3.1.1 Salinity and rice physiology

Plant physiological traits are susceptible to the high soluble salts in its rhizosphere. Salinity has bunch of adverse effects on physiology of rice plants, such as hinder the net photosynthesis (Pn), stomatal conductance (Gs), transpiration rate (Tr), photosynthetically active radiation (PAR), degradation of pigment and relative water content (RWC) as well as affect the water use efficiency (WUE) [50]. As far as photosynthesis activity is a concern, rice plants under salinity have decreased photosynthetic efficiency through the complex of photosystem II (PSII). Furthermore, chlorophyll contents in rice leave tissues are damaged by the excessive accumulation of Na<sup>+</sup> and Cl, which hamper the primary electron transport in PSII [51]. The chlorophyll contents (chl a, b, and carotenoids) in rice leaves were significantly declined under salinity [52]. High salinity also reduces the quantum yield of the complex PSII, and to decrease K<sup>+</sup> /Na<sup>+</sup> ratio. All these factors cause adverse pleiotropic effects on rice physiology and development at the molecular and biochemical levels [53], and cause abnormal rice growth, development, and ultimately plant death [19].

#### 3.1.2 Salinity and ion imbalance in rice plant

Ion imbalance is the ultimate effect of salinity. Under salinity, the severe competition of Na<sup>+</sup> and Cl with K<sup>+</sup> , Ca2+, and NO3 occurs. Generally, high NaCl concentration in the soil and plant decrease the reduce N, P, K, Ca, Mg, and Mn in rice root and shoot, and increases Na<sup>+</sup> and Cl, and increases Na<sup>+</sup> /K<sup>+</sup> and Na<sup>+</sup> /Ca2+, Ca2+/Mg2+, and Cl/NO3 ratio leads to specific ion (Na<sup>+</sup> and Cl) toxicity in plant's organelles [54, 55]. Similarly, boron (B), silicon (Si), and zinc (Zn) availability decreased to the rice plant, and increased cadmium (Cd) toxicity subjected to salinity [56, 57].
