Effects of biochar and biofertilizer on cadmium-contaminated cotton growth and the antioxidative defense system

Abstract

Consistent use of large amounts of fertilizers, pesticides, and mulch can cause the accumulation of harmful substances in cotton plants. Among these harmful substances, cadmium (Cd), an undegradable element, stands out as being particularly highly toxic to plants. The objective of this study was to evaluate the ability of biochar (3%) and biofertilizer (1.5%) to decrease Cd uptake, increase cotton dry weight, and modulate the activities of photosynthetic and peroxidase (POD), superoxide dismutase (SOD), catalase enzyme (CAT) in cotton (Gossypium hirsutum L.) grown in Cd-contaminated soil (0, 1, 2, or 4 mg Cd kg^-1 soil) in pots. These studies showed that, as expected, exogenous Cd adversely affects cotton chlorophyll and photosynthesis. However, biochar and biofertilizer increased cotton dry weight by an average of 16.82% and 32.62%, respectively. Meanwhile, biochar and biofertilizer decreased the accumulation of Cd in cotton organs, and there was a significant reduction in the amount of Cd in bolls (P < 0.05). Biochar and biofertilizer have a positive impact on cotton chlorophyll content, net photosynthesis, stomatal conductance, transpiration rate, and intercellular CO₂ concentration. Thus, the addition of biochar and biofertilizer promote cotton growth. However, biochar and biofertilizer increased the SOD activity of leaves (47.70% and 77.21%), CAT activity of leaves (35.40% and 72.82%), SOD activity of roots (33.62% and 39.37%), and CAT activity of roots (36.91% and 60.29%), respectively, and the addition of biochar and biofertilizer decreased the content of MDA and electrolyte leakage rate. Redundancy analyses showed that biochar and biofertilizer also improved SOD and POD activities by reducing the heavy metal-induced oxidative stress in cotton and reducing Cd uptake in cotton organs. Therefore, biochar and biofertilizer have a positive effect on the growth of cotton.

Figure 1

Effect of biochar and biofertilizer on the biomass of different parts of the cotton plant.

Figure 2

Effect of biochar and biofertilizer on activity of antioxidant enzymes in leaf and root of cotton plants. Values show the mean of five replicates ± SE. Means followed by same small letters are not significant different at P < 0.05 by using the Duncan test.

Figure 3

Effect of biochar and biofertilizer on malondialdehyde (MDA) and electrolyte leakage (EL) in the leaf and root of cotton plants. Values show the means of five replicate ± SE. Means followed by the same small letters are not significantly different at P < 0.05 by using the Duncan test.

Figure 4

Redundancy analysis of cotton growth index and physiological characteristics. L,R-SOD, L,R-POD, L,R -CAT, L,R -MDA, L,R -EL represents leaves and roots SOD, POD, CAT, MDA, electrolyte leakage rate, DW represents dry weight, Tr representative transpiration ratio, Gs represents stomatal conductance, Pn represents net photosynthesis rate, Ci represents intercellular CO₂ concentration.