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Remediation Effects of Urban Greening-Tree Litters on Petroleum-Contaminated Soil in Oil Producing Region of Northern Shaanxi

Soil contamination by petroleum has become a serious environmental issue in oil-producing areas. Research has showed that organic residue additions could enhance the degradation of petroleum in soils. In a laboratory experiment, the effects of litters from 19 urban greening tree species on chemical and biological properties of petroleum-contaminated soil were evaluated. A petroleum contaminated soil was collected in Northern Shaanxi and incubated with the litters for 120 d. Additions of all foliar litters significantly increased the contents of organic matters, available K and available Zn in the contaminated soil. Most of litters significantly increased the contents of alkaline-soluble N and available Mn and Fe, and enhanced the activities of catalase, sucrose, phosphatase, dehydrogenase, urease and protease. Applying the litters also promoted the growth of fungi and actinomycetes. However, litter applications generally decreased soil p H values but did not increase available P and Cu contents. In the tested 19 litters, only several litters improved bacterial population and polyphenol oxidase activity. Except Acer mono, all tree litters accelerated petroleum degradation. Such effect was in order of Melia azedarach Prunus persica Morus albaSophora japonicaSalix babylonicaAcermono MaximPrunus cerasifera. The litters from the rest species had negligible or even negative effects on petroleum degradation.