RETRACTED ARTICLE: Effect of lead pollution on soil microbiological index under spinach (Spinacia oleracea L.) cultivation

Abstract

Lead (Pb) pollution is appearing as an alarming threat nowadays in both developed and developing countries. Excessive Pb concentrations in agricultural soils result in minimizing the microbiological activities which leads to the decrease in crop production. A pot experiment was conducted with the purpose to examine the deleterious effect of Pb on microbiological index under spinach cultivation. Pb was added to 5 kg soil in each pot (with 6 seeds/pot) using Pb(NO3)2 at the rate of 0, 150, 300, 450, and 600 mg kg−1 with three replications in completely randomized design. All soil microbial, enzymatic, and chemical properties and plant growth parameters and nutrient uptake were measured by standard methods. Both soil and plant measured parameters decreased after the addition of Pb (150, 300, 450, and 600 mg Pb kg−1 soil) treatments with the passage of time (from 15 to 60 days) compared with control (CK). However, high Pb levels had more suppressive effect, therefore, highest Pb level (600 mg Pb kg−1 soil) significantly (P < 0.05) decreased the microbial biomass carbon (5.59-fold); microbial biomass nitrogen (N; 11.71-fold); microbial biomass phosphorus (P; 25.1-fold); dehydrogenase (4.02-fold); phosphatase (9.40-fold); urease (9.26-fold); pH (1.40-fold); spinach shoot (2.17-fold) and root (2.54-fold) length; shoot (2.36-fold) and root (2.69-fold) fresh weight; shoot (3.90-fold) and root (3.50-fold) dry weight; chlorophyll content (5.60-fold); carotenoid content (4.29-fold); plant macronutrients uptake, i.e., N (4.38- and 2.97-fold), P (3.88- and 6.58-fold), K (3.88- and 4.6-fold), Ca (6.60- and 6.70-fold), and Mg (5.57- and 4.45-fold); and plant micronutrient uptake, i.e., Zn (2.39- and 3.05-fold), Cu (3.70- and 2.62-fold), Fe (4.13- and 3.23-fold), and Mn (4.17- and 4.09-fold) in spinach shoot and root, respectively. Conversely, highest Pb level, i.e., 600 mg Pb kg−1 soil significantly (P < 0.05) increased the biomass carbon (C)/nitrogen (N) (4.69-fold) and C/P (6.01-fold) ratios, soil extractable Pb (5.87-fold), and Pb uptake in spinach shoot (3.58-fold) and root (4.38-fold), respectively, at the end of the experiment, i.e., day 60. Pb contamination significantly decreased the soil microbial and enzymatic activities, pH, spinach plant growth, and nutrients uptake in all the samples spiked with Pb. The degree of the influence increased with the increased Pb concentrations and incubation time, showing that Pb threshold is strongly associated with the extent of Pb concentration and time to accumulate. The soil microbial biomass, enzymatic activities, pH, and spinach physiological indices, could be used as a sensitive indicators to reflect environmental stress in soil ecosystems.