Enzyme activities of tea soils as influenced by heavy metal contamination

摘要

Heavy metal contamination has been reported to influence the activities of soil enzymes. The main objective of the current work was to find out the effect of Cd, Ni, Pb and Hg at 25 and 75 umole concentrations on acid phosphatase, alkaline phosphatase, aryl sulfatase and urease activities in tea soils of south India. Soil samples were collected from four different zones and contaminated with equimolar concentrations (25 and 75 umole) of the above mentioned heavy metals. When there was no contamination, the acid phosphatase activity was prominently higher than alkaline phosphatase activity. Similarly the aryl sulfatase and urease activities were found maximum in soils of Munnar and Nilgiris, respectively. In a few cases the inhibition was almost double due to higher concentration than lower concentration. While presence of Cd resulted in an increase in the percentage of inhibition of the acid phosphatase activities in soils of Anamallais and Munnar, Pb caused maximum inhibition in soils of NilgirisandNi caused maximum inhibition in soils of Vandiperiyar. In the case of alkaline phosphatase activities in Anamallais, maximum inhibition was noticed in the presence of Cd. Ni produced an increase in the percentage of inhibition of the alkaline phosphatase activities in Munnar and Nilgiris and Pb caused maximum inhibition in soils of Vandiperiyar. The inhibiting power of Ni and Pb was maximum towards the enzyme aryl sulfatase, which is responsible for breaking the non- available ester compounds of sulphur into available fraction like sulphate in soils. The concentration of heavy metals had positive influence on their inhibiting nature on enzyme activities. Among the various elements added, Hg resulted in maximum inhibition of aryl sulfatase at 75 umole (87 %) when compared to control in the soils of Nilgiris.