Combined colonization of alfalfa roots by an arbuscular mycorrhizal fungus and addition of non-ionic surfactant to the soil promoted root and shoot uptake and soil dissipation of DDT. AbstractA greenhouse pot experiment was conducted to investigate the colonization of alfalfa roots by the arbuscular mycorrhizal (AM) fungus Glomus etunicatum and application of the non-ionic surfactant Triton X-100 on DDT uptake by alfalfa and depletion in soil. Mycorrhizal colonization led to an increase in the accumulation of DDT in roots but a decrease in shoots. The combination of AM inoculation and Triton X-100 application enhanced DDT uptake by both the roots and shoots. Application of Triton X-100 gave much lower residual concentrations of DDT in the bulk soil than in the rhizosphere soil or in the bulk soil without Triton X-100. AM colonization significantly increased bacterial and fungal counts and dehydrogenase activity in the rhizosphere soil. The combined AM inoculation of plants and soil application of surfactant may have potential as a biotechnological approach for the decontamination of soil polluted with DDT.

a b s t r a c tThe effects of an arbuscular mycorrhizal (AM) fungus (Glomus etunicatum) on atrazine dissipation, soil phosphatase and dehydrogenase activities and soil microbial community structure were investigated. A compartmented side-arm ('cross-pot') system was used for plant cultivation. Maize was cultivated in the main root compartment and atrazine-contaminated soil was added to the side-arms and between them 650 or 37 mm nylon mesh was inserted which allowed mycorrhizal roots or extraradical mycelium to access atrazine in soil in the side-arms. Mycorrhizal roots and extraradical mycelium increased the degradation of atrazine in soil and modified the soil enzyme activities and total soil phospholipid fatty acids (PLFAs). Atrazine declined more and there was greater stimulation of phosphatase and dehydrogenase activities and total PLFAs in soil in the extraradical mycelium compartment than in the mycorrhizal root compartment when the atrazine addition rate to soil was 5.0 mg kg À1 . Mycelium had a more important influence than mycorrhizal roots on atrazine degradation. However, when the atrazine addition rate was 50.0 mg kg À1 , atrazine declined more in the mycorrhizal root compartment than in the extraradical mycelium compartment, perhaps due to inhibition of bacterial activity and higher toxicity to AM mycelium by atrazine at higher concentration. Soil PLFA profiles indicated that the AM fungus exerted a pronounced effect on soil microbial community structure.

IntroductionPolycyclic aromatic hydrocarbons (PAHs) are widely distributed hydrophobic organic contaminants (HOCs) and accumulate in soil that has been contaminated with crude oil, creosote, or coal tar. PAHs are also generated and dispersed into the environment by fossil fuel combustion, wood treatment processes, automobile exhausts, and waste incineration (Wilson and Jones, 1993). Because of their widespread distribution and their toxicity and mutagenicity, PAHs are listed as priority pollutants, and remediation of soils contaminated with PAHs is of great importance. Phytoremediation is a promising alternative approach to soil remediation due to its convenience, cost-effectiveness and environmental acceptability. The HOCs in soil usually exhibit low bioavailability to both microorganisms and plants due to their strong affinity to the soil matrix, especially to soil organic matter (Chen et al., 2005), which limits the application of phytoremediation. Solubilization agents such as the surfactant Triton X-100 have been added to soil to enhance the release of HOCs from the sorbed phase and, thereby, to increase their aqueous concentrations and bioavailability (Zhou and Zhu, 2005). Although addition of surfactants has been explored in the cleanup of contaminated soils (Zhu et al., 2003), there are few reports of their application in phytoremediation.Arbuscular mycorrhiza (AM) is a ubiquitous association between soil fungi and the roots of most herbaceous plant