Estimation of enzymatic activities under various forest tree species as index of mine soil genesis in chronosequence limestone mine spoils

Abstract

Mining activities significantly disrupt soil properties, necessitating ecological restoration efforts for sustainable land rehabilitation. Soil enzyme activities serve as vital indicators of soil genesis and restoration progress, reflecting microbial functions and nutrient cycling processes. This study assesses enzymatic activities under various forest tree species across a chronosequence of limestone mine spoils in Nandini Limestone Mine, Durg, Chhattisgarh. Four dominant tree species namely Dalbergia sissoo, Azadirachta indica, Tectona grandis, and Albizia procera were selected for evaluation at three plantation age gradations (5, 15, and 25 years). Soil samples were collected from rhizospheric regions and analyzed for invertase, phosphatase, urease, and dehydrogenase activities to determine their role in mine soil genesis and restoration. Results indicate that enzymatic activities improve with plantation age, signifying progressive soil restoration. Among the species, Dalbergia sissoo exhibited the highest enzymatic activity across all parameters, closely followed by Azadirachta indica. Albizia procera showed moderate enhancement, while Tectona grandis demonstrated the lowest enzyme activity, indicating limited contribution to soil rehabilitation. Invertase activity, critical for carbon cycling, increased significantly over time, with Dalbergia sissoo exhibiting the highest enhancement (937.39 µg/g soil/hour at 25 years). Phosphatase, a key enzyme in phosphorus mobilization, showed similar trends, reaching a peak of 172.05 µg PNP/g soil/hour under Dalbergia sissoo. Urease activity, crucial for nitrogen cycling, was highest in Dalbergia sissoo (46.89 µg NH4-N/g soil/hour at 25 years), followed by Azadirachta indica. Dehydrogenase activity, an indicator of microbial metabolic activity, was highest under Azadirachta indica, suggesting its significant role in promoting microbial proliferation. The correlation data suggests that enzymatic activities in younger soils are highly interconnected (p