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To reveal the effects of different land-use types on soil enzyme activities, soil samples were collected from 0–10, 10–20 and 20–30 cm soil layers to compare and analyze soil β-glucosidase (BG), urease (URE), protease (PROT) and catalase (CAT) activities in farmland (FL), abandoned land (AL) and three plantation forests: Platycladus orientalis (L.) Franco (PO), Robinia pseudoacacia L. (RP) and Quercus variabilis Bl. (QV) in the rocky mountainous region of North China. The results showed that the soil enzyme activities varied significantly under different land-use types, and the interannual mean values of FL and PO were remarkably higher than those of other land uses in the 0–30 cm soil layer, in which the soil BG and URE activities of FL were 22% and 12% higher than those of AL, and 428% and 179% higher than those of QV, respectively; the soil PROT and CAT activities of PO were 66% and 23% higher than those of AL, and 479% and 113% higher than those of QV, respectively. Soil BG, URE and PROT activities were all higher in June and lower in December, while soil CAT activity was slightly lower in June. The soil enzymatic activities all showed a notable decrease with the depth of the soil layer. Soil BG, URE, PROT and CAT activities were remarkably (p < 0.01) or significantly (p < 0.05) positively correlated with available nitrogen, available phosphorus, available potassium, dissolved organic carbon (DOC), NO3−-N, soil organic carbon, water content, clay and silt volume fraction, and significantly negatively correlated with sand volume fraction. Soil DOC and pH were important factors influencing soil enzymatic activity, implying that changes in soil enzymatic activity under different land-use types may be the result of a combination of temperature, moisture and plant type. In conclusion, PO plantations are conducive to improving the physicochemical and biological properties of soil and enhance soil fertility, which is a reasonable land-use method to achieve sustainable development in the rocky mountainous region of North China.

Active soil substances, which can indicate environmental changes sensitively, have the fastest turnover rate. Vegetation diversity and soil bio-physicochemical properties according to five elevations classes (800 m, 1000 m, 1100 m, 1200 m, and 1500 m a.s.l.) in the Southern Taihang Mountain were investigated. Soil ammonium-N (NH4+—N), nitrate-N (NO3−—N), microbial biomass carbon (MBC), and nitrogen (MBN), as well as soil urease (URE) and sucrose (SUC) activities were determined. The results showed that elevation gradients, soil layers, and their interaction had significant effects on most of the active soil substances. With the rise of elevation, soil NO3−—N, inorganic N, MBC, and MBN contents, as well as SUC activity and SUC/MBC ratio basically showed an inverted V-shaped distribution trend and reached the peak value at 1100 m (p < 0.05). Soil URE showed a fluctuating upward trend and reached the peak value at 1500 m (p < 0.05), and the URE/MBC ratio showed a straight upward trend. With the depth of soil layer, the contents of active soil substances tended to decrease, showing a phenomenon of surface aggregation. Active soil substances were correlated with plant community diversity indexes, soil water content, pH, available N, and available phosphorus contents, and available N was the main factor affecting active soil substances, which could explain 34.4% of the variation. In summary, at the intermediate slope of 1100 m, soil moisture and tightness were suitable for soil microbial activity and plant growth, the highest contents of active soil substances, indicating a fast turnover of soil carbon and nitrogen. The present study enriched our understanding of soil carbon and nitrogen turnover mechanisms in the mountain ecosystem.