4.1.2. Phosphorus

Phosphorus (P) is a primary macronutrient with a structural function in plants. It is involved in drivers of metabolic functions including respiration, energy storage and transportation, production of nucleic acid, membrane stability, catalyze enzymes activities, redox reactions and contribution to carbohydrate metabolism [111]. As with other plant families, P is one of the important nutrients for the Brassicaceae family that directly affects its development and productivity [112]. Holzschuh et al. [113] studied different doses of P

fertilizer in Brassicas and reported that the species of this family are highly demanding of P availability in the soil, especially broccoli (*B. oleracea* var. itálica) and cauliflower (*B. oleracea* var. botrytis). The optimal management of P fertilization in vegetables is essential for their proper growth, development and yield [112]. Phosphorus deficiency in soil and plants directly affects vegetable vigor, establishment and root development, thus disrupting water use efficiency [114]. Several plants of the Brassicas species have the capability to tolerate and respond to various types of stresses through hormonal stimulation, ion exchange, antioxidant enzymes and the activation of signaling flow in their metabolic and genetic boundaries that mitigate stressed conditions [115].

Application and management of appropriate P fertilization has increased water use efficiency against drought stress [116,117]. Jones et al. [118] indicated that adequate soil P contents compensate for the impact of drought stress on the growth and yield of plants. Application of P source fertilizers may reduce the drastic effects of water scarcity during pollen formation or the reproductive stage that could increase flower and pod production, resulting in a greater yield and high protein content in grains [119]. Phosphate fertilizers improved the performance of *B. juncea* under salt stress by increasing plant dry mass and P uptake while lowering the Na+/K+ ratio [114]. Phosphorus fertilization adapts different mechanisms that immobilize the metal content in soil [120] by reducing their dissolution under the low pH range of soil, hence leading to the reduction of the bioavailability and uptake of metals by plants [121]. Phosphate fertilization increases the pH of soil solution to constrain absorption of heavy metals, as their availability decreases with increasing P fertilization [122].
