Soil–plant Integrative Supplementation with Humic Acid and Antioxidants Improves Growth, Fruit Quality, and Antioxidant Capacity of Cd-stressed Solanum Melongena

Cadmium (Cd) is on the rise in the environment due to both anthropogenic activities and natural causes. It causes detrimental impacts on plant growth, yield, and quality, further posing a notable concern for human health. The objective was to uncover the positive consequences of the synergistic treatment of humic acid (HA) and antioxidants (Antiox) on multiple parameters, encompassing growth, physiological, and biochemical characteristics of Solanum melongena cultivated in soil contaminated with Cadmium. Plants exposed to three cadmium levels [no stress, 0.5 mM, and 1.0 mM Cd] and two treatments [control vs. HA + Antiox] were applied in three replicates using a randomized complete block design (RCBD). Our findings indicated that cadmium stress negatively impacted growth characteristics, photosynthetic efficiency, leaf integrity, and oxidative stress markers. Nevertheless, the integrative supplementation with HA + Antiox demonstrated its efficacy in alleviating the adverse consequences of Cd-induced stress by augmenting the overall soil conditions. This was achieved by reducing the toxicity of cadmium and facilitating its immobilization, thereby improving plant growth. Furthermore, HA + Antiox successfully reduced cadmium levels in all plant parts, restricted cadmium translocation from the soil to all plant parts, increased nutrient levels in leaves, boosted the abundance of enzymatic and non-enzymatic antioxidants, and promoted the accumulation of osmoprotectants. This detoxification mechanism ultimately leads to an improvement in photosynthetic efficiency, growth, and yield quality. Our findings showed that HA + Antiox enhanced the overall performance of S. melongena, reduced Cd stress toxicity, and promoted sustainable agricultural practices.