Excessive amounts of copper (Cu) in soils causes toxic effects on plants. In this study, 58 rice cultivars were classified into tolerant, moderately tolerant, and susceptible types for Cu(II) ...toxicity based on 50% germination (LC50). Nine japonica rice varieties (three each from the tolerant, moderately tolerant, and susceptible groups) and six indica rice varieties (three from the moderately tolerant and susceptible groups) were selected for the hydroponics experiments. In the short-term adsorption experiment, Cu(II) adsorbed on rice roots was differentiated into exchangeable, complexed, and precipitated forms. Similarly, it was done for long-term culture. Absorption of Cu(II) by rice roots and shoots was also measured. The results indicated that adsorbed Cu(II) mainly existed as complexed and exchangeable forms on rice roots in the short-term adsorption experiment, and the exchangeable and complexed Cu(II) levels were greater for indica rice than for japonica rice due to the larger negative charge on the indica rice roots. The adsorbed Cu(II) mainly existed as a complexed form in the long-term culture experiment, and the exchangeable Cu(II) level was much lower than that in the short-term adsorption experiment due to the absorption of Cu(II) by rice plants. The indica varieties absorbed more Cu(II) than the japonica varieties. Furthermore, the absorption and accumulation of Cu(II) by the susceptible varieties were greater than by the tolerant and moderately tolerant varieties for both the japonica and indica rice. The absorption and accumulation of Cu(II) in rice roots were much greater than in the shoots. Chlorophyll content, and the lengths and dry matter weights of the rice roots and shoots decreased with increasing Cu(II) concentration. The Cu(II) showed greater toxicity toward indica varieties than japonica varieties, and the greater negative charge on indica roots was one of reasons for the greater exchangeable Cu(II) on the roots, the increase in Cu(II) toxicity, and the higher uptake of Cu(II) by indica rice varieties compared to japonica rice varieties.
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•The roots of indica rice carry more negative charge compared to japonica rice.•Indica rice roots adsorbed more exchangeable Cu(II) than japonica rice roots.•Indica rice accumulated more Cu(II) in the roots and shoots than japonica rice.•Cu(II) showed greater toxicity to indica rice than japonica rice varieties.
The roots of 4 japonica, 4 indica, and 7 hybrid rice varieties were obtained by hydroponic experiment and used to explore the relationship between charge characteristics and exchangeable ...manganese(II) (Mn(II)) on rice roots and Mn(II) absorption in roots and shoots of the rice. Results indicated Mn(II) adsorbed on rice roots mainly existed as exchangeable Mn(II) after 2 h. The roots of indica and hybrid rice carried more negative charges than the roots of japonica rice. Accordingly, this led to more exchangeable Mn(II) to be adsorbed on roots of indica and hybrid rice after 2 h and more Mn(II) absorbed in the roots of the same varieties after 48 h. However, this was contrary to the result of Mn(II) absorption in rice shoots after 48 h. Coexisting cations of K+, Na+, Ca2+, and Mg2+ reduced the exchangeable Mn(II) on rice roots through their competition with Mn(II) for sorption sites on rice roots, which led to the decrease in Mn(II) absorption in rice roots and shoots. Ca2+ and Mg2+ showed a greater decrease in the Mn(II) absorbed in roots and shoots than K+ and Na+. The reduction of Mn(II) absorption in the roots of indica rice and hybrid rice induced by Ca2+ and Mg2+ was more than that of japonica rice. This was attributed to more negative charges on the roots of the former than the latter. Therefore, the absorption of Mn(II) by rice roots was determined by surface charge properties and exchangeable Mn(II) on the rice roots. The results suggested that Ca2+ and Mg2+ have potential to alleviate Mn(II) toxicity to rice.
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•The exchangeable Mn(II) adsorbed on roots is the main form absorbed by rice.•Indica and hybrid rice roots carry more negative charges than japonica rice roots.•Indica and hybrid rice roots adsorb more exchangeable Mn(II) than japonica rice.•The roots of indica and hybrid rice absorb more Mn(II) than japonica rice roots.•The coexisting cations of K+, Na+, Ca2+, and Mg2+ inhibit Mn(II) absorption by rice.
The effects of soil pH variations induced by submergence/drainage and biochar application on soil cadmium (Cd) availability to different rice (Oryza sativa L.) varieties are not well understood. This ...study aims to investigate the possible reasons for available Cd(II) reduction in paddy soil as influenced by biochar and to determine Cd(II) absorption and translocation rates in different parts of various rice varieties. A pot experiment in a greenhouse using four japonica and four indica rice varieties was conducted in Cd(II) contaminated paddy soil with peanut straw biochar. The results indicated that the submerging led to an increase in soil pH due to the consumption of protons (H+) by the reduction reactions of iron/manganese (Fe/Mn) oxides and sulfate (SO42−) and thus the decrease in soil available Cd(II) contents. However, the drainage decreased soil pH due to the release of protons during the oxidation of Fe2+, Mn2+, and S2− and thus the increase in soil available Cd(II) contents. Application of the biochar increased soil pH during soil submerging and inhibited the decline in soil pH during soil drainage, and thus decreased soil available Cd(II) contents under both submerging and drainage conditions. The indica rice varieties absorbed more Cd(II) in their roots and accumulated higher amounts of Cd(II) in their shoots and grains than the japonica rice varieties. The Cd(II) sensitive varieties exhibited a greater absorption and translocation rate of Cd(II) compared to the tolerant varieties of both indica and japonica rice. Biochar inhibited the absorption and accumulation of Cd(II) in the rice varieties, which ultimately lowered the Cd(II) contents in rice grains below the national food safety limit (0.2 mg kg−1). Overall, planting japonica rice varieties in Cd(II) polluted paddy soils combined with the use of biochar can effectively reduce Cd(II) content in rice grains which protects human health against Cd(II) toxicity.
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•Redox reactions were responsible for soil pH change in submergence/drainage alteration.•Biochar inhibited soil pH decline and reduced available soil Cd(II) during drainage.•Indica rice varieties absorbed more Cd(II) from soils than japonica rice varieties.•Cd(II)-sensitive rice varieties absorbed more Cd(II) than tolerant rice varieties.•Biochar decreased Cd(II) contents in the roots, shoots and grains of rice varieties.
The present study investigated the bioaccumulation and translocation of mercury (Hg) and chromium (Cr) in Yunyan 87 flue-cured tobacco (
Nicotiana tabacum
) and assessed the influence of soil pH on ...the metal uptake by plant organs at the field scale. The study was conducted in 4 different regions selected from Sichuan Province, China: Guangyuan, Luzhou, Panzhihua, and Yibin. The results revealed that Hg highly contaminated Yibin soils at 0.29 mg kg
−1
and by Cr at 147 mg kg
-1
, which is above the permissible limit. The levels of Hg in tobacco plant organs were predominantly in the order of leaves > root > stem. The overall trend for Cr contents in tobacco organs was in the order of root > leaves > stem. The results of an index of bioaccumulation (IBA) and translocation factor (TF) showed that the values observed in Panzhihua and Guangyuan tobacco leaves were generally higher, despite the low levels of soil contamination. The linear mixed model (LMM) demonstrated that the log of Hg IBA in tobacco organs was likely to decrease with soil pH increase, whereas the log of Cr IBA only decreased in the root but gradually increased in the aerial parts with soil pH increase. The total random variation in the log of metals’ IBA due to regions indicated that for Hg, 33.42% of the variation was explained by regional differences, while for Cr, only 13% was accounted. The results suggested that Yibin and Luzhou need to correct the soil acidity if they are set to reduce Hg contamination in tobacco-growing soils. Guangyuan and Panzhihua need efforts to keep the soil pH on track to avoid high contamination levels, and effective measures of soil nutrients supply are required to produce high tobacco leaf quality free from heavy metal content. The findings of this study may be used to ascertain regional differences in heavy metals, particularly Hg and Cr uptake by tobacco plant organs, and to prevent the cultivation areas contamination through soil pH monitoring.
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