Silicon as a mitigator of water deficit stress in radish crop
Graphical abstract
Introduction
Radish (Raphanus sativus L.) belongs to the Brassicaceae family, and is characterized by yield of globular roots, bright scarlet in color with white pulp, and for having a short cycle, between 25 and 35 days, cultivated in fertile soils with a pH of around 5.5–6.8 (Cardoso and Hiraki, 2001; de Paiva et al., 2013).
Although silicon is not considered an essential element for plant growth, it has numerous positive effects, such as increase photosynthetic capacity, and improve the architecture of aerial parts, tolerance to water stress, mitigates ammonium toxicity and attack by pests and pathogens (Viciedo et al., 2019; Ma and Yamaji, 2006; Bakhat et al., 2018). This element is the second most abundant in the Earth's crust, surpassed only by oxygen and found in practically all rocks and soil types, in various forms of pure or impure silica (Russell, 1994; Sommer et al., 2006).
Fertilization using silicate, containing silicon in the chemical composition, has been gaining ground in agriculture mainly due to the benefits of its application coupled with low acquisition costs. It is necessary that these silicon sources demonstrate characteristics that are favorable for their use, which aim to improve soil conditions, such as a high concentration of this element in soluble form and low concentration of heavy metals (Korndorfer and Oliveira, 2010).
Silicon presents several beneficial effects in plants by improving soil chemical conditions, such as increasing pH, acting as a corrective, decreasing Al³+ levels, increasing base saturation, acting in the conversion of toxic elements from soluble to insoluble fractions, and acting in the polymerization and precipitation of these toxic elements with silicate compounds (Korndorfer and Oliveira, 2010; Majumdar and Prakash, 2020).
The liming technique is performed by applying limestone to the soil to correct acidity, neutralizing the protons in the soil solution, however, silicates can be a viable alternative to neutralize acidity as a replacement for conventional liming (Galindo et al., 2021a). Silicate can reduce the time associated with liming reactions in the soil profile due to its greater solubility and alkalinity compared to limestone (Crusciol et al., 2016; Galindo et al., 2021b).
Available to the plant, silicon is absorbed in the form of monosilicic acid, by mass flow, accumulating mainly in the middle lamella of the leaves, the region of maximum transpiration, and assimilated in the form of polymerized silicic acid (Ma and Yamaji, 2006) .
Water stress negatively affects the accumulation of radish plant biomass (Stagnari et al., 2018) and also of other species whose agronomic interest is the roots and tubers, such as sugar beet and red beet (Beta vulgaris L.), and potatoes (Solanum tuberosum L.) (Li et al., 2016; Shaw et al., 2002; Stagnari et al., 2014a, 2014b). However, there are no conclusive studies on the use of silicates to mitigate the effects of water stress on the development of radish culture, such as growth rates and biochemical behavior in response to oxidative stress.
The central hypothesis of the experiment is that with the application of silicate in the soil, in the form of calcium and magnesium silicate, radish plants should develop anatomical and physiological mechanisms capable of protecting the tissues from the impact of hydric deficiency compared to the plants grown with dolomitic limestone.
The aim of this research was to demonstrate through physiological and biochemical parameters that the use of calcium and magnesium silicate in place of dolomitic limestone could contribute to the tolerance of radish plants when subjected to hydric deficiency.
Section snippets
Material and methods
The experiment was carried out in a 40 m² agricultural greenhouse in the Horticulture Department of the Faculty of Agricultural Sciences of the São Paulo State University-UNESP, Botucatu Campus, São Paulo-Brazil, located to 22° 52′ 55″ S, 48° 26′ 22″ W. Biochemical analyses were performed at the Department of Chemical and Biological Sciences-Biosciences Institute/UNESP. The city's climate, according to Koppen, is classified as warm temperate (mesothermal), with an average annual rainfall of
Results and discussion
The results of the ANOVA with the agricultural correctives (silicate and limestone), irrigation depths (control-10 kPa, moderate water deficiency MWD-20 kPa, and severe water deficiency SWD-30 kPa) and the interaction between factors in all parameters evaluated in radish plants are presented in Table 2. Parameters showed a significant difference for correctives and depths, with the exception of height I, leaf area ratio-LAR, and internal CO2 concentration, and also transpiration rate for the
Conclusions
It was concluded that plants treated with silicate presented better photosynthetic efficiency, including the other components of photosynthesis in the crop of radish. In metabolic terms, silicon improved aspects of stress mitigation, notably the activity of antioxidative enzymes and L-proline accumulation. In this sense, the application of silicate as a neutralizing mineral could be an interesting strategy for growing radish and other vegetables in areas with less water availability.
The
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was carried out with the support of the Coordination for the Improvement of Higher Education Personnel - Brazil (CAPES) - Financing Code 001; Foundation for Agricultural and Forestry Studies and Research (FEPAF).
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