Characteristics of Forest Soil Enzyme Activities, Nutrient Restriction, and Physicochemical Properties at Different Altitudes and Their Seasonal Dynamics

Soil enzyme not only participates in soil nutrient cycling but affects soil structure. However, the response mechanism of soil enzyme to soil nutrient restriction and aeration at different altitudes is poorly understood. Therefore, In March, June, September, and December 2022, we determined and analyzed the forest soil at 1800, 2100, 2400, and 2700 m altitude in Liziping National Nature Reserve of Sichuan Province, China, and Mantel and Person correlation analyses were employed to analyze the relationship of soil physicochemical properties, CP : NCP and ecological stoichiometric ratios with soil enzyme activities on a seasonal scale. The data showed that the vertical distribution characteristic among soil enzyme activities along the soil layer at different altitudes was similar in each season, and the altitude, season, and their interaction had important effects on forest soil enzyme activities at different altitudes. With the altitude increasing, soil urease, sucrose, acid phosphatase, and catalase showed different variation trends in each season, season, and their interaction caused obvious differences in soil stoichiometric ratios. soil CP : NCP ratio varied with altitude was 1800 > 2100 > 2400 > 2700 m. In addition, the average values of soil C : N, C : P, and N : P ratio in a year were 29.26, 109.29, and 4.52, respectively. The soil CP : NCP ratio was the dominant factor of soil acid phosphatase in March and December (P < 0.01), soil CP : NCP ratio was the dominant factor of soil catalase in September, and soil C : P and CP : NCP ratios were the dominant factors of soil acid phosphatase in June. Furthermore, Soil bulk density and soil moisture content extremely significantly influenced soil urease, sucrase, and acid phosphatase in each season (P < 0.01), and soil noncapillary porosity had a significant effect on soil acid phosphatase in March, June, and December (P < 0.05). The entropy-weighted TOPSIS method obtained that soil enzyme activities, soil physicochemical properties, and CP : NCP-stoichiometric ratios were the worst at 2400 m and in March. This study provides theoretical support for enzyme activities and nutrient restriction characteristics and the driving factors of forest soil enzyme activities in forest soil at different altitudes in this nature reserve and also provides a basis for monitoring and management in this nature reserve in time and space.