How can biochar-based metal oxide nanocomposites counter salt toxicity in plants?

Application of biochar-based metal oxide nanocomposites can acquire new composites and combine the benefits of biochar with nanomaterials. For the first time, this research was conducted to evaluate the possible effects of solid biochar (25 g biochar kg^-1 soil) and biochar-based nanocomposites (BNCs) of magnesium oxide (25 g BNC-MgO kg^-1 soil), manganese oxide (25 g BNC-MnO biochar kg^-1 soil) and combined use of these nanocomposites (12.5 g BNC-MgO + 12.5 g BNC-MnO kg^-1 soil) on salt (non-saline, 6 and 12 dSm^-1 NaCl salinities) tolerance of safflower plants (Carthamus tinctorius L.). Salinity reduced potassium, magnesium and manganese contents in root and leaf tissues, chlorophyll content index, photosynthetic pigments, maximum quantum yield of photosystem II (Fv/Fm) and relative photosynthetic electron transport rate (RETR), leaf water content and plant biomass, but increased the sodium content, reactive oxygen species generation (ROS), oxidative stress and antioxidants and ROS detoxification potential of safflower roots and leaves. Application of biochar and BNCs increased the contents of potassium, manganese and magnesium in plant tissues, photosynthetic pigments, Fv/Fm and RETR, leaf water content and reduced sodium accumulation, ROS generation and oxidative stress under saline conditions, leading to a higher plant biomass in comparison with control. The BNC-MgO + BNC-MnO was the superior treatment on reducing salt toxicity. This treatment reduced oxidative stress by enhancing photosynthetic pigments, Fv/Fm and RETR of safflower under salt stress. These results revealed that BNCs have a great potential for improving salt tolerance of plants through increasing RETR and decreasing sodium accumulation and ROS generation.