Rhizosphere Gradients of Polycyclic Aromatic Hydrocarbon (PAH) Dissipation in Two Industrial Soils and the Impact of Arbuscular Mycorrhiza

Abstract

Phytoremediation of organic pollutants depends on plant-microbe interactions in the rhizosphere, but the extent and intensity of such rhizosphere effects are likely to decrease with increasing distance from the root surface. We conducted a time-course pot experiment to measure dissipation of polycyclic aromatic hydrocarbons (PAHs) in the rhizosphere of clover and ryegrass grown together on two industrially polluted soils (containing 0.4 and 2 g kg(-1) of 12 PAHs). The impact of the fungal root symbiosis arbuscular mycorrhiza (AM) on PAH degradation was also assessed, as these fungi have previously improved plant establishment on PAH-polluted soils and enhanced PAH degradation in spiked soil. The two soils behaved differently with respect to the time-course of PAH dissipation. The less polluted and more highly organic soil showed low initial PAH dissipation rates, with small positive effects of plants after 13 weeks. At the final harvest (26 weeks), the amounts of PAHs extracted from nonplanted pots were higher than the initial concentrations. In parallel planted pots, PAH concentrations decreased as a function of proximity to roots. The most polluted soil showed higher initial PAH dissipation (25% during 13 weeks), but at the final harvest PAH concentrations had increased to values between the initial concentration and those at 13 weeks. An effect of root proximity was observed for the last harvest only. The presence of mycorrhiza generally enhanced plant growth and favored growth of clover at the expense of ryegrass. Mycorrhiza enhanced PAH dissipation when plant effects were observed.

DDT uptake by arbuscular mycorrhizal alfalfa and depletion in soil as influenced by soil application of a non-ionic surfactant

“…Phytoremediation of organic pollutants depends on plante microbe interactions in the rhizosphere (Joner and Leyval, 2003b). We observed a pronounced influence of the AM fungus on soil microbial abundance.…”

“…Research has established that AM fungi can enhance the growth of several plant species in soil with high polycyclic aromatic hydrocarbon (PAH) concentrations (Leyval and Binet, 1998). Experimental evidence has been obtained for the impact of AM on the uptake and dissipation of some organic pollutants in soil such as PAHs and atrazine (Joner and Leyval, 2003b;Huang et al, 2007). These studies indicated that AM fungi conferred some benefit on phytoremediation of soils contaminated with organic pollutants.…”

Enhanced dissipation of phenanthrene in spiked soil by arbuscular mycorrhizal alfalfa combined with a non-ionic surfactant amendment

“…Despite the potential role of AM in the phytoremediation of soils with organic contaminants, very few studies have been carried out on interactions between AM and organic pollutants such as PAHs in soil and variable results have been obtained. Positive effects of AM on the dissipation of PAHs in soils have been observed by Joner et al (Joner and Leyval, 2003;Joner et al, 2001). In contrast, no impact of AM fungi on PAH dissipation was observed by Binet et al (2000) and a depression in PAH dissipation was observed in the presence of ectomycorrhizas (Joner et al, 2006;Genney et al, 2004).…”

“…Arbuscular mycorrhiza (AM) is a ubiquitous association between soil fungi and the roots of most herbaceous plant species that permits the host plant to exploit nutrients in the soil beyond the rhizosphere through fungal transport (Joner and Leyval, 2003). Mycorrhizal colonization can result in quantitative and qualitative changes in root exudation and in the soil microbial community, particularly in the rhizosphere.…”

Effect of arbuscular mycorrhizal fungus (Glomus caledonium) on the accumulation and metabolism of atrazine in maize (Zea mays L.) and atrazine dissipation in soil

“…The fact that only the metabolites DEA and DIA were detected in the plant roots could contribute to the important role of the plant-derived enzymes in roots in degradation and then the metabolites assimilated into the plant tissue (Boyajian and Carriera, 1997). AM fungi were reported to obligate symbionts with little or no capacity for degradation of organics (Joner and Leyval, 2003b). Therefore, the increasing enzyme activity and microorganism stimulated by colonization was the possible reason for the enhanced metabolism in mycorrhizal colonized roots.…”