NaHCO3 stress and hemp (Cannabis sativa L.) adaptation: Growth physiology-metabolism synergy in saline-alkaline environments

Salt and alkaline stress pose major challenges to global agriculture, negatively affecting crop production.It is essential to understand how hemp (Cannabis sativa L.) adapt to these stresses in order to improve cultivation in affected regions.This study investigated the adaptive responses of hemp to sodium bicarbonate (NaHCO₃) stress by evaluating growth, photosynthetic performance, physiological characteristics, nutrient distribution, and secondary metabolite accumulation under different NaHCO₃ concentrations (0, 100, 200, and 300 mM).Low NaHCO₃ concentration (100 mM) had nonsignificant effect on hemp growth (p > 0.05) and even increased root dry weight by 32.31%.However, higher concentrations (200, 300 mM) significantly inhibited growth, reducing plant height by 20.70%-28.87%,stem diameter by 30.40%-52.48%, root length by 23.08%-33.25%,and leaf dry weight by up to 81.60%.Mild stress enhanced photosynthetic performance, with increases in SPAD (6.02%),net photosynthetic rate (20.64%), stomatal conductance (26.94%), transpiration rate (18.99%), and intercellular CO₂ concentration (9.61%), whereas severe stress markedly suppressed these parameters.The NaHCO₃ stress promoted Na⁺ accumulation, particularly in roots (up to 630.91%), while reducing the uptake of K⁺, Ca²⁺, Mg²⁺, N, and P. Moderate stress enhanced antioxidant defense and stimulated secondary metabolism, resulting in increases of 86.75% in total flavonoids, 145.92% in total phenolics, and 60.63% in cannabidiol, whereas these metabolites declined under severe stress.These findings could help to optimize hemp cultivation to improve salinity tolerance and contribute to the understanding of salinity stress responses in other important economic crops.