β-Glucosidase Activity in Coal Mining Technosols Along a 50-Year Chronosequence

Carbon cycling in reconstructed soils depends on the activity of enzymes such as β-glucosidase, which hydrolyzes cellulose and serves as an indicator of biological functionality in mined ecosystems. This study evaluated the activity of this enzyme and soil pH in coal mining areas under two reclamation strategies along a 50-year chronosequence: topsoil deposition and revegetation with Acacia mearnsii (CT1 and CT2) versus closure with mine waste and Eucalyptus spp. (ST1 and ST2). Samples were collected at depths of 0–0.05 m and 0.05–0.10 m. In the surface layer (0–0.05 m), topsoil addition promoted higher enzyme activities, with the maximum value observed in CT2 (364.96 µg p-nitrophenol g⁻¹ h⁻¹; pH 4.24) and the minimum in ST1 (14.10 µg p-nitrophenol g⁻¹ h⁻¹; pH 4.73), with a significant difference among treatments (p < 0.05). At 0.05–0.10 m, enzyme activity decreased in all systems, but the superiority of topsoil-treated areas persisted. The highest value was recorded in CT2 (125.18 µg p-nitrophenol g⁻¹ h⁻¹; pH 3.85), while the lowest occurred in ST1 (4.61 µg p-nitrophenol g⁻¹ h⁻¹; pH 3.55). Statistically, CT1 and CT2 were superior to ST2 (p < 0.05). Soil pH ranged from 3.55 to 5.30, indicating persistent acidity that did not prevent biological differentiation among treatments. Topographic reconstruction of mined areas through the deposition of a topsoil layer, even of low thickness, enhanced soil enzymatic activity after 50 years of restoration.