Contrasting responses of phosphatase kinetic parameters to nitrogen and phosphorus additions in forest soils

1. Global changes include increasing nitrogen (N) and phosphorus (P) deposition, which affect microbial nutrient demand and biogeochemical cycles. The responses of P-mineralizing enzymes to these global change components are poorly defined and are not specified in forest soils differing in P content.
2. We chose one site in a P-rich and two sites in P-poor forests and established sixteen 20 × 20 m plots at each site. Control, either N only, P only, or combined N and P, were randomly distributed through each forest site with 4 replicates. We investigated the effects of N and P additions over four years on the phosphomonoesterase potential activity (Vmax), its half-saturation constant (Km), and its catalytic efficiency (Vmax/Km).
3. Without N and P additions, the enzyme kinetic parameters Vmax, Km, and Vmax/Km were higher in P-rich than in P-poor forest soils. These parameters increased with soil pH, SOC, TN, and TP contents increased.
4. Remarkably, P additions caused the Vmax and Km ...