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Background and aim: Ranked among the world's top ten crops, cassava (Manihot esculenta Crantz) is the main staple food in sub-Saharan Africa. Its production is strongly limited by biotic and abiotic stresses, which proved to be mitigated in other plants by silicon (Si) uptake. The role of Si is unknown in cassava. Yet it has genes encoding specific aquaporins involved in plant water and Si influxes in numbers similar to those of some Si accumulating monocots. Methods: Cassava Si and nutrient status were studied in four sites in South-Kivu, Democratic Republic of Congo, differing in altitude, climate and soil desilication stage. Out of 720 farms, 360 plots were selected for agronomic monitoring, of which 40 for foliar/topsoil analysis using germanium to trace Si. Results: Regardless of soil type, Si concentration in cassava leaves ranged from 2 to 14 g kg−1 while root yield varied from 0.5 to 18 t ha−1 yr−1. Silicon accumulation formed fine-sized phytoliths of different morphotypes. Structural equation modelling showed that leaf Si mineralomass was an important predictor of yield, with a direct contribution of 45%. Silicon accumulation mitigated the altitude-mediated incidence of cassava mosaic disease (25%), notably through enhancing micronutrient uptake, while it could contribute to the plant tolerance to soil acidity. Conclusion: Silicon accumulates substantially in cassava leaves. Our data highlight the potential role of Si in cassava production through direct and indirect effects by alleviating biotic and abiotic stresses. The function of Si in cassava thus deserves more attention than given until now. [ABSTRACT FROM AUTHOR]

Background and aims: Phytolith analysis is a promising tool for paleovegetation reconstruction. However, compared with grass phytoliths, there are few studies that have classified the phytoliths of trees. Therefore, reliable definitions of phytolith types in woody plants and studies of representative woody phytoliths in soils are needed to provide an improved basis for reliable phytolith-based vegetation reconstruction. Methods: To explore the morphology of woody phytoliths and their preservation in soils, we described the phytolith morphology of 60 common broadleaved woody plants in the mid-subtropical zone of China, based initially on anatomical origin, and then on shape and finally on texture. We also for the first time established an index (R value) to explore the preservation of broadleaved woody phytoliths in soil in this region. Results: We divided the phytoliths of broadleaved woody plants into 6 major types and 35 sub-types. The 6 major types are: Epidermal Cell, Silicified stomata, Tracheary, Favose, Haircell, and Others. We found some degree of correspondence between different phytolith types and the parent plants. Fagaceae, Lauraceae, Magnoliaceae, Rosaceae, Anacardiaceae and Euphorbiaceae could be clearly distinguished from other families based on phytoliths. Only eight types of broadleaved woody phytoliths were present in the soils. Elongate attenuate, Elongate entire, and Polyhedral were better preserved in soils than the other types (Elongate entire attenuate, Tabular sinuate, Hair, Sclereid, and Favose). Conclusion: Our results provide a more accurate reference for broadleaved wood phytoliths in interpreting paleovegetation in this region. [ABSTRACT FROM AUTHOR]

Background and aims: The role of phytoliths as indicators of temperate forests remains a topic of ongoing debate that requires a clear understanding. This study aims to evaluate the potential of overall phytolith assemblages, as well as arboreal phytoliths, in representing the composition and abundance of temperate forests.This study, conducted in Northeast China, established 79 sample plots across four forest types. Topsoil samples were collected, and corresponding vegetation data—including tree cover, grass cover, and the normalized difference vegetation index (NDVI)—were obtained from MODIS albedo products. Subsequently, we analyzed the significance of phytoliths in relation to various temperate forests.Results indicate that the P. koraiensis mixed forest, the P. koraiensis-Picea-Abies forest, the mountainous poplar-birch forest, and the Pinus-Quercus forest exhibit significantly different characteristics in their phytolith assemblage. Furthermore, these four forest types can be distinguished based on both overall phytoliths and arboreal phytoliths. However, phytoliths proved to be ineffective in accurately quantifying vegetation data in temperate forests, with forest NDVI demonstrating relatively better accuracy at 40%. Additionally, arboreal phytoliths contribute approximately 20% to the overall phytoliths used to indicate forest composition and abundance, and they exhibit a representation bias of 30-40% regarding tree abundance in temperate forests.Our study highlighted the potential of utilizing overall phytoliths to differentiate various temperate forest types, while arboreal phytoliths were found to be more reliable indicators of forest abundance. Future work on north temperate forest phytolith should focus on establishing the quantitative relationship between phytoliths and forest abundance.Methods: The role of phytoliths as indicators of temperate forests remains a topic of ongoing debate that requires a clear understanding. This study aims to evaluate the potential of overall phytolith assemblages, as well as arboreal phytoliths, in representing the composition and abundance of temperate forests.This study, conducted in Northeast China, established 79 sample plots across four forest types. Topsoil samples were collected, and corresponding vegetation data—including tree cover, grass cover, and the normalized difference vegetation index (NDVI)—were obtained from MODIS albedo products. Subsequently, we analyzed the significance of phytoliths in relation to various temperate forests.Results indicate that the P. koraiensis mixed forest, the P. koraiensis-Picea-Abies forest, the mountainous poplar-birch forest, and the Pinus-Quercus forest exhibit significantly different characteristics in their phytolith assemblage. Furthermore, these four forest types can be distinguished based on both overall phytoliths and arboreal phytoliths. However, phytoliths proved to be ineffective in accurately quantifying vegetation data in temperate forests, with forest NDVI demonstrating relatively better accuracy at 40%. Additionally, arboreal phytoliths contribute approximately 20% to the overall phytoliths used to indicate forest composition and abundance, and they exhibit a representation bias of 30-40% regarding tree abundance in temperate forests.Our study highlighted the potential of utilizing overall phytoliths to differentiate various temperate forest types, while arboreal phytoliths were found to be more reliable indicators of forest abundance. Future work on north temperate forest phytolith should focus on establishing the quantitative relationship between phytoliths and forest abundance.Results: The role of phytoliths as indicators of temperate forests remains a topic of ongoing debate that requires a clear understanding. This study aims to evaluate the potential of overall phytolith assemblages, as well as arboreal phytoliths, in representing the composition and abundance of temperate forests.This study, conducted in Northeast China, established 79 sample plots across four forest types. Topsoil samples were collected, and corresponding vegetation data—including tree cover, grass cover, and the normalized difference vegetation index (NDVI)—were obtained from MODIS albedo products. Subsequently, we analyzed the significance of phytoliths in relation to various temperate forests.Results indicate that the P. koraiensis mixed forest, the P. koraiensis-Picea-Abies forest, the mountainous poplar-birch forest, and the Pinus-Quercus forest exhibit significantly different characteristics in their phytolith assemblage. Furthermore, these four forest types can be distinguished based on both overall phytoliths and arboreal phytoliths. However, phytoliths proved to be ineffective in accurately quantifying vegetation data in temperate forests, with forest NDVI demonstrating relatively better accuracy at 40%. Additionally, arboreal phytoliths contribute approximately 20% to the overall phytoliths used to indicate forest composition and abundance, and they exhibit a representation bias of 30-40% regarding tree abundance in temperate forests.Our study highlighted the potential of utilizing overall phytoliths to differentiate various temperate forest types, while arboreal phytoliths were found to be more reliable indicators of forest abundance. Future work on north temperate forest phytolith should focus on establishing the quantitative relationship between phytoliths and forest abundance.Conclusion: The role of phytoliths as indicators of temperate forests remains a topic of ongoing debate that requires a clear understanding. This study aims to evaluate the potential of overall phytolith assemblages, as well as arboreal phytoliths, in representing the composition and abundance of temperate forests.This study, conducted in Northeast China, established 79 sample plots across four forest types. Topsoil samples were collected, and corresponding vegetation data—including tree cover, grass cover, and the normalized difference vegetation index (NDVI)—were obtained from MODIS albedo products. Subsequently, we analyzed the significance of phytoliths in relation to various temperate forests.Results indicate that the P. koraiensis mixed forest, the P. koraiensis-Picea-Abies forest, the mountainous poplar-birch forest, and the Pinus-Quercus forest exhibit significantly different characteristics in their phytolith assemblage. Furthermore, these four forest types can be distinguished based on both overall phytoliths and arboreal phytoliths. However, phytoliths proved to be ineffective in accurately quantifying vegetation data in temperate forests, with forest NDVI demonstrating relatively better accuracy at 40%. Additionally, arboreal phytoliths contribute approximately 20% to the overall phytoliths used to indicate forest composition and abundance, and they exhibit a representation bias of 30-40% regarding tree abundance in temperate forests.Our study highlighted the potential of utilizing overall phytoliths to differentiate various temperate forest types, while arboreal phytoliths were found to be more reliable indicators of forest abundance. Future work on north temperate forest phytolith should focus on establishing the quantitative relationship between phytoliths and forest abundance. [ABSTRACT FROM AUTHOR]

In 1983, Raven suggested that silica could substitute for lignin or cellulose as a structural material in plants, and should be favoured because of its lower energetic costs. He then asked the question why more plants did not use silica for structural support. Raven's idea eventually led to a whole series of investigations into the substitution of silicon for carbon in plants, so-called trade-offs. In this Opinion we offer some, hopefully helpful, thoughts on this research, and we attempt to answer Raven's question. We conclude that more focus on the distribution of silicon and carbon at the cellular level is needed, and that we should be more careful to avoid teleological thinking. [ABSTRACT FROM AUTHOR]

Purpose: Silicon (Si) is a beneficial element for plants and plays important roles in the biogeochemical cycle of mineral elements. Yet, few studies have focused on the impact of nitrogen (N) deposition on plant Si uptake and the Si biocycle. Methods: We designed an experiment investigating canopy and understory N addition in a tropical forest to comprehensively assess the response of the Si cycle to N addition focusing on understory plants and topsoil. After six years of treatment, we compared the effects of different treatments on the concentrations of Si-related variables in the leaves of dominant understory species, and topsoil. The foliar elemental stoichiometry, plant water-use efficiency, and soil properties were also assessed to explore potential mechanisms underpinning an N-regulated biological feedback loop of Si. Results: The concentrations of SiO2 and phytoliths in the leaves of the understory plants increased under N addition, while those of phytolith and plant-available Si in the topsoil were not altered. The significant accumulation of Si in the leaves and the unaltered plant-available Si concentrations in the soil were associated with enhanced plant Si uptake and decreased soil phytolith return due to increased phosphorus (P) limitation, soil acidification, and decreased leaf C:N ratios caused by N addition. Conclusion: Our findings suggest that N addition affected plant phytolith production and its coupling with the Si biocycle in the forest which may stimulate plant Si accumulation and decrease soil Si return. Nitrogen enrichment will alter the biological Si cycle in forest ecosystems at regional and global scales. [ABSTRACT FROM AUTHOR]

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

Background and aims: Silicon (Si) deficiency is a major constraint on rice production. The objective of this study was to evaluate the long-term influence of phytolith-rich straw return and groundwater table management on labile Si fractions in paddy soil and subsequent plant Si uptake. Methods: A field experiment was conducted over 36 years in subtropical China with different application doses of phytolith-rich straw and a groundwater table of either 20 or 80 cm. An optimized sequential chemical extraction procedure allowed us to determine labile Si fractions, represented by CaCl2-Si, Acetic-Si, H2O2-Si, Oxalate-Si, and Na2CO3-Si. Additional analyses included the determination of amorphous silica particles in soil, phytoliths in supplied straw, Si in planted rice straw, and the dissolution rate of phytoliths extracted from supplied straw. Results: Long-term application of phytolith-rich straw significantly increased the H2O2-Si and Na2CO3-Si contents. The CaCl2-Si (5.21–7.91 mg kg− 1), H2O2-Si (50.0–72.4 mg kg− 1) and Na2CO3-Si (3.33–4.60 g kg− 1) contents were positively correlated with soil organic carbon. The Si content (13.6–28.9 g kg−‍1) in planted rice straw significantly (p < 0.05) increased with the application dose of phytolith-rich straw under both groundwater tables. This effect was significantly (p < 0.05) greater under 80 cm groundwater table than under 20 cm groundwater table for matching straw amendments. Conclusions: This study indicates that long-term application of phytolith-rich straw and groundwater management significantly increase soil Si bioavailability by promoting accumulation of organic matter and phytoliths, and enhancing the soil-plant Si cycle. [ABSTRACT FROM AUTHOR]

Aims: Silicophytoliths contribute to the pool of amorphous silica that is incorporated into the soils acting as intermediary in the biogeochemical cycle of silicon. Most studies focus their attention in the production of aerial parts of plants but not in roots. In order to advance into the knowledge about the relevance of root amorphous silica in soil Si cycle, we studied the silicophytolith content of roots from grasses and crops, and from soil's roots of different sites from Pampean region, Argentina, one of the most fertile and used for agricultural practices. Methods: Roots from three crops and seven grasses and from soils under three different uses were studied. Silicophytoliths were extracted by a calcination technique. Results: All the species produced silicophytoliths derived from vascular and/or endodermal tissues. Silicophytolith content was higher in Pampean grasses (6.34–15.38%) than in crops (0.01–1.58%). Root silicophytolith content in the pasture was 10 times higher than in the other sites. Conclusions: The potential input of root silica to soils is related to the type and cover of vegetation, the amount of roots in soils and the silicophytoliths accumulated in roots. Results suggested that root silicophytoliths should be consider in future studies of biogeochemical cycle of Si. [ABSTRACT FROM AUTHOR]

Aims: Supplying phytolith-rich biochar in agrosystems increases soil pH, CEC and nutrient availability, adding to the impact of Si uptake on plant growth. Here we studied this specific impact as influenced by soil properties, and assessed the role of phytoliths to provide plant available Si. Methods: We used a young Cambisol and a highly weathered, poorly buffered, desilicated Nitisol. The biochars were produced from rice plants respectively enriched (Si+) and depleted (Si-) in Si. They had identical pH and nutrient contents, but largely differed in Si content (51.3 g Si kg−1 in Si + vs 0.3 g Si kg−1 in Si-). We compared their effects to that of wollastonite (CaSiO3) on the biomass and mineralomass of wheat plants in a soil:solution:plant device. The contents of soil bioavailable Si and biogenic Si were assessed through an original CaCl2 kinetic extraction and the DeMaster Na2CO3 alkaline dissolution, respectively. Results: The DeMaster technique dissolved Si from phytolith as well as from wollastonite. The soil buffering capacity (cmolc kg−1) was 31 in the Cambisol and 0.2 in the Nitisol. An identical supply of phytolithic biochar increased pH from 4.5 to 4.8 in the Cambisol, and from 4.8 to 7.4 in NI. It further increased the content of bioavailable Si (from 55 to 97 mg kg−1 in the Cambisol, and 36 to 209 mg kg−1 in the Nitisol), as well as plant Si uptake, biomass and Si mineralomass. That increase was largest in the Nitisol. Conclusions: The DeMaster technique did not specifically quantify the phytolith pool. This pool was the main source of plant available Si in both the Cambisol and Nitisol amended with phytolithic biochar. At identical phytolithic Si supply, however, soil pH and soil buffering capacity controlled the transfer of Si in the soil-plant system, which was largest in the poorly buffered Nitisol. The effect of phytolithic biochar on Si bioavailability was depending on soil constituents and properties, and thus on soil type. [ABSTRACT FROM AUTHOR]

Background and aims: Phytolith occluded carbon (PhytOC) is of interest for isotope studies, dating of sediments and the capture and storage of carbon. Many methodologies have been used for the isolation of phytoliths from plant material; however, there are wide disparities in the PhytOC contents when determined by different methodologies. In this study we examine the utility of the two main methods used for quantifying PhytOC. Methods: These methods are: (1) a microwave digestion followed by a Walkley-Black digestion, and (2) HSO/HO. Results: Method (1) produced PhytOC values over 50 times higher than those acquired by method (2). SEM examination indicated that the differences were likely due to shattering of the phytoliths by method (2) allowing consumption by the acid and peroxide of PhytOC . Conclusion: These results indicate that for the samples analysed here: 1] the modified microwave method allowed the total PhytOC to be measured, 2] the HSO/HO method allowed the PhytOC within the tightly packed silica matrix to be measured, and 3] the PhytOC retained within the phytolith cavities could possibly be calculated by subtracting 2] from 1]. For the samples analysed here most of the PhytOC resided in the phytolith cavities. [ABSTRACT FROM AUTHOR]

Aims: Carbon (C) bio-sequestration within the phytoliths of plants, a mechanism of long-term biogeochemical C sequestration, may play a major role in the global C cycle and climate change. In this study, we explored the potential of C bio-sequestration within phytoliths produced in cultivated rice ( Oryza sativa), a well known silicon accumulator. Methods: The rice phytolith extraction was undertaken with microwave digestion procedures and the determination of occluded C in phytoliths was based on dissolution methods of phytolith-Si. Results: Chemical analysis indicates that the phytolith-occluded C (PhytOC) contents of the different organs (leaf, stem, sheath and grains) on a dry weight basis in 5 rice cultivars range from 0.4 mg g to 2.8 mg g, and the C content of phytoliths from grains is much lower than that of leaf, stem and sheath. The data also show that the PhytOC content of rice depends on both the content of phytoliths and the efficiency of C occlusion within phytoliths during rice growth. The biogeochemical C sequestration flux of phytoliths in 5 rice cultivars is approximately 0.03-0.13 Mg of carbon dioxide (CO) equivalents (Mg-e-CO) ha year. From 1950 to 2010, about 2.37 × 10 Mg of CO equivalents might have been sequestrated within the rice phytoliths in China. Assuming a maximum phytoliths C bio-sequestration flux of 0.13 Mg-e-CO ha year, the global annual potential rate of CO sequestrated in rice phytoliths would approximately be 1.94 × 10 Mg. Conclusions: Therefore rice crops may play a significant role in long-term C sequestration through the formation of PhytOC. [ABSTRACT FROM AUTHOR]

Aims: Most cereals accumulate Si in their shoots. Soil bioavailability of Si may be a constraint on the beneficial role of silica in cereals but it is not yet well supported by field data. The aim of this study is to evaluate the long-term impact of wheat straw exports on the pool of soil phytoliths, which, it is suggested, represents the most labile and renewable pool of soil Si. Methods: We measured the amorphous Si (ASi) in soils from several experiments at Rothamsted Research (UK), which provided long-term soil data back to the middle of the 19th century, using two alternative extraction techniques: NaCO (referred to as AS) or zinc bromide extraction (referred to as ASi). Results: All samples showed a similar range of AS and ASi but low values (0.1-3.4 mg g DW) compared to published data on natural ecosystems. In the Broadbalk experiment, a decrease over time in ASi in the topsoil samples is in good agreement with the hypothesis that cropping and exports of straw leads to depletion of soil phytoliths. A decrease in Si concentration in straw samples was observed between 1883 and 1944. From 1944 to the present, Si concentration increased irregularly in the straw, probably as the result of liming, which enhanced the dissolution of the remaining phytoliths through increasing pH. In the reforested Geescroft field the higher phytolith concentration in the modern topsoil samples is in good agreement with a re-building of phytolith storage from litter input in an acidic environment. Conclusions: Our results therefore support the hypothesis that export of wheat straw leads to a decrease in bioavailable Si. [ABSTRACT FROM AUTHOR]

The determination of the plant-induced Si-isotopic fractionation is a promising tool to better quantify their role in the continental Si cycle. Si-isotopic signatures of the different banana plant parts and Si source were measured, providing the isotopic fractionation factor between plant and source. Banana plantlets ( Musa acuminata Colla, cv Grande Naine) were grown in hydroponics at variable Si supplies (0.08, 0.42, 0.83 and 1.66 mM Si). Si-isotopic compositions were determined on a multicollector plasma source mass spectrometer (MC-ICP-MS) operating in dry plasma mode. Results are expressed as δ29Si relative to the NBS28 standard, with an average precision of ± 0.08‰ (±2σD). The fractionation factor 29ε between bulk banana plantlets and source solution is −0.40 ± 0.11‰. This confirms that plants fractionate Si isotopes by depleting the source solution in 28Si. The intra-plant fractionation Δ29Si between roots and shoots amounts to −0.21 ± 0.08‰. Si-isotopic compositions of the various plant parts indicate that heavy isotopes discrimination occurs at three levels in the plant (at the root epidermis, for xylem loading and for xylem unloading). At each step, preferential crossing of light isotopes leaves a heavier solution, and produces a lighter solution. Si-isotopic fractionation processes are further discussed in relation with Si uptake and transport in plants. These findings have important implications on the study of continental Si cycle. [ABSTRACT FROM AUTHOR]

Research was carried out with the objective of investigating the mineral composition and Si accumulation in tissues of young cuttings of blueberry (Vaccinum corymbosus L. cv. Bluecrop). Blueberry cuttings were irrigated every day for 1 hour (140 ml per pot) with river water containing 0.66 to 1.0 mol m-3 SiO2, and after 7 months of growth their mineral composition and silicon distribution were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mean contents of N, K, Mg, Cu and Zn in young leaves were the same as those in old ones. On the other hand, the mean contents of P, Ca, Si, Fe and Mn in old leaves were higher than those in young leaves. Although Si is not known to be an essential element for growth of blueberries, it was the element that accumulated the most in leaves, with a mean content of 32.0 and 60.0 mg g-1 dry weight in young and old leaves, respectively. The mean Si content in young leaves was 3.1, 56.7, 4.8, 4.9 and 85 times higher than the mean contents of N, P, K, Ca and Mg, respectively, and was 5.4, 60.0, 8.8, 6.8 and 100 times higher than in old leaves. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis of dry ash samples showed that Si accumulated in many parts of the leaves, forming phytoliths in the upper epidermis, including some parts of the palisade mesophyll, in the lower epidermis around the stomata, including guard cells, and in some parts of the spongy mesophyll, and in the veins. There were also silica bodies of unknown origin on the upper epidermis. [ABSTRACT FROM AUTHOR]