Si-treated Plants Research Articles

Foliar Silicon Application in the Era of Climate Change as a Part of Strategy to Reduce Water Requirements in Mediterranean Viticulture

Rising temperatures and water scarcity due to climate change are significant challenges for Mediterranean viticulture, particularly in the Douro Valley, a prominent winemaking region. Silicon (Si) has gained attention as a potential solution for mitigating these environmental stresses, especially in areas with limited water resources. This study explores the foliar application of Si as a promising strategy to reduce water requirements in vineyards, specifically for the Touriga Franca variety, thereby supporting more sustainable water use. Four treatments were tested: non-irrigated control (C−), an irrigated control under a deficit irrigation regime (25% ETc; C+), and two Si concentrations (7% Si-Si1 and 20% Si-Si2) applied to non-irrigated plants. Results demonstrate that Si-treated plants improved physiological resilience, as evidenced by enhanced photosynthetic efficiency, greater water-use efficiency, and higher biochemical quality in both leaves and berries. Additionally, Si application increased leaf flavonoids and simultaneously improved must composition due to its overall influence on vine physiology, indicating its potential as a sustainable alternative to irrigation for reducing summer stress. This research suggests that foliar Si application could be a valuable, eco-friendly strategy to support sustainable viticulture under increasingly arid conditions, reducing the irrigation needs.

Silicon supplementation can reduce infestation by azalea lace bug-(Hemiptera: Tingidae).

The azalea lace bug (ALB), Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is a pest of azaleas and rhododendrons. The application of silicon (Si) to plants has been shown to accumulate in other plants and enhance defense to other plant pests. We evaluated whether Si applications decreased ALB infestation on rhododendron leaves and increased Si accumulation in leaves. Potted plants were treated with 4 or 8 weekly applications of calcium silicate and calcium carbonate (calcium control, Ca) via foliar or soil application. In 3 out of 4 choice studies, plants treated with calcium silicate or calcium carbonate had less frass deposition and oviposition by ALB compared to controls, but treated plants did not consistently have fewer ALB adults. Leaf damage was quantified in one study and leaves with more frass as an indicator of feeding had more visible damage. In no-choice studies, there were no differences between treatments in one study, but oviposition was greater on foliar/soil Si-treated plants than controls in another study. Since rhododendron aphids (Illinoia lambersi) appeared in the greenhouse during or after studies, we compared their colonization on previously treated rhododendrons. Infestation of new leaf rosettes or random leaves by I. lambersi was lower on plants sprayed with foliar silicon or calcium applied via soil in 2 studies. Treated rhododendrons did not accumulate extra Si or Ca in leaves compared to controls. In general, silicon or calcium application protected rhododendrons from ALB oviposition and aphid colonization in free-choice conditions, and may be part of an integrated pest management program.

The silicon regulates microbiome diversity and plant defenses during cold stress in Glycine max L.

With climate change, frequent exposure of bioenergy and food crops, specifically soybean (Glycine max L.), to low-temperature episodes is a major obstacle in maintaining sustainable plant growth at early growth stages. Silicon (Si) is a quasi-essential nutrient that can help to improve stress tolerance; however, how Si and a combination of cold stress episodes influence plant growth, plant physiology, and microbiome diversity has yet to be fully discovered. The soybean plants were exposed to cold stress (8-10°C) with or without applying Si, and the different plant organs (shoot and root) and rhizospheric soil were subjected to microbiome analysis. The plant growth, physiology, and gene expression analysis of plant defenses during stress and Si were investigated. We showed that cold stress significantly retarded soybean plants' growth and biomass, whereas, Si-treated plants showed ameliorated negative impacts on plant growth at early seedling stages. The beneficial effects of Si were also evident from significantly reduced antioxidant activities - suggesting lower cold-induced oxidative stress. Interestingly, Si also downregulated critical genes of the abscisic acid pathway and osmotic regulation (9-cis-epoxy carotenoid dioxygenase and dehydration-responsive element binding protein) during cold stress. Si positively influenced alpha and beta diversities of bacterial and fungal microbiomes with or without cold stress. Results showed significant variation in microbiome composition in the rhizosphere (root and soil) and phyllosphere (shoot) in Si-treated plants with or without cold stress exposures. Among microbiome phyla, Proteobacteria, Bacteroidota, and Ascomycota were significantly more abundant in Si treatments in cold stress than in control conditions. For the core microbiome, we identified 179 taxa, including 88 unique bacterial genera in which Edaphobacter, Haliangium, and Streptomyces were highly abundant. Enhanced extracellular enzyme activities in the cold and Si+cold treatments, specifically phosphatase and glucosidases, also reflected the microbiome abundance. In conclusion, this work elucidates cold-mediated changes in microbiome diversity and plant growth, including the positive impact Si can have on cold tolerance at early soybean growth stages - a step toward understanding crop productivity and stress tolerance.

Impacts of Silicon Foliar Spraying and Nitrogen Application Techniques on Quantitative and Qualitative Parameters of Rice at Different Planting Spaces

The silicon (Si) foliar application along with timely application of nitrogen (N) can be help to increase the quantity and quality of crops. Also, planting spaces is an agronomic technique that can affect yield and quality of rice. The objective of this study was to evaluate the effects of Si foliar application and N application techniques on yield components, grain yield and accumulation of Si and N in rice grains at different planting spaces. The experiment was conducted as a split-split-plot in a randomized complete block design with three replications during two crop years of 2018 and 2019. The experimental treatments included the main plot assigned to planting spaces (25×10 cm, 20×10 cm), the sub-plot assigned to N application techniques (N application as 33.3% at basal + 33.3% at panicle initiation + 33.3% at full heading, N application as 40% at basal + 40% at panicle initiation + 20% at full heading), and the sub-sub-plot assigned to foliar application of Si (control or non-use of Si, Si foliar application). The results indicated that the reducing planting space (20×10 cm) resulted in an increase in the number of panicle number m–2 by 9.3%, followed by an improvement in grain yield by 9.7% compared with planting distance of 25×10 cm. The plants that received N in three equal splits had higher grain yield (6993.1 kg.ha–1 ). The Si-treated plants showed both higher yield parameters and greater physiological characteristics when compared with control plants. We observed an increase in grain yield (10%), N concentration (7%) and uptake (14.3%) in grain, protein content (6.8%), and nitrogen use efficiency (7.1%) by supplying Si fertilizer. Overall, our results revealed that foliar application of Si could be an effective technique for increasing rice grain yield and improving rice nutritional quality.

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 ± 0.30g 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.

Silicon as a plant defense inducer against the two-spotted spider mite Tetranychus urticae (Trombidiformes: Tetranychidae) invasion on strawberry

Strawberry is an essential strategic crop in Egypt that has been severely affected by the two-spotted spider mite (TSSM). A field trial was conducted to investigate the effects of the foliar application of two silicon (Si) forms, oligomeric silicic acid (OSAB®) and potassium silicate (Silica K®), on strawberry resistance against TSSM invasion. Two Si concentrations (2 mL L−1 and 4 mL L−1) were applied with two-sprays strategy. The foliar application of both Si forms (4 mL L−1) and spray sessions caused a significant reduction in the number of TSSM adults, nymphs, and eggs compared to the control group. Both Si forms achieved a marked increase in the activity of defense-related enzymes (peroxidase, catalase, and polyphenol oxidase) and the elevation of the total protein, and phenol contents in Si-treated plants as compared to the control group. There was a significantly negative correlation between the Si leaf content and TSSM population density. Our results suggest that Si could be easily incorporated into TSSM integrated pest management programs in strawberry as an inducer of plant defense.

Impact of Silica Addition on Alleviating Cadmium Stress: Case Studies of Three Afforestation Tree Species Seedlings in Southern China

Cadmium (Cd) stress is becoming an increasing menace for plants, inducing a series of negative effect. Silicon (Si) plays an important role in mitigating Cd stress in plants. Here, we conducted a one-year experiment with three kinds of tree species seedlings (Schima superba, Chinese sweetgum, Chinese fir) and five levels of Cd treatments (0 mg·kg−1, 6 mg kg−1, 12 mg kg−1, 24 mg kg−1, 36 mg kg−1) with or without 1 g kg−1 Si addition to investigate the mitigation effect of Si on woody plants. The results in this study showed that Cd stress triggered morphological and physiological changes, inhibiting the growth of the three kinds of tree species seedlings. Low concentrations of Cd treatment stimulated the biomass production of Schima superba and Chinese sweetgum seedlings, whereas the biomass production of Chinese fir was not stimulated by Cd treatment. The stimulatory effects were also observed in the antioxidant enzyme (SOD, POD, CAT) activities of the three kinds of seedlings. The MDA contents decreased with the rise of Cd treatments. Soil pH decreased under Cd stress. BCF values of different fractions were observed to increase with the rise of Cd treatments, except for the leaf BCF value of Chinese sweetgum. The root−to−stem TF values of all increased compared with the control, while the root-to-leaf TF values were observed to decrease. Si addition enhanced the growth of the three kinds of tree species seedlings, inducing the increase of heights, ground diameter, leaf morphological parameters, biomass production, the content of chlorophyll and the activities of antioxidant enzymes. Treatment with Si significantly decreased the Cd concentration in different fractions of the three kinds of seedlings. Soil pH increased after treatment with Si. The BCF values for Si-treated plants were all observed to be lower than the non-Si-treated ones. However, the addition Si did not affect the root-to-stem and root-to-leaf TF values in the three kinds of seedlings.

Alleviation of Ammonium Toxicity in Salvia splendens 'Vista Red' with Silicon Supplementation.

Ammonium (NH4+) toxicity seriously hampers the yield and quality of salvia plants because most varieties or sub-species are highly sensitive to NH4+. Silicon (Si) is an alternative that is used to minimize these disturbances and maintain better growth under NH4+ toxicity. Nevertheless, the mitigatory effects of Si on NH4+-stressed salvia are unknown. Therefore, this study was carried out to determine how Si assists to alleviate the NH4+ toxicity degree in salvia. To this end, salvia plants were cultivated in a controlled environment supplied with a constant N (nitrogen) level (13 meq·L−1) in the form of three NH4+:NO3− ratios (0:100, 50:50, 100:0), each with (1.0 meq·L−1) or without Si. Physiological disorders and typical NH4+ toxicity symptoms, as well as interrupted photosynthesis, were observed in the 100% NH4+-treated plants. Furthermore, cation uptake inhibition and oxidative damage were also imposed by the 100% NH4+ supply. In contrast, in the presence of Si, the NH4+ toxicity degree was attenuated and plant growth was ensured. Accordingly, the NH4+ toxicity appearance ratio decreased significantly. Furthermore, Si-treated plants showed an ameliorated photosynthetic ability, elevated internal K and Ca levels, and enhanced antioxidative capacity, as reflected by improved major antioxidant enzyme activities, as well as diminished accumulation of ROS (reactive oxygen species) and MDA (malondialdehyde). Our findings enlightened the agronomic importance of additional Si to nutrient solutions, especially pertaining to bedding plants at risk of NH4+ toxicity.

Silicon Mitigates Ammonium Toxicity in Cabbage (Brassica campestris L. ssp. pekinensis) ‘Ssamchu’

Ammonium (NH4+) toxicity hinders the cabbage yield because most subspecies or varieties exhibit extreme sensitivity to NH4+. Current knowledge indicates that silicon (Si) can alleviate or reverse the ammonium toxicity severity. However, few investigations have been conducted on NH4+-stressed cabbage to elucidate the mechanism underlying the Si alleviation. The study described herein analyzes induced physio-chemical changes to explore how Si helps mitigate NH4+ toxicity. We applied one of three NH4+:NO3- ratios (0:100, 50:50, and 100:0) at a constant N (13 meq·L−1) to the cabbage plants, corresponding with two Si treatment levels (0 and 1.0 meq·L−1). Chlorosis and foliage necrosis along with stunted roots occurred following 100% NH4+ application were ameliorated in the presence of Si. The NH4+ toxicity ratio was reduced accordingly. Similarly, inhibition on the uptake of K and Ca, restricted photosynthesis (chlorophyll, stomatal conductance, and Fv/Fm), and accumulation of reactive oxygen species (ROS, O2·-, and H2O2), as well as lipid peroxidation (MDA, malondialdehyde) in NH4+-stressed cabbages were mitigated with added Si. The lower observed oxidative stresses in solely NH4+-treated plants were conferred by the boosted antioxidant enzymes (SOD, superoxide dismutase; CAT, catalase). Concomitantly, Si-treated plants showed higher activities of key NH4+ assimilation enzymes (GS, glutamine synthetase; GOGAT, glutamate synthase; NADH-GDH, glutamate dehydrogenase) and NH4+ content in leaves. However, excessive NH4+ assimilations cause the acidic stress, which has been demonstrated to be the primary cause of NH4+ toxicity. Therefore, further investigation regarding the Si effects on H+ regulation and distribution should be warranted.

Assessing the Effect of Silicon Supply on Root Sulfur Uptake in S-Fed and S-Deprived Brassica napus L.

Silicon (Si) is known to alleviate many nutritional stresses. However, in Brassica napus, which is a highly S-demanding species, the Si effect on S deficiency remains undocumented. The aim of this study was to assess whether Si alleviates the negative effects of S deficiency on Brassica napus and modulates root sulfate uptake capacity and S accumulation. For this, Brassica napus plants were cultivated with or without S and supplied or not supplied with Si. The effects of Si on S content, growth, expression of sulfate transporter genes (BnaSultr1.1; BnaSultr1.2) and sulfate transporters activity in roots were monitored. Si supply did not mitigate growth or S status alterations due to S deprivation but moderated the expression of BnaSultr1.1 in S-deprived plants without affecting the activity of root sulfate transporters. The effects of Si on the amount of S taken-up and on S transporter gene expression were also evaluated after 72 h of S resupply. In S-deprived plants, S re-feeding led to a strong decrease in the expression of both S transporter genes as expected, except in Si-treated plants where BnaSultr1.1 expression was maintained over time. This result is discussed in relation to the similar amount of S accumulated regardless of the Si treatment.

Silicon Application Differentially Modulates Root Morphology and Expression of PIN and YUCCA Family Genes in Soybean (Glycine max L.).

Silicon (Si) is absorbed and accumulated by some plant species; it has been shown to improve plant growth and performance. The beneficial role of Si in plants is based on the fundamental assumptions, and the biological function of Si is still being researched due to its complex nature, distinctiveness, and interaction. The present study included two distinct experiment sets: a screening test and an advanced test. In the initial examination, we used 21 soybean (Glycine max L.) cultivars. Following the evaluation, we chose four cultivars to investigate further. In particular, the positive response cultivars, Taeseon and Geomjeongsaeol, showed a 14% increase in net photosynthesis (PN), and a 19–26% increase in transpiration in Si-treated plants when compared to the control plants. Si-treated Taeseon, Geomjeongsaeol, and Somyongkong, Mallikong cultivars showed significant differences in root morphological traits (RMTs) and root system architecture (RSA) when compared to the control plants. Taeseon and Geomjeongsaeol showed a 26 and 46% increase in total root length (TRL) after Si application, respectively, compared to the control, whereas Mallikong and Somyongkong showed 26 and 20% decrease in TRL after Si treatment, respectively, compared to the control. The Si application enhanced the overall RMTs and RSA traits in Taeseon and Geomjeongsaeol; however, the other two cultivars, Somyongkong and Mallikong, showed a decrease in such RMTs and RATs. Furthermore, to understand the underlying molecular mechanism and the response of various cultivars, we measured the Si content and analyzed the gene expression of genes involved in auxin transport and root formation and development. We showed that the Si content significantly increased in the Si-treated Somyongkong (28%) and Taeseon (30%) compared to the control cultivars. Overall, our results suggested that Si affects root development as well as the genes involved in the auxin synthesis, transport pathway, and modulates root growth leading to cultivar-dependent variation in soybeans.

Characterization of priming, induced resistance, and tolerance to Spodoptera frugiperda by silicon fertilization in maize genotypes

Fall armyworm (FAW) Spodoptera frugiperda is considered the main defoliating insect pest of maize in many countries. Silicon (Si) applied to plants has been shown to increase the resistance to insects, especially in grasses such as maize. This study characterized the effects of Si fertilization regarding priming, induced resistance, and tolerance to FAW in a landrace variety and hybrid of maize. Si was applied in soil of potted-plants as H4SiO4 at 2 t ha−1 when maize plants were at V2 stage, and when they reached V3 two FAW neonates were placed in the plant’s whorls to cause herbivory. FAW performance was evaluated on excised leaf sections in the laboratory and on plants with larvae infesting V4-stage plants in the greenhouse. Concentrations of H2O2, malondialdehyde, and Si, and the activities of antioxidant enzymes were recorded and correlated to Si-based responses on plant growth, and FAW injury and performance. As main results, there was reduced FAW injury and larval weight gain in Si-treated plants subjected to herbivory. Greater root dry mass was observed in the landrace variety with Si and without herbivory. Landrace plants showed higher shoot weights than the hybrid under FAW infestation. Si-fertilized plants showed higher H2O2 concentrations. The highest peroxidase activities occurred in Si-treated plants without herbivory, and the catalase and superoxide dismutase activities were highest in Si-treated plants without herbivory or herbivory-injured plants without Si. In conclusion, Si-based defense in maize to FAW involve mixed effects of priming and tolerance, and were more pronounced in the landrace variety.

Silicon enhances the tolerance to moderate NaCl-salinity in tomato grown in a hydroponic recirculating system

Salinity is a major threat to the productivity of agroecosystems as it affects the soil structure and the osmotic potential of the soil solution, resulting in nutritional imbalances, Na toxicity and reduction in crop growth and yield. As Silicon (Si) has been considered a beneficial element for alleviating plant stress, the present study was performed to determine if it could enhance tomato plant tolerance to NaCl-salinity in a closed-loop hydroponic system. Plants were irrigated with solutions containing 0, 20 or 60 mM NaCl combined with 0 or 1.50 mM Si. Shoot dry weight and fruit yield decreased with salinity, however, Si partially restored biomass and yield when the solutions contained 20 mM NaCl. Shoot and root K decreased with salinity, however, supplementary Si restored K in plants with 60 mM NaCl. Root and shoot Si was unaffected by NaCl or Si, however, shoot Na increased. Nonetheless, compared to non-Si plants, Si-treated plants showed a 19% and 32% lower shoot Na concnetration in 20 and 60 mM NaCl-plants, respectively. Silicon partly alleviated the K/Na imbalance caused by salinity. Increased shoot K/Na and Ca/Na balances were correlated with higher shoot biomass. Supplemental Si allowed an 80% increase in peroxidase activity and proline in plants with 60 mM NaCl. Fruit yield under moderate salinity was partially restored by Si, due to an increased root Na exclusion, lower shoot Na, and improved K, Ca and K/Na balance, which was correlated with increased shoot growth, POD activity and proline concentration.

Downregulation of Polyamine and Diamine Oxidases in Silicon-Treated Cucumber.

Silicon (Si) is a ubiquitous element in soil with well-known beneficial effects under certain conditions, in several plant species, if supplied in available form for uptake. It may alleviate damage in various stress situations and may also promote growth when no obvious stressors are applied. Effects of Si are often linked to mitigation of oxidative stress, in particular to the induction of antioxidant defense mechanisms. In the work presented, the impact of silicon provision on pro-oxidant systems was investigated in cucumber. Plants of the F1 cultivar hybrid ‘Joker’ were grown under in vitro conditions in the absence of any applied external stressor. Silicon provision decreased H2O2 content and lowered lipid peroxidation in the leaves of the treated plants. This was paralleled by declining polyamine oxidase (PAO) and diamine oxidase (DAO) activities. Several PAO as well as lipoxygenase (LOX) genes were coordinately downregulated in Si-treated plants. Unlike in similar systems studied earlier, the Si effect was not associated with an increased transcript level of gene coding for antioxidant enzymes. These results suggest an inhibitory effect of Si provision on pro-oxidant amine oxidases, which may decrease the level of reactive oxygen species by retarding their production. This extends the molecular mechanisms linked to silicon effects onto redox balance in plants.

Silicon Enhances Resistance to Red Crown Rot Caused by Calonectria ilicicola in Soybean

Silicon (Si) application is known to enhance plant resistance to diverse pathogens. Therefore, a greenhouse study was conducted to determine whether Si reduces red crown rot (RCR) of soybean caused by the soil-borne fungal pathogen Calonectria ilicicola. The soybean cultivar Enrei was grown in soil mixed with different concentrations of sodium silicate (Na2SiO3) and inoculated with C. ilicicola (1% w/v). Si application significantly reduced RCR severity and relative fungal growth in the roots, as per qPCR, at both sampling time points. Notably, the shoot Si content correlated significantly with RCR severity in the roots. In addition, Si application reduced the accumulation of malondialdehyde, indicating that the maintenance of cellular membrane integrity is an important mechanism underlying Si-mediated protection of soybean plants from RCR. Furthermore, Si-treated plants exhibited improved water and nitrogen uptake and root and shoot growth. Aboveground biomass and seed yield at harvest increased with increasing Si concentration (0.0–3.0 g Na2SiO3 kg−1 soil). However, further increase in Si concentration (6.0 g Na2SiO3 kg−1 soil) reduced seed yield. Therefore, Si treatment can be used as an effective strategy to control RCR in soybean.

Silicon supplementation improves early blight resistance in Lycopersicon esculentum Mill. by modulating the expression of defense-related genes and antioxidant enzymes.

Early blight is the most devastating disease in tomato which causes huge yield losses across the globe. Hence, development of specific, efficient and ecofriendly tools are required to increase the disease resistance in tomato plants. Here, we systematically investigate the defensive role and priming effect of silicon (Si) in tomato plants under control and infected conditions. Based on the results, Si-treated tomato plants showed improved resistance to Alternaria solani as there was delay in symptoms and reduced disease severity than non-Si-treated plants. To further examine the Si-mediated molecular priming in tomato plants, expression profiling of defense-related genes like PR1, PR2, WRKYII, PR3, LOXD and JERF3 was studied in control, Si-supplemented, A. solani-inoculated and Si + A. solani-inoculated plants. Interestingly, Si significantly increased the expression of jasmonic acid (JA) marker genes (PR3, LOXD and JERF3) than salicylic acid (SA) marker genes (PR1, PR2 and WRKYII). However, Si + A. solani-inoculated plants showed higher expression levels of defence genes except WRKYII than A. solani-inoculated or Si-treated plants. Furthermore, pre-supplementation of Si to A. solani-infected tomato plants showed increased activity of antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and peroxidase (POD) than control, Si-treated and A. solani-inoculated plants. Altogether, present study highlights the defensive role of Si in tomato plants in response to A. solani by increasing not only the transcript levels of defense signature genes, but also the activity of antioxidant enzymes.

Effect of seed priming with silicon on growth, yield and nutrient uptake of maize under water-deficit stress

Drought is one of the major abiotic stresses reducing productivity of field crops including maize. Silicon (Si) has been known to enhance plant tolerance against various biotic and abiotic stresses. The objective of this study was to evaluate the effects of seed priming of maize with Si on growth, yield, physiological traits and nutrient uptake under different soil moisture regimes. Completely randomized design with factorial arrangement was employed where treatments consisted of three Si doses (0, 1 and 2 mM) and three soil moisture regimes (100%, 75% and 50% field capacity [FC]). Si at 1 mM significantly increased growth and grain yield (∼38%) of stressed plants compared with the control, and these values did not significantly change when Si dose was increased to 2 mM. At 75 days after sowing, 1 mM Si at 50% FC increased the actual photochemical efficiency of photosystem II by 33% and the electron transport rate by 31% compared with the control. Silicon significantly reduced the amount of proline accumulation and increased total soluble sugar content at 50% FC. There was no clear increase/decrease in the contents of N, P, K, Ca and Mg in shoot and grain of Si-treated plants under water-deficit stress, except that N content in shoot was significantly increased with the addition of 1 mM Si. Priming seed with 1 mM Si was optimum in improving most of the studied parameters under water-deficit stress, and could offer perspectives for using it as the recommended dose for maize.

Root Silicon Addition Induces Fe Deficiency in Cucumber Plants, but Facilitates Their Recovery After Fe Resupply. A Comparison With Si Foliar Sprays.

Silicon has not been cataloged as an essential element for higher plants. However, it has shown beneficial effects on many crops, especially under abiotic and biotic stresses. Silicon fertilization was evaluated for the first time on plants exposed to fluctuations in an Fe regime (Fe sufficiency followed by Fe deficiency and, in turn, by Fe resupply). Root and foliar Si applications were compared using cucumber plants that were hydroponically grown in a growth chamber under different Fe nutritional statuses and Si applied either to the roots or to the shoots. The SPAD index, Fe, and Mn concentration, ROS, total phenolic compounds, MDA concentration, phytohormone balance, and cell cycle were determined. The results obtained showed that the addition of Si to the roots induced an Fe shortage in plants grown under optimal or deficient Fe nutritional conditions, but this was not observed when Si was applied to the leaves. Plant recovery following Fe resupply was more effective in the Si-treated plants than in the untreated plants. A relationship between the ROS concentration, hormonal balance, and cell cycle under different Fe regimes and in the presence or absence of Si was also studied. The contribution of Si to this signaling pathway appears to be related more to the induction of Fe deficiency, than to any direct biochemical or metabolic processes. However, these roles could not be completely ruled out because several hormone differences could only be explained by the addition of Si.

Ecophysiological study of SiK impact on Castanea sativa Mill. tolerance to drought stress

Drought is an abiotic stress that may be aggravated by climate changes with increasingly warmer and drier summers. This is a severe problem in the chestnut crop in Portugal due to its need for water during this time, which is essential for good formation and development of the fruit. Si fertilization is referenced by several authors as important in the tolerance of plants under drought. The experiments were carried out in the field trial and chestnuts were fertilized with 0, 5, 7.5, and 10 mM potassium silicate (SiK), which was applied to the soil and to the leaves and exposed to a non-irrigation and an irrigation phase during the summer. Results indicate that Si fertilization increased the relative water content and water potential, while the transpiration rate, stomatal conductance, and stomatal density were reduced under deficit irrigation in Si-treated plants (10 mM SiK). Moreover, the Si induces a higher photosynthetic activity and vessel frequency with a smaller diameter, promoting a higher relative hydraulic conductivity and a lower vulnerability to cavitation. This work suggests that Si can be used as a potential source to induce drought tolerance in chestnuts.

Stress Oxidative Evaluation on SiK®-Supplemented Castanea sativa Mill. Plants Growing Under High Temperature

The protective effect of silicon (Si) against environmental stress has been observed in many crops. The objective of this work was to evaluate the impact of SiK® (potassium silicate) fertilization on the resilience capacity of chestnut plants growing under high air temperature conditions and their recovery capacity after a turnover to adequate temperatures. Castanea sativa plants were supplied with 0 mM, 5 mM, 7.5 mM, and 10 mM SiK® and exposed sequentially to 25 °C, 32 °C, and 25 °C for 1 month each. Data suggested that silicon are involved in increasing the heat tolerance of chestnut plants by reducing the oxidative damage and improving the antioxidant enzymes and metabolites. Under heat stress (32 °C), there was an increase in the catalase, ascorbate peroxidase, and peroxidase activities, as well as in the phenol content of supplemented plants, which consequently reduced the electrolyte leakage, lipid peroxidation, and hydrogen peroxide content. Additionally, a lower proline content was measured inside the leaves’ tissues of Si-treated plants. Besides the resilience against heat stress, after exposure to 32 °C, the recovery was also quick.