Contrasting soil physicochemical properties influence the stability and activity of hydrolytic enzymes in a podzolic soil

Extracellular enzymes catalyze the depolymerization of soil organic matter (SOM), thus influencing the fate of organic carbon and nutrient release rates in soils. The rate of enzyme-catalyzed processes depends on the pool size and lifespan of enzymes. Both are strongly affected by environmental conditions, yet how soil-forming process and resulting physicochemical and mineralogical properties influence enzyme activity remains poorly documented by experimental data. In this study, we added three pure enzymes (β-glucosidase, acid phosphatase, and leucine aminopeptidase) to three soil horizons from a Podzol with contrasting pedogenic characteristics (BC horizon: mainly primary minerals; Ae horizon: quartz and SOM enriched; and Bhs horizon: organo-metallic complexes and iron oxide enriched). Although the addition of pure enzymes increased enzyme activities by 1.3–2.3 times, only 7–22% of enzymes remained active one day after their addition into soil. Moreover, the active portion of added enzymes dropped to 5–12% over one week. The decay of enzymes followed the first-order model with rates ranging from 0.047 to 0.104 day −1 . The weak enzyme stabilization in BC horizon is explained by the presence of primary minerals with lower specific surface area and reactivity, which led to greater activity loss of acid phosphatase compared to horizons enriched with SOM (Ae) and/or pedogenic iron subproducts (Bhs). The enrichment of organo-metallic complexes and iron oxides in Bhs horizon most likely reduced the activity of leucine aminopeptidase but prolonged the persistence of activity. However, the catalytic efficiency of enzymes in Bhs horizon was lower than that in Ae and BC horizons. Our findings highlight the need for further investigation into how soil physicochemical and mineralogical properties can influence enzyme activity and SOM decomposition rate.