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Phytolith have been recognized as an important soil bioavailable Si source for plants, as well as a sink of C and heavy metals in soils. Though the impacts of fire and heat on phytolith sequestration of some nutrients (phosphorus, potassium) and heavy metals have been addressed, little attention has been paid to fire's effects on phytolith carbon sequestration. In this study, the carbon and dissolved Si content of phytoliths extracted from 6 common grass species and their burned ashes, as well as phytoliths collected from different areas (burned, transitional, and unburned) of a pine forest, were compared to characterize the effects of open fire on phytolith carbon content, solubility, and carbon sequestration. The carbon content and Si dissolution of ashed phytoliths varied between plant species, and differed with phytoliths from modern plants. The topsoil phytoliths had increased carbon content, and generally decreased solubility across the gradient of unburned, transitional, and burned pine forest. We therefore conclude that open fire can cause changes in phytolith related carbon content and solubility, as well as its preservation in soils. This study provides new perspective on the effects of open fire on phytolith carbon sequestration and its estimation. [ABSTRACT FROM AUTHOR]

Abstract Phytolith have been recognized as an important soil bioavailable Si source for plants, as well as a sink of C and heavy metals in soils. Though the impacts of fire and heat on phytolith sequestration of some nutrients (phosphorus, potassium) and heavy metals have been addressed, little attention has been paid to fire’s effects on phytolith carbon sequestration. In this study, the carbon and dissolved Si content of phytoliths extracted from 6 common grass species and their burned ashes, as well as phytoliths collected from different areas (burned, transitional, and unburned) of a pine forest, were compared to characterize the effects of open fire on phytolith carbon content, solubility, and carbon sequestration. The carbon content and Si dissolution of ashed phytoliths varied between plant species, and differed with phytoliths from modern plants. The topsoil phytoliths had increased carbon content, and generally decreased solubility across the gradient of unburned, transitional, and burned pine forest. We therefore conclude that open fire can cause changes in phytolith related carbon content and solubility, as well as its preservation in soils. This study provides new perspective on the effects of open fire on phytolith carbon sequestration and its estimation.

The rising CO2 content in the atmosphere is the major cause of the greenhouse gas effect. Biological carbon capture and storage is a useful strategy for decreasing CO2 levels in terrestrial ecosystems. The capacity of terrestrial ecosystems to store carbon is enormous, which is essential to the global carbon cycle and climate change mitigation. It is achieved by sequestering the carbon in plant phytolith. Silicon, which is resistant to both weathering and decomposition, is found in phytolith. Plant phytoliths provide long-term carbon stabilization through carbon sequestration. External silicon fertilizer application will enhance phytolith content in plants. Compared to monocots, dicots absorb less amount of silicon. Carbon occluded in phytoliths can remain stable and undecomposed over a long period. Long-term carbon storage in terrestrial carbon sinks such as plants and trees are the most effective way to overcome climate change challenges. Fixed carbon-produced biomass reaches the soil carbon reservoir and is stored there for millennia. Implementing carbon sequestration techniques can significantly sulk down the increasing atmospheric CO2 levels. This review paper focuses on the role of silicon fertilizer in terrestrial carbon sequestration, agriculture crops in particular. [ABSTRACT FROM AUTHOR]

In the context of global climate change, one central interest is an improved understanding of the global carbon cycle. A large number of studies have investigated carbon cycling and associated elements, mainly nitrogen and phosphorus. However, as an essential element for diatom growth, Si has been largely ignored. Si is the second most abundant element and is widely distributed on Earth. The chemical weathering of silicates on land and photosynthesis of diatoms in the ocean play an important role in atmospheric CO2 levels at various timescales. Diatoms are the primary producers in the ocean and account for as much as 40% of the annual ocean carbon fixation, which have an absolute requirement for Si to form siliceous cells. The main mechanism underlying ocean carbon sinks is a "biological pump." The biological pump is driven by the biological Si pump to a large extent. Therefore, the biogeochemical process of Si has become one of the key research issues for global environmental change.Based on previous studies, the regulation and influence of the Si biogeochemical cycle on the carbon cycle are discussed in this review. The coupling effect and mechanism of the Si and carbon cycles in shellfish culture ecosystems were analyzed and the key research questions were explored. Chemical weathering of silicates and the cycling of their products form the basis of Si biogeochemistry. CO2 is consumed during weathering reactions. Therefore, silicate weathering on land represents an important sink for atmospheric CO2. Furthermore, at the geological timescale, primary silicate mineral weathering is the source of secondary silicate. Terrestrial plants absorb soluble silica through their root system during growth. Amorphous silica deposited in plant tissue after maturity is called phytolith. Phytoliths have excellent geochemical stability and occlude a certain amount of organic carbon during the formation process. The organic carbon occluded within phytolith is called phytolith-occluded carbon (PhytOC) and is buried in the soil. PhytOC is released into the soil with phytolith and may be preserved in soils for several thousands of years. As a consequence, PhytOC in terrestrial ecosystems could be significant potential carbon sinks globally due to the refractory phytolith. Primarily through river input, the dissolved silicate (DSi) is transported into the coastal ocean (approximately 84% of DSi input to the oceans). As the major primary producer, diatoms absorb DSi during growth and account for a large fraction of the total carbon fixation in the modern oceans. DSi is converted into biogenic silica via biological processes, is transported to the deep ocean, and is finally buried into sediments with organic carbon in the marine ecosystem. Thus, by controlling the contribution of diatoms to the total primary production, DSi can affect the carbon cycle in oceans. The carbon pump is driven by the Si pump.Mariculture has developed quickly in recent decades. Shellfish, which are dominated by filter-feeding species, are the main mariculture species. The filter-feeding shellfish consume particulate organic carbon as phytoplankton and use dissolved inorganic carbon to build their shell during growth. Filter-feeding shellfish are an import fishery carbon sink. As one of the important feed sources of filter-feeding shellfish, diatoms form fishery carbon sinks in coastal shellfish culture areas. Silicate is an essential salt for diatom growth. Consequently, the carbon sink of filter-feeding shellfish culture is connected with DSi through diatoms. Si could play an important role in driving the formation of carbon sinks in filter-feeding shellfish culture. Hence, it is necessary to consider all processes and coupling effects in the study of the Si biogeochemical cycle. It is important to understand its role in the carbon sinks of shellfish culture.Nowadays, in many systems, human perturbation has resulted in a decline in the ratio of Si: N to 1:1 or less, with severe impacts on the quality and structure of aquatic ecosystems. DSi limitation has been reported in many studies, in both coastal and marine waters. DSi limitation causes shifts from diatoms to non-siliceous algae and is supposedly related to the decreasing export of carbon. A shift from diatoms to other species would enhance the recycling of organic matter in the upper water column because diatoms are very effective in carbon sequestration. DSi limitation has also appeared in some aquaculture bays in China, such as Jiaozhou Bay and Laizhou Bay, in spring. Regarding future directions, it is suggested that more research be conducted on Si biogeochemistry in shellfish culture systems and coupling with the carbon cycle. The subsequent results could evaluate the role of Si in the carbon sink of filter-feeding shellfish culture. Future studies are expected to provide ideas for alleviating Si deficiency in the aquaculture bay and exploring the expansion path in shellfish farming.

The accumulation of phytolith-occluded organic carbon (PhytOC) in soils is great significance for carbon sink of terrestrial ecosystems. To clarify the accumulation law of soil PhytOC in Masson pine forests and to elucidate whether forest management significantly influences the accumulation of PhytOC in soils, soil PhytOC accumulation of the typical Masson pine forests in Southwest China karst area were studied. We tested the hypothesis that forest age obviously affects soil PhytOC accumulation in Masson pine forests and mature Masson pine forests have higher soil PhytOC accumulation than young Masson pine forests. The followed results and conclusions were obtained: (1) Soil phytolith and PhytOC content range of 0–30 cm soil profile in the karst Masson pine forests was 9.67–12.81 g·kg− 1 and 0.17–0.25 g·kg− 1, respectively. (2) Forest stand condition significantly influenced soil PhytOC accumulation in the Masson pine forests. With increasing stand age, soil PhytOC accumulation rose remarkably in the Masson pine forests. (3) Soil physical and chemical properties largely influenced the soil PhytOC accumulation. The calcium-rich, high Si and alkalescent soils in Southwest China karst area were propitious to the preservation and accumulation of PhytOC. (4) There were huge potential of soil phytolith carbon sequestration of Masson pine forests in Southwest China. Forest management measures changing stand density or canopy density is of great significance in increasing soil phytolith carbon sink of Masson pine forests and should be paid more attention for increasing carbon sink of terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Background and aims Palm fossils are often used as evidence for warm and wet palaeoenvironments, reflecting the affinities of most modern palms. However, several extant palm lineages tolerate cool and/or arid climates, making a clear understanding of the taxonomic composition of ancient palm communities important for reliable palaeoenvironmental inference. However, taxonomically identifiable palm fossils are rare and often confined to specific facies. Although the resolution of taxonomic information they provide remains unclear, phytoliths (microscopic silica bodies) provide a possible solution because of their high preservation potential under conditions where other plant fossils are scarce. We thus evaluate the taxonomic and palaeoenvironmental utility of palm phytoliths. Methods We quantified phytolith morphology of 97 modern palm and other monocot species. Using this dataset, we tested the ability of five common discriminant methods to identify nine major palm clades. We then compiled a dataset of species' climate preferences and tested if they were correlated with phytolith morphology using a phylogenetic comparative approach. Finally, we reconstructed palm communities and palaeoenvironmental conditions at six fossil sites. Key results Best-performing models correctly identified phytoliths to their clade of origin only 59 % of the time. Although palms were generally distinguished from non-palms, few palm clades were highly distinct, and phytolith morphology was weakly correlated with species' environmental preferences. Reconstructions at all fossil sites suggested that palm communities were dominated by Trachycarpeae and Areceae, with warm, equable climates and high, potentially seasonal rainfall. However, fossil site reconstructions had high uncertainty and often conflicted with other climate proxies. Conclusions While phytolith morphology provides some distinction among palm clades, caution is warranted. Unlike prior spatially restricted studies, our geographically and phylogenetically broad study indicates phytolith morphology may not reliably differentiate most palm taxa in deep time. Nevertheless, it reveals distinct clades, including some likely to be palaeoenvironmentally informative. [ABSTRACT FROM AUTHOR]

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]

Nickel (Ni) is extremely toxic to plants at high concentrations. Phytoliths have the potential to sequester the heavy metals absorbed by plants and act as a detoxification mechanism for the plant. The authors of the present study aimed to evaluate the effects of Ni on the growth and phytolith yield of grasses in two artificially contaminated soils. Two experiments separated by soil types (Typic Quartzipsamment and Rhodic Hapludox) were conducted in a completely randomized design in a 2 × 4 factorial scheme with three replications. The factors were two species of grass (Urochloa decumbens and Megathyrsus maximus) and three concentrations of Ni (20, 40, and 120 mg kg−1) and control treatment. The grasses were influenced by the increase in Ni rates in the soils. Ni exerted a micronutrient function with the addition of 30 mg kg−1 of Ni in soils, but this concentration caused toxicity in grasses. Such a level is lower than the limits imposed by the Brazilian environmental legislation. Higher Ni availability in Typic Quartzipsamment promoted Ni toxicity, with reduced growth and increased phytolith yield in the shoot, increased Ni in the shoot, and Ni occlusion in phytoliths by grasses, in comparison with Rhodic Hapludox. The yield and Ni capture in phytoliths by grasses in Ni-contaminated soils are related to the genetic and physiological differences between grasses and Ni availability in soils. Ni capture by phytoliths indicates that it may be one of the detoxification mechanisms of Urochloa decumbens to Ni contamination, providing additional tolerance. Megathyrsus maximus may be a future grass for the phytoremediation technique in Ni-contaminated soils. [ABSTRACT FROM AUTHOR]

Ancient faecal material is becoming a highly valuable more frequently investigated proxy with which to address a wide range of research questions. With advancing scientific methodologies it is becoming easier to identify and to analyse. The aim of this paper is to use a set of archaeological and ethnographic case studies to illustrate and evaluate the range of methods that can be used in conjunction with each other to aid investigation of archaeological faecal material. This multi-scalar and multi-method approach uses portable x-ray fluorescence (pXRF), spot sampling and smear slide analysis, micromorphology, gas chromatography mass spectrometry (GC-MS), environmental scanning microscopy with energy dispersive x-ray spectroscopy (ESEM-EDX), and phytolith analysis. The case studies presented here focus on the Neolithic because of this unique opportunity to examine concentrations of animal dung from managed or early domesticated herds. This research illustrates a range of the methods that can be used in conjunction with each other to locate, identify and analyse faecal material. The results demonstrate that an integrated, multi-scalar, multi-methodological approach enables detection, identification, and investigation of a range of faecal attributes and provides new insights into key issues and themes on environment, animal management, diet, health, the built environment and energy sources. This integrated methodology and pilot study highlights two main recommendations. Firstly, modern faecal comparative material should always be consulted within the study region as a baseline for identifying and classifying different types of faecal material. Secondly, micromorphology and GC-MS samples are always vital proxies in further investigations to confirm the nature and identity of the dung sources once potential sample locations have been identified. [ABSTRACT FROM AUTHOR]

The southeast coast of China is a crucial area for the spread of agriculture from mainland Asia to Taiwan and the islands of Southeast Asia. However, whether prehistoric rice cultivation in this region was lowland or upland remains unclear. This study used a detailed phytolith analysis to evaluate temporal changes in structure at three coastal sites of varying altitudes in the Fujian Province of China, Longgang, Zhengjiashan, and Gehongshan. Samples were collected from two cultural phases, the Neolithic Huangguashan and Bronze Age Huangtulun cultures. Additionally, a new physical index, the sensitive-to-fixed phytolith ratio, was used to identify the environmental conditions in which crops were cultivated. Using this method, the number of sensitive types can be less or greater than that of fixed types, corresponding to drought or paddy field rice cultivation systems, respectively. The results showed an interplay of rice and millet farming at these sites. The crop phytolith ratio revealed that rice was dominant in the crop structure. However, notable differences existed in the proportion of different crops and phytolith assemblages across the various sites. The sensitive-to-fixed phytolith ratios, indicative of wet-dry environmental changes, were 1.56 and 1.07 at the low-altitude Longgang and water-rich Zhengjiashan sites, respectively, suggesting lowland rice cultivation. In contrast, the sensitive-to-fixed ratio at the high-altitude Gehongshan site was only 0.8, implying upland rice cultivation. The phytolith assemblage variation among the different sites also revealed an increase in dryland crops from low to high altitudes, indicating that the inhabitants of the southeastern coastal mountainous area modified their crop structure and rice cultivation methods during the Neolithic–Bronze Age transition to overcome environmental limitations. In summary, this study presents phytolith evidence for prehistoric upland rice cultivation on the southeast coast of China, offering valuable insights into the development of the prehistoric subsistence economy in the region. [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]

The selection of a non‐shattering phenotype is a pivotal change in the process of rice domestication. However, current research is heavily restricted by the preservation conditions of macro‐plant remains in early and middle Neolithic sites, as very limited well‐preserved rice spikelet bases could be retrieved. We present a non‐destructive method based on micro‐computed tomographic (CT) scanning, which could provide detailed visualization of the internal structures of charred spikelet bases and efficiently discriminate the shattering and non‐shattering phenotypes of rice spikelet bases according to the abundance of fusiform echinate phytoliths. It could be widely applied in different contexts, especially those poorly preserved specimens and tempers in pottery sherds, greatly improving our knowledge of rice domestication. [ABSTRACT FROM AUTHOR]

BACKGROUND: The micro/nano silicon-carbon deposit in Fengcheng City, Jiangxi Province, is the first sedimentary deposit mineralized by phytoliths in the world. According to the research carried out here, micro/nano silicon-carbon ore may have been formed by the long-term accumulation and consolidation of phytoliths. In terms of distribution range, genetic type and resource type, the micro/nano silicon-carbon deposit has many new features. Therefore, considering the particularity of the deposit, it is of great significance to carry out research, especially chronological research. Moreover, Re-Os isotope system of organic-enriched sedimentary rocks has been applied to directly dating deposition ages or stratigraphic boundary age, which has made many achievements in chronological research. However, most of the studies focus on marine sediments samples, while lacustrine sediments samples are rarely affected by many factors, such as provenance, geological processes, and terrigenous clastic materials. OBJECTIVES: To accurately determine the mineralization age of the natural micro/nano silicon-carbon deposit. METHODS: Re-Os isotope testing was used to date the phytolith rock samples (lacustrine sediment samples) in the lower section of the Shilukeng Formation in the mining area. Isotope ratios were determined by NTIMS, and GBW04477 (JCBY) was used as the reference material. RESULTS: The Re-Os isotope age of the samples is 43.1±3.7Ma (n=7, MSWD=6.2) which directly defines the diagenetic mineralization age of phytolith rock of the deposit. The high 187Re/188Os value of the samples is closely related to the sedimentary environment and the origin of biological sedimentation. The high initial 187Os/188Os ratio may be related to tectonic movement events, high Os content and migration rate of adjacent strata. The study shows that Re and Os isotopes are adsorbed and sealed in phytolith with organic carbon in the process of enrichment. Owing to the phytolith’s stable silica structure, high temperature resistance and corrosion resistance, the Re-Os isotope system has a good sealing property in it. Protected by the special structure, the organic carbon in phytolith mainly exists in the tiny cavity of phytolith, and the organic carbon has not been exchanged with the outside world due to its storage, which provides favorable conditions for dating. Moreover, the large amount of phytolith in the samples also provides favorable conditions for the enrichment of Re and Os isotopes. CONCLUSIONS: The results of this study provide for the determination of sedimentary age about lacustrine sediments samples by the Re-Os isotope analysis. It is important to strengthen research about the study of Re-Os enrichment mechanism by micro/nano silicon-carbon ore samples. [ABSTRACT FROM AUTHOR]

Silicon (Si) is abundant in the lithosphere, and previous studies have confirmed that silicon plays an important role in plant growth. Higher plants absorb soluble silicon from soil through roots which is deposited in plant tissues mainly in the form of phytoliths. Based on previous studies, the research progress in silicon and phytoliths in the structural protection, enhancement on photosynthesis and transpiration of plants and plant growth and stress resistance was reviewed. Meanwhile, gaps in phytolith research, including phytolith morphology and function, impact of diverse environmental factors coupling with phytoliths, phytolith characteristics at different stages of plant development and phytoliths in regional vegetation are identified. The paper intends to promote the wider application of phytolith research findings and provides reference for further research on phytoliths.

The moisture, ash, and silicon content, as well as the phytolith morphotype and concentration in the tissue-cultured, seed-cultured, and grafted seedling leaves of Dendrocalamus brandisii were determined to investigate the differences in silicon uptake and phytolith morphology in the leaves from different rearing methods. The results showed that ash, silicon content, and phytolith concentration were higher in the mature leaves. Tissue-cultured seedlings had a significantly higher moisture content than grafted seedlings. Ash and silicon demonstrated the same order of grafted seedlings > tissue-cultured seedlings > seed-cultured seedlings. The highest phytolith concentration was found in tissue-cultured seedlings. The phytolith morphotypes in D. brandisii seedling leaves raised by different methods were identical and grouped into eight morphotypes. The phytolith assemblage was characterized by a high frequency of bilobate and saddle, accounting for more than 60%, whereas the morphotypes of elongate, blocky, flabellate, and circular phytoliths accounted for the smallest proportion, normally all below 4.5%. The phytolith size demonstrated an increasing trend in the maturing leaves. The sizes of bilobate, saddle, and acute phytoliths expanded the fastest in tissue-cultured seedling leaves, implying rapid growth of the cell in tissue-cultured seedlings. Accordingly, the tissue-cultured seedlings contained more silicon and phytoliths of larger sizes, which could be a better choice of stock supply for establishing large-scale plantations. If the stock of the seed-cultured and grafted seedlings is to be used, silicon fertilizer application is an optimal option to boost seedling growth. [ABSTRACT FROM AUTHOR]

Phytoliths are composed of 66 to 91% SiO2 and 1 to 6% organic carbon (C) known as phytolith occluded carbon (PhytOC). PhytOC is critical for long-term C storage in the agroecosystem. A field experiment was carried out to investigate the effect of three different sources of exogenous Si, i.e., diatomaceous earth (DE), silicic acid (SA) and rice husk biochar (RHB) on 1) plant phytolith, C content in phytolith and PhytOC content in different rice organs; 2) relationship between plant phytolith, C content in phytolith, PhytOC content, and soil properties (soil physicochemical properties and readily soluble silicon pools). Different Si sources produced significantly higher phytolith, PhytOC content, and readily soluble Si pools (CCSi, AASi, and ASi) than the control (RDF), with treatment receiving 4 t RHB ha-1 outperforming the other treatments. Phytolith and PhytOC production were found to be significantly correlated to soil organic carbon (OC), available nitrogen (N) and potassium (K), 0.01 M CaCl2 extractable Si (CCSi) and amorphous Si (ASi) content in the soil. Redundancy analysis showed that treatments receiving 4 t RHB ha-1 have a stronger relationship with the CCSi and ASi which majorly contributed to the higher phytolith and PhytOC production. Thus, practices such as Si fertilizers and RHB application have a high potential for phytolith production and PhytOC sequestration, a critical mechanism of the global biogeochemical C sink. [ABSTRACT FROM AUTHOR]

Plant‐available silicon (Si) concentrations vary considerably across tropical soils, yet the ecological importance of that variation remains largely unresolved. Increased Si availability can enhance growth and modulate foliar nutrient status in many crop species suggesting similar effects might occur in natural systems. However, how growth, foliar Si and macronutrient concentrations as well as their stoichiometry respond to plant‐available Si and how these responses differ across tropical tree species is unknown. We experimentally exposed seedlings of 12 tropical tree species to a gradient of plant‐available Si concentrations, representing 85 % of the variation found across central Panama, and assessed responses in aboveground growth and foliar nutrient status. Furthermore, we assessed whether higher plant‐available Si increases P availability. Increasing plant‐available Si led to increased foliar Si concentrations (by up to 140%). It also led to higher aboveground growth (by up to 220%), and it affected foliar C and N concentrations, and nutrient stoichiometry across species. However, at the species‐level only a small subset of two to four species showed significant growth and foliar nutrient responses. At the soil‐level, plant‐available P remained unchanged along the experimental soil Si gradient. Our results showed that Si can improve growth and/or modulate foliar nutrient status in a number of tropical tree species. Furthermore, species' growth and foliar nutrient concentrations might vary differently across tropical forest sites varying in plant‐available Si. Additionally, Si‐induced responses in foliar nutrient stoichiometry have the potential to affect herbivory and litter decomposition. Taken together, natural variation in plant‐available Si might influence plant performance unequally across tropical tree species, and change trophic interactions, with potential implications for ecosystem processes. [ABSTRACT FROM AUTHOR]

Amorphous silica, a specialised silicate adsorbent is extensively extracted from agricultural residues for application in various environmental domains. Wheat straws are a rich source of silica that have earlier been overlooked however demand for value addition. The study presents an innovative approach to extracting silica from wheat straw and standardising the extraction process to produce clean product. The sodium silicate solution and the amorphous silica synthesis were obtained by modifying the template mediated sol–gel method. Optimum temperature, concentration and pH were identified for the cleaner production of silica with maximum yield and favourable adsorbent characteristics. The crystallographic properties analysed by the X-Ray Diffraction revealed the amorphous nature of silica extracted from ash at 650 °C for 4 h. The structure of phytolith present in the wheat straw was observed in the form of articulated elongate undulate epidermal phytolith under scanning electron microscopy. The Energy Dispersive X-ray spectrum exhibited higher amount of silica (Si %) of 70.10% with a minimal percentage of potassium (9.96%). The sharp bend at 1025 cm−1 is attributed to the siloxane (Si–O-Si) vibrations in Fourier transform infrared spectroscopic graph of amorphous silica. The specific surface area measurements of amorphous silica showed type II isotherm curve with a hysteresis of H3 type. The optimum conditions derived to produce amorphous silica were 3 M NaOH and 3 M H2SO4 at pH 9. [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]

The underrepresentation of many important rainforest species in pollen records still hinders accurate paleovegetation reconstructions in tropical Southeast Asia. In this study, we conducted a modern phytolith study of 141 plant and 15 surface soil samples around the forests of Jerai Hill in western Peninsular Malaysia to evaluate the potential of phytolith assemblages as a proxy for indicating tropical vegetation types. In the plant samples, including many Dipterocarpaceae species, tracheary annulate/helical phytoliths occur most commonly, followed by silicified epidermis, silicified stomata, elongate entire, sclereid, trichomes, irregular. A few diagnostic phytoliths with unique morphological features are found in dicotyledonous trees, palms, and ferns, such as spheroid ornate (sph_orn) and spheroid echinate (sph_ech). In contrast, the phytolith assemblage of surface sediment is dominated by sph_orn, sph_ech, and spheroid psilate. This suggests that similar to pollen, the contribution from dominating forest vegetation rich in Dipterocarpaceae species is obscure in phytolith deposits. However, phytolith analysis highlights the representation of monocotyledons and a few dicotyledonous trees. The more sensitive indication of Poaceae short-cell phytoliths than pollen for parent plants implies that their ratio to forest indicator phytoliths might be a valuable proxy of landscape openness. Additionally, the statistical analysis confirms that phytolith assemblages in the heath forest are slightly different from those in the lowland dipterocarp forest, exhibiting their potential to indicate various vegetation types. [ABSTRACT FROM AUTHOR]

The middle and lower Huai River Valley, located between the Yangtze and Yellow Rivers, was a key transitional zone for the northward spread of rice and southward migration of millet agriculture in central-eastern China during the Holocene. Knowing when millets spread here, how they were combined with rice in mixed farming, the reasons for their spread, and the temporal variation of cropping patterns is of crucial significance to the development of our understanding of ancient adaptation strategies adopted by human societies in response to climatic and cultural changes. Focusing on crops, phytolith analyses of the soil samples, in tandem with radiocarbon dating from the Wanbei site, reveal evidence of a multicropping pattern of combining rice (Oryza sative), broomcorn millet (Panicum miliaceum), and foxtail millet (Setaria italica) during the Dawenkou culture period between 5720 and 4426 cal. BP in the middle and lower Huai River Valley, China. The data show that rice was always the principal crop of the pattern, and that domesticated rice was developed during the early and middle Dawenkou culture periods. However, its domestication rate became lower during the late Dawenkou culture period. Broomcorn millet and foxtail millet with domesticated traits appeared only in lower proportions of the total produced throughout the period. The proportions of rice and foxtail millet increased slightly, while the proportions of broomcorn millet decreased over time. Finally, the formation of the multicropping pattern at Wanbei may have been primarily influenced by both the warm and wet climatic environment and the cultural exchange and communication between the Haidai region and the middle and lower Huai River Valley during the Dawenkou culture period. The findings in this paper may not only contribute to mapping the spatiotemporal route for the northward expansion of rice agriculture and southward spread of millet agriculture, but also assist in understanding the human adaptation strategies employed in eastern China during the Holocene. [ABSTRACT FROM AUTHOR]

Silicon (Si) enhances plant tolerance to various biotic and abiotic stressors such as salinity, drought, and heat. In addition, Si can be biomineralized within plants to form organic carbon-containing phytoliths that can have ecosystem-level consequences by contributing to long-term carbon sequestration. Si is taken up and transported in plants via different transporter proteins such as influx transporters (e.g., Lsi1, Lsi6) and efflux transporters (e.g., Lsi2). Additionally, the imported Si can be deposited in plant leaves via silicification process using the Siliplant 1 (e.g., Slp1) protein. Functional homologs of these proteins have been reported in different food crops. Here, we performed a genome-wide analysis to identify different Si transporters and Slp1 homologs in the bioenergy crop poplar (Populus trichocarpa Torr. and A. Gray ex W. Hook). We identified one channel-type Si influx transporter (PtLsi1; Potri.017G083300), one Si efflux transporter (PtLsi2; Potri.012G144000) and two proteins like Slp1 (PtSlp1a; Potri.004G168600 and PtSlp1b; Potri.009G129900) in the P. trichocarpa genome. We found a unique sequence (KPKPPVFKPPPVPI) in PtSlp1a which is repeated six times. Repeated presence of this sequence in PtSlp1a indicates that this protein might be important for silicification processes in P. trichocarpa. The mutation profiles of different Si transporters in a P. trichocarpa genome-wide association study population identified significant and impactful mutations in Potri.004G168600 and Potri.009G129900. Using a publically accessible database (http://bar.utoronto.ca/eplant%5fpoplar/), digital expression analysis of the putative Si transporters in P. trichocarpa found low to moderate expression in the anticipated tissues, such as roots and leaves. Subcellular localization analysis found that PtLsi1/PtLsi2 are localized in the plasma membrane, whereas PtSlp1a/PtSlp1b are found in the extracellular spaces. Protein–Protein interaction analysis of PtLsi1/PtLsi2 identified Delta-1-pyrroline-5-carboxylate synthase (P5CS) as one of the main interacting partners of PtLsi2, which plays a key role in proline biosynthesis. Proline is a well-known participant in biotic and abiotic stress tolerance in plants. These findings will reinforce future efforts to modify Si accumulation for enhancing plant stress tolerance and carbon sequestration in poplar. [ABSTRACT FROM AUTHOR]

Phytoliths are composed of 66 to 91% SiO2 and 1 to 6% organic carbon (C) known as phytolith occluded carbon (PhytOC). PhytOC is critical for long-term C storage in the agroecosystem. A field experiment was carried out to investigate the effect of three different sources of exogenous Si, i.e., diatomaceous earth (DE), silicic acid (SA) and rice husk biochar (RHB) on 1) plant phytolith, C content in phytolith and PhytOC content in different rice organs; 2) relationship between plant phytolith, C content in phytolith, PhytOC content, and soil properties (soil physicochemical properties and readily soluble silicon pools). Different Si sources produced significantly higher phytolith, PhytOC content, and readily soluble Si pools (CCSi, AASi, and ASi) than the control (RDF), with treatment receiving 4 t RHB ha-1 outperforming the other treatments. Phytolith and PhytOC production were found to be significantly correlated to soil organic carbon (OC), available nitrogen (N) and potassium (K), 0.01 M CaCl2 extractable Si (CCSi) and amorphous Si (ASi) content in the soil. Redundancy analysis showed that treatments receiving 4 t RHB ha-1 have a stronger relationship with the CCSi and ASi which majorly contributed to the higher phytolith and PhytOC production. Thus, practices such as Si fertilizers and RHB application have a high potential for phytolith production and PhytOC sequestration, a critical mechanism of the global biogeochemical C sink.

Organic carbon occluded in phytoliths is extremely stable and plays important roles in long-term preservation of soil and stable carbon sequestration in terrestrial ecosystems. To clarify the effects of land-use changes on the accumulation of soil phytolith-occluded organic carbon (PhytOC), the typical six land-use types of forest, open forest, shrub, grassland, corn field and abandoned farmland in Southwest China were used to study the associations of soil PhytOC accumulation with land-use change. The present results showed that land-use changes significantly affected soil PhytOC accumulation and its proportion to TSOC (total soil organic carbon). Compared to vegetation coverage, vegetation productivity increased soil PhytOC accumulation more effectively. The content and reserves of soil PhytOC in the open forest all ranked highest among the six land uses studied. Forest thinning not only substantially increased soil stable organic carbon sequestration but also obviously increased the TSOC pool. When land use changed from forest to grassland, there were obvious releases or run off of soil organic carbon, but the stability of the soil organic C pool improved obviously. After the corn field was abandoned, the PhytOC pool did not vary obviously. Soil pH was the important factor influencing the soil PhytOC pool, and acidic soils were made against PhytOC accumulation in soils. Soil PhytOC accumulation was significantly affected by soil C, N and P nutrition contents and stoichiometric ratios. Significant negative effects of bulk density on PhytOC accumulation in soils were observed. The present results are of great significance in land use regulation for increasing the soil carbon sink of terrestrial ecosystems.

Nickel (Ni) is extremely toxic to plants at high concentrations. Phytoliths have the potential to sequester the heavy metals absorbed by plants and act as a detoxification mechanism for the plant. The authors of the present study aimed to evaluate the effects of Ni on the growth and phytolith yield of grasses in two artificially contaminated soils. Two experiments separated by soil types (Typic Quartzipsamment and Rhodic Hapludox) were conducted in a completely randomized design in a 2 × 4 factorial scheme with three replications. The factors were two species of grass (Urochloa decumbens and Megathyrsus maximus) and three concentrations of Ni (20, 40, and 120 mg kg−1) and control treatment. The grasses were influenced by the increase in Ni rates in the soils. Ni exerted a micronutrient function with the addition of 30 mg kg−1 of Ni in soils, but this concentration caused toxicity in grasses. Such a level is lower than the limits imposed by the Brazilian environmental legislation. Higher Ni availability in Typic Quartzipsamment promoted Ni toxicity, with reduced growth and increased phytolith yield in the shoot, increased Ni in the shoot, and Ni occlusion in phytoliths by grasses, in comparison with Rhodic Hapludox. The yield and Ni capture in phytoliths by grasses in Ni-contaminated soils are related to the genetic and physiological differences between grasses and Ni availability in soils. Ni capture by phytoliths indicates that it may be one of the detoxification mechanisms of Urochloa decumbens to Ni contamination, providing additional tolerance. Megathyrsus maximus may be a future grass for the phytoremediation technique in Ni-contaminated soils.

The study of macroscopic, microscopic, and biomolecular remains recovered from coprolites can provide a wide range of information on past human and animal behavior and environments. In earlier studies, research tended to focus on one or two proxies, but multiproxy approaches combining data from all remains within coprolites are becoming more common. Multiproxy analyses have demonstrated value for strengthening our understanding of the past and reducing equifinality. Here we present a sequential biomolecular, macrofossil, and microfossil extraction protocol that separates all different coprolite components and is intended as a best-practice guideline for coprolite analysis. We demonstrate the effectiveness of this method by applying it to an assemblage of coprolites from the Paisley Caves, Oregon, USA. By combining a wide range of proxies, this study provides important information on the taxonomy and behavior of organisms in the past as well as the paleoecological context of behavior.

The accumulation of phytolith-occluded carbon (PhytOC) in Moso bamboo could be a novel long-term carbon sequestration strategy. The objective of this study was to investigate the effects of temperature change and different fertilization on PhytOC accumulation. The pot experiment was established with different fertilization (including control (CK), nitrogen fertilizers (N), silicon fertilizers (Si), and a combination of nitrogen and silicon (NSi)) under high- and low-temperature. Despite the different fertilization, the PhytOC accumulation of the high-temperature group increases by 45.3% on average compared with the low-temperature group, suggesting higher temperature is greatly beneficial to the PhytOC accumulation. Fertilization significantly increases the accumulation of PhytOC (increased by 80.7% and 48.4% on average for the low- and high-temperature group, respectively) compared with CK. However, the N treatment increased both Moso bamboo biomass and PhytOC accumulation. The difference in the accumulation of PhytOC in Si and NSi was insignificant, indicating the combination of N and Si didn't bring extra benefit to PhytOC accumulation compared to Si fertilizer alone. These results indicated the application of nitrogen fertilizer is a practical and effective method for enhancing long-term carbon sequestration for Moso bamboo. Based on our study, we conclude that global warming poses a positive effect on promoting the long-term carbon sequestration of Moso bamboo. [ABSTRACT FROM AUTHOR]

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Copyright of Advances in Earth Science (1001-8166) is the property of Advances in Earth Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Phytoliths make up the predominant fraction of biogenic silica in plant litter and soils. Thus, they represent a major source of dissolved silicon (Si) in soil-plant systems. Dissolution of phytoliths from Si-accumulating crops such as rice has been well studied in recent years. However, phytolith dissolution in oil-palm plantations remains largely understudied. In this study, we compared dissolution rates of phytoliths isolated from oil-palm fronds, oil-palm litter, and rainforest litter. Our results showed that phytoliths from oil-palm fronds represent an important reservoir of easily dissolvable Si with high dissolution rates (0.44 - 0.69 mg g - 1 d - 1 ). Compared to fresh phytoliths from oil-palm fronds, phytoliths isolated from litter showed up to 18 times lower dissolution rates, reflecting silica aging over time. The dissolution rate of phytoliths isolated from rainforest litter (0.067 mg g - 1 d - 1 ) was significantly higher than that of phytoliths from oil-palm litter (0.038 mg g - 1 d - 1 ). These results demonstrate that transformation of rainforest into oil-palm plantation involves a major change in phytolith production and Si release from litter, considerably altering Si cycling in the soil-plant system. We identified cut-off palm fronds that are usually piled up between the palm rows as most important Si sources maintaining biogeochemical Si cycling in oil-palm plantations. [ABSTRACT FROM AUTHOR]

China is one of the main locations in which rice agriculture occurs, with East China now playing a significant role in research on rice domestication and culture interactions. However, the exact timing of sustained rice domestication and the process of prehistoric cultural exchange in East China remain unclear. Here, we present phytolith records of two profiles from Lingjiatan in the Chaohu Lake Basin. Our results show that rice cultivation was practiced throughout the Lingjiatan culture period (5800-5300 cal BP), and that sustained rice domestication began around 5500 cal BP, which was later than on the Taihu Plain (∼6200 cal BP), Ningshao Plain (∼5800 cal BP), and along the middle and lower Huai River (∼5800 cal BP). Combining other archaeological records and geomorphological features in East China, we hypothesize three possible routes for the spread of rice cultivation and cultural exchange between the lower Yangtze River and the middle and lower Huai River. Lingjiatan, situated at the intersection of two of the possible routes, experienced a gradual increase in its settled population as a result of cultural exchange and technological innovations in cultivation, thereby giving rise to its distinctive culture. This study demonstrates the significant role of Lingjiatan in facilitating transportation and fostering cultural exchange in East China during the mid-Holocene. • First study to reconstruct the process of rice cultivation at Lingjiatan (5800-5300 cal BP). • Evidence to elucidate the timing of sustained rice domestication in East China. • Three possible routes of cultural exchange in East China are proposed. [ABSTRACT FROM AUTHOR]

• Phytolith based paleoenvironmental reconstruction is reported first time from the Kashmir Himalaya. • Phytolith assemblages of the last 42 ka reveal interplay of warm and cold events preserved in LPS. • The substantial decrease in phytolith count during cold events could be linked to the Heinrich events. The temporal vegetation development provides vital information for understanding past climatic changes. In this study, we reconstruct vegetation dynamics from the last glacial period using phytoliths as a proxy from the Wanihama loess-paleosol sequence (LPS) near Srinagar in Kashmir Himalaya, India. Different phytolith assemblages and indices (Ic and Iw) revealed a series of warm and cold events documented in the LPS. The data indicate the predominance of broad-leaved and sparse conifer vegetation from ca. 42 ka to 39 ka, suggesting a comparatively warm and humid climate. After ca. 39 ka, conifers and grasses increased, indicating a transition to a cold climate. The cold climate, intervened by a short stadial, continued until ca. 31 ka with the predominance of conifers, grasses, and sedges. Subsequently, three other cold events were noted until ca. 14 ka, which resulted in vegetation disappearance and a substantial decrease in phytolith count. These cold events roughly coincide with the climatic instability in the Atlantic Ocean that caused severe cooling at high northern latitudes and likely impacted the Asian climate. Phytolith assemblages showed an overall increasing proportion of C4 grasses towards the top of the LPS, suggesting warm and dry climatic conditions. We also correlated the phytolith-based vegetation reconstruction with other paleoenvironmental proxies recorded from the same section, as well as with the last glacial climatic changes documented in different regions, to determine the reliability of phytoliths in LPSs as a proxy for past vegetation and climate reconstruction in the Kashmir Himalaya. [ABSTRACT FROM AUTHOR]

Abstract Silica is the best-known component filling the spaces that form phytoliths in many plants, but phytoliths may also contain other elements. We used scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDX) to map element distributions in the leaves of Guadua bamboo, which is a successful competitor in southwestern Amazonian forests. We emphasize immobile elements that can be mineralized (silicon and calcium) as well as potassium, an abundant mobile nutrient with many vital functions. We discovered high silicon (Si) content with little or no calcium (Ca) or potassium (K) in bulliform cells, bilobate shaped short cells and stomata, all of which can form phytoliths, and moderately high Si content in the bundle sheet, prickle tips and papillae. K often surrounded Si-loaded cells, Si and K had overlapping distributions in the intercostal areas near vein margins, and Ca showed abundant spotted distribution in the intercostal areas. The dark inside content of the costal zones of some samples in light microscopy showed no mineralization but prominently contained sulfur. Adjacent fusoid cells showed different Si, K and Ca combinations, which may suggest potentially variable functions of these cells. Widespread Si deposition strengthens Guadua bamboo leaves and may help it to outcompete tree species during periods of drought.

The accumulation of metal(loid)s in phytoliths can physically immobilize the toxic materials and reduce toxicity in plant bodies and soil. Spider brake (Pteris multifida) is a well-known As hyperaccumulator that also harbors phytolith. However, As accumulation in phytoliths has not yet been studied with P. multifida. Soil water content is considered the main factor influencing phytolith accumulation. In this study, the As concentration in the phytoliths of P. multifida was compared with that in common reed (Phragmites australis) phytoliths with various soil water content. The range of As concentration in the phytoliths of P. multifida was 414.70–1610.74 mg kg−1, and the range for P. australis phytoliths was 41.67–126.54 mg kg−1. In P. multifida, higher soil water content increased As accumulation in the phytolith but did not affect the phytolith content in the plant. In P. australis, the higher soil water content increased phytolith content in the plant but decreased As concentration in phytoliths. This study suggests that P. multifida has higher As content in phytoliths than P. australis, and this accumulation can be affected by soil water content. The current findings provide how As encapsulated in phytolith and detoxified in different plants and conditions. [ABSTRACT FROM AUTHOR]

The paddy field ecosystem and diversified plant food resources in the middle and late Liangzhu Culture were revealed at the Zhumucun site. Based on pollen and phytolith records, this paper presents local vegetation landscape of the site: (1) evergreen-deciduous broad-leaved forests dominated by Quercus , Castanopsis , and Ulmus distributed on the nearby hills, (2) terrestrial herbs represented by Poaceae plants tend to expand on the plain, (3) aquatic plants such as Typha , Trapa , Myriophyllum and Euryale ferox grew in rivers and lakes, and (4) plants such as Phragmites australis , Echinochloa , Polygonum lapathifolium , Haloragidaceae, Rumex , Cyperus , Cyperaceae, and Polygonaceae were distributed in and around the wetland. Water activities tended to be intense, and the climate was generally warm and humid with short-term anomalously cold or wet fluctuations. This is in line with the characteristics of environmental changes revealed by regional natural accumulations. In this conditions, local rice ecosystem was recorded with diachronic changes. [ABSTRACT FROM AUTHOR]

Crop cultivation has great potential to result in a phytolith carbon sink and can play important roles in the long-term stable carbon sequestration of terrestrial ecosystems. Buckwheat, an important multigrain crop with a very long cultivation history, is widely planted around the world. The phytolith carbon sink potential of buckwheat planting is still limited in the in-depth understanding of biogeochemical carbon sequestration in croplands. In order to estimate the phytolith carbon sink potential of buckwheat planting, in the present study, six species including 17 populations of Fagopyrum plants were selected as study materials. Firstly, their phytoliths were extracted using the wet oxidation method; then, the phytolith-occluded organic carbon (PhytOC) contents were determined using the spectrophotometry method; finally, the phytolith carbon sink potential of buckwheat planting was estimated. Results showed the following: 1) The PhytOC content range of the six Fagopyrum species studied was 0.006%~0.038%, which was significantly lower than that of rice, wheat, sugarcane, and some cereal and oil crops. There were significant differences in total silicon, phytolith, and PhytOC content of Fagopyrum plants among the different species, different organs (root, stem, and leaf), and different living forms (annual, partly perennial, and completely perennial). There were significant positive relationships between PhytOC and phytolith content and between phytolith and total silicon content. 2) The average phytolith carbon sequestration rate of Fagopyrum esculentum and Fagopyrum tataricum planting was 2.62 × 10-3 and 1.17 × 10-3 t CO2 hm-2·a-1, respectively, being approximately equal to that of terrestrial shrub vegetation. 3) The global total amount of phytolith carbon sequestration of buckwheat planting reached 5,102.09 t CO2 in 2018, and the Chinese total amount of phytolith carbon sequestration of buckwheat cultivation was 624.79 t CO2 in 2020. The phytolith carbon sink of buckwheat planting had significant potential for playing obvious roles in the carbon cycle. The present results are of great significance in crop phytolith studies and provide important references for phytolith carbon sink potential estimation of farmland ecosystems. [ABSTRACT FROM AUTHOR]

Research has generally outlined that the Neolithic East Asian farmers expanded into Southeast Asia, leading to substantial social and cultural transformations. However, the associated archaeobotanical evidence until now has been insufficient to clarify the exact timing, dispersal route, and farming package of the emergence of agriculture in Mainland Southeast Asia. To clarify these issues, the micro-plant remains of phytolith and starch from three Neolithic sites in Ha Long Bay were extracted and analyzed. This study validates the earliest evidence of co-cropping in northern Vietnam, involving the cultivation of rice together with foxtail millet at 4000 years BP or slightly earlier. Moreover, the results indicate that at least two patterns of subsistence strategy were practiced simultaneously during the initial farming phase in the region. The Trang Kenh people, a regional variant of the Phung Nguyen cultural group often have been seen as the first farmers in northern Vietnam, and they mainly practiced a cereal-based subsistence strategy with more vital cultural characteristics of southern China origin. Meanwhile, the Ha Long people, mainly composed of indigenous hunter-gatherer descendants, continued to utilize a wide range of their preferred plant resources such as taros, yams, and acorns, while they absorbed and incorporated new elements such as millet and rice into their food system. This study provides solid information to understand the diverse economic systems among different cultural groups in Vietnam. [ABSTRACT FROM AUTHOR]

Phytogenic silica (PhSi) is suggested to control silicon (Si) cycling in soil–plant systems in tropical and subtropical regions. However, the role of crop residues and its biochar as a source of available Si has not been well investigated in agricultural soils. In our study, we determined and compared the effects of rice straw and its biochar on soil Si forms and Si availability. Soil Si forms were characterised by a sequential extraction method, and soil Si availability was assessed by rice growth and soil Si extraction methods. A soil incubation experiment showed that the addition of rice straw and biochar increased plant‐available Si in soil (including mobile Si and adsorbed Si), as well as soil amorphous Si (especially in rice straw treatments). Moreover, this increase was more significant when higher Si (e.g., Si added at the rates of 1.6 and 2.0 g kg−1 soil) was added via rice straw and its biochar, which is most likely a result of PhSi dissolution. Rice‐straw biochar, particularly at higher Si addition rates, tended to have a higher efficiency in increasing soil Si availability than rice straw, mainly due to its greater proportion of readily labile Si. A rice growth pot experiment showed that it is difficult to determine the extent of Si dissolution from PhSi in rice straw using a short‐term experiment with a normal single‐season straw return rate, where the increased pH played a more crucial role in regulating soil Si availability. Our results imply that, in terms of enhancing Si availability, long‐term biochar application with abundant Si input is more effective than straw retention for improving soil fertility in subtropical and tropical regions with highly weathered soils. Highlights: Effect of phytolith‐rich rice straw and its biochar on soil Si availability was studied.Biochar had greater efficiency in increasing plant‐available Si in soil than rice straw.Over the short term, Si dissolution from PhSi is insignificant with a typical single‐season straw return rate.Increased pH played a crucial role in regulating soil Si availability in a short‐term study. [ABSTRACT FROM AUTHOR]

Located on the southeast coast of China, Fujian is an important junction for the spread and migration of agriculture and populations from mainland Asia to Taiwan and the Island Southeast Asia. Research on the emergence of agriculture and its relationship with the regional environmental context is key to understanding the evolution of ancient human-land interactions in the coastal zone of China. This paper presents a detailed microfossil analysis of the Dapingding site, which is located in the lower reaches of the Min River on the southeast coast of China. We found a large number of phytoliths produced in rice stems and leaves from the cultural layers of this site, dated to 7,500 cal. a BP. In addition, we found rice husk impressions and rice phytoliths in the pottery sherds of these cultural layers. Among these phytoliths, rice bulliform phytoliths with ≥9 fish-scale patterns indicating the degree of rice domestication, accounted for 44%. This percentage is much higher than the established standard for wild rice bulliform phytoliths with fish-scale patterns, suggesting that rice cultivation had already occurred on the southeast coast of China approximately 7,500 years ago. Subsequently, the starting time of agricultural activity on the southeast coast of China was pushed from 5,000 to 7,500 years ago. Comparing the regional history of sea level and coastline changes in the early to mid-Holocene, we suggest that the emergence of early rice cultivation in Southeast China was associated with high sea levels in the mid-Holocene and the last transgression in the Fuzhou Basin. The 'Fuzhou Bay', formed by the retreating coastline and transgression driven by high sea levels, may have provided a sea channel for the southward movement of northern rice farmers. [ABSTRACT FROM AUTHOR]

It has been unclear whether Holocene lake evolution in the Badain Jaran Desert of northwestern China, an area in which lakes are mainly recharged by groundwater, responded to climate change. In this study, we analyzed the Mg/Ca ratio and phytolith assemblages from 10 Holocene calcareous root tube samples from the desert to reconstruct changes in effective moisture and mean annual precipitation (MAP) at the millennial scale during the Holocene and to explore the factors affecting lake evolution. Our results revealed that the effective moisture at 7000-5000 cal yr BP was higher than that of 5000-2000 cal yr BP. Similarly, the MAP was higher at 7000-5000 cal yr BP (175 ± 37 to 205 ± 37 mm) than at 5000-2000 cal yr BP (145 ± 37 to 165 ± 39 mm). The expansion of the lakes during the Early Holocene would have resulted from the input of groundwater from the meltwater in the recharge area. High lake levels in the Middle Holocene corresponded to increased monsoonal precipitation and groundwater recharge. The gradual decline of lake levels in the Late Holocene indicated a relatively arid climate with decreased monsoonal precipitation and groundwater recharge. [ABSTRACT FROM AUTHOR]