Variation in Soil Biochemical Properties and Soil Enzyme Activities Among Four Temperate Plantation Types: A Case Study from Beijing, China

We compared soil biochemical properties in four 11-year-old plantations established under Beijing’s Plain Afforestation Project in the Yanqing–Huailai Basin. The plantations were dominated by Populus alba, Ulmus pumila, Salix matsudana, and Pinus tabuliformis, with three plots per plantation. Soil properties were measured at 0–10, 10–30, and 30–60 cm; β-glucosidase (BG), N-acetyl-β-D-glucosaminidase, urease (UE), and dehydrogenase activities were measured at the two upper depths. Two-way mixed-design analysis of variance assessed plantation type, soil depth, and their interaction. Plantation-type effects were significant for available potassium (AK), soil organic carbon (SOC), nitrate (NO3−), and all four enzyme activities, but not for pH, available phosphorus, or alkali-hydrolyzable nitrogen. Significant interactions occurred for NO3−, AK, UE, and BG. Mean enzyme activities were higher at 0–10 cm than at 10–30 cm. Pearson analysis of 24 plot-by-depth observations showed positive BG–SOC (r = 0.516) and UE–AK (r = 0.766) associations and a negative UE–NO3− association (r = −0.665). Redundancy analysis based on eight plantation-by-depth means identified AK as the only significant explanatory variable, accounting for 41.0% of enzyme activity variation (p = 0.018). These findings provide a regional baseline for assessing soil nutrient conditions and selected biochemical activities across plantation types and soil depths.