Physiological tolerance of black locust (Robinia pseudoacacia L.) and changes of rhizospheric bacterial communities in response to Cd and Pb in the contaminated soil.

Woody plants possess great potential for phytoremediation of heavy metal-contaminated soil. A pot trial was conducted to study growth, physiological response, and Cd and Pb uptake and distribution in black locust (Robinia pseudoacacia L.), as well as the rhizosphere bacterial communities in Cd and Pb co-contaminated soil. The results showed that R. pseudoacacia L. had strong physiological regulation ability in response to Cd and Pb stress in contaminated soil. The total chlorophyll, malondialdehyde (MDA), soluble protein, and sulfhydryl contents, as well as antioxidant enzymes (superoxide dismutase, peroxidase, catalase) activities in R. pseudoacacia L. leaves under the 40 mg·kg-1 Cd and 1000 mg·kg-1 Pb co-contaminated soil were slightly altered. Cd uptake in R. pseudoacacia L. roots and stems increased, while the Pb content in the shoots of R. pseudoacacia L. under the combined Cd and Pb treatments decreased in relative to that in the single Pb treatments. The bacterial α-diversity indices (e.g., Sobs, Shannon, Simpson, Ace, and Chao) of R. pseudoacacia L. rhizosphere soil under Cd and Pb stress were changed slightly relative to the CK treatment. However, Cd and Pb stress could significantly (p < 0.05) alter the rhizosphere soil microbial communities. According to heat map and LEfSe (Linear discriminant analysis Effect Size) analysis, Bacillus, Sphingomonas, Terrabacter, Roseiflexaceae, Paenibacillus, and Myxococcaceae at the genus level were notably (p < 0.05) accumulated in the Cd- and/or Pb-contaminated soil. Furthermore, the MDA content was notably (p < 0.05) negatively correlated with the relative abundances of Isosphaeraceae, Gaiellales, and Gemmatimonas. The total biomass of R. pseudoacacia L. was positively (p < 0.05) correlated with the relative abundances of Xanthobacteraceae and Vicinamibacreraceae. Network analysis showed that Cd and Pb combined stress might enhance the modularization of bacterial networks in the R. pseudoacacia L. rhizosphere soil. Thus, the assembly of the soil bacterial communities in R. pseudoacacia L. rhizosphere may improve the tolerance of plants in response to Cd and/or Pb stress.

[Effects of Phosphorus Sufficiency and Deficiency on Cadmium Uptake and Transportation by Rice].

Phosphorus (P) is an essential nutrient element for crop growth. The effects of P surplus or deficit on Cd absorption and transport in rice in Cd-polluted farmland is not clear. The effects of P deficiency and P sufficiency on Cd uptake, transport, and accumulation in rice under Cd stress were investigated by applying different levels of phosphorus (NaH2PO4) in a hydroponic experiment. The results showed that:① with the increase in ρ(P) (1.5-48.0 mg·L-1), the biomass in all parts of the rice plants had no obvious change, and the contents of photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoid) firstly ascended and then descended; high concentrations of P inhibited the synthesis of photosynthetic pigments. ② Under Cd stress, when the P was deficient (1.5-6.0 mg·L-1) or sufficient (12.0-48.0 mg·L-1), the Cd content in different parts of the rice increased with the increase in P addition level, and the maximum increase in Cd content in brown rice was 132.1% and 191.2%, respectively. ③ The P/Cd of brown rice showed a piecewise decreasing rule under P deficiency and P sufficiency, and the Cd content in brown rice was significantly negatively correlated with P/Cd (P<0.01). These results indicated that elevating phosphorus concentration when rice was under both the conditions of P deficiency and P sufficiency could promote the uptake and transport of Cd by rice roots under Cd stress, thus increasing the accumulation of Cd in aboveground parts and the risk of excessive Cd in rice.

[Remedying Effects of a Combined Amendment for Paddy Soil Polluted with Cd for Spring and Autumn Rice].

An in-situ paddy experiment was conducted to study the remedying effects of a combined amendment(calcium carbonate+diatomite+ferric sulfate) on Cd bioavailability in soil and Cd accumulation in rice for spring and autumn rice planted in a certain Cd contaminated paddy soil in Beishan Town, Changsha, Hunan Province. The results showed that:Application of the combined amendment significantly increased soil pH and CEC values in both cultivated seasons, but decreased soil OM contents for the spring rice. During the experiment, the contents of TCLP-extractable Cd and CaCl2-extractable Cd in soil were reduced by 18.0%-33.0% and 5.4%-57.9%, respectively. The Cd contents in brown rice, husk, leave and root for the spring rice decreased by 29.6%-56.1%, 52.1%-54.0%, 18.1%-80.7% and 24.4%-41.6%, respectively, due to application of the combined amendment. There were significant differences in Cd transport capacity between spring rice and autumn rice, and the transportation of soil Cd in autumn rice was smoother than that in spring rice. For the autumn rice, the effects of the combined amendment were not significant(P>0.05), except that the Cd content in husk increased a little after applying 2 g·kg-1 of the combined amendment. Significant positive correlations were found between the Cd contents in brown rice and the contents of TCLP-extractable Cd or CaCl2-extractable Cd in soil. Application of the combined amendment effectively inhibited Cd uptake by rice root and reduced Cd content in brown rice for the spring rice; however, these remedying effects were significantly weakened for the autumn rice due to loss of the combined amendment with the movement of irrigation water in the spring season. Therefore, we suggest that supplement of the combined amendment is necessary between two rice cultivated seasons.

Effect of calcium carbonate on cadmium and nutrients uptake in tobacco (Nicotiana tabacum L.) planted on contaminated soil.

In the present study, calcium carbonate (CaCO3) was applied to Cd-contaminated soil at rates of 0, 0.5 and 1.0 g kg(-1). The effect of CaCO3 on soil pH, organic matter, available Cd, exchangeable Cd and level of major nutrients in a tobacco field and on accumulation of various elements in tobacco plants was determined. The results showed that CaCO3 application significantly increased the pH level, available P and exchangeable Ca but decreased organic matter, available Cd, exchangeable Cd, available heavy metals (Fe, Mn, Zn and Cu) and available K in soil. Additionally, CaCO3 application substantially reduced Cd accumulation in tobacco roots, stems, upper leaves, middle leaves and lower leaves, with maximum decrease of 22.3%, 32.1%, 24.5%, 22.0% and 18.2%, respectively. There were large increase in total Ca and slight increases in total N and K but decrease to varying degrees in total Fe, Cu and Zn due to CaCO3 application. CaCO3 had little effect on total P and Mn levels in tobacco leaves.

[Effects of phosphorus-containing substances on arsenic uptake by rice].

The disodium hydrogen phosphate (DSP) and hydroxyapatite (HAP) were added into arsenic contaminated soil, then rice pot experiment was conducted to study the effects of phosphorus (P)-containing substances on arsenic (As) uptake by rice. The results showed that: DSP and HAP significantly increased soil pH and the contents of available P in soil (P < 0.05), activating soil arsenic. And DSP was stronger than HAP in improving the migration ability of As in soil. DSP and HAP treatments both significantly reduced the contents of total As in root, as well as total As and inorganic As in brown rice. But HAP significantly increased total As contents in stem. DSP and HAP treatments had better reducing effects on inorganic As than on total As in brown rice. And DSP had the same reducing effects as HAP on total As and inorganic As in brown rice. Analysis results showed that the contents of As in rice were affected by the antagonism between P and As and the increase of As bio-availability in soil. The antagonism played the major role in this study and it was clearly exhibited in both root and rice. Lower dosage (< or = 0.12 g x kg(-1)) of DSP and HAP increased total biomass of rice and brown rice yield, but with the increase of P addition, the two kinds of P-containing substances obviously inhibited the growth of rice, and inhibition by HAP was relatively light.

[Effects of hydroxyapatite on growth and quality of potato (Solanum tuberosum L.) in Cd polluted soil].

A pot experiment was conducted in a glasshouse to study effects of hydroxyapatite amending Cd polluted soil on growth and quality of potato (Solanum tuberosum L.). In the experiment, 3 levels of Cd pollution (0, 5, and 10 mg x kg(-1)) and 6 levels of hydroxyapatite application (0, 4, 8, 10, 16, and 30 g x kg(-1)) in soil were prepared to plant 2 potato varieties (Zhongshusanhao and Daxiyang in Chinese system). The results showed that Cd pollution in soil resulted in decrease in yield per plant of potato; for example, in the soils with 5 and 10 mg x kg(-1) of Cd, the yield per plant decreased 24%-31% and 41%-45%, respectively. Applying hydroxyapatite to Cd pollution could greatly increase yield per plant of potato. Compared to the soil without hydroxyapatite, 10 or 30 g x kg(-1) hydroxyapatite added to the soil with 5 or 10 mg x kg(-1) of Cd increased 17%-9% or 45%-58% in yield per plant. Due to hydroxyapatite amending Cd polluted soil, chlorophyll contents in leaves and superoxide dismutase (SOD) activities in tubers enhanced and malondialdehyde (MDA) contents in tubers declined apparently. Meanwhile, quality of potato tubers was obviously improved, such as increase in vitamin C contents, starch contents, and protein contents in potato tubers. With hydroxyapatite applying from 0 to 30 g x kg(-1), Cd contents in potato tubers deceased from 0.87-0.95 mg x kg(-1) to 0.13-0.21 mg x kg(-1) by 78%-85% in the soils with 5 mg x kg(-1) of Cd, and from 1.86-1.93 mg x kg(-1) to 0.52-0.65 mg x kg(-1) by 66%-72% in the soils with 10 mg x kg(-1) of Cd. The experiment indicated that the mechanism of hydroxyapatite alleviating soil Cd toxicity main included rising soil pH values, reducing effective Cd contents in soil, and Ca from hydroxyapatite blocking soil Cd moving to potato. However, ability of hydroxyapatite alleviating soil Cd toxicity was limited, and excessive hydroxyapatite to soil exhibited stress effects on growth and quality of potato. In the Cd polluted soils with proper hydroxyapatite, growth and quality of Zhongshusanhao were better than those of Daxiyang, indicating different responses of various potato varieties to environment amelioration.

[Effects of surfactants on adsorption of methyl parathion by neutral alumina].

The sorption of methyl parathion by neutral alumina which was modified by ionic surfactants such as SDS, SDBS and CTMAB was studied. It showed that the adsorbability of alumina to methyl parathion were related to the type and concentration of surfactant and pH of the system. The adsorbabilities of alumina on three kinds of surfactants were different. When pH = 7, the adsorbance of SDS was the largest, but the adsorbance of CTMAB was the smallest. When pH = 4, the adsorbance of SDS or SDBS was increased, while the adsorbance of CTMAB was decreased. The adsorbability of alumina was strengthened, not weakened, by the cooperation of pollutant and anionic surfactant, while the sorption of methyl parathion by alumina with cationic surfactant was weakened. These features had the practical value when neutral alumina is used to remove more than one contaminants from wastewater.