Effects of arbuscular mycorrhizal fungi inoculation on arsenic accumulation by tobacco (Nicotiana tabacum L.)

A pot experiment was conducted to study the effects of arbuscular mycorrhizal （AM） fungi （from contaminated or uncontaminated soils） on arsenic （As） uptake of tobacco （Nicotiana tabacurn L.） in As-contaminated soil. Mycorrhizal colonization rate, dry weight, As and P uptake by plants, concentrations of water-extractable As and As fractions were determined. A low mycorrhizal colonization rate （〈 25%） was detected. Our research indicated that AM fungi isolated from polluted soils were no more effective than those from unpolluted soils when grown in symbiosis with tobacco. No significant differences were observed in roots and stalks dry weights among all treatments. Leaves and total plant dry weights were much higher in Glomus versiforme treatment than that in control treatment. As contents in roots and stalks from mycorrhizal treatments were much lower than that from control treatment. Total plant As content exhibited the same trend. P concentrations in tobacco were not affected by colonization, nor were stalks, leaves and total plant P contents. Roots P contents were remarkably lower in HN treatments than in other treatments. Meanwhile, decreased soil pH and lower water-extractable As concentrations and higher levels of As fraction bound to well-crystallized hydrous oxides of Fe and AI were found in mycorrhizal treatments than in controls. The protective effect of mycorrhiza against plant As uptake may be associated with changes in As solubility mediated by changing soil pH. These results indicated that under As stress, proper mechanisms employed by AM fungi can protect tobacco against As uptake. Results confirmed that AM fungi can play an important role in food quality and safety.

Effects of Arbuscular Mycorrhizal Fungi and Earthworm on Nematode Communities and Arsenic Uptake by Maize in Arsenic-Contaminated Soils

The influences of arbuscular mycorrhizal fungi (AMF,Acaulospora spp.and Glomus spp.) and rice straw and earthworms (RE,Eisenia foetida) on nematode communities and arsenic (As) uptake by maize (Zea mays L.) in Ascontaminated soils were examined in a field experiment conducted in Wujiang,Jiangsu Province,China.The experiment was designed as a 2 × 2 factorial with the factors of AMF (inoculated or uninoculated) and RE (added or not added).The results demonstrated that AMF inoculation led to significantly higher root colonization of AMF and root dry weight.Plants inoculated with both AMF and RE had the highest As concentrations in root.The number of total nematodes increased with AMF inoculation when RE was absent,and decreased with RE addition when AMF was inoculated.The improved abundance of nematodes with the AMF treatment implied that the tested AMF acted as food sources for fungivores.The abundances of omnivores-predators and plant parasites were reduced by earthworm activity.Twentyseven genera of nematodes were identified,with Filenchus dominant in all treatments.Trophic diversity,Shannon-Weaver diversity,Simpson dominance index,and species richness indicated higher species diversity,more proportionate species composition,evenly distributed species,and more food sources in the AMF,RE,and their interaction treatments.Maturity index showed a moderately disturbed environment due to As pollution.Besides enhancing plant uptake of contaminants,AMF and RE amendments could also improve soil health by restoring the structure of soil communities,as reflected by more stable nematode community structure.

Carbonaceous aerosol in ambient air: Parallel measurements between water cyclone and carbon analyzer

A water cyclone,developed to collect and preserve biological aerosols in a small liquid flow,was interfaced with a total organic carbon analyzer to measure the aerosol organic and inorganic carbon fractions.The total carbon was compared against parallel measurements of elemental carbon (EC) and organic carbon (OC) using a Sunset Real Time ECOC Analyzer between 12-29 January 2009.A National Institute for Occupational Safety and Health (NIOSH) like protocol for the measurements included four temperature steps ending at 840 ℃ for OC under a helium atmosphere followed by two temperature steps ramped to 850 ℃ for EC in a helium-oxygen atmosphere,Carbon data comparison between the water cyclone-TOC and the TOC measured by the analyzer indicated good agreement (r2 =0.82,linear regression slope =0.98,p < 0.001).Analyses of the relationship between total water organic carbon and OC,investigated using data sets from case studies spanning two different events,suggested it was possible to distinguish between the primary and secondary sources.