Thursday, 10 November 2005 - 9:45 AM
318-6

Microbiological Response to Lead Contamination in Variable Charge Soils with and without Plants.

Jinyan Yang1, Zhenli He2, and Xiaoe Yang1. (1) Zhejiang University, 268 Kaixun Road, Hangzhou, China, (2) University of Florida, 2199 South Rock Rd., Fort Pierce, FL 34945

Lead (Pb) is classified as a carcinogen and toxic to most living organisms at high exposures. The major objectives of this study were to understand microbial response to Pb contamination in variable charge soils and to develop microbial indicator of soil contamination. Lead ecological dose response and temporal changes of basal respiration, microbial biomass, and community diversity were investigated in two variable charge soils (RAR soil-clayey, mixed siliceous thermic typic Dystrochrept and REQ soil-clayey, kaolinitic thermic plinthite aquult RAR and REQ soils) at Pb2+ loadings of 0, 100, 400, 800, 1600, 2400 mg kg-1. Results from this study indicate that the microbial biomass carbon, microbial quotient, and the average well color development (AWCD) significantly decreased with increasing Pb2+loading. Lead slightly enhanced soil basal respiration at low concentrations of Pb2+ (≤100 mg kg-1), but had inhibitory effects at higher concentrations (≥400 mg kg-1). Soil microbial functional diversities were affected, to varying extent, by the stress of Pb2+ pollution. The AWCD, microbial community richness, and McIntosh index were lower in the Pb-polluted soil than the control. Planting celery and Chinese cabbage generally increased the activity and community in the soils. There were negative relationships between soil microbial carbon, microbial quotient, or AWCD and soil total Pb2+ or bioavailable Pb2+. At 10% reduction in biomass carbon, the critical levels of NH4OAc extractable Pb2+ were 230.3 and 246.8 mg kg-1, respectively for RAR and REQ soil with celery, and 163.2 and 202.3 mg kg-1 with Chinese cabbage. At 10% reduction in microbial quotient, the critical levels of NH4OAc extractable Pb2+ were 254.4 mg kg-1 and 243.5 mg kg-1, respectively in RAR and REQ soil with Chinese cabbage. The critical levels based on Food Hygiene Standard were very similar to the levels according to 10% reduction in microbial biomass carbon or microbial quotient.

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