Difference in activation and absorption of different insoluble Cd between two tomato varieties with different Cd accumulation

Soil Cd pollution is becoming increasingly hazardous, and the effective state of Cd largely affects its biological effectiveness. The difference in the activation of insoluble Cd directly affects the uptake and accumulation of Cd in vegetables, and there are obvious differences in the uptake and accumulation capacity of different tomato varieties for Cd. However, the difference in the activation of Cd insoluble forms of CdS and CdCO₃ by different Cd-accumulation tomato varieties remains unclear. Therefore, in this study, the seedlings of two tomato varieties with different Cd-accumulation capacity (high-Cd-accumulation type ‘Cooperative 8’ and low-Cd-accumulation type ‘Provence’) were used as research objects. The activation effects and absorption differences of two types of insoluble Cd (CdS and CdCO₃) were studied through hydroponic experiments, and the effects of two types of insoluble Cd on plant growth were analyzed. The purpose of this study was to provide a theoretical basis for reducing the risk of tomato Cd pollution, ensuring the safety of tomato production and reasonable selection of tomato varieties. The results showed that the activation effect of CdCO₃ and CdS of high-Cd-accumulation type ‘Cooperative 8’ significantly increased the available Cd concentration in solution by 62.1% and 51.0% compared to the Cd concentration in non-planting tomato solution (P<0.05), while the low-Cd-accumulation type ‘Provence’ significantly promoted the dissolution of insoluble CdCO₃ by 39.4% (P<0.05). However, the activation of insoluble CdS was not significant, and the activation of insoluble Cd by ‘Cooperative 8’ was significantly higher than that of ‘Provence’. In terms of plant Cd uptake, the shoot and root Cd contents of ‘Cooperative 8’ were significantly higher than those of ‘Provence’ under insoluble CdS treatment, which increased by 80.2% and 111.7% (P<0.05), respectively. Under insoluble CdCO₃ treatment, the shoot and root Cd contents of ‘Cooperative 8’ were 105.2% and 153.8% higher than those of ‘Provence,’ respectively (P<0.05). Compared with the treatment without insoluble Cd, the treatment with insoluble CdS increased the plant height, root length, and biomass of ‘Provence’ by 15.0%, 10.1%, and 15.5% (P<0.05), respectively, while decreased the plant height, root length, and biomass of ‘Cooperative 8’ by 5.0%, 9.8% and 11.3% (P<0.05), respectively. Plant height, root length, and biomass of ‘Cooperative 8’ were significantly lower than those of ‘Provence’ under the two insoluble Cd treatments (P<0.05). In conclusion, the high-Cd-accumulation variety of tomato promoted the activation of the two insoluble Cd forms significantly more than the low-Cd-accumulation variety of tomato, and the bioeffectiveness of Cd was significantly improved. The absorption and accumulation of available Cd by high-Cd-accumulation tomato variety were significantly higher than those of low-Cd-accumulation tomato variety, which significantly inhibited the growth of tomato plants with high accumulation. However, CdS treatment had a significant stimulating effect on the growth of the low-Cd-accumulation variety ‘Provence’.