Soil inorganic amendments produce safe rice by reducing the transfer of Cd and increasing key amino acids in brown rice

Tomato sprayed monocalcium phosphate had production-phytoremediation dual function with high soil Cd extraction and safer fruit production

In order to make use of the large biomass of tomato plant to fulfill the purpose of remediating-while-producing, two commercial tomato varieties, 'Baiguoqiangfeng' (BG) and 'Ouguan' (OG) were grown in Cd contaminated acidic soil to compare their performance on Cd phytoextraction, and monocalcium phosphate (Ca) was foliar applied to reduce their fruit Cd concentration. The results showed that the BG was a more Cd tolerant variety, comparing with OG, it suffered lighter tissue peroxidation and photosynthesis obstacle, owning weaker amino acid metabolism, secondary metabolism and stress signal transduction under Cd stress. The Ca application reduced its ABA level but increased the GSH, IAA, ZR and GA3 level, and enhanced its lysine degradation, tyrosine metabolism, alanine, asparagine and glutamate metabolism, plant hormone signal transduction and phenylpropanoid biosynthesis under Cd stress. With these metabolic regulations, the Ca application promoted its leaf biomass accumulation, guaranteeing the total Cd extraction amount (0.88 mg pot-1 as 0.20 mg kg -1), and reduced the fruit Cd partition, decreasing the fruit Cd concentration by 71.4% with higher yield. Meanwhile, the OG had lower Cd phytoextraction capacity than the BG, and Ca spray enhanced its cell energy generation, flavonoids biosynthesis and photosynthetic carbon fixation, but had no effect on fruit Cd concentration. The two tomato varieties had different responses to Ca application under Cd stress in their hormone signaling, energy metabolism, secondary metabolism and amino acids metabolism, which furtherly differed their Cd phytoextraction capacity and production safety. Therefore, the monocalcium phosphate spray combined 'Baiguoqiangfeng' tomato realized the dual function of production-phytoremediation, and the mechanism of plant Cd sensitivity adjustment through phenylpropanoid biosynthesis and amino acids metabolism deserved further study.

Biochar reduces the cadmium content of Panax quinquefolium L. by improving rhizosphere microecology

Cadmium (Cd) accumulation in American ginseng (Panax quinquefolium L.) can negatively impact its yield and safety. Our previous study found that biochar could reduce cadmium content of P. quinquefolius, however, the mechanism was yet to be elucidated. In the present study, we tested four treatments in order to reveal the mechanism by which this phenomenon occurs: control, Cd, Cd + biochar and biochar. The results showed that the following responses were induced by the addition of biochar under Cd stress. Firstly, the soil physicochemical properties were improved, this is especially true for the soil pH value and soil organic matter content, which were increased by 20.42 % and 15.57 %, respectively. Secondly, the relative abundances of several beneficial microorganism phyla; such as Proteobacteria, Bacteroidota and Actinobacteria; were increased by 10.69 %, 20.11 % and 60.86 %, respectively. Thirdly, treatment with biochar reduced the Cd content by increasing cadmium-chelated metabolites within the soil (e.g., naringenin, caffeic acid, and valine) and increasing detoxification substances in plants (e.g., malic acid, flavonoids, and fumaric acid). Changes in these metabolites were significantly correlated with rhizosphere microecology. In summary, biochar treatment reduced the Cd content in seedlings by improving the soil properties, rhizosphere community, soil metabolites, and plant metabolites.

The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L-1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L-1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.