Plant Enhanced Microbial Degradation Of Phenanthrene And Pyrene In Spiked Soils

Polycyclic aromatic hydrocarbons (PAHs), a class of POPs, are widely distributed in the environment. Phytoremediation haslong been recognized as a cost-effective method for removal of PAHs pollutants from soil.In the first study, we have estimated the efficacy of phytoremediation of phenanthrene and pyrene in a typical low organic matter soil (3.75 g kg-1), and ascertained the contribution proportion of each pathway in the process of PAHs phytoremediation. The results indicated that contribution of abiotic losses from this soil was high both for phenanthrene (83.4%) and pyrene (57.2%), with the remaining fraction being degraded by root exudates enhanced microbes and soil indigenous microbes. The contributions of root exudates enhancing biodegradation of phenanthrene (15.5%) and pyrene (21.3%) were higher than those of indigenous microbial degradation. The role of root exudates on dissipation of phenanthrene and pyrene was evident in this experiment. By the way, with the increasing of ring numbers in PAHs structures, the root exudates enhanced degradation became more and more important. BIOLOG–ECO plate analysis indicated that microbial community structure of the soil receiving root exudates had changed. The removal rate and substrate utilization rate in the treatment with plant roots were lower than the treatment only with root exudates, which suggested that possible competition between roots and microbes for nutrients had occurred.In the second study, we investigated the capability of two plant species separately and their combination to promote the degradation of phenanthrene and pyrene in soil. The result showed that the presence of plants significantly enhanced the dissipation of phenanthrene and pyrene in the soil environment. This effect was especially marked with ryegrass. At the end of 40 days treatment, phenanthrene and pyrene concentrations in treated soils declined from an initial to 0.78ppm and 7.33ppm in T1, 2.97ppm and 12.54ppm in T2 and 2.63ppm and 19.53ppm in T3 respectively, indicating that phenanthrene and pyrene was successfully removed by plants. Within approximately 40 days experimental period, the dissipation extent showed that the 4-ring pyrene was more recalcitrant than 3-ring phenanthrene. From the BIOLOG data, we concluded that the activities and functional diversity of soil microbiology were improved significantly with the existence of plants. However, the utilization of carbon source was different among the different plant types, which suggested that plants enhanced microbial functional diversity was not specified.