[Effect of Chelating Agents and Organic Acids on Remediation of Cadmium and Arsenic Complex Contaminated Soil Using Xanthium sibiricum].

In order to improve the phytoextraction efficiency of Xanthium sibiricum on farmland soil that had been contaminated by Cd and As, this study explored the effects of chelating agents and organic acids (EDTA, SAP, CA, and MA) on the extraction of Cd and As heavy metals using X. sibiricum. The results showed that the four different chelating agents and organic acids had little effect on the biomass of the roots, stems, and leaves of X. sibiricum. However, they had different effects on the concentrations and accumulation of Cd and As in various organs of X. sibiricum. Compared with the those in the CK treatment, EDTA, SAP, CA, and MA significantly increased the Cd concentrations in the leaves of X. sibiricum by 44.1%, 32.4%, 41.2%, and 38.2% and the As concentrations in the roots of X. sibiricum by 89.6%, 7.4%, 94.8%, and 61.5%, respectively. The four treatments (EDTA, SAP, CA, and MA) improved the total Cd accumulation of X. sibiricum, with increasing ranges, respectively, of 70.2%, 29.4%, 28.9%, and 33.1%, and the As accumulation increased by 67.0%, 19.6%, 81.9%, and 40.8%, respectively, compared with that of the CK treatment. The four chelating agents and organic acids had different effects on the Cd and As bioconcentration factor and transfer factor of various organs of X. sibiricum. Treatments with EDTA, SAP, CA, and MA resulted in a decrease of 32.7%-38.2% in soil Cd concentrations and a decrease of 14.6%-20.5% in soil As concentrations. These four chelating agents can be used for enhancing the efficiency of extraction Cd and As heavy metals by X. sibiricum.

[Cd Runoff Load and Soil Profile Movement After Implementation of Some Typical Contaminated Agricultural Soil Remediation Strategies].

Owing to the strong ability to immobilize and hyperaccumulate some toxic heavy metals in contaminated soils, the biochar, lime and such as hyperaccumulator ramie received increasing interests from crops and environment safety in recent years. Outdoor pot experiment was conducted to compare the impacts of lime and biochar addition in paddy rice treatment, hyperaccumulator ramie and ramie combined with EDTA of plant Phytoremediation methods on soil available Cd dynamics in rainfall runoff and the mobility along soil profile, under both natural acid precipitation and acid soil conditions. The results showed that, biochar addition at a 2% mass ratio application amount significantly increased soil pH, while ramie with EDTA application obviously decreased soil pH compared to ramie monoculture. Within the same rainfall events, water soluble Cd concentration in surface runoff of ramie treatments was significantly higher than those of waterlogged rice treatments, and Cd concentration in runoff was obviously increased after EDTA addition, whereas lime at a 0.3% mass ratio application amount as additive had no obvious impact on soil pH and Cd speciation change, which may be due to the low application amount. During the whole experimental period , water soluble Cd concentration of rainfall runoff in spring was higher than that in summer, showing the same seasonal characteristics in all treatments. Biochar addition could significantly decrease available Cd content in 0-20 cm soil layer and with certain preferable persistency effects, whereas EDTA addition treatment obviously increased available Cd of 0-20 cm soil layer compared to other treatments, and obvious Cd element activation phenomenon in 20-40 cm soil layer was observed after EDTA addition. In conclusion, lime and biochar as environmental and friendly alkaline Cd immobilization materials showed lower environment risk to surface and ground receiving water, but attention should be paid to phytoremediation enhanced with EDTA or other organic acid before promotion and field application for heavy metals removal from contaminated soils.

Field released transgenic papaya effect on soil microbial communities and enzyme activities.

Soil properties, microbial communities and enzyme activities were studied in soil amended with replicase (RP)-transgenic or non-transgenic papaya under field conditions. Compared with non-transgenic papaya, significant differences (P<0.05) were observed in total nitrogen in soils grown with transgenic papaya. There were also significant differences (P<0.05) in the total number of colony forming units (CFUs) of bacteria, actinomycetes and fungi between soils amended with RP-transgenic plants and non-transgenic plants. Compared with non-transgenic papaya, the total CFUs of bacteria, actinomycetes and fungi in soil with transgenic papaya increased by 0.43-1.1, 0.21-0.80 and 0.46-0.73 times respectively. Significantly higher (P<0.05) CFUs of bacteria, actinomycetes and fungi resistant to kanamycin (Km) were obtained in soils with RP-transgenic papaya than those with non-transgenic papaya in all concentrations of Km. Higher resistance quotients for Kmr (kanamycin resistant) bacteria, actinomycetes and fungi were found in soil planted with RP-transgenic papaya, and the resistance quotients for Kmr bacteria, actinomycetes and fungi in soils with transgenic papaya increased 1.6-4.46, 0.63-2.5 and 0.75-2.30 times. RP-transgenic papaya and non-transgenic papaya produced significantly different enzyme activities in arylsulfatase (5.4-5.9x), polyphenol oxidase (0.7-1.4x), invertase (0.5-0.79x), cellulase (0.23-0.35x) and phosphodiesterase (0.16-0.2x). The former three soil enzymes appeared to be more sensitive to the transgenic papaya than the others, and could be useful parameters in assessing the effects of transgenic papaya. Transgenic papaya could alter soil chemical properties, enzyme activities and microbial communities.

[Analyses of virus resistance and transgenes for transgenic papaya].

Virus resistance in field and molecular biological characterizations of the transgenes were analyzed for two lines of T(1) generation of transgenic papaya with the replicase mutant gene from papaya ringspot virus (PRV). The transgenic plants showed highly resistant or immune against PRV. Results indicated that the transgenes inherited to and expressed at RNA level in the progenies.