Effects of ascorbic acid and salicylic acid on drought resilience and mitigation of lead and cadmium toxicity in dryland maize ( Zea mays L.)

This study evaluated individual and combined applications of AA (100 mg·L ⁻¹ , equivalent to 0.57 mM) and SA (0.5 mM) on maize (‘Zhengdan No. 16’) subjected to four water regimes: well‐watered (WW 100%), mild water stress (MWS 75%), moderate water stress (MoWS, 50%), and severe water stress (SWS, 30% field capacity), with or without Pb (200 μM) or Cd (100 μM) exposure. Photosynthetic pigments, gas exchange, phytohormones (ABA, IAA), oxidative stress markers (H ₂ O ₂ , SOD), and macronutrient uptake (N, P, K) were quantified. The Pb concentration (200 μM) was selected based on preliminary dose–response experiments (0, 100, 200, 400 μM), where 200 μM caused significant but non‐lethal growth inhibition (30%–40% biomass reduction), allowing assessment of AA/SA mitigation without complete growth arrest.

Under WW conditions, AA increased chlorophyll a by 11.0% and SA by 14.5% versus controls. Combined AA+SA + Cd improved selected nutrient responses, including a 2.8% increase in leaf N and a 4.5% increase in leaf K relative to Cd alone under WW conditions; however, leaf P did not increase under all water regimes. AA reduced Cd‐triggered H ₂ O ₂ by approximately 30% and Pb‐triggered H ₂ O ₂ by approximately 18% ( P  < 0.05). Under SWS, combined treatments improved selected photoprotective responses, including a 14.3% increase in carotenoid content, although Chl a responses were treatment and metal‐specific.

Exogenous AA and SA, particularly in combination, enhance dryland maize resilience to combined drought and HM stress through improved photosynthesis, reduced oxidative damage, and optimized nutrient acquisition. These findings support antioxidant biostimulants as sustainable tools for crop stress.