Cadmium toxicity and soil biological index under potato (Solanum tuberosum L.) cultivation

Increasing cadmium (Cd) pollution in soil is of great concern. A pot experiment was conducted with the aim of assessing the effect of Cd on soil biological indices under potato cultivation. Cadmium was added to 10 kg soil in each pot (6 seeds pot–1) as Cd(NO3)2 at 0, 15, 30, 45 and 60 mg kg–1 with three replications. All soil and plant parameters decreased with all Cd treatments; however, high levels of Cd had a significant (P < 0.05) suppressive effect. The highest Cd level significantly (P < 0.05) decreased microbial biomass carbon (2.16-fold), nitrogen (11.37-fold) and phosphorus (10.3-fold), as well as enzyme activities of dehydrogenase (4.36-fold), phosphatase (9.23-fold), and urease (9.61-fold). The highest Cd level also decreased pH (1.46-fold), potato shoot (3.55-fold) and root (7.43-fold) length, root (10.9-fold) and shoot (6.04-fold) fresh weight, root (7.51-fold) and shoot (13.7-fold) dry weight, chlorophyll content (27.0-fold), carotenoid content (4.08-fold), and plant macronutrient and micronutrient uptake in potato root and shoots. Conversely, the highest level of Cd significantly (P < 0.05) increased the biomass C : N (5.27-fold) and C : P (4.77-fold) ratios, soil extractable Cd (5.38-fold), and Cd uptake in potato root (5.05-fold) and shoot (4.82-fold) at the end of the experiment (day 60). Cadmium contamination substantially affected soil biological indices and growth of potato, and the Cd threshold was strongly associated with the extent of Cd concentration and duration to accumulate. Soil microbial biomass, enzymatic activities, pH and potato physiological parameters could be used as a sensitive indicators to reflect environmental stresses in soil ecosystems.