Relative importance of influencing factor-driven soil enzyme activity during the early plantation stage in the hilly-gully Loess regions

Widespread and rapid land-use changes have changed the ecosystem structure and threatened soil functions. Soil enzymes are the important driving force and sensitive indicators for soil ecological function. However, the effect of afforestation on soil enzyme activity and the relative importance of the influencing factors (plants, soil, structure, and nutrition) are still inconclusive, especially in the early stage of afforestation. Here, the enzymatic activities and influencing factors of five types of plantations (18 years old) and natural grassland topsoil (0-20 cm) in the hilly-gully region of the Loess Plateau were studied. The results showed that the soil enzyme activity of the plantations was significantly lower than that of the natural grassland, and the activities of invertase, urease, and alkaline phosphatase were decreased by 32%, 26%, and 10% on average, respectively. Partial correlation analysis and multiple regression analysis showed that the influence of soil and nutrient factors on invertase and alkaline phosphatase was more important than that of plant and structural factors, while urease was more influenced by plant and nutrition factors. Our results suggest that soil and nutrient characteristics were important factors affecting soil enzyme activity in plantations, but the disturbance of vegetation may be the main reason for the decrease in enzyme activity in the early stage of restoration.