The Combined Use of Beneficial Soil Microorganisms Enhanced the Growth and Efficiently Reduced Lead Content in Leaves of Lettuce (Lactuca sativa L.) Plant under Lead Stress

Abstract

Two pots experiments were conducted, during two successive winter seasons of 2016/2017 and 2017/2018, to test the role of biofertilizer inoculations (arbuscular mycorrhizal fungi, AMF; Bacillus megaterium, B. megaterium; and their mixture) in improving growth and quality of lettuce (Lactuca sativa L. cv. Balady) under different levels (0, 100, 200 and 300 ppm) of lead (Pb). The results illustrated that the growth and quality of lettuce were greatly affected by the escalated levels of Pb in soil. Clearly, the increased levels of Pb decreased plant growth parameters, the contents of macronutrient and micronutrient as well as photosynthetic pigments, but increased the contents of Pb in the different parts of lettuce plants. Among the tested biofertilizer inoculations, the combined inoculation (AMF + B. megaterium) showed superior effects for increasing plant growth, contents of nutrient and photosynthetic pigments. AMF and the combined inoculation treatment exhibited an equal efficiency for reducing the content of Pb in the old and new leaves (edible parts) of lettuce plants, while B. megaterium showed the best performance in reducing the content of Pb in lettuce roots. Our study suggested that the combined inoculation (AMF + B. megaterium) is an effective tool for improving growth and quality of lettuce in high-contaminated soil with Pb.