Effect of Heavy Metal Stress on Biochemical and Microbial Responses of Cicer arietinum L.

Abstract

Heavy metal contamination of agricultural soil is an important environmental constraint that can adversely affect crop growth, metabolism and soil microbial communities. The present study was designed to evaluate the effects of increasing heavy metal stress on the biochemical characteristics of chickpea (Cicer arietinum L.) and the associated rhizospheric microbial population. Healthy seeds of Cicer arietinum L. were grown in soil amended with graded concentrations of a representative heavy metal. A control treatment without heavy metal addition was maintained for comparison. Biochemical parameters including chlorophyll, total soluble protein, total soluble carbohydrate, proline, total phenolic content and antioxidant enzyme activities were evaluated at the vegetative stage. Rhizospheric microbial population was assessed in terms of total viable bacterial and fungal counts. The representative results showed that increasing heavy metal concentration progressively reduced chlorophyll, protein and carbohydrate contents, whereas proline and phenolic compounds increased under moderate stress. Antioxidant enzymes such as superoxide dismutase, catalase and peroxidase showed increased activity at moderate stress but declined at the highest concentration, suggesting disruption of the antioxidant defense system under severe stress. Heavy metal exposure also reduced the cultivable bacterial and fungal populations of the rhizosphere. The findings indicate that heavy metal stress causes coordinated biochemical and microbial changes in chickpea and that the rhizosphere microbiome may play an important role in determining plant tolerance to metal toxicity.