Growth and Physiological Responses of Brassica chinensis to Pristine and Fe/Mn-Modified Pteroceltis tatarinowii Biochar in Copper-Contaminated Soil

The ecological restoration of heavy metal-contaminated soil and the evaluation of its remediation efficacy have drawn considerable research interest. This 90-day pot experiment examined the effects of pristine and modified Pteroceltis tatarinowii biochars on Brassica chinensis grown in copper-contaminated soil; treatment-specific day-0 soil Cu concentrations ranged from 111.25 to 136.45 mg kg−1. Pristine biochar (BC), FeCl3-modified biochar (FBC), and KMnO4-modified biochar (MBC) were applied at 1%, 3%, and 5% relative to soil mass, with three pots per treatment and an unamended control. Responses varied with the material, application rate, and measured endpoint. At 5% FBC, plant height and root length reached 12.47 and 14.13 cm, respectively, representing increases of 55.29% and 120.78% relative to the control. At this rate, FBC also produced significantly greater shoot fresh weight and root dry weight than every other treatment. Both 3% and 5% FBC increased shoot dry weight and reduced POD and SOD relative to the control; 3% FBC also reduced MDA. All amended treatments had lower mean shoot Cu concentrations than CK, but concentration and organ burden did not change in parallel. Treatment-mean estimates showed that shoot Cu burden decreased from approximately 0.50 μg plant−1 in CK to 0.21–0.28 μg plant−1 in the 5% treatments, whereas root Cu burden in 5FBC was approximately 0.092 μg plant−1 compared with 0.065 μg plant−1 in CK. Together, the growth and physiological responses identify FBC as a priority candidate for the further evaluation of P. tatarinowii branch biochar in mine-affected farmland. They do not establish a uniform ranking across physiological indicators, an intrinsic advantage of Fe over Mn modification, or alleviation of Cu toxicity independent of an uncontaminated-soil control.