ABSTRACT
The world’s population increases day by day, especially in developing countries, and people are facing the problem of meeting nutritious food and health security requirements. It has become a major concern for scientists to improve the fertility of agricultural soil, so that the productivity, as well as the quality, increases and one can have a sufficient and healthy source of food. Soil contains many macronutrients (N, P, Mg, Ca, K, and S) and micronutrients (B, Mn, P, Cl, Cu, Fe, Mo, and Zn) for the growth and development of plants, but due to the increasing content of heavy metals by any means, like high atmospheric deposition, improper weathering of parental rocks, high mineralization, industrial waste inputs, and some other anthropogenic activities, the adequate concentration of beneficial elements decreases and that of heavy metals (macro-and micronutrients) increases excessively in the soil or agricultural field (Chen et al., 2010a,b; Elbaz et al., 2010; Singh and Prasad, 2011; Gill et al., 2013; Gangwar et al., 2014). This increased level of heavy metals may lead to an alteration in the properties and pH of soils and ultimately affect the uptake of nutrients in plants, hence lowering the quality and quantity of a plant’s yield (Tripathi et al., 2014a,b, 2015a,b). Generally, heavy metals are known to cause deleterious effects in the morphology, as well as physiology, of plants, such as uptake of minerals, photosynthesis, and alteration in many genetic processes (Rodriguez et al., 2012; Ali et al., 2013; Li et al., 2013; Gangwar et al., 2014). Moreover, several methods have been used to overcome the adverse effects of heavy metals in plants, and the application of silicon is regarded as one of the most effective and beneficial elements, which increases the uptake of nutrients, and thus the growth of plants. However, it has been found that silicon plays remarkably many
13.1 Introduction .......................................................................................................................... 227 13.2 Dynamics of Silicon .............................................................................................................228 13.3 Silicon in Soil and Plants ...................................................................................................... 229
13.3.1 Silica in Soil .............................................................................................................. 229 13.3.2 Silicon in Plants ........................................................................................................ 229
13.4 Silicon under Deficiency and Toxicity of Nutrient Uptake and Other Stresses in Plants..... 231 13.5 Silicon and Other Environmental Stresses in Plants ............................................................ 232 13.6 Silicon and Antioxidant Activities ........................................................................................ 233 13.7 Silicon and Anatomical Structures .......................................................................................234 13.8 CO2 and Silica Uptake in Plants ...........................................................................................234 13.9 Assessment of Current Status and Future Conjecture of Silicon Research .......................... 235 References ...................................................................................................................................... 235
roles in plants, in which some are most beneficial to plants. Tripathi et al. (2012a) tested the effect of silicon on the growth of rice seedlings against cadmium and concluded that silicon successfully alleviated the toxicity of cadmium in plants and reduced the its accumulation. Similar beneficial effect of silicon was also demonstrated by Hussain et al. (2015) in Triticum aesativum under the cadmium stress. In addition to this, Malčovská et al. (2014) found that, in the presence of silicon, oxidative stresses were significantly reduced in Zea mays caused by cadmiun stress. Furthermore, it has been also observed that silicon can also alleviate aluminum, manganese, iron, and heavy metal toxicity as well as drought, water, salinity, stresses, and UV radiation damage (Cocker et al., 1998; Epstein, 1999; Britez et al., 2002; Liang et al., 2006; Shen et al., 2010; Chen et al., 2011, Singh et al., 2011; Tripathi et al., 2011, 2012b; De Souza et al., 2013; Mehrabanjoubani et al., 2015; Tripathi et al., 2016b). Silicon in the form of fertilizers is also used against the biotic and abiotic stresses and also in the case of other nutrient deprivation condition. Many scientists also observed that silica enhances the yield and quality, and make appropriate defense against fungal and other pathogenic attack (Lanning et al., 1966; Brwen et al., 1992; Korndorfer et al., 2001; Gillman et al., 2003; Rodrigues et al., 2004; Liang et al., 2006).
