Increased Si Uptake Research Articles

Induction of silicon defences in wheat landraces is local, not systemic, and driven by mobilization of soluble silicon to damaged leaves.

In response to herbivory, many grasses, including crops such as wheat, accumulate significant levels of silicon (Si) as an antiherbivore defence. Damage-induced increases in Si can be localized in damaged leaves or be more systemic, but the mechanisms leading to these differences in Si distribution remain untested. Ten genetically diverse wheat landraces (Triticum aestivum) were used to assess genotypic variation in Si induction in response to mechanical damage and how this was affected by exogenous Si supply. Total and soluble Si levels were measured in damaged and undamaged leaves as well as in the phloem to test how Si was allocated to different parts of the plant after damage. Localized, but not systemic, induction of Si defences occurred, and was more pronounced when plants had supplemental Si. Damaged plants had significant increases in Si concentration in their damaged leaves, while the Si concentration in undamaged leaves decreased, such that there was no difference in the average Si concentration of damaged and undamaged plants. The increased Si in damaged leaves was due to the redirection of soluble Si, present in the phloem, from undamaged to damaged plant parts, potentially a more cost-effective defence mechanism for plants than increased Si uptake.

Effects of silicon and titanium dioxide nanoparticles on arsenic accumulation, phytochelatin metabolism, and antioxidant system by rice under arsenic toxicity.

Arsenic (As) is known to be one of the most toxic metalloids for humans and plants; however, little is known about the use of silicon (Si) and titanium dioxide (TiO2) nanoparticles (NPs) in reducing As toxicity in rice (Oryza sativa L.). The experiment was conducted to examine the effects of Si-NPs (50 and 100mg/L), TiO2-NPs (25 and 50mg/L) and As (50µM) on growth, photosynthetic pigments, antioxidant defense system, glyoxalase system, expression of Si/As transporters, and genes involved in As sequestration in rice under hydroponic conditions. The results revealed that Si- and TiO2-NPs by upregulating the activity of antioxidant enzymes and glyoxalase cycle reduced hydrogen peroxide, methylglyoxal, malondialdehyde, and electrolyte leakage, and thus protected the photosynthetic apparatus and improved plant growth under As stress. By increasing the expression of GSH1, PCS, and ABC1 genes, Si- and TiO2-NPs increased leaf and root accumulation of glutathione and phytochelatins and sequestered As in vacuoles, which protected plant cells from As toxicity. Si-NPs diminished As uptake and increased Si uptake in As-exposed rice plants by modulating the expression of Si/As transporters (Lsi1, Lsi2, and Lsi6). The results depicted that 100mg/L Si-NPs treatment had the highest positive effect on plant growth and tolerance under As stress compared to other treatments. In general, Si- and TiO2-NPs augmented the growth of rice under As stress through different strategies, which can be used to design effective fertilizers to enhance the crop growth and yield in areas contaminated with toxic metals.

The NIP Genes in Sugar Beet: Underlying Roles in Silicon Uptake and Growth Improvement

Silicon (Si) can stimulate plant growth and stress resistance. This study aimed at elucidating the physiological responses and molecular characterization of different NIP (nodulin 26-like intrinsic protein) genes in sugar beet. The addition of exogenous Si increased plant biomass and Si concentration in the root and shoot, implying that increased Si uptake has beneficial effects on sugar beet. The quantitative gene expression analysis showed a significant upregulation of the BvNIP5–1 gene in roots, while the BvNIP1–1, BvNIP6–1, BvNIP7–1, and BvNIP-type were unchanged following Si supplementation. It suggests that BvNIP5–1 is one of the genes localized in the plasma membrane responsible for Si uptake in sugar beet. Besides, the BvNIP5–1 gene contained promoter, transcription start site, transcription binding site, and PolyA at 800 bp, 528 bp, 557 bp, and 1637 bp, respectively. The MEME results further revealed the association of three motifs related to major intrinsic protein (MIP). In the phylogenetic tree, the BvNIP5–1 showed a close association with CqNIP5–1, AnNIP2–1 and SoNIP5–1. Interactome analysis showed functional partnership of aquaporin SIP1–2 and SIP2–1 genes with NIP genes in sugar beet. In addition, BvNIP5–1 possessed close association with several functional partners (BOR1, BOR1, NodGS, SIP1A, ACR3) and co-expressed genes (i.e., AtNIP5–1, AtBOR1, AtNodGS, AtSIP1A, AtACR3) of Arabidopsis thaliana mainly responsible for boron, arsenite, and aquaporin transport activity. NIP promoters revealed cis-regulatory elements linked to auxin, salicylic acid, and methyl jasmonate-responsive factors. These findings may advance our understanding of Si transporters underlying growth and stress tolerance in sugar beet.

Silicon Enhances Plant Resistance of Rice against Submergence Stress.

Flooding is an important natural disaster limiting rice production. Silicon (Si) has been shown to have an important role in alleviating varied environmental stress. However, very few studies have investigated the effects and mechanisms of Si in alleviating flood stress in rice. In the present study, wild type rice (cv. Oochikara, WT) and Si-defective mutant (lsi1) were chosen to examine the impacts of Si application on plant growth, photosynthesis, cell structure, and antioxidant enzyme activity of rice exposed to submergence stress at tillering stage. Our results showed that Si application improved root morphological traits, and increased Si uptake and plant biomass of WT under submergence stress, but non-significantly influenced lsi1 mutant. Under submergence stress, leaf photosynthesis of WT was significantly inhibited, and Si application had no significant effects on photosynthetic rate, transpiration rate, stomatal conductance, and intercellular carbon dioxide concentration for both of WT and lsi1 mutant, but the photochemical quenching of WT was increased and the integrity of cell structure was improved. In addition, Si application significantly reduced malondialdehyde concentration and increased the activity of peroxidase and catalase in WT leaves under submergence stress. These results suggested that Si could increase rice plant resistance against submergence stress by improving root morphological traits and chloroplast ultrastructure and enhancing antioxidant defense.

Silicon-induced thermotolerance in Solanum lycopersicum L. via activation of antioxidant system, heat shock proteins, and endogenous phytohormones

BackgroundAbiotic stresses (e.g., heat or limited water and nutrient availability) limit crop production worldwide. With the progression of climate change, the severity and variation of these stresses are expected to increase. Exogenous silicon (Si) has shown beneficial effects on plant growth; however, its role in combating the negative effects of heat stress and their underlying molecular dynamics are not fully understood.ResultsExogenous Si significantly mitigated the adverse impact of heat stress by improving tomato plant biomass, photosynthetic pigments, and relative water content. Si induced stress tolerance by decreasing the concentrations of superoxide anions and malondialdehyde, as well as mitigating oxidative stress by increasing the gene expression for antioxidant enzymes (peroxidases, catalases, ascorbate peroxidases, superoxide dismutases, and glutathione reductases) under stress conditions. This was attributed to increased Si uptake in the shoots via the upregulation of low silicon (SlLsi1 and SlLsi2) gene expression under heat stress. Interestingly, Si stimulated the expression and transcript accumulation of heat shock proteins by upregulating heat transcription factors (Hsfs) such as SlHsfA1a-b, SlHsfA2-A3, and SlHsfA7 in tomato plants under heat stress. On the other hand, defense and stress signaling-related endogenous phytohormones (salicylic acid [SA]/abscisic acid [ABA]) exhibited a decrease in their concentration and biosynthesis following Si application. Additionally, the mRNA and gene expression levels for SA (SlR1b1, SlPR-P2, SlICS, and SlPAL) and ABA (SlNCEDI) were downregulated after exposure to stress conditions.ConclusionSi treatment resulted in greater tolerance to abiotic stress conditions, exhibiting higher plant growth dynamics and molecular physiology by regulating the antioxidant defense system, SA/ABA signaling, and Hsfs during heat stress.

Silicon-Solubilizing Media and Its Implication for Characterization of Bacteria to Mitigate Biotic Stress.

Silicon (Si), the second most abundant element on earth, remains unavailable for plants' uptake due to its poor solubility. Microbial interventions to convert it in soluble forms are well documented. However, studies on discrimination of Si and P solubilizing microbes due to common estimation method and sharing of solubilization mechanism are still obscure. A defined differential media, i.e. silicon-solubilizing media (NBRISSM) is developed to screen Si solubilizers. NBRISN13 (Bacillus amyloliquefaciens), a Si solubilizer, exhibiting antagonistic property against Rhizoctonia solani, was further validated for disease resistance. The key finding of the work is that NBRISSM is a novel differential media for screening Si solubilizers, distinct from P solubilizers. Dominance of Pseudomonas and Bacillus spp. for the function of Si solubilization was observed during diversity analysis of Si solubilizers isolated from different rhizospheres. Sphingobacterium sp., a different strain has been identified for silicon solubilization other than Pseudomonas and Bacillus sp. Role of acidic phosphatase during Si solubilization has been firstly reported in our study in addition to other pH dependent phenomenon. Study also showed the combinatorial effect of feldspar and NBRISN13 on elicited immune response through (i) increased Si uptake, (ii) reduced disease severity, (iii) modulation of cell wall degrading and antioxidative enzyme activities, and (iv) induced defense responsive gene expression.

Applying Wollastonite to Soil to Adjust pH and Suppress Powdery Mildew on Pumpkin

Although not considered an essential nutrient, silicon (Si) can be beneficial to plants. Si accumulator species such as pumpkin (Cucurbita pepo var. pepo) can absorb Si from soil. Si uptake may reduce plant susceptibility to fungal diseases such as cucurbit powdery mildew (Podosphaera xanthii and Erysiphe cichoracearum). We previously reported that wollastonite, an Organic Materials Reviews Institute–approved natural mineral, can increase soil Si level, increase soil pH, provide pumpkin plants with Si, and increase their resistance to powdery mildew. In this study, we examined the optimum application rate of wollastonite for pumpkins grown in pots and exposed to cucurbit powdery mildew. We confirmed that wollastonite has liming capabilities similar to regular limestone. Regardless of the application rates, wollastonite and limestone showed similar effects on soil chemistry and plant mineral composition. Pumpkin plants grown with the lower doses of wollastonite amendments (3.13 and 6.25 tons/acre) had the greatest tissue Si concentrations and demonstrated the greatest disease resistance. We conclude that wollastonite is a useful material for organic cucurbit (Cucurbitaceae) growers who want to increase soil pH and improve plant resistance to powdery mildew at the same time. Applying wollastonite at rates beyond the amount required to achieve a desirable soil pH for pumpkin production did not further increase Si uptake, nor did it further suppress powdery mildew development.

Silicon Compensates Phosphorus Deficit-Induced Growth Inhibition by Improving Photosynthetic Capacity, Antioxidant Potential, and Nutrient Homeostasis in Tomato

Phosphorus (P) deficiency in soils is a major problem for sustainable crop production worldwide. Silicon (Si) is a beneficial element that can promote plant growth, development and responses to stresses. However, the effect of Si on tomato (Solanum lycopersicum L.) growth, photosynthesis and mineral uptake under P deficit conditions and underlying mechanisms remain unclear. Here, we showed that low P (LP) supply inhibited tomato growth as revealed by significantly decreased fresh and dry weights of shoots and impaired root morphological traits. LP-induced growth inhibition was associated with decreased photosynthetic pigment content, net photosynthetic rate (Pn), stomatal conductance, transpiration rate and water use efficiency. However, exogenous Si application alleviated LP-induced decreases in growth and physiological parameters. In particular, Si increased Pn by 65.2%, leading to a significantly increased biomass accumulation. Biochemical quantification and in situ visualization of reactive oxygen species (ROS) showed increased ROS (O2−· and H2O2) accumulation under LP stress, which eventually elevated lipid peroxidation. Interestingly, exogenous Si decreased ROS and malondialdehyde levels by substantially increasing the activity of antioxidant enzymes, including superoxide dismutase, peroxidase, and catalase. In addition, Si increased concentrations of osmoregulatory substances, such as proline, soluble sugar, soluble proteins, free amino acids, and organic acids under LP stress. Analysis of major element concentrations revealed that exogenous Si application under LP stress not only increased Si uptake but also enhanced the concentrations of most essential elements (K, Na, Ca, Mg, Fe, and Mn) in different tissues (roots, leaves, and stems). These results reveal that Si mitigates LP stress by improving photosynthetic capacity, antioxidant potential, and nutrient homeostasis and that it can be used for agronomic management of vegetable crops in P-deficient soils.

Comparative efficacy of organic and inorganic silicon fertilizers on antioxidant response, Cd/Pb accumulation and health risk assessment in wheat (Triticum aestivum L.)

In wheat production areas of China, soil lead (Pb) pollution is generally accompanied by cadmium (Cd) pollution and it is of considerable significance in repairing the Cd and Pb co-contaminated soils for safe agronomic production. Organosilicon fertilizer (OSiF) is a new type of silicon (Si) fertilizer that can effectively alleviate heavy metal toxicity in plants, but the mechanisms on its heavy metal detoxification are poorly understood. A soil pot experiment was conducted to evaluate and compare the effects of two OSiFs (OSiFA and OSiFB) and an inorganic silicon fertilizer (InOSiF) on wheat heavy metal uptake and biochemical parameters in a Cd and Pb co-contaminated soil. The results demonstrated that OSiFA, OSiFB and InOSiF could alleviate the Cd and Pb toxicity of wheat, as indicated by increasing wheat grain yield by 65%, 45% and 22%, respectively. The Si fertilizers enhanced leaf gas exchange attributes and chlorophyll content, whereas diminished the oxidative damage, as indicated by a lower level of hydrogen peroxide (H2O2) and malondialdehyde (MDA) content, and lower activity of superoxide dismutase (SOD) and catalase (CAT) activity, as compared with control. Adding OSiFA, OSiFB and InOSiF increased Si uptake in roots and shoots, thus reducing Cd and Pb accumulation in the wheat shoot, bran and flour, especially, flour Cd contents by 17%, 10% and 31% respectively, flour Pb contents by 74%, 53% and 48% respectively. Also, Si fertilizers application decreased the health risk index (HRI) of both Cd and Pb. The grey correlation degrees of OSiFA, OSiFB and InOSiF are 0.72, 0.77 and 0.61, respectively, indicating that the effects of OSiFs on detoxifying Cd and Pb could be better than that of InOSiF in wheat. Thus, the use of OSiFs might be a feasible approach to reduce Cd and Pb entry into the human body through crops.

Effects of single and successive applications of rice husk charcoal on paddy soil carbon content and rice productivity during two cropping seasons

ABSTRACT A two-year field experiment was conducted to evaluate residual and cumulative effects of rice husk charcoal (RC) application on physicochemical soil properties and rice productivity in an Andosol paddy field. Three RC application rates, 10, 20, and 40 Mg ha−1, one rice husk (RH) application rate of 20 Mg ha−1, and a control with no application of RC or RH were laid out in the first year of the experiment. In the second year, the experimental plot was divided into halves: one with the same application rates as in the first year (successive applications) and the other without additional RC or RH (single application). Significant impacts of RC application were observed from the first year on soil bulk density, porosity, carbon (C) content, and carbon-to-nitrogen (C/N) ratio. Soil C content was directly proportional to the amount of RC application over the 2 years showing that the C derived from RC was markedly recalcitrant in soil compared to that from RH. The increased C was present not only in the plow layer but also spread over the top 20 cm of paddy field. As compared to the control, successive RC applications at 20 Mg ha–1 increased soil C contents by 12.7 g kg–1 and 14.4 g kg–1 in the 0–10 cm and 10–20 cm layers after two rice seasons, respectively. Successive RC applications significantly increased straw weight and panicle number, partly due to the increased Si uptake by rice plants. However, grain yield did not significantly differ among the treatments because RC application decreased 1000-grain weight. We speculate that the reduction in 1000-grain weight may be due to immobilization of available N at the reproductive stage under high soil C/N ratio conditions. This suggests the need for N fertilizer top-dressing to obtain the potential yield in the RC-applied fields. Furthermore, the diminishing residual effects of RC application on the rice growth and yield parameters in the second season suggest that successive, or applications at an interval of 2–3 years, would be required to maintain the higher Si deposits in plants, thereby sustaining rice productivity.

Silicon uptake by a pasture grass experiencing simulated grazing is greatest under elevated precipitation

BackgroundGrasses are hyper-accumulators of silicon (Si) and often up-regulate Si following herbivory. Positive correlations exist between Si and plant water content, yet the extent to which Si uptake responses can be mediated by changes in soil water availability has rarely been studied and never, to our knowledge, under field conditions. We used field-based rain-exclusion shelters to investigate how simulated grazing (shoot clipping) and altered rainfall patterns (drought and elevated precipitation, representing 50% and 150% of ambient precipitation levels, respectively) affected initial patterns of root- and shoot-Si uptake in a native Australian grass (Microlaena stipoides) in Si-supplemented and untreated soils.ResultsSi supplementation increased soil water retention under ambient and elevated precipitation but not under drought, although this had little effect on Si uptake and growth (tiller numbers or root biomass) of M. stipoides. Changes in rainfall patterns and clipping had strong individual effects on plant growth and Si uptake and storage, whereby clipping increased Si uptake by M. stipoides under all rainfall treatments but to the greatest extent under elevated precipitation. Moreover, above-ground–below-ground Si distribution only changed following elevated precipitation by decreasing the ratio of root:shoot Si concentrations.ConclusionsResults highlight the importance of soil water availability for Si uptake and suggest a role for both active and passive Si transport mechanisms. Such manipulative field studies may provide a more realistic insight into how grasses initially respond to herbivory in terms of Si-based defence under different environmental conditions.

Effect of KOH-enhanced biochar on increasing soil plant-available silicon

Bio-based alternative Si fertilizers were developed by pyrolyzing Si-rich agricultural crop residue biomass of rice straw, sugarcane harvest residue, miscanthus, and switchgrass with KOH pretreatment at 0:100, 1:100, 5:100, 10:100, 25:100 and 50:100 KOH:Feedstock biomass ratios (termed 0 KB, 1 KB, 5 KB, 10 KB, 25 KB and 50 KB) and were evaluated for enhancing bioavailable Si in soils. KOH pretreatment enhanced plant-available Si in all feedstocks-derived biochars with rice straw-derived 10 KB biochar exhibiting the highest Si release. SEM-EDX mapping images showed morphological and structural changes of phytoliths in KOH-enhanced biochars which contributed to the increased bioavailable Si. Application of 1% KOH-enhanced biochars to soils significantly increased plant-available Si in soils with minimum effect on soil pH. Perennial ryegrass grown in 10 KB rice straw biochar treated soil increased Si uptake by 31% over 0 KB treated soil and was comparable with mineral Si treatment. Overall, KOH-enhanced biochar as alternative Si source could provide multiple functions in disease control, K nutrition, and C sequestration.

Effects of Si fertilization on Si in soil solution, Si uptake by rice, and resistance of rice to biotic stresses in Southern Vietnam

Silicon (Si) mitigates abiotic and biotic stresses for rice plants (Oryza sativa L.). Here, we test relationships between Si cycling, plant growth, and pest and fungal attacks in rice agroecosystems. We conducted a plot experiment on Si fertilization in a Southern Vietnamese paddy, where plant-available Si was inherently low. For two cropping seasons, we investigated the temporal dynamics of Si in soil solution, plant Si uptake, and the occurrence of leaf folders (Cnaphalocrocis medinalis) and rice blast caused by the fungus Magnaporthe oryzae. Silicon application increased Si concentrations in soil solutions collected in the field as expected from previous laboratory experiments. Soil solution Si concentrations were furthermore affected by Si uptake by plants and by recycling Si with rice straw ash. Silicon concentrations in rice leaves at tillering stage increased with increasing Si application. However, surprisingly, no relationship between Si in soil solution and Si concentration in straw at maturity stage was found. The occurrences of leaf folders and rice blast disease were mitigated by increased Si uptake. However, rice biomass production was not affected, probably because the biotic stress level was generally low. Our field data emphasize the importance of recycling crop residues in rice fields for the Si supply to plants, especially in regions with low Si availability. They furthermore show that under field conditions, the relationship between dissolved Si in soil solution and Si uptake by rice plants is not as straightforward as expected and thus needs to be further investigated.

Arbuscular Mycorrhiza Rhizophagus irregularis and Silicon Modulate Growth, Proline Biosynthesis and Yield in Cajanus cajan L. Millsp. (pigeonpea) Genotypes Under Cadmium and Zinc Stress

Cd is a non-essential metal and is hazardous for plant growth. Although Zn is regarded as an essential element, its elevated levels are highly toxic for plants. Silicon (Si) fertilization and Arbuscular mycorrhiza (AM) have been recognized in alleviating phytotoxicity of heavy metals. Benefits of Si are limited in legumes because they are low Si accumulators. Recently, reports have indicated increased Si uptake in a few plants through mycorrhization. The present work investigated the roles of Si and/or Rhizophagus irregularis on growth, nutrient acquisition, proline biosynthesis and productivity of two pigeonpea genotypes (metal tolerant—PUSA 2002, metal sensitive—PUSA 991) under Cd (25, 50 mg kg−1), Zn (600, 1000 mg kg−1) stress. Plants were subjected to potassium silicate (300 mg kg−1) alone and in combination with R. irregularis. Cd and Zn stress hampered growth, chlorophylls, nutrients uptake and productivity with more negative effects in PUSA 991 than PUSA 2002. AM improved root biomass and nutrient status (P, N, Mg, Fe), whereas Si was more effective in increasing shoot biomass, K and Ca under both heavy metals. Moreover, AM boosted proline biosynthesis by enhancing glutamate dehydrogenase and pyrroline-5-carboxylate synthetase activities along with a decline in proline dehydrogenase activity under heavy metal stress. Application of AM to Si-amended soils was highly beneficial in modulating proline biosynthesis and further improving growth, nutrient, water status and yield with complete amelioration at Zn600, 1000 as well as Cd25 in PUSA 2002 due to its better ability for mycorrhizal symbiosis. Highly positive impacts of combined applications (+Si+AM) could be correlated to mycorrhiza-mediated enhanced Si uptake and resultant metal tolerance.

The functional ecology of plant silicon: geoscience to genes

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Intraspecific biogenic silica variations in the grass species Pennisetum pedicellatum along an evapotranspiration gradient in South Niger

Climate influences terrestrial Si and C cycles. To evaluate how drought influences Si dynamics in African savannahs we studied 12 sites along a climatic gradient of precipitation and drought-stress in South Niger. We analysed plant traits and Si (phytolith) content in 12 specimens of a drought adapted grass species (Pennisetum pedicellatum Trin.), and in surface soils. Phytolith/amorphous silica (ASi) was quantified by the 1%Na2CO3 (nc) digestion method, and the acid plus heavy-liquid extraction method (bz). Phytolith morphotypes were also analysed under the microscope. Our results show that with increasing drought-stress (decreasing AET/PET and precipitation, and increasing temperature), ASi in P. pedicellatum (ApSinc and ApSibz) increases, while ASi in soils (AsSibz) decreases. ApSinc shows higher correlation with precipitation of the wettest month (Pwet, r=−0.84, p<0.001), AET/PET (r=−0.73, p<0.01) and length of dry season (r=0.83, p<0.001) than with AsSibz (r=−0.59, p<0.05). Plant height increases with increasing precipitation (r=0.61, p<0.05). Leaf area is positively correlated with AsSibz (r=0.81, p<0.01). Bulliform phytoliths in P. pedicellatum growing under driest climate represent up to 12% of the leaf phytolith assemblage and just 2% in specimens sampled south of ∼13°N at more humid sites. Thus, the abundance of silicified bulliform cells is strongly negatively correlated with Pwet (r=−0.92, p<0.001) and AET/PET (r=−0.93, p<0.001). Other intra-specific variations, e.g. the length of bilobate phytoliths, are not observed along the climatic gradients documented here. We conclude that drought and evapotranspiration rates influence plant height and leaf size, increase Si uptake by the C4 grass P. pedicellatum, and favour silicification of the bulliform (motor) cells triggering leaf movements. In surface soils, greater phytolith accumulation is likely due to higher plant productivity and weaker soil erosion at humid sites.

Interaction between silicon cycling and straw decomposition in a silicon deficient rice production system

Rice plants (Oryza sativa L.) contain large quantities of silicon (Si) in form of phytoliths, which increase their resistance to abiotic and biotic stresses. The Si cycle through rice fields is hardly studied. We tested how increasing Si availability affects rice growth and the decomposability of the straw. Secondly we tested the role of straw recycling for Si availability. In a field experiment, we applied three levels of silica gel during one rice cropping season. In a follow-up laboratory experiment, we used straw produced in the field experiment, having different Si concentrations, and studied straw decomposition, straw Si release, and Si uptake by plants. Silicon fertilization increased Si contents, biomass production, and grain yield of rice plants. Increased Si uptake by rice decreased concentrations of C and some essential nutrients (N, P, K, Ca, and Mg) in the straw, and increased straw decomposability and Si release. Fertilization with silica gel is an option to improve Si supply to rice plants growing on weathered soils with low levels of plant-available Si. Phytoliths from fresh rice straw dissolve fast in soil, thus, recycling of rice straw is an important source of plant-available Si.

Silicon nutrition and mycorrhizal inoculations improve growth, nutrient status, K+/Na+ ratio and yield of Cicer arietinum L. genotypes under salinity stress

Salinity is a major abiotic stress that limits plant growth and productivity. Role of silicon (Si) nutrition and arbuscular mycorrhiza (AM) in mitigating salt stress has gained importance in recent years. Legumes are sensitive to salinity and are considered low Si-accumulators. AM have been reported to increase Si uptake in mycorrhizal plants. However, little is known about the alleviative role of Si and/or AM in mitigating salt stress in Cicer arietinum L. (chickpea). Therefore, the present study was aimed to evaluate the individual and cumulative effect of Si and AM (Funneliformis mosseae) on nutrient status, growth and productivity of salt tolerant HC 3 and salt sensitive CSG 9505 genotypes of chickpea under salinity stress conditions. The genotypes were subjected to 0, 60, 80,100 mM NaCl and 0, 4 mM potassium silicate—K2SiO3 treatments in the presence and absence of AM fungi. The results indicated that the Si and AM treatments improve the endogenous nutrients profile, growth characteristics and yield attributes under salinity stress. AM was found to be more efficient in improving growth and productivity while Si was more beneficial in improving K+/Na+ ratio. Mycorrhization mediated significant improvement in Si uptake and as a result, Si supplementation along with mycorrhization reduced Na+ content significantly, improved growth, yield and nutrient uptake, arrested chlorophyll pigment damage and increased RUBISCO activity. HC 3 was more responsive to mycorrhization and Si nutrition than CSG 9505. The study will contribute to our understanding of Si and/or AM mediated salinity tolerance mechanism for developing chickpea genotypes resistance to salt stress.

Provision of nitrogen as ammonium rather than nitrate increases silicon uptake in sugarcane.

Silicon (Si) is important in mitigating abiotic and biotic plant stresses, yet many agricultural soils, such as those of the rainfed production areas of the South African sugar industry, are deficient in plant-available Si, making Si supplementation necessary. However, Si uptake by sugarcane (Saccharum spp. hybrids) is limited even where silicate amendments improve soil Si status. Rhizosphere pH, which can affect Si uptake, can be manipulated using different N-form fertilizers. We tested whether (i) fertilization with [Formula: see text] (rhizosphere acidification) increased Si uptake compared with [Formula: see text] (rhizosphere alkalinization); and (ii) uptake differed between an N-efficient, more acid-tolerant cultivar (N12) and an N-inefficient, less acid-tolerant cultivar (N14). Two pot trials with low-Si soil were fertilized with calcium silicate (Ca2SiO4) slag, plus N from ammonium sulphate [(NH4)2SO4], ammonium thiosulphate [(NH4)2S2O3] and calcium nitrate [Ca(NO3)2] (Trial 1) or N from (NH4)2S2O3 and Ca(NO3)2 only (Trial 2). Trial 2 included cultivars N12 and N14. Nitrate treatments significantly increased soil pH and soil Si compared with [Formula: see text] However, [Formula: see text] treatments significantly increased leaf and stalk Si content compared with [Formula: see text] reflected in a significant negative relationship between soil pH and leaf Si. Acid-extracted soil Si was negatively related to leaf and stalk Si, likely due to adsorption of silicic acid to soil surfaces under higher pH of the [Formula: see text] treatment and its reduced availability for plant uptake. We conclude that [Formula: see text] increased Si uptake into leaf and stalk, and propose that reduced rhizosphere pH solubilized Si from Ca2SiO4 and increased silicic acid availability for plant uptake. By contrast, [Formula: see text] may have reduced Si uptake due to adsorption of Si to soil surfaces at higher pH. Our results indicate that ammoniacal fertilizers, such as (NH4)2SO4 and urea, have potential for promoting dissolution of applied Ca2SiO4 and subsequent uptake of Si by sugarcane.

Exogenous silicon nutrition ameliorates salt-induced stress by improving growth and efficiency of PSII in Oryza sativa L. cultivars

Nutrient management of plants is the most practical and easiest way of combating salt stress. The effect of silicon (Si) nutrition on salt stress symptoms was investigated in hydroponically grown rice seedlings. Seeds from Khazar (salt sensitive) and Zayandehrood (salt tolerant) cultivars of rice were exposed to 0 and 100 mM NaCl in the absence and presence of silicon (3 mM) using sodium silicate. Plant growth parameters, sodium (Na+) and potassium (K+) concentrations, Si accumulation, chlorophyll content and efficiency of PSII (Fv/Fm) were determined in 25 days old seedlings exposed to salinity for 96 h. The results showed that salt stress generally inhibited seedling growth and reduced photosynthesis efficiency. However, the addition of Si significantly decreased shoot Na+ concentration, but increased Si uptake. Additionally, in salinized plants, the addition of Si increased Fv/Fm in Khazar cultivar. It could be concluded that Na+ concentration, Si accumulation and Fv/ Fm ratio play key role in salinity stress tolerance. Application of Si, however, alleviated to some extent detrimental effects of salinity stress by improving growth and physiological performance of both cultivars under saline conditions.