Effect of the Substrate and Inoculation of Phosphate-Dissolving Bacterial and Fungal with Humic Acids in the Activity of the Alkaline Phosphatase Enzyme in Cadmium-Contaminated Soil

Abstract

A laboratory experiment was carried out in the laboratories of the Department of Soil Sciences and Water Resources, College of Agriculture, University of Basrah, to identify the role of the bacteria Bacillus subtilis and the fungus Aspergillus niger, with humic acids extracted from fermented cow dung, the effectiveness of the alkaline phosphatase enzyme in soil contaminated with cadmium and compare it with uncontaminated soil. The soil was treated with a cadmium sulfate solution up to the critical limit (3 mg Cd L-1) and humic and fulvic acid were added at a level of 50 L ha-1 separately, leaving the treatment without addition for control. Then the soil was inoculated with bacterial B. subtilis and fungal A. niger isolates individually and with a mixture of isolates, leaving a treatment without inoculation for control, the treatments were incubated at a temperature of 28±2 °C. Different levels of substrate concentration were used (0.010, 0.025, 0.050, 0.075, and 0.100 M). The results showed that cadmium contamination decreased alkaline phosphatase enzyme activity by 12.28%. There was also an increase in the activity of the alkaline phosphatase enzyme at all inoculation treatments compared to the control treatment, with the bio-mixture treatment being superior to the rest of the treatments, reaching 436.944 µg P. nitrophenol gm-1 soil 1 hour-1 in uncontaminated soil and 402.558 µg P. nitrophenol gm-1 soil 1 hour-1 in cadmium contaminated soil. The humic acid treatment showed a similar increase in the activity of the alkaline phosphatase enzyme compared to the control treatment the highest increase was in the fulvic acid treatment. As for the effect of the substrate, the concentration of 0.075 M recorded the highest increase in alkaline phosphatase enzyme activity in unpolluted and cadmium-polluted soil for all treatments.