Determining the appropriate soil cadmium (Cd) criteria for vegetable production is important for ensuring that the Cd concentrations of the vegetables meet food safety standards. The soil extractable Cd criteria for vegetable production are also essential for both food safety and environmental management, especially in areas with a high natural background level. In the present study, soil total and extractable Cd criteria were derived using the approach of species sensitivity distribution integrated with soil aging and bioavailability as affected by soil properties. A dataset of 90 vegetable species planted in different soils was compiled by screening the published in literature in five bibliographic databases using designated search strings. The empirical soil–plant transfer model was applied to normalize the bioaccumulation data. After normalization, the intra-species variability was reduced by 18.3 to 84.4%. The soil Cd concentration that would protect 95% (HC₅) of the species was estimated by species sensitivity distribution curves that were fitted by the Burr III function. The soil Cd criteria derived from the added approach for risk assessment were proposed as continuous criteria based on a combination of organic carbon and pH in the soil. Criteria for total Cd and EDTA-extractable Cd in the soil ranged from 0.23 to 0.61 mg kg^–1 and from 0.09 to 0.25 mg kg^–1, respectively. Field experimental data were used to validate the applicability and validity of these criteria. Most of the predicted HC₅ values in the field experimental sites were below the 1:1 line. These results provide a scientific basis for soil Cd criteria for vegetable production that will ensure food safety.

Cell wall architecture plays a key role in stalk strength and forage digestibility.  Lignin, cellulose, and hemicellulose are the three main components of plant cell walls, and they can impact stalk quality by affecting the structure and strength of the cell wall.  To explore cell wall development during secondary cell wall lignification in maize stalks, conventional and conditional genetic mapping were used to identify the dynamic quantitative trait loci (QTLs) of the cell wall components and digestibility traits during five growth stages after silking.  Acid detergent lignin (ADL), cellulose (CEL), acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVDMD) were evaluated in a maize recombinant inbred line (RIL) population.  ADL, CEL, ADF, and NDF gradually increased from 10 to 40 days after silking (DAS), and then they decreased.  IVDMD initially decreased until 40 DAS, and then it increased slightly.  Seventy-two QTLs were identified for the five traits, and each accounted for 3.48–24.04% of the phenotypic variation.  Six QTL hotspots were found, and they were localized in the 1.08, 2.04, 2.07, 7.03, 8.05, and 9.03 bins of the maize genome.  Within the interval of the pleiotropic QTL identified in bin 1.08 of the maize genome, six genes associated with cell wall component biosynthesis were identified as potential candidate genes for stalk strength as well as cell wall-related traits.  In addition, 26 conditional QTLs were detected in the five stages for all of the investigated traits.  Twenty-two of the 26 conditional QTLs were found at 30 DAS conditioned using the values of 20 DAS, and at 50 DAS conditioned using the values of 40 DAS.  These results indicated that cell wall-related traits are regulated by many genes, which are specifically expressed at different stages after silking.  Simultaneous improvements in both forage digestibility and lodging resistance could be achieved by pyramiding multiple beneficial QTL alleles identified in this study.

High nitrate (NO₃⁻) in vegetables, especially in leaf vegetables poses threaten to human health.  Selenium (Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies.  Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses.  However, the influence of exogenous Se on NO₃⁻ accumulation in hydroponic vegetables is still not clear.  In the present study, hydroponic lettuce plants were subjected to six different concentrations (0, 0.1, 0.5, 5, 10 and 50 µmol L^–1) of Se as Na₂SeO₃.  The effects of Se on NO₃⁻ content, plant growth, and photosynthetic capacity of lettuce (Lactuca sativa L.) were investigated.  The results showed that exogenous Se positively decreased NO₃⁻ content and this effect was concentration-dependent.  The lowest NO₃⁻ content was obtained under 0.5 µmol L^–1 Se treatment.  The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate (P_n), stomatal conductance (Cs) and the transpiration efficiency (T_r) of lettuce.  The transportation and assimilation of NO₃⁻ and activities of nitrogen metabolism enzymes in lettuce were also analysed.  The NO₃⁻ efflux in the lettuce roots was markedly increased, but the efflux of NO₃⁻ from the root to the shoot was decreased after treated with exogenous Se.  Moreover, Se application stimulated NO₃⁻ assimilation by enhancing nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS) and glutamate synthase enzyme (GOGAT) activities.  These results provide direct evidence that exogenous Se shows positive function on decreasing NO₃⁻ accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce.  We suggested that 0.5 µmol L^–1 Se can be used to reduce NO₃⁻ content and increase hydroponic lettuce yield.