The anomaly of silicon in plant biology

Variations of silicon species, dissolution and crystallinity within sichars prepared under different heating rate

Silicon within Si-rich biochars (sichar) plays a crucial role in immobilizing heavy metals and providing slow-releasing bioavailable silicon for silicophilic plants. However, the impact of heating rate on the silicon properties and carbon‑silicon interactions in sichars remains unclear. In this study, rice husk was used as a silicon-rich biomass to prepare sichars at different heating rates (10, 30 and 60 °C per minute, and ultra-fast-pyrolysis), then experiments such as silicon concentration measurement, Raman and XRD characterization were conducted. The results showed that a faster heating rate reduced the carbon content during pyrolysis while promoted the formation of amorphous silica, resulting in a threefold increase in dissolved silicon in sichars prepared at 400 °C. Additionally, we observed the formation of a meta-stable SiO2 polymorph (tridymite) in rice husk-derived biochars under fast heating, differing from the previously observed quartz generated at slow heating rates. Regarding the CSi relationship, a faster heating rate facilitated the removal of the surface carbon layer, exposing the underlying silicon layer. This led to more soluble silicon species and less encapsulated silicon, resulting in a continuous release and cumulative silicon dissolution amount 1.2 times and 1.6-1.9 times higher, respectively, than those in slow heating rate-derived sichars. Consequently, this enhanced silicon uptake in rice seedlings. Our findings indicate that beyond pyrolysis temperature, the heating rate significantly affects the silicon species, silicon dissolution behavior, and carbon‑silicon relationships of biochar, ultimately determines the properties and applications of sichars.

PhytOC sequestration characteristics and phytolith carbon sink capacity of the karst grasslands in southwest China

Grassland is an important component of terrestrial ecosystems and plays a crucial role in the global carbon cycle. PhytOC (phytolith-occluded organic carbon) is an extremely important long-term and stable carbon pool in terrestrial ecosystems. Southwest China karst soil exhibits obvious characteristics of alkalinity, high silicon content, and rich calcium, which can significantly influence the characteristics and mechanisms of PhytOC sequestration in vegetation. To elucidate the sequestration characteristics and mechanisms of PhytOC in the karst grasslands, three typical karst grasslands of tropical shrub tussock (TST), warm-temperate shrub tussock (WST), and mountain meadow (MM) from Guizhou province of southwest China were studied. The following results and conclusions were obtained that: 1) the range of PhytOC content of aboveground plant parts, underground roots, and soil in the karst grasslands was 4.03-16.54 g·kg-1, 10.67-33.92 g·kg-1, and 0.63-1.89 g·kg-1, respectively. The underground roots are an important site for phytolith carbon sequestration in grassland ecosystems, and the PhytOC content of underground roots may be higher than that of the aboveground parts. 2) The PhytOC sequestration rate of vegetation was 7.34-15.93 kg·ha-1·yr-1, and the annual sequestration amount of PhytOC of the whole grasslands in southwest China could reach 0.48 × 103-1.48 × 103 t CO2. Compared to grasslands in non-karst regions of China, karst grasslands in southwest China have a higher sequestration rate of PhytOC in vegetation and a greater capacity for phytolith carbon sequestration. 3) Soil available silicon, pH, and stoichiometric characteristics of C, N and P nutrients significantly affected the phytolith carbon sequestration of vegetation and the soil accumulation of PhytOC in the karst grasslands. The research results are of great significance for estimating the phytolith carbon sequestration capacity of grassland ecosystems and for grassland construction and management based on enhancing carbon sequestration.

Silicon mediated heavy metal stress amelioration in fruit crops

Fruit crops are essential for human nutrition and health, yet high level of heavy metal levels in soils can degrade fruit quality. These metals accumulate in plant roots and tissues due to factors like excessive fertilizer and pesticide use, poor waste management, and unscientific agricultural practices. Such accumulation can adversely affect plant growth, physiology, and yield. Consuming fruits contaminated with toxic metals poses significant health risks, including nervous system disorders and cancer. Various strategies, such as organic manuring, biomaterials, and modified cultivation practices have been widely researched to reduce heavy metal accumulation. Recently, silicon (Si) application has emerged as a promising and cost-effective solution for addressing biological and environmental challenges in food crops. Si, which can be applied to the soil, through foliar application or a combination of both, helps reduce toxic metal concentrations in soil and plants. Despite its potential, there is currently no comprehensive review that details Si's role in mitigating heavy metal stress in fruit crops. This review aims to explore the potential of Si in reducing heavy metal-induced damage in fruit crops while enhancing growth by alleviating heavy metal toxicity.

Comparative study on mechanical properties and biomineralization of hooks in the diaspores of three epizoochorous plant species

Most of the plants using epizoochory show adaptations to this diaspore dispersal strategy by having the diaspores covered by barbs, hooks, spines or viscid outgrowths, which allow diaspores to easily attach to an animal surface. Many previous studies have been mainly focused on the dispersal distances and efficiency, or effectiveness of diverse attachment structures depending on their size, anatomy, and morphology. However, the knowledge about the mechanical properties of these structures remains rather poor. In this study, we use a combination of scanning electron microscopy, energy dispersive X-ray element analysis and nanoindentation, to examine the microstructure, biomineralization and mechanical properties of single hooks in Arctium minus, Cynoglossum officinale and Galium aparine. Both the biomineralization and mechanical properties of the hooks strongly differ in examined plant species; mechanical properties depend on the biomineralization pattern, such as the accumulation of silicon and calcium. Elastic modulus and hardness decrease in the series C. officinaleG. aparineA. minus. Anisotropic mechanical properties are found between the radial and longitudinal directions in each single hook. By characterizing the mechanical properties and biomineralization of plant hooks, this paper contributes to the understanding of attachment biomechanics related to seed dispersal. STATEMENT OF SIGNIFICANCE: The dispersal of seeds is essential for plant survival. Many of the plants that use the outside surface of animals to transport the seeds show adaptations to this dispersal strategy by having the seeds covered with hooks. Although these hooks have various sizes, morphologies and anatomical structures, all of them provide mechanical interlocking to animal surfaces. To reduce the risk of interlocking failure, the hooks are usually reinforced by mineralization. However, the relationship between mineralization, mechanical properties and specialized function of plant hooks has been largely overlooked. Here we perform a characterization study on the hooks of three plant species. Our results deepen the current understanding of the mineralization-material-function relationship in specialized hooks of plant seeds.

Deciphering physiological and transcriptional mechanisms of maize seed germination

Maize is a valuable raw material for feed and food production. Healthy seed germination is important for improving the yield and quality of maize. Seed aging occurs relatively fast in crops and it is a process that delays germination as well as reduces its rate and even causes total loss of seed viability. However, the physiological and transcriptional mechanisms that regulate maize seeds, especially aging seed germination remain unclear. Coronatine (COR) which is a phytotoxin produced by Pseudomonas syringae and a new type of plant growth regulator can effectively regulate plant growth and development, and regulate seed germination. In this study, the physiological and transcriptomic mechanisms of COR-induced maize seed germination under different aging degrees were analyzed. The results showed that 0.001-0.01 μmol/L COR could promote the germination of aging maize seed and the growth of primary roots and shoots. COR treatment increased the content of gibberellins (GA3) and decreased the content of abscisic acid (ABA) in B73 seeds before germination. The result of RNA-seq analysis showed 497 differentially expressed genes in COR treatment compared with the control. Three genes associated with GA biosynthesis (ZmCPPS2, ZmD3, and ZmGA2ox2), and two genes associated with GA signaling transduction (ZmGID1 and ZmBHLH158) were up-regulated. Three genes negatively regulating GA signaling transduction (ZmGRAS48, ZmGRAS54, and Zm00001d033369) and two genes involved in ABA biosynthesis (ZmVP14 and ZmPCO14472) were down-regulated. The physiological test results also showed that the effects of GA and ABA on seed germination were similar to those of high and low-concentration COR, respectively, which indicated that the effect of COR on seed germination may be carried out through GA and ABA pathways. In addition, GO and KEGG analysis suggested that COR is also highly involved in antioxidant enzyme systems and secondary metabolite synthesis to regulate maize seed germination processes. These findings provide a valuable reference for further research on the mechanisms of maize seed germination.

Increased absorption and use of nutrients induced by Si is an indicator for tolerance to water deficit in a common bean cultivar cultivated in the field with and without application of K

Introduction

Reduced water content in the soil triggers physiological, biochemical, and morphological damage to plants, aggravated by nutritional deficiency. One possible strategy to mitigate this damage comprises the use of silicon (Si). This study investigated whether Si can mitigate the damage caused by water deficit through nutritional mechanisms in bean plants grown under field conditions. Furthermore, it investigated whether the effectiveness of Si is influenced by water availability in the soil and the Si dose supplied.

Methods

Therefore, two split-plot experiments were carried out: with and without K supply. In both experiments,the treatments comprised a 3 × 4 factorial scheme. Treatments included three water regimes: 80% (no water deficit), 60% (moderate water deficit), and 40% (severe water deficit) of the soil's water retention capacity. Moreover, they comprised four doses of Si supplied via fertigation-0 kg/ha, 4 kg/ha, 8 kg/ha, and 12 kg/ha-arranged in a randomized block design with four replications.

Results and discussion

The appropriate dose of Si to be applied increased with the severity of the water deficit, with the recommended dose being 6 kg/ha, 7 kg/ha, and 8 kg/ha of Si for adequate water conditions, moderate water deficit, and severe water deficit, respectively.

Synergistic effects of silicon and goethite co-application in alleviating cadmium stress in rice (Oryza sativa L.): Insights into plant growth and iron plaque formation mechanisms

Rice is one of the most important staple food crops; however, it is prone to cadmium (Cd) accumulation, which has negative health effects. Therefore, methods to reduce Cd uptake by rice are necessary. At present, there is limited research on the effects of co-application of silicon (Si) and goethite in mitigating Cd stress in rice. Furthermore, the specific mechanisms underlying the effects of their combined application on iron plaque formation in rice roots remain unclear. Therefore, this study analyzed the effects of the combined application of Si and goethite on the biomass, physiological stress indicators, Cd concentration, and iron plaques of rice using hydroponic experiments. The results revealed that co-treatment with both Si and goethite increased the plant height and dry weight, superoxide dismutase and catalase activities, photosynthetic pigment concentration, and root activity. Moreover, this treatment decreased the malondialdehyde concentration, repaired epidermal cells, reduced the Cd concentration in the roots by 57.2 %, and increased the number of iron plaques and Cd concentration by 150.9 % and 266.2 % in the amorphous and crystalline fractions, respectively. The Cd/Fe ratio in amorphous iron plaques also increased. Our findings suggest that goethite serves as a raw material for iron plaque formation, while Si enhances the oxidation capacity of rice roots. The application of a combination of Si and goethite increases the quantity and quality of iron plaques, enhancing its Cd fixation capacity. This study provides theoretical evidence for the effective inhibition of Cd uptake by iron plaques in rice, providing insights into methods for the remediation of Cd contamination.

Silicon in paddy fields: Benefits for rice production and the potential of rice phytoliths for biogeochemical carbon sequestration

Silicon (Si) biogeochemical cycling is beneficial for crop productivity and carbon (C) sequestration in agricultural ecosystem, thus offering a nonnegligible role in alleviating global warming and food crisis. Compared with other crops, rice plants have a greater quantity of phytolith production, because they are able to take up a lot of Si. However, it remains unclear on Si supply capacity of paddy soils across the world, general rice yield-increasing effect after Si fertilizer addition, and factors affecting phytolith production and potential of phytolith C sequestration in paddy fields. This study used a meta-analysis of >3500 data from 87 studies to investigate Si supply capacity of global paddy soils and elaborate the benefits of Si regarding rice productivity and phytolith C sequestration in paddy fields. Analytical results showed that the Si supply capacity of paddy soils was insufficient in the major rice producing countries/regions. Dealing with this predicament, Si fertilization was an effective strategy to supply plant-available Si to improve rice productivity. Our meta-analysis results further revealed that Si fertilization led to the average increasing rate of 36 % and 39 % in rice yield and biomass, which could reach up to 52 % and 46 % with the increasing doses of Si fertilizer, respectively. Especially, this strategy also improved the potential of phytolith C sequestration through the increased phytolith content and rice biomass, despite that this potential might have a decline in old paddy soils (≥ 7000 year) compared to in young paddy soils (≤ 1000 year) due to the slow migration and dissolution of phytoliths at millennial scale. Our findings thus indicate that a deep investigation on the benefits of Si in agroecosystem will further improve our understanding on regulating crop production and the potential of biogeochemical C sequestration within phytoliths in global cropland.

Mechanistic insights into the plant biostimulant activity of a novel formulation based on rice husk nanobiosilica embedded in a seed coating alginate film

Seed coating ensures the targeted delivery of various compounds from the early stages of development to increase crop quality and yield. Silicon and alginate are known to have plant biostimulant effects. Rice husk (RH) is a significant source of biosilica. In this study, we coated mung bean seeds with an alginate-glycerol-sorbitol (AGS) film with embedded biogenic nanosilica (SiNPs) from RH, with significant plant biostimulant activity. After dilute acid hydrolysis of ground RH in a temperature-controlled hermetic reactor, the resulting RH substrate was neutralized and calcined at 650°C. The structural and compositional characteristics of the native RH, the intermediate substrate, and SiNPs, as well as the release of soluble Si from SiNPs, were investigated. The film for seed coating was optimized using a mixture design with three factors. The physiological properties were assessed in the absence and the presence of 50 mM salt added from the beginning. The main parameters investigated were the growth, development, metabolic activity, reactive oxygen species (ROS) metabolism, and the Si content of seedlings. The results evidenced a homogeneous AGS film formation embedding 50-nm amorphous SiNPs having Si-O-Si and Si-OH bonds, 0.347 cm3/g CPV (cumulative pore volume), and 240 m2/g SSA (specific surface area). The coating film has remarkable properties of enhancing the metabolic, proton pump activities and ROS scavenging of mung seedlings under salt stress. The study shows that the RH biogenic SiNPs can be efficiently applied, together with the optimized, beneficial alginate-based film, as plant biostimulants that alleviate saline stress from the first stages of plant development.

Silicon nanoparticles vs trace elements toxicity: Modus operandi and its omics bases

Phytotoxicity of trace elements (commonly misunderstood as 'heavy metals') includes impairment of functional groups of enzymes, photo-assembly, redox homeostasis, and nutrient status in higher plants. Silicon nanoparticles (SiNPs) can ameliorate trace element toxicity. We discuss SiNPs response against several essential (such as Cu, Ni, Mn, Mo, and Zn) and non-essential (including Cd, Pb, Hg, Al, Cr, Sb, Se, and As) trace elements. SiNPs hinder root uptake and transport of trace elements as the first line of defence. SiNPs charge plant antioxidant defence against trace elements-induced oxidative stress. The enrolment of SiNPs in gene expressions was also noticed on many occasions. These genes are associated with several anatomical and physiological phenomena, such as cell wall composition, photosynthesis, and metal uptake and transport. On this note, we dedicate the later sections of this review to support an enhanced understanding of SiNPs influence on the metabolomic, proteomic, and genomic profile of plants under trace elements toxicity.

Silicon nanoparticles in sustainable agriculture: synthesis, absorption, and plant stress alleviation

Silicon (Si) is a widely recognized beneficial element in plants. With the emergence of nanotechnology in agriculture, silicon nanoparticles (SiNPs) demonstrate promising applicability in sustainable agriculture. Particularly, the application of SiNPs has proven to be a high-efficiency and cost-effective strategy for protecting plant against various biotic and abiotic stresses such as insect pests, pathogen diseases, metal stress, drought stress, and salt stress. To date, rapid progress has been made in unveiling the multiple functions and related mechanisms of SiNPs in promoting the sustainability of agricultural production in the recent decade, while a comprehensive summary is still lacking. Here, the review provides an up-to-date overview of the synthesis, uptake and translocation, and application of SiNPs in alleviating stresses aiming for the reasonable usage of SiNPs in nano-enabled agriculture. The major points are listed as following: (1) SiNPs can be synthesized by using physical, chemical, and biological (green synthesis) approaches, while green synthesis using agricultural wastes as raw materials is more suitable for large-scale production and recycling agriculture. (2) The uptake and translocation of SiNPs in plants differs significantly from that of Si, which is determined by plant factors and the properties of SiNPs. (3) Under stressful conditions, SiNPs can regulate plant stress acclimation at morphological, physiological, and molecular levels as growth stimulator; as well as deliver pesticides and plant growth regulating chemicals as nanocarrier, thereby enhancing plant growth and yield. (4) Several key issues deserve further investigation including effective approaches of SiNPs synthesis and modification, molecular basis of SiNPs-induced plant stress resistance, and systematic effects of SiNPs on agricultural ecosystem.

Yield, lodging, and water use efficiency of Tef [Eragrostis tef (zucc) Trotter] in response to carbonized rice husk application under variable moisture condition

Terminal drought and lodging are among the major yield-limiting factors for tef cultivation in the highly weathered soils of the Ethiopian highlands. Therefore, a study was conducted to assess the yield and lodging responses of tef to varying moisture depletion levels (MDL) and the application of carbonized rice husk (CRH). A two-year 4×4 factorial experiment with 20, 35, 55, and 75% MDL and 0, 291, 582, and 873 kg ha-1 of CRH was laid out in a split-plot design, with each treatment replicated four times. The pooled mean ANOVA showed leaf area index (LAI) and lodging index (LI) were not significantly influenced by the main and interaction effects of MDL and CRH (p > 0.05); however, individual year ANOVA showed that both LI and LAI were influenced by the interaction of MDL and CRH (p<0.05) in 2021 and 2022, respectively. The lowest LI (19.7%) was obtained from the application of 873 kg CRH ha-1, followed by 20.6% from 582 kg CRH ha-1 in 2022. A 20.7% LI reduction was recorded in 2022 compared to 2021. Tef plant height and number of tillers per plant were significantly affected by MDL at p<0.05 and p<0.01, respectively, but not by CRH and its interaction with MDL. The effect of MDL was significant on tef HI (p<0.01) but not on traits including grain yield, straw yield, and water use efficiency. In conclusion, the pooled mean analysis result showed that, though there was no significant difference in yield, tef irrigated at 55% MDL provided a maximum HI of 33.8%, which was 6.21% more than the control, and increased the level of lodging resistance with a LI of 31.9%, which was next to 75% MDL with 582 kg ha-1 CRH. The authors suggested that the research should further be verified across locations for wide application.

Silicon, a quasi-essential element: Availability in soil, fertilizer regime, optimum dosage, and uptake in plants

The essentiality of silicon (Si) has always been a matter of debate as it is not considered crucial for the lifecycles of most plants. But beneficial effects of endogenous Si and its supplementation have been observed in many plants. Silicon plays a pivotal role in alleviating the biotic and abiotic stress in plants by acting as a physical barrier as well as affecting molecular pathways involved in stress tolerance, thus widely considered as "quasi-essential". In soil, most of Si is found in complex forms as mineral silicates which is not available for plant uptake. Monosilicic acid [Si(OH)4] is the only plant-available form of silicon (PAS) present in the soil. The ability of a plant to uptake Si is positively correlated with the PAS concentration of the soil. Since many cultivated soils often lack a sufficient amount of PAS, it has become common practice to supplement Si through the use of Si-based fertilizers in various crop cultivation systems. This review outlines the use of natural and chemical sources of Si as fertilizer, different regimes of Si fertilization, and conclude by identifying the optimum concentration of Si required to observe the beneficial effects in plants. Also, the different mathematical models defining the mineral dynamics for Si uptake at whole plant scale considering various natural factors like plant morphology, mineral distribution, and transporter expression have been discussed. Information provided here will further help in increasing understanding of Si role and thereby facilitate efficient exploration of the element as a fertilizer in crop production.

Equisetum praealtum and E. hyemale have abundant Rubisco with a high catalytic turnover rate and low CO2 affinity

The kinetic properties of Rubisco, a key enzyme for photosynthesis, have been examined in numerous plant species. However, this information on some plant groups, such as ferns, is scarce. This study examined Rubisco carboxylase activity and leaf Rubisco levels in seven ferns, including four Equisetum plants (E. arvense, E. hyemale, E. praealtum, and E. variegatum), considered living fossils. The turnover rates of Rubisco carboxylation (kcatc) in E. praealtum and E. hyemale were comparable to those in the C4 plants maize (Zea mays) and sorghum (Sorghum bicolor), whose kcatc values are high. Rubisco CO2 affinity, estimated from the percentage of Rubisco carboxylase activity under CO2 unsaturated conditions in kcatc in these Equisetum plants, was low and also comparable to that in maize and sorghum. In contrast, kcatc and CO2 affinities of Rubisco in other ferns, including E. arvense and E. variegatum were comparable with those in C3 plants. The N allocation to Rubisco in the ferns examined was comparable to that in the C3 plants. These results indicate that E. praealtum and E. hyemale have abundant Rubisco with high kcatc and low CO2 affinity, whereas the carboxylase activity and abundance of Rubisco in other ferns were similar to those in C3 plants. Herein, the Rubisco properties of E. praealtum and E. hyemale were discussed regarding their evolution and physiological implications.

Elemental composition of grass phytoliths: Environmental control and effect on dissolution

Plant phytoliths, which represent the main pool of silica (Si) in the form of hydrous Si oxide, are capable of providing valuable information on different aspect of environmental issues including paleo-environmental reconstruction and agricultural sustainability. Phytoliths may have different chemical composition, which, in turn, affects their preservation in soils ad impacts terrestrial cycle of the occluded elements including micro-nutrients and environmental toxicants. Yet, in contrast to sizable work devoted to phytoliths formation, dissolution and physico-chemical properties, the mechanisms that control total (major and trace) elemental composition and the impact that various elements exert on phytolith reactivity and preservation in soils remains poorly known. In order to fil this gap in knowledge, here we combined two different approaches - analytical trace element geochemistry and experimental physical chemistry. First, we assessed full elemental composition of phytoliths from different plants via measuring major and trace elements in 9 samples of grasses collected in northern Eurasia during different seasons, 18 grasses from Siberian regions, and 4 typical Si-concentrating plants (horsetail, larch, elm and tree fern). We further assessed the dissolution rates of phytoliths exhibiting drastically different concentrations of trace metals. In the European grasses, the variations of phytolith chemical composition among species were highly superior to the variations across vegetative season. Compared to European samples, Siberian grass phytoliths were impoverished in Ca and Sr, exhibited similar concentrations of Li, B, Na, Mg, K, V, Zn, Ni, Mo, As, Ba, and U, and were strongly enriched (x 100-1000) in lithogenic elements (trivalent and tetravalent hydrolysates), P, Mn, Fe and divalent metals. Overall, the variations in elemental composition between different species of the same region were lower compared to variations of the same species from distant regions. The main factors controlling phytoliths elemental composition are the far-range atmospheric (dust) transfer, climatic conditions (humidity), and, in a lesser degree, local lithology and anthropogenic pollution. Despite significant, up to 3 orders of magnitude, difference in TE composition of grass and other plant phytoliths, the dissolution rates of grass phytoliths measured in this study were similar, within the experimental uncertainty, to those of other plants studied in former works. Therefore, elemental composition of phytoliths has relatively minor impact on their preservation in soils.

Silicon fractionations in coastal wetland sediments: Implications for biogeochemical silicon cycling

Coastal wetland sediment is important reservoir for silicon (Si), and plays an essential role in controlling its biogeochemical cycling. However, little is known about Si fractionations and the associated factors driving their transformations in coastal wetland sediments. In this study, we applied an optimized sequential Si extraction method to separate six sub-fractions of non-crystalline Si (Sinoncry) in sediments from two coastal wetlands, including Si in dissolved silicate (Sidis), Si in the adsorbed silicate (Siad), Si bound to organic matter (Siorg), Si occluded in pedogenic oxides and hydroxides (Siocc), Si in biogenic amorphous silica (Siba), and Si in pedogenic amorphous silica (Sipa). The results showed that the highest proportion of Si in the Sinoncry fraction was Siba (up to 6.6 % of total Si (Sitot)), followed by the Sipa (up to 1.8 % of Sitot). The smallest proportion of Si was found in the Sidis and Siad fractions with the sum of both being <0.1 % of the Sitot. We found a lower Siocc content (188 ± 96.1 mg kg-1) when compared to terrestrial soils. The Sidis was at the center of the inter-transformation among Si fractions, regulating the biogeochemical Si cycling of coastal wetland sediments. Redundancy analysis (RDA) combined with Pearson's correlations further showed that the basic biogenic elements (total organic carbon and total nitrogen), pH, and sediment salinity collectively controlled the Si fractionations in coastal wetland sediments. Our research optimizes sediment Si fractionation procedure and provides insights into the role of sedimentary Si fractions in controlling Si dynamics and knowledge for unraveling the biogeochemical Si cycling in coastal ecosystems.

Exploring the potential: Can arsenic (As) resistant silicate-solubilizing bacteria manage the dual effects of silicon on As accumulation in rice?

Rice (Oryza sativa L.) cultivation in regions marked by elevated arsenic (As) concentrations poses significant health concerns due to As uptake by the plant and its subsequent entry into the human food chain. With rice serving as a staple crop for a substantial share of the global population, addressing this issue is critical for food security. In flooded paddy soils, where As availability is pronounced, innovative strategies to reduce As uptake and enhance agricultural sustainability are mandatory. Silicon (Si) and Si nanoparticles have emerged as potential candidates to mitigate As accumulation in rice. However, their effects on As uptake exhibit complexity, influenced by initial Si levels in the soil and the amount of Si introduced through fertilization. While low Si additions may inadvertently increase As uptake, higher Si concentrations may alleviate As uptake and toxicity. The interplay among existing Si and As availability, Si supplementation, and soil biogeochemistry collectively shapes the outcome. Adding water-soluble Si fertilizers (e.g., Na2SiO3 and K2SiO3) has demonstrated efficacy in mitigating As toxicity stress in rice. Nonetheless, the expense associated with these fertilizers underscores the necessity for low cost innovative solutions. Silicate-solubilizing bacteria (SSB) resilient to As hold promise by enhancing Si availability by accelerating mineral dissolution within the rhizosphere, thereby regulating the Si biogeochemical cycle in paddy soils. Promoting SSB could make cost-effective Si sources more soluble and, consequently, managing the intricate interplay of Si's dual effects on As accumulation in rice. This review paper offers a comprehensive exploration of Si's nuanced role in modulating As uptake by rice, emphasizing the potential synergy between As-resistant SSB and Si availability enhancement. By shedding light on this interplay, we aspire to shed light on an innovative attempt for reducing As accumulation in rice while advancing agricultural sustainability.

Silicon-mediated herbivore defence in a pasture grass under reduced and Anthropocene levels of CO2

The uptake and accumulation of silicon (Si) in grass plants play a crucial role in alleviating both biotic and abiotic stresses. Si supplementation has been reported to increase activity of defence-related antioxidant enzyme, which helps to reduce oxidative stress caused by reactive oxygen species (ROS) following herbivore attack. Atmospheric CO2 levels are known to affect Si accumulation in grasses; reduced CO2 concentrations increase Si accumulation whereas elevated CO2 concentrations often decrease Si accumulation. This can potentially affect antioxidant enzyme activity and subsequently insect herbivory, but this remains untested. We examined the effects of Si supplementation and herbivory by Helicoverpa armigera on antioxidant enzyme (catalase, CAT; superoxide dismutase, SOD; and ascorbate peroxidase, APX) activity in tall fescue grass (Festuca arundinacea) grown under CO2 concentrations of 200, 410, and 640 ppm representing reduced, ambient, and elevated CO2 levels, respectively. We also quantified foliar Si, carbon (C), and nitrogen (N) concentrations and determined how changes in enzymes and elemental chemistry affected H. armigera relative growth rates and plant consumption. Rising CO2 concentrations increased plant mass and foliar C but decreased foliar N and Si. Si supplementation enhanced APX and SOD activity under the ranging CO2 regimes. Si accumulation and antioxidant enzyme activity were at their highest level under reduced CO2 conditions and their lowest level under future levels of CO2. The latter corresponded with increased herbivore growth rates and plant consumption, suggesting that some grasses could become more susceptible to herbivory under projected CO2 conditions.

The synergistic effects of soil-applied boron and foliar-applied silicon on cotton fiber quality and yield

Studies of boron (B) and silicon (Si) synergy in cotton crops have shown promising results; however, the focus was on the foliar application of B and Si. Nonetheless, B is an element with little mobility in the plant and its best form of application is in the soil. Thus, the objective of this study was to evaluate the synergistic effect of soil applied B and foliar applied sSi on fiber quality and crop yield of cotton. For this purpose, a field experiment was carried out using cotton cultivar FM 985 GLTP. The soil's B in the experimental site is classified as low for cotton cultivation. The experiment was conducted in a randomized complete-block design, in a 3 × 2 factorial scheme, with three doses of B: 0.0 kg ha-1 (deficiency), 2.0 kg ha-1 (recommended dose), and 4.0 kg ha-1 (high dose) in the absence and presence (920 g L-1) of Si, with four replications. One week after the 4th application of Si, B and Si leaf content was determined. At boll opening, crop yield was estimated, and fiber quality analysis was realized. Boron deficiency reduced cotton yield, in 11 and 9%, compared to the application of 2 and 4 kg ha-1 of B, respectively. The presence of Si, however, increased plant yield in 5% in the treatments with 0 and 2 kg ha-1 of B, respectively. Cotton fiber length and elongation were not influenced by the B doses and Si presence. Fiber breaking strength was increased in 5% by the presence of Si and was not influenced by B deficiency. Micronaire was 8% smaller in the treatment with 0 kg ha-1 of B and 6% smaller in the absence of Si. Short fiber index was 4% greater in the plants of the treatment with 0 kg ha-1 of B. The results of this study reports that the complementation with Si via foliar application increases fiber quality by enhance breaking strength and micronaire. In conclusion, the interaction between soil-applied B and foliar-applied Si is beneficial for cotton cultivation, resulting in high cotton yield with better fiber quality.

A silicon transporter gene required for healthy growth of rice on land

Silicon (Si) is the most abundant mineral element in the earth's crust. Some plants actively accumulate Si as amorphous silica (phytoliths), which can protect plants from stresses. Here, we report a gene (SIET4) that is required for the proper accumulation and cell-specific deposition of Si in rice and show that it is essential for normal growth. SIET4 is constitutively expressed in leaves and encodes a Si transporter. SlET4 polarly localizes at the distal side of epidermal cells and cells surrounding the bulliform cells (motor cells) of the leaf blade, where Si is deposited. Knockout of SIET4 leads to the death of rice in the presence but not absence of Si. Further analysis shows that SIET4 knockout induces abnormal Si deposition in mesophyll cells and the induction of hundreds of genes related to various stress responses. These results indicate that SIET4 is required for the proper export of Si from leaf cells to the leaf surface and for the healthy growth of rice on land.

An improved digestion and analysis procedure for silicon in plant tissue

Silicon (Si) in plant tissues reduces abiotic and biotic stress, but it is incorporated as silica (SiO2), which is difficult to solubilize for analysis. We modified an oven-induced tissue-digestion and analysis method to improve Si solubilization and validated its accuracy by quantifying the mass-balance recovery of Si from the hydroponic solution and plant tissues of cucumber (Cucumis sativus). Leaf, stem, and root tissues were dried, finely-ground, and digested in 12.5 molar sodium hydroxide at 95°C for 4 hours. Solutions were then acidified with 6 molar hydrochloric acid to achieve a pH below 2 for measurement of Si using the molybdate blue colorimetric method. Interference of phosphorus in the analysis was minimized by increasing the addition of oxalic acid from 0.6 to 1.1 molar. We recovered 101% ± 13% of the expected Si, calculated using mass-balance recovery, in leaf, stem, and root tissues across 15 digestions. This Si recovery was fourteen-fold higher than the standard acid-extraction method and similar to a USDA-ARS alkaline-extraction method. Our procedure offers a low-cost, accurate method for extraction and analysis of Si in plant tissues.

Silica nanoparticles mediated insect pest management

Silicon is known for mitigating the biotic and abiotic stresses of crop plants. Many studies have proved beneficial effects of bulk silicon against biotic stresses in general and insect pests in particular. However, the beneficial effects of silica nanoparticles in crop plants against insect pests were barely studied and reported. By virtue of its physical and chemical nature, silica nanoparticles offer various advantages over bulk silicon sources for its applications in the field of insect pest management. Silica nanoparticles can act as insecticide for killing target insect pest or it can act as a carrier of insecticide molecule for its sustained release. Silica nanoparticles can improve plant resistance to insect pests and also aid in attracting natural enemies via enhanced volatile compounds emission. Silica nanoparticles are safe to use and eco-friendly in nature in comparison to synthetic pesticides. This review provides insights into the applications of silica nanoparticles in insect pest management along with discussion on its synthesis, side effects and future course of action.

Progress on Separation and Hydrothermal Carbonization of Rice Husk Toward Environmental Applications

Owing to the increasing global demand for carbon resources, pressure on finite materials, including petroleum and inorganic resources, is expected to increase in the future. Efficient utilization of waste resources has become crucial for sustainable resource acquisition for creating the next generation of industries. Rice husks, which are abundant worldwide as agricultural waste, are a rich carbon source with a high silica content and have the potential to be an effective raw material for energy-related and environmental purification materials such as battery, catalyst, and adsorbent. Converting these into valuable resources often requires separation and carbonization; however, these processes incur significant energy losses, which may offset the benefits of using biomass resources in the process steps. This review summarizes and discusses the high value of RHs, which are abundant as agricultural waste. Technologies for separating and converting RHs into valuable resources by hydrothermal carbonization are summarized based on the energy efficiency of the process.

The concept of mineral plant nutrient in the light of evolution

The concept of mineral plant nutrient has been the subject of a long debate. Here, we suggest that an updated discussion on this issue requires considering three dimensions. The first one is ontological as it refers to the fundamentals that underlie the category of being a mineral plant nutrient, the second one refers to the practical rules helping to assign a given element to that category, while the third dimension implies the consequences of those rules for human activities. We highlight the idea that the definition of what is a mineral plant nutrient can be enriched by incorporating an evolutionary perspective, thus giving biological insight and helping to integrate information from different disciplines. Following this perspective, mineral nutrients can be contemplated as the elements adopted and/or retained, along evolution, for survival and reproductive success. We suggest that the operational rules stated in both early and recent works, while highly valuable for their original purposes, will not necessarily account for fitness under the conditions prevailing in natural ecosystems where elements were adopted and are retained -as a result of natural selection processes- covering a wide spectrum of biological activities. We outline a new definition that considers the mentioned three dimensions.

Regulation of thermodynamics and kinetics of silica nucleation during the silicification process in higher plants

The formation mechanism of SiO₂ aggregates is controversial because two contrasting hypotheses are often proposed to explain plant silicification. In this review, we summarize the physicochemical fundamentals of amorphous silica nucleation and discuss how plants regulate the process of silicification by influencing the thermodynamics and kinetics of silica nucleation. At silicification positions, plants overcome the thermodynamic barrier by establishing the supersaturation of the H₄SiO₄ solution and reducing the interfacial free energy. Among the thermodynamic-drivers, the establishment of supersaturation of H₄SiO₄ solution mainly depends on the expression of Si transporters for H₄SiO₄ supply, evapotranspiration for concentrating Si, and the other solutes in H₄SiO₄ solution for influencing the dissolution equilibrium of SiO₂; while the interfacial free energy was reduced seemingly by the overexpression Na⁺/H⁺ antiporter SOS1 in high NaCl-stressed rice. Moreover, some kinetic-drivers, such as silicification-related proteins (Slp1 and PRP1) and new cell wall components, are actively expressed or synthesized by plants to interact with silicic acid, thereby reducing the kinetic barrier. According to classical nucleation theory, when the thermodynamic barrier is overcome, the super-saturated silicic acid solution (such as H₄SiO₄ in xylem sap) does not necessarily have to precipitate, just has the potential ability to precipitation. Thus, based on the mediators of SiO₂ deposition at the thermodynamic-driven stage, it is difficult to evaluate whether the process of plant silicification is active or passive. We conclude that the characteristics of kinetic-drivers determine the mechanism of plant silicification.

The mechanism of silicon on alleviating cadmium toxicity in plants: A review

Cadmium is one of the most toxic heavy metal elements that seriously threaten food safety and agricultural production worldwide. Because of its high solubility, cadmium can easily enter plants, inhibiting plant growth and reducing crop yield. Therefore, finding a way to alleviate the inhibitory effects of cadmium on plant growth is critical. Silicon, the second most abundant element in the Earth's crust, has been widely reported to promote plant growth and alleviate cadmium toxicity. This review summarizes the recent progress made to elucidate how silicon mitigates cadmium toxicity in plants. We describe the role of silicon in reducing cadmium uptake and transport, improving plant mineral nutrient supply, regulating antioxidant systems and optimizing plant architecture. We also summarize in detail the regulation of plant water balance by silicon, and the role of this phenomenon in enhancing plant resistance to cadmium toxicity. An in-depth analysis of literature has been conducted to identify the current problems related to cadmium toxicity and to propose future research directions.

Silicon in sporoderms of micro- and megaspores of Isoetes echinospora Durieu registered by EDS and EELS

The present study reveals silica in sporoderms of micro- and megaspores of the modern quillwort Isoetes echinospora Durieu and homologizes layers of the sporoderm in spores of this plant. Here, the presence of silica in sporoderms of microspores has been documented for the first time, and observations of megaspore sporoderms were used to test various methods, such as energy dispersive (EDS) and electron energy loss (EELS) spectroscopies. The results elucidate the occurrence of silicon in the quillworts and will influence on the interpretation of their modern and fossil sporoderms.

Why do plants silicify?

Despite seminal papers that stress the significance of silicon (Si) in plant biology and ecology, most studies focus on manipulations of Si supply and mitigation of stresses. The ecological significance of Si varies with different levels of biological organization, and remains hard to capture. We show that the costs of Si accumulation are greater than is currently acknowledged, and discuss potential links between Si and fitness components (growth, survival, reproduction), environment, and ecosystem functioning. We suggest that Si is more important in trait-based ecology than is currently recognized. Si potentially plays a significant role in many aspects of plant ecology, but knowledge gaps prevent us from understanding its possible contribution to the success of some clades and the expansion of specific biomes.

Application of earthworm and silicon can alleviate antibiotic resistance in soil-Chinese cabbage system with ARGs contamination

Organic fertilization is a major contributor to the spread of antibiotic resistance genes (ARGs) in the agroecosystem, which substantially increases the risk of ARGs acquisition and their transmission into human food chains. Earthworms are among the most vital soil faunas involved in the link between belowground and aboveground, and silicon is beneficial for soil health and plant stress resistance. This study aims to explore the effect of different amendment strategies (earthworm and/or silicon) and the related influencing factors on the alleviation of ARGs using high-throughput qPCR. The results showed that the application of earthworms and silicon fertilizers reduced the absolute abundance of ARGs in the rhizosphere soils, either singly or in combination. According to the structural equation model and random forest analysis, mobile genetic elements are the major factors enhancing ARGs transfers and the treatment affects ARGs in direct or indirect ways. Our results highlight the role of "rhizosphere effect" in alleviating antibiotic resistance and suggest that silicon fertilizers, together with the earthworms, can be considered as a sustainable and natural solution to mitigate high-risk ARGs spread in the soil-plant systems. Our findings provide guidance in formulating strategies for halting the spread of ARGs in the agroecosystem.

The Multi-Causal Basis of Developmental Potential Construction

In this article we analyse the issue of what accounts for developmental potential, i.e., the possible phenotypes a developing organism can manifest during ontogeny. We shall argue in favour of two theses. First, although the developing organism is the unit of development, the complete causal basis for its potential to develop does neither lie entirely in itself as a whole nor in any specific part of itself (such as its genome). Thus, the extra-organismal environment must be counted as one of the three necessary, partial and complementary causal bases for development potential. Secondly, we shall defend a constructivist view of the developmental process. If the genome, the developing organism and the extra-organismal environment are to be counted as proper elements of the causal basis for an organism's developmental potential, the latter is not a given. Rather, it is the result of an interaction-based construction, a process sometimes generating genuine developmental novelty. We will thus argue for an interactionist multi-causal basis view of developmental potential construction. We contend that our view provides a biologically tenable and metaphysically coherent account of developmental dynamics.

Biochar application enhanced rice biomass production and lodging resistance via promoting co-deposition of silica with hemicellulose and lignin

Biochar, an environmentally friendly soil amendment, is created via a series of thermochemical processes from carbon-rich organic matter. The biochar addition enhances soil characteristics dramatically and increases crop growth and yields. However, the mechanism by which biochar improves plant lodging resistance, which is heavily influenced by cell walls, remains unknown. Three rice cultivars were grown in an experimental field provided with four concentrations of biochar (10, 20, 30, 40 t ha^-1). The biochar application enhanced biomass production and lodging resistance in all three cultivars by up to 29 % and 22 %, respectively, with the largest improvement at a biochar application rate of 30 t ha^-1. Biochar application significantly enhanced stem cell wall-related characteristics, with an increase in stem breaking force, wall thickness, and plumpness of 52 %, 32 %, and 21 %, respectively, which are suggested to be major contributors to enhanced lodging resistance and biomass yield. Notably, cell wall composition and silica content analysis indicated a significant increase in hemicellulose, lignin, and silica content in biochar-treated samples up to 36 %, 13 %, and 58 %, respectively, when compared to plants not treated with biochar. Integrative analysis suggested that silica, hemicellulose, and lignin were co-deposited in cell walls, which influenced biomass production and lodging resistance. Furthermore, the transcriptome profile revealed that biochar application increased the expression of genes involved in biomass production, cell wall formation, and silica deposition. This study suggests that biochar application might improve both biomass production and lodging resistance by promoting the co-deposition of silicon with hemicellulose and lignin in cell walls.

Impact of Silicon on Plant Nutrition and Significance of Silicon Mobilizing Bacteria in Agronomic Practices

Globally, rejuvenation of soil health is a major concern due to the continuous loss of soil fertility and productivity. Soil degradation decreases crop yields and threatens global food security. Improper use of chemical fertilizers coupled with intensive cultivation further reduces both soil health and crop yields. Plants require several nutrients in varying ratios that are essential for the plant to complete a healthy growth and development cycle. Soil, water, and air are the sources of these essential macro- and micro-nutrients needed to complete plant vegetative and reproductive cycles. Among the essential macro-nutrients, nitrogen (N) plays a significant in non-legume species and without sufficient plant access to N lower yields result. While silicon (Si) is the 2nd most abundant element in the Earth’s crust and is the backbone of soil silicate minerals, it is an essential micro-nutrient for some plants. Silicon is just beginning to be recognized as an important micronutrient to some plant species and, while it is quite abundant, Si is often not readily available for plant uptake. The manufacturing cost of synthetic silica-based fertilizers is high, while absorption of silica is quite slow in soil for many plants. Rhizosphere biological weathering processes includes microbial solubilization processes that increase the dissolution of minerals and increases Si availability for plant uptake. Therefore, an important strategy to improve plant silicon uptake could be field application of Si-solubilizing bacteria. In this review, we evaluate the role of Si in seed germination, growth, and morphological development and crop yield under various biotic and abiotic stresses, different pools and fluxes of silicon (Si) in soil, and the bacterial genera of the silicon solubilizing microorganisms. We also elaborate on the detailed mechanisms of Si-solubilizing/mobilizing bacteria involved in silicate dissolution and uptake by a plant in soil. Last, we discuss the potential of silicon and silicon solubilizing/mobilizing to achieve environmentally friendly and sustainable crop production.

Silicon reduces zinc absorption and triggers oxidative tolerance processes without impacting growth in young plants of hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L.) is a promising crop for non-food agricultural production on soils contaminated by moderate doses of heavy metals, while silicon, as a beneficial element, is frequently reported to improve stressed plant behavior. Using a hydroponic system, plants of Cannabis sativa (cv. Santhica 27) were exposed for 1 week to 100 µM Zn in the presence or absence of 2 mM Si. Zinc accumulated in all plant organs but was mainly sequestered in the roots. Additional Si reduced Zn absorption but had no impact on Zn translocation. Zn accumulation had a slight negative impact on leaf number, stem length, and chlorophyll content, and additional Si did not mitigate these symptoms. Exogenous Si reduced the Zn-induced membrane lipid peroxidation (assessed by malondialdehyde quantification) and increased the total antioxidant activities estimated by the FRAP index. In the absence of Si, leaf phytochelatin and total glutathione were the highest in Zn-treated plants and Si significantly decreased their concentrations.

Silicon and soil microorganisms improve rhizospheric soil health with bacterial community, plant growth, performance and yield

The interaction of silicon and soil microorganisms stimulates crop enhancement to ensure sustainable agriculture. Silicon may potentially increase nutrient availability in rhizosphere with improved plants' growth, development as it does not produce phytotoxicity. The rhizospheric microbiome accommodates a variety of microbial species that live in a small area of soil directly associated with the hidden half plants' system. Plant growth-promoting rhizobacteria (PGPR) play a major role in plant development in response to adverse climatic conditions. PGPRs may enhance the growth, quality, productivity in variety of crops, and mitigate abiotic stresses by reprogramming stress-induced physiological variations in plants via different mechanisms, such as synthesis of indole-3-acetic acid, 1-aminocyclopropane-1-carboxylate deaminase, exopolysaccharides, volatile organic compounds, atmospheric nitrogen fixation, and phosphate solubilization. Our article eye upon interactions of silicon and plant microbes which seems to be an opportunity for sustainable agriculture for series of crops and cropping systems in years to come, essential to safeguard the food security for masses.

Combination of Biochemical, Molecular, and Synchrotron-Radiation-Based Techniques to Study the Effects of Silicon in Tomato (Solanum Lycopersicum L.)

The work focused on the analysis of two cultivars of tomato (Solanum lycopersicum L.), Aragon and Gladis, under two different treatments of silicon, Low, 2 L of 0.1 mM CaSiO3, and High, 0.5 mM CaSiO3, weekly, for 8 weeks, under stress-free conditions. We subsequently analyzed the morphology, chemical composition, and elemental distribution using synchrotron-based µ-XRF techniques, physiological, and molecular aspects of the response of the two cultivars. The scope of the study was to highlight any significant response of the plants to the Si treatments, in comparison with any response to Si of plants under stress. The results demonstrated that the response was mainly cultivar-dependent, also at the level of mitochondrial-dependent oxidative stress, and that it did not differ from the two conditions of treatments. With Si deposited mainly in the cell walls of the cells of fruits, leaves, and roots, the treatments did not elicit many significant changes from the point of view of the total elemental content, the physiological parameters that measured the oxidative stress, and the transcriptomic analyses focalized on genes related to the response to Si. We observed a priming effect of the treatment on the most responsive cultivar, Aragon, in respect to future stress, while in Gladis the Si treatment did not significantly change the measured parameters.

If All Else Fails: Impact of Silicon Accumulation in Maize Leaves on Volatile Emissions and Oviposition Site Selection of Spodoptera exigua Hübner

Silicon (Si) fertilization alleviates biotic stresses in plants. Si enhances plant resistance against phytophagous insects through physical and biochemical mechanisms. In particular, Si modifies jasmonic acid levels and the emissions of herbivore-induced plant volatiles (HIPVs). Here, we investigated whether Si accumulation in the tissues of maize leaves modifies the emissions of constitutive and herbivore-induced plant volatiles, with cascade deterrent effects on oviposition site selection by Spodoptera exigua Hübner (Lepidoptera: Noctuidae). Maize plants were cultivated in a hydroponic system under three Si concentrations, resulting in three groups of plants expressing different Si concentrations in their tissues (0.31 ± 0.04, 4.69 ± 0.49, and 9.56 ± 0.30 g Si. Kg^- 1 DW). We collected volatiles from undamaged and caterpillar-infested plants, and found that Si concentration in plant tissues had no significant impact. Jasmonic acid content was high in insect-infested plants, but was similar across all Si treatments. Oviposition site selection bioassays using fertilized S. exigua females showed that Si concentration in plant tissues did not affect the number of eggs laid on Si-treated plants. In conclusion, our study shows that the Si content in maize tissues does not impact the semiochemical interactions with S. exigua.

Modulation of physiological and biochemical traits of two genotypes of Rosa damascena Mill. by SiO2-NPs under In vitro drought stress

BACKGROUND

Drought is a major abiotic stress that restricts plant growth and efficiency although some nutrients such as silicon improve drought tolerance by regulating the biosynthesis and accumulating some osmolytes. In this regard, a completely randomized factorial design was performed with three factors including two genotypes ('Maragheh' and 'Kashan'), three concentrations of silicon dioxide nanoparticles (SiO2-NPs) (0, 50, and 100 mg L- 1), and five concentrations of PEG (0, 25, 50, 75, and 100 g L- 1) with three replications.

RESULTS

The findings showed that drought stress decreased protein content and it was improved by SiO2-NPs, so the genotype of 'Maragheh' treated with 100 mg L- 1 SiO2-NPs had the highest protein content. Under severe drought stress, had a higher membrane stability index (MSI) than 'Kashan', and the 'Maragheh' explants subjected to 100 mg L- 1 SiO2-NPs exhibited the uppermost MSI. The explants supplemented with 100 mg L- 1 SiO2-NPs sustained their photosynthetic parameters more in comparison with other treatments under drought stress conditions and as well as 100 mg L- 1 SiO2-NPs showed higher content of protein and proline of 'Maragheh' than 'Kashan'. Drought stress reduced Fm, Fv/Fm, and Fv, while SiO2-NPs treatment enhanced these parameters. SiO2-NPs also improved water deficit tolerance by enhancing the activity of antioxidant enzymes such as catalase (CAT), peroxidase (POD), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) and reducing lipid peroxidation and H2O2 concentration.

CONCLUSIONS

According to the findings, the genotype 'Maragheh' was more tolerance to drought stress than 'Kashan' by improving water balance, antioxidant enzyme activities, and membrane stability as it was obtained from the unpublished previous evaluation in in vivo conditions and we concluded based on these results, in vitro culture can be used for drought screening in Damask rose plants. The results of the current study revealed that the induced drought stress by polyethylene glycol (PEG) in two Damask rose genotypes was ameliorated with SiO2-NPs and the tolerance genotypes were better than the sensitive ones in response to SiO2-NPs treatment.

Nitrogen availability and plant-plant interactions drive leaf silicon concentration in wheat genotypes

Estimating plasticity of leaf silicon (Si) in response to abiotic and biotic factors underpins our comprehension of plant defences and stress resistance in natural and agroecosystems. However, how nitrogen (N) addition and intraspecific plant-plant interactions affect Si concentration remains unclear.We grew 19 durum wheat genotypes (Triticum turgidum ssp. durum) in pots, either alone or in intra- or intergenotypic cultures of two individuals, and with or without N. Above-ground biomass, plant height and leaf [Si] were quantified at the beginning of the flowering stage.Nitrogen addition decreased leaf [Si] for most genotypes, proportionally to the biomass increase. Si plasticity to plant-plant interactions varied significantly among genotypes, with both increases and decreases in leaf [Si] when mixed with a neighbour, regardless of the mixture type (intra-/intergenotype). Besides, increased leaf [Si] in response to plant-plant interactions was associated with increased plant height.Our results suggest the occurrence of both facilitation and competition for Si uptake from the rhizosphere in wheat mixtures. Future research should identify which leaf and root traits characterise facilitating neighbours for Si acquisition. We also show that Si could be involved in height gain in response to intraspecific competition, possibly for increasing light capture. This important finding opens up new research directions on Si and plant-plant interactions in both natural ecosystems and agroecosystems. More generally, our results stress the need to explore leaf Si plasticity in responses to both abiotic and biotic factors to understand plant stress resistance. Read the free Plain Language Summary for this article on the Journal blog.

Silicon Resorption from Equisetum arvense Tea - A Randomized, Three-Armed Pilot Study

Equisetum arvense tea (TEA) contains high concentrations of silicon and has been used in folk medicine for the treatment of inflammatory ailments. We examined the resorption of silicon after TEA consumption. Safety and immunological effects were secondary outcomes. A monocentric, randomized, three-armed pilot study was conducted with 12 voluntary, healthy, male subjects. The study is registered in the German register for clinical trials (DRKS-ID: DRKS00016628). After a low silicon diet for 36 hours, 1000 mL TEA1 with approximately 200 000 µg silicon/L, TEA2 with approximately 750 000 µg silicon/L, or Si-low-Water (approximately 10 - 10 000 µg silicon/L as a control) were ingested on three consecutive days. Blood and urine samples were collected at baseline, day 1 examining silicon kinetics, day 3 examining silicon accumulation, and day 8 (safety, immunological parameters). Si-low-Water intake did not change silicon serum (Cmax 294 µg/L) or urine (19 000 µg/24 h) concentrations compared to baseline. Cmax was 2855 µg/L for TEA1 and 2498 µg/L for TEA2; tmax was 60 and 120 min, respectively. Silicon accumulation did not occur. Urine silica within 24 h (E24 h) was higher after TEA2 compared to TEA1 ingestion (142 000 vs. 109 000 µg/24 h). Serum silicon levels at t = 120 min differed significantly after intake of TEA2 or intake of Si-low-Water (p = 0.029). The immunological parameters did not show any significant changes indicating immunosuppressive effects in volunteers. TEA1 was well tolerated, while TEA2 caused diarrhoea in 4 subjects. Our investigations show that intake of TEA1 leads to significant rise in serum silicon concentration.

Atmospheric silicon wet deposition and its influencing factors in China

Silicon (Si) is considered a "quasi-essential" nutrient element for plants and is also an essential nutrient for some phytoplankton. Except for the silicate provided by weathering, atmospheric deposition has gradually become an important supplementary method for Si nutrients to enter the ecosystem. However, national observational studies on atmospheric silicon deposition have not yet been reported. Herein, based on the China Wet Deposition Observation Network, we continuously collected monthly wet deposition samples from 43 typical ecosystems from 2013 to 2020 and measured the content of dissolved silica (dSi) in precipitation to quantify the spatiotemporal patterns of Si wet deposition in China. The results showed that the mean annual dSi wet deposition in China during 2013-2020 was approximately 2.07 ± 0.27 kg ha^-1 yr^-1. Atmospheric dSi deposition was higher in Southwest, North, and South China but lower in the Northwest and Northeast China, which was mainly regulated by precipitation and soil available Si content. There was no significant annual variation trend in dSi deposition during 2013-2020 in China, which showed disorderly fluctuations from year to year. This study revealed the spatiotemporal patterns of atmospheric dSi deposition in China for the first time, which can provide unique scientific data to explore the potential effect of dSi deposition on carbon sequestration in aquatic ecosystems. A comprehensive evaluation of the nutrient balance of aquatic ecosystems from the perspective of nitrogen, phosphorus, and silicon stoichiometry is required in the future.

Action of silicon on the activity of antioxidant enzymes and on physiological mechanisms mitigates water deficit in sugarcane and energy cane plants

Production of sugarcane and more recently of energy cane strengthen renewable bioenergy production capacity. However, droughts resulting from climate change have limited the production of these crops. One of the strategies to attenuate water deficit damage in these crops is the use of silicate, which contributes to plant physiology. This strategy is likely to increase water use efficiency, thus promoting crop sustainability. Notwithstanding, studies on this issue are still incipient. This study assesses whether Si applied via fertigation and foliar spraying in the seedling production phase and as a complement after seedling transplanting to the soil is efficient in attenuating water deficit in sugarcane and energy cane. The study further elucidates physiological and biochemical mechanisms involved in this process. For this, the authors conducted two experiments: one with sugarcane and the other with energy cane. Treatments were arranged in randomized blocks with 5 replications, in a 2 × 2 factorial scheme. Factors consisted of the absence (-Si) and presence of Si (+ Si) applied via fertigation and foliar spraying; and two water regimes: 70% (without water deficit) and 30% (severe water deficit) of the soil water retention capacity. Silicon was supplied during the formation phase of presprouted seedlings and during the transplanting of seedlings to pots filled with samples of Entisol (Quartzipsamment). In these pots, water regimes were induced from 7 to 160 days after transplanting. Severe water deficit reduced the water content and water potential of plants. This situation induced oxidative stress and impaired gas exchange and photosynthetic water use efficiency, reducing plant growth. Silicon supply via fertigation in association with foliar spraying in the seedling formation phase with complementation after transplanting was efficient in increasing Si accumulation in the plants. Silicon was effective in attenuating severe water deficit damage up to initial culm formation through mechanisms that maintain water and physiological balance by favoring the antioxidant defense system in sugarcane and energy cane plants.

Silicon nanoparticles in higher plants: Uptake, action, stress tolerance, and crosstalk with phytohormones, antioxidants, and other signalling molecules

Silicon is absorbed as uncharged mono-silicic acid by plant roots through passive absorption of Lsi1, an influx transporter belonging to the aquaporin protein family. Lsi2 then actively effluxes silicon from root cells towards the xylem from where it is exported by Lsi6 for silicon distribution and accumulation to other parts. Recently, it was proposed that silicon nanoparticles (SiNPs) might share a similar route for their uptake and transport. SiNPs then initiate a cascade of morphophysiological adjustments that improve the plant physiology through regulating the expression of many photosynthetic genes and proteins along with photosystem I (PSI) and PSII assemblies. Subsequent improvement in photosynthetic performance and stomatal behaviour correspond to higher growth, development, and productivity. On many occasions, SiNPs have demonstrated a protective role during stressful environments by improving plant-water status, source-sink potential, reactive oxygen species (ROS) metabolism, and enzymatic profile. The present review comprehensively discusses the crop improvement potential of SiNPs stretching their role during optimal and abiotic stress conditions including salinity, drought, temperature, heavy metals, and ultraviolet (UV) radiation. Moreover, in the later section of this review, we offered the understanding that most of these upgrades can be explained by SiNPs intricate correspondence with phytohormones, antioxidants, and signalling molecules. SiNPs can modulate the endogenous phytohormones level such as abscisic acid (ABA), auxins (IAAs), cytokinins (CKs), ethylene (ET), gibberellins (GAs), and jasmonic acid (JA). Altered phytohormones level affects plant growth, development, and productivity at various organ and tissue levels. Similarly, SiNPs regulate the activities of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and ascorbate-glutathione (AsA-GSH) cycle leading to an upgraded defence system. At the cellular and subcellular levels, SiNPs crosstalk with various signalling molecules such as Ca²⁺, K⁺, Na⁺, nitric oxide (NO), ROS, soluble sugars, and transcription factors (TFs) was also explained.

Structure and function of a silicic acid channel Lsi1

Silicon is a beneficial element for plant growth and production, especially in rice. Plant roots take up silicon in the form of silicic acid. Silicic acid channels, which belong to the NIP subfamily of aquaporins, are responsible for silicic acid uptake. Accumulated experimental results have deepened our understanding of the silicic acid channel for its uptake mechanism, physiological function, localization, and other aspects. However, how the silicic acid channel efficiently and selectively permeates silicic acid remains to be elucidated. Recently reported crystal structures of the silicic acid channel enabled us to discuss the mechanism of silicic acid uptake by plant roots at an atomic level. In this mini-review, we focus on the crystal structures of the silicic acid channel and provide a detailed description of the structural determinants of silicic acid permeation and its transport mechanism, which are crucial for the rational creation of secure and sustainable crops.

Ameliorative Effects of Silicon against Salt Stress in Gossypium hirsutum L

Silicon (Si) could alleviate the adverse effect of salinity in many crops, but the effect in cotton remains unclear. In this study, we evaluated the role of Si in regulating the salt stress tolerance of cotton by analyzing the induced morpho-physiological changes. A hydroponic experiment was conducted by using contrasting salt-tolerant cotton genotypes (sensitive Z0102; tolerant Z9807) and four treatments (CK, control; CKSi, 0.4 mM Si; NaCl, 150 mM NaCl; NaClSi, 150 mM NaCl+0.4 mM Si). The results showed that Si significantly enhanced the net photosynthesis rate and improved the growth of cotton seedling under salt stress in both salt-sensitive and salt-tolerant genotypes. Exogenous Si significantly reduced the accumulation of reactive oxygen species (ROS) and decreased the malondialdehyde (MDA) content in salt-stressed cotton. In addition, the application of Si up-regulated the expression of CAT1, SODCC and POD, and significantly enhanced the antioxidant enzymatic activities, such as catalase (CAT) and peroxidase (POD), of the salt-stressed cotton seedlings. Further, Si addition protected the integrity of the chloroplast ultrastructure, including key enzymes in photosynthesis such as ferredoxin-NADP reeducates (FNR), ATP synthase (Mg2+Ca2+-ATPase) and ribulose-1, 5-bisphosphate carboxylase/oxygenase (RubisCO), and the structure and function of the photosynthetic apparatus PSII from salt stress. Moreover, Si significantly increased the effective stomatal density and stomatal aperture in the salt-stressed cotton seedlings. Taken together, Si could likely ameliorate adverse effects of salt stress on cotton by improving the ROS scavenging ability and photosynthetic capacity.

Limiting silicon supply alters lignin content and structures of sorghum seedling cell walls

Sorghum has been recognized as a promising energy crop. The composition and structure of lignin in the cell wall are important factors that affect the quality of plant biomass as a bioenergy feedstock. Silicon (Si) supply may affect the lignin content and structure, as both Si and lignin are possibly involved in plant mechanical strength. However, our understanding regarding the interaction between Si and lignin in sorghum is limited. Therefore, in this study, we analyzed the lignin in the cell walls of sorghum seedlings cultured hydroponically with or without Si supplementation. Limiting the Si supply significantly increased the thioglycolic acid lignin content and thioacidolysis-derived syringyl/guaiacyl monomer ratio. At least part of the modification may be attributable to the change in gene expression, as suggested by the upregulation of phenylpropanoid biosynthesis-related genes under -Si conditions. The cell walls of the -Si plants had a higher mechanical strength and calorific value than those of the +Si plants. These results provide some insights into the enhancement of the value of sorghum biomass as a feedstock for energy production by limiting Si uptake.

Foliar Silicon Spray to Strawberry Plants During Summer Cutting Propagation Enhances Resistance of Transplants to High Temperature Stresses

Silicon (Si) has been reported to benefit plant growth and stress resistance. This work aimed to find out an optimal method of Si application to enhance the resistance of strawberry (Fragaria × ananassa Duch.) transplants to high temperatures, commonly experienced in the summer when strawberries are propagated for greenhouse production in Korea. Plants of strawberry “Sulhyang”, “Maehyang”, and “Kuemsil” were subjected to one of five treatments before the cutting propagation: no treatment (control), substrate dressing of a water-soluble silicate fertilizer, substrate drench of 75 mg·L−1 Si (from potassium silicate) to the mother plants, or foliar spray of 75 mg·L−1 Si to either the mother plants or daughter plants. Half of the daughter plants in each Si treatment received continued application of Si through either substrate dressing of a water-soluble silicate fertilizer, substrate drench, or foliar spray after the cutting propagation. A high temperature (43°C) resistance test was conducted in plant growth chambers for 7 days with a 16-h photoperiod with a light intensity of 300 mmol·m−2·s−1 PPFD. During the high temperature test, the rate of decline in the photosynthesis was lower in plants treated with Si than in the control. After the high temperature test, it was observed that Si application significantly increased the shoot fresh weight of transplants. Moreover, the contents of sugars, proteins, and enzymatic (CAT, SOD, POD, and APX) and non-enzymatic (anthocyanin and proline) antioxidants were higher in plants treated with Si throughout the entire propagation period, compared to the control and plants only treated with Si before or after the cutting propagation. Overall, the Si application improved the growth of the transplants regardless of the application method used. Moreover, spraying the daughter plants with Si, and continually spraying the transplants were found to be the best and is recommended to increase the resistance of strawberries to high temperatures during propagation.

Silicon Enhances Plant Vegetative Growth and Soil Water Retention of Soybean (Glycine max) Plants under Water-Limiting Conditions

Silicon has been implicated as a factor affecting the degree of resistance to abiotic stresses in several plant species. However, the role of silicon in soybean (Glycine max) under water-limiting conditions is not yet fully understood. This study was conducted to evaluate the effects of silicon application on the vegetative growth of two soybean cultivars (Asgrow 5332 and Progeny 5333) grown under water-limiting conditions. Silicon was provided by adding silicate to the soil. Water-limiting treatments were imposed on plants at two vegetative growth stages for 20 days by irrigating with a reduced amount of water (66% or 33% of the required water). Silicate application enhanced plant height, leaf area, and total dry weight of soybean plants. Significant increases in root volumes were observed in both the silicate-treated cultivars compared to the control plants under water-limiting conditions (33% irrigation). Net photosynthesis and stomatal conductance were decreased, but the quantum efficiency of photosystem II (Fv’/Fm’) did not change under the same irrigation condition, which indicates photosynthesis downregulation through stomatal limitation. Silicate-treated plants in both cultivars had higher water use efficiency as compared to control plants under water-limiting conditions (irrigated with 66% or 33% of required water). Under water-limiting conditions, the soil moisture content was significantly higher in pots containing silicate than in those without added silicate, suggesting that silicon application improves water holding capacity. Taken together, the results from this study indicate that silicon application can improve the vegetative growth of soybeans under low water conditions by increasing the water use efficiency of plants and enhancing the soil’s ability to retain moisture.