Soil Nutrient and Enzyme Analysis

To determine soil physical and chemical properties, we ground the air-dried soil samples and passed them through a 2.0 mm sieve before assessing their soil nutrient content. Soil pH was measured at a water: soil ratio of 1: 2.5. The total nitrogen (TN) was determined using the Kjeldahl method by an automatic Kjeldahl analyzer K1100F device (Jinan Hannong Instrument Company, Jinan, China; Wang et al., 2020 (link)). Soil organic matter (SOM), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and available potassium (AK) were determined according to the method described by Zhao M. et al. (2014) (link) and Wang et al. (2021) (link). Soil urease (S-UE), soil alkaline phosphatase (S-ALP), soil sucrase (S-SC), soil catalase (S-CAT), and soil polyphenol oxidase (S-PPO) activities were determined using Solarbio soil urease kit (Solarbio, BC0120), soil alkaline phosphatase kit (Solarbio, BC0280), soil sucrase kit (Solarbio, BC0240), soil catalase kit (Solarbio, BC0100) and soil polyphenol oxidase kit (Solarbio, BC0110). The above soil enzyme kits are manufactured by Solarbio (Beijing Solarbio Science & Technology Co., Ltd., Beijing, China). The specific methods and measurement procedures were carried out according to the instructions in the manual.