Nanobiochar-assisted phytostabilization of lead and cadmium in mustard ( Brassica campestris L.) is associated with reduced metal availability and improved physiological performance

Nanobiochar is well documented for heavy metal removal from water, but its efficacy in soil phytostabilization remains less explored. This study compared nanobiochar (NB) and rice husk powder (RH) at 50 and 100 g kg−1 for improving Pb and Cd phytostabilization in mustard (Brassica campestris L.) under pot conditions. Compared with the no-adsorbent treatment, NB at 100 g kg−1 increased shoot fresh weight by 73.2% under Pb stress and 2.02-fold under Cd stress. It also increased pod number by 46.8% under Pb and 52.5% under Cd stress, while total seeds per plant increased by 80.1% and 2.26-fold, respectively. NB enhanced chlorophyll a, total chlorophyll, carotenoids, soluble sugars, and shoot accumulation of N, P, S, Ca, and K. Importantly, NB at 100 g kg−1 increased total Pb and Cd retention in soil by 12.5% and 6.6%, respectively, while reducing available Pb and Cd by 90.3% and 81.8%, respectively. It also reduced Pb and Cd accumulation in roots and shoots and decreased BAF values for both metals. Pb TF declined, whereas Cd TF showed a metal-specific response. Overall, NB-assisted phytostabilization was associated with reduced metal availability, lower plant metal accumulation, improved nutrient acquisition, and better physiological performance.