Salicylic Acid with Phosphorus Strengthens Antioxidative System, Secondary Metabolite Accumulation, and Limited Resource Enrichment to Enhance Photosynthesis Under Drought in Mustard

Infrequent and untimely rainfall restricts plants’ water availability which reduces photosynthetic potential, growth, and yield. To cope with drought-induced adversities, utilization of available water and nutrients together with reduction in oxidative stress is primary concern. This study aims to unravel the approach applied by supplementation of salicylic acid (SA) with phosphorus (P) to reduced drought stress in mustard. In a randomized block design, 30 mg P kg −1 soil and 0.5 mM SA were used to study their effect on drought-stressed plants. Drought stress was imposed after 15 days of sowing (DAS) by withholding water to 50% of holding capacity and sampling was done at 30 DAS. We observed that supplementation of SA with P was effective in enhancing the content of nutrient together with N and S assimilation which resulted in higher proline and reduced glutathione (GSH) content responsible for scavenging reactive oxygen species (ROS) and maintaining osmotic balance. Enhancement in the activities of antioxidative enzymes and secondary metabolites further reduced oxidative stress by decreasing content of hydrogen peroxide (H 2 O 2 ) and thiobarbituric acid reactive substances (TBARS). Increased root length and enhancement in photosynthetic nitrogen use efficiency (PNUE) and water use efficiency (WUE) maximally protected photosynthetic potential under drought to increase growth and yield of mustard. Thus, when foliar SA and soil applied P are added to mustard under drought, there is much higher increase in antioxidants, secondary metabolites, and efficient use of nutrient and water to reduce oxidative stress and protect photosynthesis and growth under drought in mustard.