Lysobacter may drive the hormetic effects of Pb on soil alkaline phosphatase

It has become increasingly recognized that hormesis phenomena exist in soil ecosystem, but the research on the hormetic responses of soil enzymes are still limited. This study was conducted to investigate the hormetic effects of lead (Pb) on the activity of soil alkaline phosphatase (ALP) and the associated microbial groups. Soils were treated by adding Pb (NO₃)₂ solution with 0, 10, 100, 500, 1000, 2000, 4000, and 5000 mg/kg of Pb, respectively. A moist heat sterilization method (121 °C × 30 min) was used to discriminate the microbial effect on soil ALP hormesis from other factors. The bacterial community composition and abundance in the control (CK) and Pb-treated soils were detected by the high-throughput sequencing technique. The ALP activity at doses of 500-1000 mg/kg of Pb was significantly higher than that of CK (0 mg/kg of Pb), showing a typical inverted U-shaped dose response with the stimulation magnitude of 9.8-10.3% within 48 h of incubation. In addition, ALP activity decreased by 80% on average after soil sterilization. Analysis of bacterial community composition indicated that the relative abundance of Lysobacter at 1000 mg Pb/kg was higher than that of CK at genus level, with the increase of 69.82%. The highly significant correlation between soil ALP activities and relative abundance of Lysobacter indicated that this bacterial genus could possibly contribute to the hormetic responses of soil ALP to added doses of Pb in soils.