed at the sites previously occupied by the phytoliths. Few rounded phytoliths survive at 1400 °C HTT, but disappear at higher HTTs (1600-2000 °C). It is likely that the ensembles of micro- and sub-micro-SiO2 particles observed in many sites correspond to the inner remaining part of the original phytoliths, whose most external SiO2 structures (at and near the surface) decompose and take part in the carbothermal reaction for the formation of SiC. [ABSTRACT FROM AUTHOR]

Recent studies have shown that phytoliths are softer than dental enamel but still act as abrasive agents. Thus, phytolith content should be reflected in dental wear. Because native phytoliths show lower indentation hardness than phytoliths extracted by dry ashing, we propose that the hydration state of plant tissue will also affect dental abrasion. To assess this, we performed a controlled feeding experiment with 36 adult guinea pigs, fed exclusively with three different natural forages: lucerne, timothy grass, and bamboo with distinct phytolith/silica contents (lucerne < grass < bamboo). Each forage was fed in fresh or dried state for 3 weeks. We then performed 3D surface texture analysis (3DST) on the upper fourth premolar. Generally, enamel surface roughness increased with higher forage phytolith/silica content. Additionally, fresh and dry grass feeders displayed differences in wear patterns, with those of fresh grass feeders being similar to fresh and dry lucerne (phytolith-poor) feeders, supporting previous reports that "fresh grass grazers" show less abrasion than unspecialized grazers. Our results demonstrate that not only phytolith content but also properties such as water content can significantly affect plant abrasiveness, even to such an extent that wear patterns characteristic for dietary traits (browser-grazer differences) become indistinguishable. [ABSTRACT FROM AUTHOR]

Highlights • Caatinga plants produce a large amount of biomineralizations. • The deposition of Si in plant cells may be a survival strategy in this semi-arid environment. • The most prevalent types of phytoliths are tracheids, polyhedral, globular granulate, elongate and trichomes. • There is a great variation in the quantity and types of phytoliths among the species. Abstract Located in northeastern Brazil, the Caatinga biome is characterized by a semi-arid climate with vegetation adapted to high temperatures, low precipitation and uneven rainfall distribution throughout the year. The unjustified belief that the Caatinga ecosystem is poor in biodiversity and endemism, makes it the most undervalued and botanically unknown Brazilian biome, despite there being several phytogeographical areas, and a significant number of rare endemic taxa. Phytoliths are biomineralizations of silica (Si) that precipitate inside or between plant cells during the process of photosynthesis or evapotranspiration, giving the plant organism a series of benefits and evolutionary advantages. In this study, 33 species from 16 different families typical to the region were analyzed, in order to establish modern reference collections enabling further environmental reconstitution studies using phytoliths as proxy, contributing, therefore, to improved knowledge on the Caatinga biome. The results showed that Caatinga plants produce a large amount of biomineralizations, the most prevalent being tracheids, followed by polyhedral, globular granulate, elongate and trichomes (lanceolate hair cells), among others. The types of silicification found may be related to the environmental characteristics of the Caatinga , whereby plants develop mechanisms against desiccation. The deposition of Si in plant cells may be a survival strategy in this environment. Despite some limitations, phytoliths have been shown to be promising tools for improving knowledge on the vegetation of this region, as well as for use in paleoenvironmental studies in the biome. [ABSTRACT FROM AUTHOR]

Background and Aims: The role and significance of phytoliths in taxonomic diagnosis of grass species has been well documented with a focus on the types found in foliar epidermis and the synflorescence. The present paper is an attempt to broaden the scope of phytoliths in species diagnosis of grasses by developing phytolith signatures of some species of the foxtail genus Setaria P. Beauv. through in situ location and physico-chemical analysis of various phytolith morphotypes in different parts of the plant body.Methods: Clearing solution and dry ashing extraction methods were employed for in situ location and isolation of phytolith morphotypes respectively. Ultrastructural details were worked out by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy. Morphometric and frequency data of phytolith morphotypes were also recorded. Biochemical architecture of various phytolith types was worked out through SEM-EDX, XRD, and FTIR analysis. Data were analyzed through Principal Component Analysis and Cluster Analysis.Key Results:In situ location of phytoliths revealed species specific epidermal patterns. The presence of cystoliths (calcium oxalate crystals) in the costal regions of adaxial leaf surface of S. verticillata (L.) P. Beauv. is the first report for the genus Setaria. Our results revealed marked variations in epidermal ornamentation and undulation patterns with a novel “Λ” (Lamda) type of undulated ornamentation reported in S. verticillata. Dry ashing method revealed species specific clusters of phytolith morphotypes.Conclusions: The study revealed that phytoliths can play a significant role in resolution of taxonomic identity of three species of Setaria. Each species was marked out by a unique assemblage of phytolith morphotypes from various parts of the plant body. Apart from in situ location and epidermal patterning, diagnostic shapes, frequency distribution, size dimensions, and biochemical architecture emerged as complementary traits that help in developing robust phytolith signatures for plant species.

Rattan, a climbing palm of the tropical region of Southeast Asia (SEA), supplied material for objects of myriad purposes including ceremonial, religious, utilitarian, and artistic as exemplified by the collections at the National Museum of Singapore, Asian Civilization Museum, and the Singapore Art Museum. The aim of this analysis of rattan is to further the understanding of rattan, in particular its surface, and to propose a protocol-enabling positive identification of rattan in artifacts, thus guiding conservation decisions. The rattan surface defines an artifacts esthetic appearance and stability, and understanding its characteristics is essential to the development of an informed preservation strategy. Rattan epidermis morphology, topography, and cellular structure were characterized by a multi-scale and a multi-sensory approach using optical microscopy, confocal laser scanning microscopy, and field-emission scanning electron microscopy (FESEM). The chemical composition was analyzed with energy dispersive X-ray spectroscopy and macro-X-ray fluorescence spectroscopy (m-XRF) and indicated the presence of a siliceous compound, biogenic silica, in the epidermis and phytoliths in vascular tissue. A parallel analytical protocol was applied to samples extracted from museum artifacts (nineteenth-twentieth century) and contemporary objects acquired during field studies in Indonesia, Malaysia, Myanmar, and Cambodia. The methods of processing rattan have a direct impact on the siliceous layer thus leading to a better understanding of surface patterns found on artifacts. An attempt to find correlations between the percentage of silica and thickness of the siliceous layer did not produce conclusive results; both varied greatly in all studied examples. Darkening of rattan was clearly associated with aging but did not indicate any distinct effect on the chemical composition of the outer layer. The chemical analysis of the biogenic silica layer combined with recording methods of processing rattan observed during field studies in SEA provide a basis for a better understanding of rattan collections in the museum context. [ABSTRACT FROM AUTHOR]

Background and Aims: The role and significance of phytoliths in taxonomic diagnosis of grass species has been well documented with a focus on the types found in foliar epidermis and the synflorescence. The present paper is an attempt to broaden the scope of phytoliths in species diagnosis of grasses by developing phytolith signatures of some species of the foxtail genus Setaria P. Beauv. through in situ location and physico-chemical analysis of various phytolith morphotypes in different parts of the plant body. Methods: Clearing solution and dry ashing extraction methods were employed for in situ location and isolation of phytolith morphotypes respectively. Ultrastructural details were worked out by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy. Morphometric and frequency data of phytolith morphotypes were also recorded. Biochemical architecture of various phytolith types was worked out through SEM-EDX, XRD, and FTIR analysis. Data were analyzed through Principal Component Analysis and Cluster Analysis. Key Results: In situ location of phytoliths revealed species specific epidermal patterns. The presence of cystoliths (calcium oxalate crystals) in the costal regions of adaxial leaf surface of S. verticillata (L.) P. Beauv. is the first report for the genus Setaria. Our results revealed marked variations in epidermal ornamentation and undulation patterns with a novel "Λ" (Lamda) type of undulated ornamentation reported in S. verticillata. Dry ashing method revealed species specific clusters of phytolith morphotypes. Conclusions: The study revealed that phytoliths can play a significant role in resolution of taxonomic identity of three species of Setaria. Each species was marked out by a unique assemblage of phytolith morphotypes from various parts of the plant body. Apart from in situ location and epidermal patterning, diagnostic shapes, frequency distribution, size dimensions, and biochemical architecture emerged as complementary traits that help in developing robust phytolith signatures for plant species. [ABSTRACT FROM AUTHOR]

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 km 2 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. [ABSTRACT FROM AUTHOR]

We analyzed phytolith and diatom remains preserved at 45 Miocene and Pliocene localities dated between 8 and 1 Ma in northern Chad (16–17°N). Some of these localities yielded cranial remains, lower jaws, and teeth of the hominin species Australopithecus bahrelghazali (∼3.6 Ma) and Sahelanthropus tchadensis (∼7 Ma). Of the 111 sediment samples analyzed, 41 yielded phytoliths, 20 yielded diatoms, and seven yielded both phytoliths and diatoms. Freshwater planktonic and tychoplanktonic diatom species, indicative of lacustrine conditions, are dominant (>91%) in the samples. The phytolith assemblages indicate an opening of the vegetation and a general trend toward an expansion of grass-dominated environments during the time spanning the two hominin occurrences in Chad. The phytoliths suggest the presence of a mosaic environment, including closed forest patches, palm groves, and mixed/grassland formations, between 7.5 and 7 Ma, the replacement by palm grove-like vegetation at approximately 6.5–5 Ma, and the presence of exclusive grass-dominated formations after 4.5 Ma. The type-locality of S. tchadensis (TM266) was likely similar to modern palm grove formations with an arboreal cover percentage ≥40%. The type locality of A. bahrelghazali (KT12) was a grass-dominated ecosystem (likely savanna) with an unrated percentage of arboreal cover. Furthermore, the grass phytolith data support the existence of a (recurrent) Sahelian-like dry climate in northern Chad since at least 8 Ma. Therefore the local closed vegetation formations in the Djurab region at 7.5–7 Ma were sustained by aquatic systems (such as lakes or related rivers, marshes) rather than by extensive annual precipitation. [ABSTRACT FROM AUTHOR]

Grass short cell phytoliths (GSCP) are a valuable tool for the reconstruction of former grass-dominated ecosystems, especially in Africa. GSCP are highly diverse and most of them show affinities with certain taxonomic groups within the Poaceae. Taxonomic affiliation of the GSCP can be exploited for palaeoecology because many subfamilies, tribes and genera have specific ecological requirements. Finer classification of GSCP can improve the taxonomic resolution and palaeoecological reconstructions, but the numerous existing GSCP classification schemes have not been standardized yet, and are hardly comparable. It is therefore important to identify clearly defined morphotypes with taxonomic and ecological significance. We studied GSCP from 51 West African common grass species belonging to 32 genera, representing the entire ecological gradient from the Sahara to the Guinean savanna zones. We used 153 detailed GSCP morphotypes, considering variations in shape, size and 3D morphology, and eventually merged them into 20 supertypes. Correspondence analysis (CA) was applied to reveal correlations between morphotypes and taxonomic groups; ecological parameters were introduced as passive variables. In spite of redundancy among bilobates, crosses and saddles, the subfamilies Panicoideae, Aristidoideae, Chloridoideae and Ehrhartoideae can be clearly distinguished by their GSCP assemblages. Aristidoideae are characterized by very long bilobates with convex ends and very long shanks, Chloridoideae by squat saddles, Ehrhartoideae by scooped bilobates, and Panicoideae by Stipa -type bilobates and polylobates. The three Chloridoideae tribes can be separated, but not the panicoid tribes Paniceae and Andropogoneae. Rondels do not seem to have any taxonomic or ecological significance. Except for very long bilobates with very long shanks which are most common in xerophytic grasses, there is no direct correlation of certain morphotypes with the habitat requirements of the species. In the aquatic and mesophytic species, statistically significant GSCP rather mirror the taxonomic affiliation, e.g. the scooped bilobates in the aquatic Oryza species, or polylobates in mesophytic Panicoideae. The results of the Canonical CA for the detailed morphotypes and the merged supertypes are comparable. We conclude that the easily recognizable 20 supertypes are appropriate for future ecological and palaeoecological phytolith studies in Africa. For the supertypes of bilobates and crosses, the size of the particle and the length of the shank are important features whereas 3D morphology and the shape of the lobe ends can be neglected. [ABSTRACT FROM AUTHOR]

Long-term wood anatomical research has shown that 10% of the world's trees and shrubs produce silica in their wood, but silica production in bark had never been systematically investigated. We present here the results of the first comprehensive study on phytoliths in bark and compare them with data on wood phytoliths. We studied 103 bark samples from 92 species and 35 wood samples from 31 species mainly distributed in the West African savannas, altogether representing 34 plant families. The presence of silica in >90% of the studied bark samples indicates that silica production in bark is much more common than in wood. We developed a classification with three anatomical and five morphological classes and recorded their abundance in the processed phytolith samples. With a few exceptions, the phytoliths of bark and wood belong to different classes and can be clearly distinguished from each other. Wood produces Globulars s.l. and Aggregates with their own shape independent from the cells in which they had been formed. In bark, unspecific Blockies and Silica particles/Accumulations are omnipresent while 31% of the species have specific morphotypes with consistent morphologies. These phytoliths reflect the anatomy of the cells and tissues and develop either through silification of the cell lumen or the cell walls. They belong to the anatomical classes Sclerenchyma (with two subclasses Fibres and Sclereids), Cork/Parenchyma, and Cork aerenchyma. Phytoliths in bark and wood have taxonomic relevance, but the distribution is uneven on different taxonomic levels. Some Urticalean Rosids, Bignoniaceae and Capparaceae develop diagnostic phytoliths in the bark. Wood and bark phytoliths can be identified in special archaeological and palaeoecological contexts, but because they are from vegetative tissues, redundancy with similar morphotypes from other plant organs and taxonomic groups has to be considered in mixed assemblages. [ABSTRACT FROM AUTHOR]

The study was carried out to address a method for separation of terrestrial and marine biogenic silica (BSi) in estuaries based on BSi compositions and δ 13 C values in BSi associated organic matter (δ 13 C BSi ). We used two world-class major rivers - the Changjiang (Yangtze) and Huanghe (Yellow) Rivers as examples to illustrate our approach. Our results for these rivers indicate that riverine BSi is comprised mainly of phytoliths and diatoms. River BSi concentrations vary with terrestrial inputs and in-stream primary production. Although the fluvial BSi sources are complex, the terrestrial δ 13 C BSi signals are quite unique (− 24.7 ± 0.8), significantly lower than the marine δ 13 C BSi values (− 21.3 ± 0.07, central Yellow Sea) ( p < 0.01). Thus, the variation of δ 13 C within BSi organic matter can provide terrestrial source information on the biogeochemistry of silicon in estuaries and the adjacent shelf. The δ 13 C BSi combination could potentially act as an efficient tool to study environmental change in coastal areas on decadal time-scales since this index may respond to variable terrestrial fluxes from land, as well as to changed phytoplankton assemblages in the coastal ocean. [ABSTRACT FROM AUTHOR]

Phytolith-rich layers in archaeological sites constitute well defined stratigraphic horizons that would be invaluable if absolutely dated. Previous attempts to radiocarbon date phytoliths produced inconsistent results using plants with known ages. In this study a new approach to extract and analyze the silica occluded carbon was tested on well-dated archaeological contexts in Beth Shemesh and Tell es-Safi/Gath, and on modern wheat plants that grew in a controlled environment. Results show that by dissolving the silica using mild conditions, phytolith insoluble fractions can be extracted and their radiocarbon contents analyzed reproducibly. After phytolith dissolution, the remaining insoluble fractions with 10–30%C have radiocarbon concentrations that are statistically similar to associated charred seeds (within 2σ), and insoluble fractions with 40%C show concentrations that are identical to the seeds. These results show that the insoluble fraction of phytoliths is a suitable material for answering chronological questions. [ABSTRACT FROM AUTHOR]

Silicon (Si) plays an essential role in biogeochemical processes, but is still poorly characterized in the river system. This study addressed the biogenic silica (BSi) composition, origin and variation in the Changjiang River, and estimated the impacts of natural processes and human activities on the river Si cycling. Our results indicate that phytoliths comprised 14%–64% of BSi, while diatoms accounted for 34%–85% of BSi. The Changjiang River transported 620 Gg yr − 1 of BSi and 2100 Gg yr − 1 of dissolved silicate (DSi) loadings, respectively; 55% of the BSi and 51% of the DSi fluxes are transported during the high discharge period from June to September. The Changjiang River carried phytolith BSi mostly comes from the middle and lower reaches area. The ratio of BSi/(BSi + DSi) has decreased from 0.47 before 1980 to 0.19 in 2013–2014 due to the direct retention of BSi. The BSi sedimentation in the Three Gorges Reservoir would cause a decrease of total reactive silica, but contribute to approximately 4%–16% of the DSi loading at the Jiangyin station due to its dissolution. This study demonstrates that phytoliths represent a significant contribution to the biogeochemical cycle of silica in coastal waters, and in-stream process exerts a great influence on the river Si loading and cycling. [ABSTRACT FROM AUTHOR]

O entendimento dos processos que causam as diferentes distribuições de corpos silicosos no solo é essencial para a interpretação dos possíveis fatores ambientais responsáveis pela estabilidade deles, deposição de sedimentos, formação de paleossolos e para análise de sítios arqueológicos. Assim, a presente pesquisa objetivou identificar a ocorrência de corpos silicosos encontrados em horizontes superficiais de solos oriundos de diferentes ecossistemas terrestres. Amostras de horizonte superficial de 10 perfis de solo foram coletadas e queimadas em mufla, para remoção da matéria orgânica. Posteriormente, as amostras foram tratadas com HCl 10 cL L-1, para remoção das impurezas contidas na cinza. A fração silte foi obtida por sedimentação, usando o procedimento de análise granulométrica. A maior parte dos corpos silicosos em solos encontra-se na fração silte. Dessa fração, montaram-se lâminas, utilizando óleo de imersão tipo A para identificação dos corpos silicosos em microscópio óptico. A análise dos resultados permitiu observar a variedade de formas e abundância de corpos silicosos nos solos estudados, sendo mais abundantes e diversificados no solo desenvolvido de quartzito. Nos Latossolos, não houve diferença em abundância de fitólitos em relação aos solos dos biomas do Cerrado, Mata Atlântica e Caatinga.The understanding of the processes that cause the varied distribution of silica bodies in soils is essential for the interpretation of the possible environmental factors related to their stability, sediment deposition, paleosol formation and for the analysis of archaeological sites. Thus, this study had the objective of identifying and characterizing the silica bodies morphology from surface soil horizons collected at different terrestrial ecosystems. Samples of surface horizons were collected from 10 soil profiles and heated in a muffle furnace to remove organic matter. Thereafter the samples were treated with HCl 10 % (vol/vol) to remove the soluble matter contained in each sample. The silt fraction was determined by sedimentation using particle size analysis. Most biogenic silica in soils is associated to the silt fraction. Glass microscope slide containing of this fraction were mounted on an immersion oil type A for silica body identification. The results showed a variety of forms and abundance of silica bodies in the studied soils. The variation in form and abundance was highest in the soil formed from quartzite. No differences in abundance of phytoliths were observed in the Oxisols from the Cerrado, Mata Atlântica and Caatinga biomes.

Biomass from grasses such as sugarcane contains bodies of biogenic silica, the phytoliths. In industrial biomass processing, phytoliths can be harmful to equipment causing wear and ash deposits. However, phytoliths can also be beneficial if they are valorized into silica-based products. This work investigates the fate of phytolith in the industrial crushing of sugarcane stalks using biomass fractionation, ashing, and imaging techniques. Phytoliths can be traced by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) due to their proximity to the outer surface and fingerprint size, shape, and chemistry. In native sugarcane stalks, phytoliths are concentrated in the epidermal region. Industrial crushing promotes tissue ruptures that transform stalks into bagasse, where the epidermal tissues and phytoliths are found with preserved integrity, fractured, or even detached from the native tissue structures. The observations presented in this work suggest novel strategies for the isolation of phytoliths in biorefinery designs integrable to the well-established industrial crushing of sugarcane stalks. [Display omitted] • Grasses contain silica phytoliths usually overlooked in biorefining. • Fractionation, ashing, and imaging used to trace phytoliths from sugarcane stalks. • Industrial crushing promotes ruptures of tissues and phytoliths. • Observations suggest strategies for the isolation of phytoliths from cane bagasse. [ABSTRACT FROM AUTHOR]

Morphological and chemical characterization of phytoliths from aerial and underground parts of Arundo donax L. and Phragmites karka (Retz.) Trin. ex Steud. was undertaken to substantiate their taxonomic demarcation with reference to one representative species of each genus. Thirty phytolith morphotypes including some new ones were recovered. Apart from individual types, diagnostic phytolith assemblages unique to Arundo donax L. included long trapezoids, narrow bilobates, orbicular, polylobate, spiral and rugose elongate morphotypes. Phragmites karka (Retz.) Trin. ex Steud. was marked by an assemblage of polyhedral, tracheid, cylindric, cross, dendritic, quadrilobate and the rondel morphotypes. Morphometric data for shape descriptors were analysed by descriptive statistics and t -test (for independent-samples) using Paleontological Statistics (PAST) software. Estimation of total silica content revealed higher values for Phragmites karka (Retz.) Trin. ex Steud. than Arundo donax L. from most of the parts. Elemental analysis of phytolith morphotypes from various parts in both the species revealed the presence of Aluminium (Al), Calcium (Ca), Chlorine (Cl), Copper (Cu), Iron (Fe), Magnesium (Mg), Nitrogen (N), Potassium (K) and Titanium (Ti) in small amounts in addition to major elements including Carbon (C) and Oxygen (O) and Si (Silicon). Principal Component Analysis (PCA) of elemental composition grouped Arundo donax L. (leaf) and Phragmites karka (Retz.) Trin. ex Steud. (leaf) together in a single group. The Si (wt%) amounts varied significantly among various parts of Arundo donax L. (p ≤ 0.05), whereas differences with Phragmites karka (Retz.) Trin. ex Steud. parts were insignificant. Similarly, Si (wt%) between the various parts of both species showed significant differences (p ≤ 0.05). Chemical characterization of silica from leaf and synflorescence of both the species using X-ray Diffraction (XRD) showed polymorphic forms of silica and zeolites. Fourier Transform-Infrared (FTIR) Spectroscopy has confirmed the presence of silanol group and siloxane linkages in all the samples. [ABSTRACT FROM AUTHOR]

Solid biosilica (phytoliths) deposited in plant tissues is thought to function as structural support, as a cost-effective alternative to lignin, and in herbivore defence, by limiting nutrient access/extraction and abrading herbivore mouthparts. It has been assumed that active phytolith accumulation evolved for these purposes, but these hypotheses remain untested. For example, an influential idea holds that grasses became so silica-rich through antagonistic co-evolution with mammalian grazers during the Cenozoic., We examine whether phytoliths fulfil criteria established for adaptations, focusing on three aspects. First, we evaluate the recent debate concerning whether plant silica wears herbivore mouthparts/teeth. Secondly, we test whether the evolutionary pattern of phytolith accumulation is consistent with adaptive hypotheses by mapping silica content onto time-calibrated land plant and grass phylogenies. Thirdly, we compare with palaeontological evidence for the timing of the 'demand' for the hypothesized function (structural support, herbivore defence)., Our survey demonstrates that phytoliths meet several criteria for adaptations, but key aspects require further study. For example, phytoliths wear teeth but are likely less important than dietary grit, suggesting that silica deterrence is ineffective against large mammalian grazers., Mapping analysis indicates that active silica accumulation evolved numerous times, rather than being ancestral in land plants. However, a clear temporal link between these events and hypothesized functional 'demands' is still missing. For example, we find no convincing evidence for Cenozoic grass-grazer co-evolution., Synthesis. Phytoliths help support and defend plants today, but the adaptive origin of this trait requires further testing. Such tests should integrate the phylogenetic distributions of phytoliths with ecology and biomechanics and use fossil evidence to evaluate the correlation between functional 'demand' and plant evolution. [ABSTRACT FROM AUTHOR]

We studied bacterial and fungal colonization of submerged plant litter, using a known Si-accumulator (Equisetum arvense), in experimental microcosms during one month. We specifically addressed the microbial decomposer role concerning biogenic silica (bSiO2) dissolution from the degrading litter. To vary the rates and level of microbial colonization, the litter was combined with a range of mineral nitrogen (N) and phosphorous (P) supplements. Overall microbial growth on plant litter increased with higher levels of N and P. There was a tendency for higher relative bacterial than fungal stimulation with higher nutrient levels. Differences in microbial colonization of litter between treatments allowed us to test how Si remineralization from plants was influenced by microbial litter decomposition. Contrary to previous results and expectations, we observed a general reduction in Si release from plant litter colonized by a microbial community, compared with sterile control treatments. This suggested that microbial growth resulted in a reduction of dissolved Si concentrations, and we discuss candidate mechanisms to explain this outcome. Hence, our results imply that the microbial role in plant litter associated Si turnover is different from that commonly assumed based on bSiO2 dissolution studies in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from several agriculturally important monocotyledonous species play a significant role in atmospheric CO2 sequestration. However, anomalous phytC radiocarbon (14C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14C and δ13C) of phytC, plant tissues, atmospheric CO2, and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemicalthermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it was found that phytC is partially derived from soil carbon that can be several thousand years old. The fact that phytC is not uniquely constituted of photosynthetic C limits the usefulness of phytC either as a dating tool or as a significant sink of atmospheric CO2. It additionally calls for further experiments to investigate how SOM-derived C is accessible to roots and accumulates in plant biosilica, for a better understanding of the mechanistic processes underlying the silicon biomineralization process in higher plants. [ABSTRACT FROM AUTHOR]

Grasses (Poaceae) lack the complex biochemical pathways and structural defenses employed by other plant families; instead they deposit microscopic silica (SiO2) granules in their leaf blades (i.e. phytoliths) as a putative defense strategy. Silica accumulation in grasses has generally been considered an inducible defense; other research suggests silica accumulation occurs by passive diffusion and should therefore be closely coupled with whole plant transpiration. We tested the hypothesis that grasses increase leaf silica concentration in response to artificial defoliation in a common garden study in the Serengeti ecosystem of East Africa. Additionally, a watering treatment tested the alternative hypothesis that leaf silica was largely driven by plant water status. Leaf silica content of two dominant C4 Serengeti grass species, Themeda triandra and Digitaria macroblephara, was quantified after a 10-month clipping x water experiment in which defoliation occurred approximately every two months and supplementary water was added every two weeks. Themeda had greater silica content than Digitaria, and Themeda also varied in foliar silica content according to collection site. Clipping had no significant effect on leaf silica in either species and watering significantly increased silica content of the dominant tall grass species, Themeda, but not the lawn species, Digitaria. Our data, and those collected as part of a supplementary literature review, suggest that silicon induction responses are contingent upon a combination of plant identity (i.e., species, genotype, life history limitations) and environmental factors (i.e., precipitation, soil nutrients, grazing intensity). Specifically, we propose that an interaction between plant functional type and water balance plays an especially important role in determining silica uptake and accumulation.

Many plants, including grasses and some important human food sources, accumulate, and precipitate silica in their cells to form opaline phytoliths. These phytoliths contain small amounts of organic matter (OM) that are trapped during the process of silicification. Previous work has suggested that plant silica is associated with compounds such as proteins, lipids, lignin, and carbohydrate complexes. It is not known whether these compounds are cellular components passively encapsulated as the cell silicifies, polymers actively involved in the precipitation process or random compounds assimilated by the plant and discarded into a "glass wastebasket." Here, we used Raman spectroscopy to map the distribution of OM in phytoliths, and to analyze individual phytoliths isolated from Sorghum bicolor plants grown under different laboratory treatments. Using mapping, we showed that OM in phytoliths is distributed throughout the silica and is not related to dark spots visible in light microscopy, previously assumed to be the repository for phytolith OM. The Raman spectra exhibited common bands indicative of C-H stretching modes of general OM, and further more diagnostic bands consistent with carbohydrates, lignins, and other OM. These Raman spectra exhibited variability of spectral signatures and of relative intensities between sample treatments indicating that differing growth conditions altered the phytolith carbon. This may have strong implications for understanding the mechanism of phytolith formation, and for use of phytolith carbon isotope values in dating or paleoclimate reconstruction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three entities of taxonomically difficult genus Bolboschoenus collected from India were subjected to micromorphological and phytolith studies. For micromorphological study, silica bodies in the outer cells of the achene epidermis were revealed by acetolysis and sonication and examined by scanning electron microscopy. A silica body consists of a basal platform, one or more large elevated protuberances, and sometimes smaller satellite protuberances. Significant differences have been found in the number of protuberances, the presence/absence of satellites, the texture of the platform, and the occurrence of nodules on the larger protuberances at individual species level. These features, combined with achene shape and characteristics of the anticlinal walls of the epidermal cells (undulate vs. straight, thick vs. thin, buttressed or not), are expressed in a unique combination for each entity. It is clearly evident from the study that micromorphological characters of the achene epidermis vary significantly between different species. Therefore, the micromorphology of the achene epidermis of Bolboschoenus is valuable in understanding the taxonomy at infraspecific, specific and supraspecific levels in the genus. Results provided by phytolith analysis are useful not only in taxonomic demarcation of Bolboschoenus, but they will be useful in future archaeobotanical and paleoecological investigations also. In conclusion, present study confirms the presence of B. affinis and B. glaucus in India, while suggests more investigation on presence of B. maritimus in India. [ABSTRACT FROM AUTHOR]

Silica phytoliths are microscopic structures of amorphous hydrated silica (SiO· nHO) formed by specialized plant cells. Besides their biological roles, physical, chemical, and structural properties of biogenic silica offer a wide spectrum of applications in many fields of industry and technology. Therefore, processes involved in their formation recently become a very interesting topic to study. However, optical transparency and microscopic sizes of silica phytoliths do not allow their visualization and localization by classical light microscopy methods. Their observation thus requires phytolith isolation, technically difficult or lengthy sample preparation procedures, or a work with toxic chemicals. In this paper we are proposing a novel method for visualization of silica phytoliths in Sorghum bicolor root endodermal cells by fluorescence microscopy using alkali mounting solution (pH 12). This method offers an easy and quick preparation of the samples and high contrast imaging. Based on our results we can assume that the proposed fluorescent method for silica phytolith investigation allows observation of multiple samples in relatively short time period and thus might be applicable also for high-throughput screenings. Using this method we found out that after a 3-day cultivation of sorghum plants the minimal needed concentration of sodium silicate, limiting the formation of silica phytoliths in the root endodermis, was 25 µmol dm. The positive correlation of sodium silicate concentration in the substrate with the phytolith diameter was also observed. [ABSTRACT FROM AUTHOR]

Grasses (Poaceae) lack the complex biochemical pathways and structural defenses employed by other plant families; instead they deposit microscopic silica (SiO2) granules in their leaf blades (i.e., phytoliths) as a putative defense strategy. Silica accumulation in grasses has generally been considered an inducible defense; other research suggests silica accumulation occurs by passive diffusion and should therefore be closely coupled with whole plant transpiration. We tested the hypothesis that grasses increase leaf silica concentration in response to artificial defoliation in a common garden study in the Serengeti ecosystem of East Africa. Additionally, a watering treatment tested the alternative hypothesis that leaf silica was largely driven by plant water status. Leaf silica content of two dominant C4 Serengeti grass species, Themeda triandra and Digitaria macroblephara, was quantified after a 10-month clipping × water experiment in which defoliation occurred approximately every 2 months and supplementary water was added every 2 weeks. Themeda had greater silica content than Digitaria, and Themeda also varied in foliar silica content according to collection site. Clipping had no significant effect on leaf silica in either species and watering significantly increased silica content of the dominant tall grass species, Themeda, but not the lawn species, Digitaria. Our data, and those collected as part of a supplementary literature review, suggest that silicon induction responses are contingent upon a combination of plant identity (i.e., species, genotype, life history limitations) and environmental factors (i.e., precipitation, soil nutrients, grazing intensity). Specifically, we propose that an interaction between plant functional type and water balance plays an especially important role in determining silica uptake and accumulation. [ABSTRACT FROM AUTHOR]

Abstract: Phytoliths (silica bodies) occur in Poaceae species in large numbers and have been shown to have antiherbivory roles. However, phytoliths occur also in many other taxa in much smaller numbers, which raises the question of the extent of both their potential and actual antiherbivory role in these taxa. In order to address the question of their potential antiherbivory role, we sampled 20 wild-growing southwest Asian species of the family Asteraceae, species of which have a much lower phytolith concentrations than Poaceae taxa. We studied the potential positive effect of grazing on phytolith formation and the possible tendency of plants to have higher concentrations of such defence structures in their reproductive organs. We sampled plants from populations of 12 non-spiny and eight spiny species growing in un-grazed and grazed plots in seven sites along a large rainfall gradient (80–900mm mean annual) in Israel, a region known for its long and intensive grazing history. The study included 21 pairs of un-grazed and grazed plants from 16 of these 20 species. In addition, ten populations of eight species were sampled in order to examine whether phytolith concentrations in the reproductive organs are higher than in vegetative organs. We did not find consistently higher phytolith concentrations in grazed plants compared to un-grazed plants of the same species and habitat (15 species), and in 12 out of 21 pairs of un-grazed and grazed plants (from 15 species) we even found higher phytolith concentrations in un-grazed plants, a phenomenon which was more common in the more arid sites. Phytolith concentrations in inflorescences are commonly (6 out of the 8 species) lower than in the rest of the shoot. We conclude that the antiherbivory potential of phytoliths in the southwest Asian Asteraceae as a group is much smaller than in the Poaceae. [Copyright &y& Elsevier]