Jiyan Shi

Subcellular distribution and chemical forms of cadmium in Phytolacca americana L.

Phytolacca americana L. (pokeweed) is a promising species for Cd phytoextraction with large biomass and fast growth rate. To further understand the mechanisms involved in Cd tolerance and detoxification, the present study investigated subcellular distribution and chemical forms of Cd in pokeweed. Subcellular fractionation of Cd-containing tissues indicated that both in root and leaves, the majority of the element was located in soluble fraction and cell walls. Meanwhile, Cd taken up by pokeweed existed in different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 80% ethanol in roots, followed by 1 M NaCl, d-H(2)O and 2% HAc, while in leaves and stems, most of the Cd was extracted by 1 M NaCl, and the subdominant amount of Cd was extracted by 80% ethanol. It could be suggested that Cd compartmentation with organo-ligands in vacuole or integrated with pectates and proteins in cell wall might be responsible for the adaptation of pokeweed to Cd stress.

Phytotoxicity and accumulation of copper oxide nanoparticles to the Cu-tolerant plant Elsholtzia splendens

Abstract The release of nanoparticles (NPs) to the environment poses an increasing potential threat to biological systems. This study investigated the phytotoxicity and accumulation of copper oxide (CuO) NPs to Elsholtzia splendens (a Cu-tolerant plant) under hydroponic conditions. The 50% effective concentration (EC50) of CuO NPs to E. splendens was about 480 mg/L, implying the tolerance of E. splendens to CuO NPs. The Cu content in the shoots treated with 1000 mg/L CuO NPs was much higher than those exposed to the comparable 0.5 mg/L soluble Cu and CuO bulk particles. CuO NPs-like deposits were found in the root cells and leaf cells. Cu K-edge X-ray absorption near-edge structure analysis further revealed that the accumulated Cu species existed predominantly as CuO NPs in the plant tissues. All these results suggested that CuO NPs can be absorbed by the roots and translocated to the shoots in E. splendens.

Heavy metal availability and impact on activity of soil microorganisms along a Cu/Zn contamination gradient

All the regulations that define a maximum concentration of metals in the receiving soil are based on total soil metal concentration. However, the potential toxicity of a heavy metal in the soil depends on its speciation and availability. We studied the effects of heavy metal speciation and availability on soil microorganism activities along a Cu/Zn contamination gradient. Microbial biomass and enzyme activity of soil contaminated with both Cu and Zn were investigated. The results showed that microbial biomass was negatively affected by the elevated metal levels. The microbial biomass-C (C(mic))/organic C (C(org)) ratio was closely correlated to heavy metal stress. There were negative correlations between soil microbial biomass, phosphatase activity and NH4NO3 extractable heavy metals. The soil microorganism activity could be predicted using empirical models with the availability of Cu and Zn. We observed that 72% of the variation in phosphatase activity could be explained by the NH4NO3-extractable and total heavy metal concentration. By considering different monitoring approaches and different viewpoints, this set of methods applied in this study seemed sensitive to site differences and contributed to a better understanding of the effects of heavy metals on the size and activity of microorganisms in soils. The data presented demonstrate the relationship between heavy metals availability and heavy metal toxicity to soil microorganism along a contamination gradient.

Accumulation and detoxification of manganese in hyperaccumulator Phytolacca americana

Pokeweed (Phytolacca americana) has recently received much attention because of its ability to hyperaccumulate manganese (Mn). The internal mechanism of detoxification of Mn, however, is not fully understood. In the present study, we investigated Mn accumulation, subcellular distribution, chemical speciation and detoxification through oxalate in pokeweed. The plant accumulated excess Mn in the leaves, mainly in the water-soluble fraction, and over 80% of Mn was in a water-soluble form, while accumulation of excess Mn in the cellular organelle and membrane fraction caused phytotoxicity. In addition, pokeweed has an intrinsically high oxalate content. In all experiments, there was sufficient oxalate to chelate Mn in leaf water extracts at all different levels of Mn application. Phase analysis of X-ray diffraction detected oxalate-Mn chelate complexes, and gel chromatography further confirmed the chelation of Mn by oxalate. In conclusion, pokeweed accumulates excess Mn in the soluble fraction of leaf cells, most likely in vacuoles, in which detoxification of Mn could be achieved by chelation with oxalate.

Manure biochar influence upon soil properties, phosphorus distribution and phosphatase activities: A microcosm incubation study

Using manure-derived-biochar as an alternative phosphorus (P) source has bright future prospects to improve soil P status. A 98-day microcosm incubation experiment was set up for two soils which were amended with manure biochar at proportions of 0, 0.5% and 1.5%. Swine manure samples were air-dried and manure biochar was prepared by pyrolysis at 400 °C for 4 h. As determined by P-31 nuclear magnetic resonance ((31)P NMR) spectroscopy, manure biochar mainly increased the contents and fractions of orthophosphate and pyrophosphate in two soils, while decreased those of monoesters (P<0.05). At the end of incubation, 1.5% of manure biochar raised soil pH by 0.5 and 0.6 units, cation exchange capacity by 16.9% and 32.2%, and soil total P by 82.1% and 81.1% for silt loam and clay loam soils, respectively, as compared with those soils without biochar. Simultaneously, 1.5% of manure biochar decreased acid phosphomonoesterase activities by 18.6% and 34.0% for clay loam and silt loam, respectively; while it increased alkaline phosphomonoesterase activities by 28.5% and 95.1% for clay loam and silt loam, respectively. The enhancement of soil P availability after manure biochar addition was firstly due to the orthophosphate and pyrophosphate as the major P species in manure biochar which directly increased contents of soil inorganic P, and also attributed to the decomposition of some organic P like monoesters by enhanced alkaline phosphomonoesterase activities from manure biochar addition.

Complementary Phosphorus Speciation in Agricultural Soils by Sequential Fractionation, Solution P Nuclear Magnetic Resonance, and Phosphorus K-edge X-ray Absorption Near-Edge Structure Spectroscopy.

Ultisols in China need phosphorus (P) fertilization to sustain crop production but are prone to P loss in runoff. Balancing P inputs and loss requires detailed information about soil P forms because P speciation influences P cycling. Analytical methods vary in the information they provide on P speciation; thus, we used sequential fractionation (SF), solution P nuclear magnetic resonance (P-NMR), and P K-edge X-ray absorption near-edge structure (XANES) spectroscopy to investigate organic P (P) and inorganic P (P) species in Chinese Ultisols managed for different crops and with different fertilizer inputs in the first study to combine these techniques to characterize soil P. Sequential fractionation showed that moderately labile NaOH-P was the largest P pool in these soils, P varied from 20 to 47%, and residual P ranged from 9 to 31%. Deoxyribonucleic acid (1-5%) and -inositol hexakisphosphate (-IHP, 4-10%) were the major P forms from P-NMR. Orthophosphate diesters determined by NMR were significantly correlated with labile NaHCO-P in SF ( > 0.981; < 0.001). Soil P was shown to be predominantly associated with iron and soluble calcium (Ca) by XANES. Furthermore, XANES identified hydroxyapatite in the soil receiving the highest rates of Ca-phosphate fertilizer, which had the highest HCl-P pool by SF, and also identified IHP (7%) in the soil with the highest proportion of -IHP from P-NMR. These results strongly suggest that a combined use of SF, solution P-NMR, and P K-edge XANES spectroscopy will provide the comprehensive information about soil P species needed for effective soil P management.

EDTA and industrial waste water improving the bioavailability of different Cu forms in contaminated soil

It is common to find that low bioavailability can prevent the phytoremediation process of heavy metal-contaminated soils. Heavy metals in soil are associated with various forms having different bioavailability. In this study, the bioavailability of various Cu forms in contaminated soils was investigated using ion-exchange resins, a sequential extraction procedure, and combined with methods including partial dissolution procedure, simulated Cu forms, seedling culture, pot experiment when treated with EDTA, or waste water from monosodium glutamate and citric acid production. Results showed that the bioavailability, in decreasing order of different Cu forms to tall fescue (Festuca arundinacea Schreb.) is: exchangeable Cu (EX-Cu) and organic matter bound Cu (OM-Cu)> Cu bound to carbonate (CAB-Cu)> Fe/Mn oxide bound Cu (OX-Cu)> residual Cu (RES-Cu). Effect of EDTA on the activation of Cu contaminated soil or simulated Cu and the uptake and translocation of tall fescue was better than that of monosodium glutamate waste water (MGW) and citric acid waste water (CAW). EDTA, CAW and MGW all improved the plant availability of different Cu forms in contaminated soil, which could be used in chelate-assisted phytoremediation of heavy metal polluted soil.

Effect of sulphur on soil Cu/Zn availability and microbial community composition.

Successful phytoremediation depends mainly on the bioavailability of copper (Cu) and zinc (Zn) in the soil. We studied the potential effects of sulphur (S) amendment on mobility of copper, zinc and microbial community composition in soil under laboratory conditions. The results showed that with S application at 20 g S kg(-1), soil pH decreased about 3 units and the solubility of the Cu and Zn significantly increased after 64 days of incubation. The concentration of Cu in Cu-accumulator Elsholtzia splendens shoots and roots increased with S treatment. Concentration of Cu in the shoots was 156.5 mg kg(-1) under S treatment. It was 2.5 times of without application of S. PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprint analysis revealed that there were certain groups of acidophilic soil bacteria in the soil after addition of S. We found specific clones such as 1 (from biofilter-treating hydrogen sulfide and methanol) and 4 (from metal-rich and acidic River Tinto) in the soil with S treatment. The above results indicated that S facilitated the mobility of Cu and Zn by soil microorganism and provided a basis for further studies of S-assisted phytoremediation.

Hormesis response of marine and freshwater luminescent bacteria to metal exposure

The stimulatory effect of low concentrations of toxic chemicals on organismal metabolism, referred to as hormesis, has been found to be common in the widely used luminescence bioassay. This paper aims to study the hormesis phenomenon in both marine and freshwater luminescent bacteria, named Photobacterium phosphorem and Vibrio qinghaiensis. The effects of Cu (II), Zn (II), Cd (II) and Cr (VI) on luminescence of these two bacteria were studied for 0 to 75 minutes exposure by establishing dose- and time-response curves. A clear hormesis phenomenon was observed in all four testing metals at low concentrations under the condition of luminescence assays.

Determination of copper binding in Pseudomonas putida CZ1 by chemical modifications and X-ray absorption spectroscopy

Previously performed studies have shown that Pseudomonas putida CZ1 biomass can bind an appreciable amount of Cu(II) and Zn(II) ions from aqueous solutions. The mechanisms of Cu- and Zn-binding by P. putida CZ1 were ascertained by chemical modifications of the biomass followed by Fourier transform infrared and X-ray absorption spectroscopic analyses of the living or nonliving cells. A dramatic decrease in Cu(II)- and Zn(II)-binding resulted after acidic methanol esterification of the nonliving cells, indicating that carboxyl functional groups play an important role in the binding of metal to the biomaterial. X-ray absorption spectroscopy was used to determine the speciation of Cu ions bound by living and nonliving cells, as well as to elucidate which functional groups were involved in binding of the Cu ions. The X-ray absorption near-edge structure spectra analysis showed that the majority of the Cu was bound in both samples as Cu(II). The fitting results of Cu K-edge extended X-ray absorption fine structure spectra showed that N/O ligands dominated in living and nonliving cells. Therefore, by combining different techniques, our results indicate that carboxyl functional groups are the major ligands responsible for the metal binding in P. putida CZ1.