Cadmium (Cd) contamination in agricultural soils threatens crop productivity and food safety worldwide. Pepper ( Capsicum annuum L.) readily accumulates Cd in edible tissues, which increases potential health risks. Nitrogen (N) fertilization can improve chlorophyll content and yield in pepper, but it may also increase Cd uptake. Poly-γ-glutamic acid (PGA), a microbial biopolymer with metal-chelating ability, may help reduce this negative effect. A pot experiment was conducted with two soil Cd levels, three urea application rates, and two foliar PGA concentrations. Chlorophyll content, yield and yield components, N and P concentrations, micronutrient concentrations, and Cd concentrations were measured. Under Cd stress, nitrogen was the main factor improving yield. PGA provided an additional benefit, especially at the moderate urea level. Compared with the Cd treatment alone, Cd × N1 increased total yield by 121.36%, and Cd × N1 × PGA further increased total yield by 179.55%. The Cd × N1 × PGA treatment also reduced fruit Cd concentration by 58.44% and decreased the root-to-fruit Cd translocation factor by 60.19%. These results show that the effect of PGA on Cd mitigation depended on urea rate. Within the tested range, PGA was more effective at limiting root-to-fruit Cd translocation at the moderate urea level, whereas the higher urea level gave a greater yield increase. The effect of PGA on reducing fruit Cd concentration and root-to-fruit Cd translocation depended on the N input level. Within the tested range, foliar PGA combined with a moderate urea rate was more effective for limiting root-to-fruit Cd translocation, while a higher urea rate was more favorable for yield improvement.
Yang et al. (Tue,) studied this question.