Relationship between soil nutrient properties and biological activities along a restoration chronosequence of Pinus tabulaeformis plantation forests in the Ziwuling Mountains, China.

The goal of this study was to determine the dynamics of physicochemical properties and biological activities of soil, and their relationship following afforestation. Soil samples were collected at 0–10 cm from five Pinus tabulaeformis plantation forests restored for 15, 25, 30, 45, and 70 years, as well as a millet ( Setaria italica ) farmland in the Damaiji catchment area. These five afforested lands were converted from similar farmlands. The activities of catalase (CAT), saccharase (SAC), urease (URE) and alkaline phosphatase (ALP), microbial biomass, soil water content, pH, soil bulk density, soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen, nitrate nitrogen, total phosphorus (TP), and available phosphorus (AP) were measured. The results revealed that the contents of SOC, TN, AP, microbial biomass C, N, and P, CAT, SAC, URE, and ALP in the P . tabulaeformis forest soil were significantly higher than those in the farmland by 64.97%–262.02%, 75.44%–254.28%, 46.63%–114.21%, 125.95%–554.83%, 101.35%–464.21%, 15.80%–167.35%, 22.57%–49.95%, 96.78%–145.73%, 6.98%–56.08% and 89.15%–177.89%, respectively. The soil properties, microbial biomass, enzymatic activities, and C:P and N:P ratios in soil and microbial biomass improved with increasing plantation chronosequence. Variations in C:N:P stoichiometry and higher C:P and N:P ratios in the soil and microbial biomass revealed the P limitation. Simultaneously, N:P ratios included more serviceable information that reflected the relationship between soil and microbes. Soil enzymatic activities had a high correlation with soil nutrient cycling and could be indicators of soil fertility status, particularly for ALP. The significant correlation between SOC, TN, enzymatic activities, and microbial biomass revealed that the substrate availability of carbon and nitrogen could influence the activity of soil enzymes and microorganisms. This study demonstrated that soil enzymatic activities and microorganisms respond to the process of afforestation and hence have the potential to affect nutrient balance and quality of soil. [ABSTRACT FROM AUTHOR]