Abstract
Nano-biochar (n-BC) is an emerging eco-friendly material with potential to improve crop performance under salt stress. This study aimed to evaluate the effects of foliar applications of bamboo-derived n-BC on the morphological and biochemical responses of lettuce plants under salt stress (40 mM NaCl). n-BC solutions (1.0, 3.0, and 5.0% w/v) were foliar-applied every five days until harvest. Salt stress markedly increased hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) by 264.54% and 14.02%, disrupted Na(+)/K(+) homeostasis, and reduced biomass. Foliar n-BC mitigated these effects by reducing Na(+) accumulation by 22.24-25.11% and enhancing K(+), Ca(2+), and Mg(2+) uptake. The treatments also improved photosynthetic pigments and increased proline, soluble proteins, and soluble sugars. Oxidative damage was alleviated, as reflected by reductions in H(2)O(2) and MDA together with enhanced ascorbate peroxidase, catalase, and superoxide dismutase activities. Total phenolics, flavonoids, and ABTS and DPPH scavenging activities also increased under n-BC application. Among all the concentrations, 3.0% (w/v) n-BC consistently produced the greatest improvements in growth, ionic balance, and antioxidant responses. These findings demonstrate that bamboo-derived n-BC is a promising foliar biostimulant for enhancing lettuce performance under saline conditions.