Overview
Feng and colleagues exposed rice seedlings to cadmium, sodium chloride, and combined cadmium-plus-sodium stress under two temperatures and three CO2 levels. The study is supply-chain and plant-uptake mechanism evidence for rice cultivation stressors, not market occurrence evidence for rice grain, salt, or finished foods.
Key numbers
The experiment used Oryza sativa L. cv. XZX 45 seedlings grown for 16 days, acclimated in modified ISO 8692 nutrient solution, then exposed for 3 days. Temperature/CO2 conditions were 23 C or 27 C crossed with 360 ppm, 450 ppm, or 700 ppm CO2. Relative humidity was 60 +/- 2%, and the chamber CO2 resolution was 1 ppm.
Exposure solutions were:
| Exposure condition | Nominal concentrations |
|---|---|
| cadmium (Cd) stress | 0.0, 0.2, 1.8, and 5.4 mg Cd/L |
| Na stress | 0.0, 0.2, 0.6, and 1.1 g Na/L |
| Cd+Na stress | 0.0; 0.2 mg Cd/L + 0.2 g Na/L; 1.8 mg Cd/L + 0.6 g Na/L; 5.4 mg Cd/L + 1.1 g Na/L |
The preliminary inhibition-rate test used nominal cadmium (Cd) concentrations of 0, 0.25, 0.50, 1.00, 2.00, 4.00, and 8.00 mg Cd/L and Na concentrations of 0, 0.1, 0.3, 0.5, 0.9, 1.2, and 1.6 g Na/L. EC values based on relative-growth-rate inhibition were EC20 = 0.14 mg Cd/L, EC50 = 1.81 mg Cd/L, and EC75 = 5.66 mg Cd/L for Cd; and EC20 = 0.2 g Na/L, EC50 = 0.64 g Na/L, and EC75 = 1.08 g Na/L for Na.
For relative growth rate, the source reports these ranges under 23 C and 27 C for ambient/medium/high CO2 treatments:
| Stressor | 23 C RGR range | 27 C RGR range |
|---|---|---|
| Na | 6.69-21.07%, 6.85-23.27%, 9.94-24.58% | 8.91-25.29%, 11.35-31.68%, 19.38-38.23% |
| cadmium (Cd) | 5.43-21.07%, 6.97-23.27%, 8.06-24.58% | 7.80-25.29%, 11.03-31.68%, 22.34-38.23% |
| Na+Cd | 6.55-21.07%, 7.14-23.27%, 8.09-24.58% | 7.58-25.29%, 10.58-31.68%, 16.26-38.23% |
The authors state that growth was significantly better at 27 C and at higher CO2. Approximately 25%, 50%, and 75% growth inhibition corresponded to Na treatments of 0.2, 0.6, and 1.1 g/L and Cd treatments of 0.2, 1.8, and 5.4 mg/L.
Measured Cd concentrations in rice shoots and roots were reported as ug/g dry weight:
| Temperature and CO2 | Cd-only shoot | Cd-only root | Cd+Na shoot | Cd+Na root |
|---|---|---|---|---|
| 23 C, 360 ppm CO2 | 4.97-13.21 | 95.31-1787.23 | 3.80-25.93 | 107.5-1411.33 |
| 23 C, 450 ppm CO2 | 7.31-27.66 | 94.46-2652.8 | 8.35-31.25 | 126.5-2928.09 |
| 23 C, 700 ppm CO2 | 7.02-22.67 | 95.15-1852.19 | 6.14-22.50 | 126.77-1574.02 |
| 27 C, 360 ppm CO2 | 7.21-30.55 | 97.81-2267.69 | 5.55-29.33 | 113.65-1474.37 |
| 27 C, 450 ppm CO2 | 8.84-30.43 | 127.72-3191.39 | 9.09-29.61 | 131.20-2387.40 |
| 27 C, 700 ppm CO2 | 9.38-28.23 | 110.39-2955.65 | 8.18-30.95 | 126.13-1970.16 |
The source reports that Cd concentrations were much lower in shoots than roots. Root Cd concentrations tended to be higher under Cd-only exposure than under Cd+Na exposure, and root Cd was highest at 450 ppm CO2.
Measured Na concentrations were reported as ug/g dry weight. At 23 C and 360 ppm CO2, Na-only shoots ranged 3011.61-11655.06 and roots 7569.71-12545.83; Cd+Na shoots ranged 2813.51-11340.46 and roots 7453.15-12805.63. At 23 C and 450 ppm CO2, Na-only shoots ranged 2568.85-8641.81 and roots 5500.33-10866.99; Cd+Na shoots ranged 2220.49-8589.50 and roots 6425.30-10252.57. At 23 C and 700 ppm CO2, Na-only shoots ranged 2257.15-6848.62 and roots 5067.89-9131.93; Cd+Na shoots ranged 1825.34-5020.30 and roots 6657.62-9354.65.
The text then reports the second temperature block with the same T1 label, but context indicates this is the 27 C block. Under that block, Na-only shoots ranged 4004.82-13243.01 and roots 8057.37-14898.06 at 360 ppm CO2; Cd+Na shoots ranged 2006.02-10301.83 and roots 3867.43-13083.43. At 450 ppm CO2, Na-only shoots ranged 2607.55-9115.69 and roots 6500.54-8351.60; Cd+Na shoots ranged 2457.76-8309.92 and roots 6459.82-12013.72. At 700 ppm CO2, Na-only shoots ranged 2635.73-8979.19 and roots 5062.06-8811.56; Cd+Na shoots ranged 2187.13-7068.07 and roots 4223.16-7396.10.
The authors summarize that Na concentrations were generally higher in roots than shoots, maximum Na reached about 15 mg/g dry weight in roots and more than 12 mg/g dry weight in shoots, and Na concentrations tended to be lower at high CO2.
Methods (brief)
Rice seedlings were exposed in 50 mL Erlenmeyer flasks containing 50 mL of Cd, Na, or combined Cd+Na solution. After 3 days, seedlings were rinsed with distilled water, held in MES-Tris buffer with CaCl2 for 4 hours to remove surface/apparent-free-space ions, separated into shoots and roots, dried, digested with HNO3-HClO4 (4:1), and analyzed for total Cd and Na by ICP-AES using a PerkinElmer Optima 700 DV. Relative growth rate was calculated from initial and final fresh weights. Statistical comparisons used ANOVA and Tukey’s multiple range test at alpha = 0.01 or 0.05.
Related evidence
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