Influence of Silicon Forms on Nutrients Accumulation and Grain Yield of Wheat Under Water Deficit Conditions

Wheat (Triticum aestivum L.) occupies a pivotal position among cereals around the world and contributes a significant part of daily calories and protein intake (Kizilgeci et al. 2021). Beneficial components to human health such as proteins, minerals, vitamins, phytochemicals, and dietary fibers could be provided from wheat (Shewry and Hey 2015). Owing to its contribution as the major staple food crop universally, wheat is ranked at the first position among cereals (Iqbal et al. 2021). Nevertheless, yield potential of wheat is limited due to climate change effects, especially abiotic stresses, including heat, salinity, and drought (Yadav et al. 2020).

It is well known that water is one of the most significant factors affecting growth and development of crop plants. It has been proved the critical role of water in physiological processes especially photosynthesis and nutrient uptake. Accordingly, deficiency or unavailability of water will cause imbalance in all plant biological pathways. In this respect, drought as an environmental factor mutates the pathway stability of water and nutrients to become out of balance (Meena et al. 2017; Saudy and El-Metwally 2019), hence, reductions in plant growth and yield owing to low water supply were obtained (El-Metwally et al. 2022; Saudy et al. 2021; Abd–Elrahman et al. 2022). While, in arid and semi-arid conditions, farmers are forced to irrigate the crops with less water than required, due to lack of irrigation water, although the shortage in yield is realized. In this concern, applying practices that mitigate the adverse effect of water deficit is a crucial action. In several plant species, as wheat, the potentiality of silicon (Si) to reinforce the environmental stresses tolerance was obtained (Rodrigues et al. 2015). Si could enhance plant growth under normal and stress conditions (Saudy and Mubarak 2015). The induction of plant resistance by Si to stress might be attributed to formation of phytoliths and polymerization of insoluble Si in cell walls and around the vascular bundle, reducing water loss, by controlling transpiration (Mecfel et al. 2007). Also, Si activates the antioxidant mechanisms to quench the reactive oxygen species (ROS) production, hence, reduce lipid peroxidation (Ye et al. 2013; Rodrigues et al. 2015; Abdel-Haliem et al. 2017). Application of Si increased water and osmotic potential in roots and leaves as well as alleviated water stress partially (Ming et al. 2012). Since Si has a vital role in enhancing growth and yield (Salim 2014), in the future, its application will become a sustainable strategy and mitigate the adverse impacts under abiotic stress (Etesami and Ryong Jeong 2018).

The effect of cation associated Si in the used compounds should not be neglected. There are several forms of Si could be used as fertilizers like aluminum silicate, calcium silicate and potassium silicate. Although potassium silicate has received great attentions, very little information is available about aluminum silicate and calcium silicate. The harmful impacts of low water supply were reduced by application of potassium silicate (Abu-Muriefah 2015).

The most favorite form of Si for plant growth, especially under stresses, is still unclear. In the current work we hypothesized that the different forms of Si supply have different impacts toward the plant response to water stress. Thus, the aim was to compare the potentialities of aluminum, calcium, and potassium silicates for alleviating the water deficit impacts on wheat.

There is no doubt that the nutrients balance within plants is substantially correlated with water status of plant cells. In this regard, it has been reported that deficit irrigation reduces plant growth by affecting various physiological and biochemical processes, such as photosynthesis, respiration, translocation, ion uptake, carbohydrates, nutrient metabolism, and growth promoters (Farooq et al. 2008; Razmjoo et al. 2008; Salem et al. 2021). Also, reducing water supply caused severe depression in plant physiological, anatomical, and agronomic traits (El-Bially et al. 2018; El-Metwally et al. 2021; Makhlouf et al. 2022). In the stressed plants accumulation of abscisic acid is stimulated in leaves, which sets up ionic imbalance that compels potassium ion (K⁺) to leak out from guard cells and loss of guard cell turgor pressure. Thus, narrowing the aperture mostly would be due to reduced leaf relative water content and increased stomatal closure (Abd El-Mageed et al. 2021; Makhlouf et al. 2022). Water deficit reduced the concentration of N and P in plant tissue (He and Dijkstra 2014) and decreased nutrient uptake from soil (Ge et al. 2012; Sardans and Peñuelas 2012). Decreases in nutrient uptake during drought could be attributed to the reduction of nutrient supply through mineralization process (Sanaullah et al. 2012; Saudy et al. 2020), and by reducing nutrient diffusion and mass flow in the soil (Lambers et al. 2008). Disturbing the kinetics of nutrient under drought could decrease nutrient uptake by plant roots (Christophe et al. 2011). On the contrast, our results showed that macronutrients concentration did not affect by low water supply (Table 2). Since the impact of drought depends on its intensity and duration during a plant’s life cycle (Bradford and Hsiao 1982), irrigating wheat by 60 or 80% of crop evapotranspiration could not represent a significant issue for macronutrient uptake. However, Si concentration was the pronounced element that drastically reduced with water deficit (Table 4). Reductions in Si concentration with Irr60 were 31.5 and 13.7% in the first and second seasons, respectively.

Drought not only affects the plant nutrient balance but also plant growth and development. In this respect, the revealed results in Table 5 clarified that all yield traits were reduced with lowering water supply. As averages of the two seasons, the reductions owing to Irr60 and Irr80 compared to Irr100 were 11.1 and 4.4% in SPAD value, 6.7 and 1.4% in spike length, 25.1 and 11.2% in grains weight spike⁻¹, 17.4 and 7.0% in weight of 1000 grains, as well as 34.8 and 13.2% in grain yield ha⁻¹, respectively (Fig. 1). Under deficit irrigation at 80% of crop evapotranspiration, the growth and yield index of spring wheat were not influenced greatly and reached 5–13% lower than under full irrigation. While, under deficit irrigation at 60% crop evapotranspiration, the growth and yield index were greatly reduced by about 10–37% lower than under full irrigation (Zhou 2020). Water stress occurred decreases in water uptake by roots, leaf expansion and stomatal conductance, causing a decrease in carbon assimilation in photosynthesis process and yield (Christophe et al. 2011; Sharma et al. 2020a; El-Metwally and Saudy 2021). Declined frequency of cell division and cell enlargement, root differentiation, shoot length, altered stomatal movements, water and mineral nutrition association with decreased plant yield and water use efficiency are the major outcomes of drought (Kumawat and Sharma 2018; Mubarak et al. 2021). Photosynthesis activity is decreased primarily by closing of stomata, membrane injury and altered functioning of several enzymes, particularly those which are associated with ATP synthesis (Kumawat and Sharma 2018; Sharma et al. 2020a). Drought stress conditions also enhanced generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which disturb the cell redox regulatory functioning (Laxa et al. 2019; Sharma et al. 2020b). Accordingly, water deficit, especially at elongation and heading stages would reduce the yield of wheat (Tari 2016).

To mitigate against the detrimental impacts of water deficit, new tactics are urgently needed to ensure future food security. Results of the current study showed the beneficial effect of Si in enhancing leaf greenness (Table 5). Improvements in SPAD or chlorophyll content were noted with silicate fertilizer (Silva et al. 2012; Radkowski and Radkowska 2018). Moreover, Si fertilization had the potentiality to improve plant tolerance to drought (Debona et al. 2017; Luyckx et al. 2017). In this situation, Si can improve anti-oxidative both enzymatic and non-enzymatic defense mechanisms thus, avoid damage from ROS produced by various abiotic stresses (Maghsoudi et al. 2019; Sattar et al. 2019). Si influences water relations in drought-treated plants, since it induces the formation of a silica cuticle double layer under the leaf epidermis which reduces water losses through cuticular transpiration (Gong et al. 2003). Si also reduces stomatal conductance in relation to turgor loss of guard cells resulting from Si deposition and modified cell wall properties (Zhu and Gong 2014). The improvement of drought resistance due to Si application could be ascribed to its strong abilities to extract water from the soil because of Si-related promotion of root elongation (Hattori et al. 2005) and up-regulation of aquaporin genes (Liu et al. 2015). Si has been described to reduce many of the effects including the biological and abiotic stresses of plants at high evaporation rates, and maintain the water potential of plants, photosynthesis, stomatal conductivity, and leaf erection (Das et al. 2017). Si improves the plant growth by modulating the nutrient (Na, Mg and Si) uptake and phytohormone levels and alleviating plant stress levels (Gong et al. 2008). Enhancing the tolerance of the wheat plants against drought stress was achieved, since Si caused balance of endogenous hormones (Xu et al. 2017). Moreover, the associated cation with silicon could has a promotive role for enhancing drought tolerance. In this respect, osmotic adjustment is considered an effective component of drought resistance (Gomathi et al. 2010). Potassium affects the osmotic adjustment of the plant and increases drought resistance by enhancing the translocation of assimilates and maintaining osmotic charge (Marschner 1995; Mubarak et al. 2016). Accordingly, supplying wheat plants by potassium silicate, particularly under severe water deficit is regarded as a crucial action to enhance the tolerance of plants with reducing yield losses.

Since lower accumulation of Si in plant tissues under water deficit than well-watered was recorded, the significance of foliar application of Si when plants receive low water supply become more essential. Moreover, potassium, calcium, and aluminum silicates showing similar yield, farmers could choose any available Si form to fertilize wheat irrigated by water less than the full irrigation. However, under moderate water supply (irrigation by 80% of crop evapotranspiration), potassium silicate could be the favorite Si form for obtaining better yield.