The influence of light combination on the physicochemical characteristics and enzymatic activity of soil with multi-metal pollution in phytoremediation

Light irradiation with suitable quality and intensity could influence the success of phytoremediation by improving the biomass yield of plants. However, mechanisms involved in this influence on the contaminant accumulation and translocation ability of plants have rarely been studied. Five light combinations with different red (R) and blue (B) ratios (0, 10, 50, 75 and 100 % blue) at the same intensity (220 mu mol m(-2) s(-1)) were used to assist phytoremediation using Noccaea caerulescens, and the change in physicochemical characteristics and enzymatic activities of soils after phytoremediation were evaluated. Compared with the control, the light combinations and monochromic blue light significantly increased the activities of soil ureases, invertases, and phosphatases, whereas monochromic red light strongly inhibited the activities of these enzymes, because different light irradiations altered the formation and excretion of carbohydrates from plants for soil microorganism consumption. Plants under B50R50 treatment accumulated the highest concentrations of metals, but their chlorophyll concentrations and lipid peroxidation were similar to those other species with lower metal concentrations. Hence, light with a proper blue/red ratio can simultaneously improve the physicochemical characteristics and enzymatic activities of soils, increase the metal uptake capacity and oxidation resistance of plants, and reduce the leaching risk during phytoremediation processes.