Combination of magnesium and iron nanoparticles with biochar mitigated salt toxicity and altered antioxidant activity and essential oil production of chamomile

This research was conducted in a greenhouse to examine the effects of solid biochar (25 g kg^-1 soil), and biochar-based nanoparticles of magnesium (BNP-MgO), iron (BNP-Fe₃O₄), and magnesium + iron (BNP-MgO + BNP-Fe₃O₄) in comparison with control (soil) on German chamomile (<i>Matricaria chamomilla</i> L.) under salinity levels (0.9, 6, and 12 dS m^-1 as non-saline treatment and moderate and high salinities, respectively). Salinity increased sodium uptake, generation of reactive oxygen species and enzymatic and non-enzymatic antioxidant activities, leading to a reduction in leaf nutrients and pigments, and organs masses. High salinity significantly decreased the essential oil percentage and yield. However, solid and especially enriched biochars with BNP-MgO, BNP-Fe₃O₄, and their combined form reduced hydrogen peroxide and consequently enzymatic and non-enzymatic antioxidant activities under saline conditions. The BNP-MgO was the best treatment for enhancing leaf pigments, and the BNP-Fe₃O₄ was generally the best choice for improving organs masses and essential oil percentage and yield of chamomile under salinity. Therefore, solid and especially enriched biochars, due to their excellent physicochemical properties, were suggested as the suitable soil amendments to mitigate salt toxicity and improve the growth and essential oil production of medicinal plants in the greenhouse and field cultivations.