Colonization of Penicillium oxalicum SL2 in Pb-contaminated paddy soil and its immobilization effect on soil Pb

Penicillium oxalicum SL2 (SL2) is a previously screened Pb-tolerant fungus that can promote crops growth. The relationship between SL2 colonization and Pb immobilization was studied to provide a theoretical basis for microbial remediation of Pb-contaminated paddy soil. In this study, green fluorescent protein (GFP) labeled SL2 was inoculated into different Pb-contaminated paddy soils(S1-S6). The Pb extracted from the soil by HNO3, EDTA and CaCl2 were used to characterize the available Pb. The results showed that the colonization of SL2 was divided into lag phase (0-7 days), growth phase (7-30 days), and mortality phase (30-90 days). SL2 colonized well in sandy soils rich in clay and total phosphorus with initial pH of 4.5-7.0. In addition, SL2 increased soil pH and decreased soil Eh, which was beneficial to immobilize Pb. In different soils, the highest percentages of CaCl2-Pb, EDTA-Pb, and HNO3-Pb immobilized by SL2 were 34.34%-40.53%, 17.05%-20.11%, and 7.39%-15.62%, respectively. Pearson correlation analysis showed that the percentages of CaCl2-Pb and EDTA-Pb immobilized by SL2 were significantly positively correlated with the number of SL2 during the growth phase. SL2 mainly immobilized Pb in the growth phase and a higher peak number of SL2 was beneficial to the immobilization of Pb.