## 2 Materials and Methods
### Measurement of Soil Enzyme Activities  
(1) Catalase: titration with potassium permanganate [19; 22]. A 2 g air-dried soil sample sieved through 1 mm was weighed and placed in a 100 mL triangular flask and filled with 40 mL of distilled water and 5 mL of 0.3% H\({}_{2}\)O\({}_{2}\) solution. The triangular flask was placed on a round-trip oscillator at 120 r min\({}^{-1}\) for 20 min, and then 5 mL of 3 mol L\({}^{-1}\) sulfuric acid was added immediately to stabilize the undecomposed hydrogen peroxide, and then the suspension in the flask was filtered through a quantitative filter paper. A total of 25 mL of the filtrate was aspirated and titrated with 0.1 mol L\({}^{-1}\) KMnO\({}_{4}\) to a pale pink endpoint. (2) Urease: indophenol blue colorimetric method [19; 22]. A total of 5 g of air-dried soil sample sieved through a 1 mm sieve was weighted and placed in a 50 mL volumetric flask. From there, 1 mL of toluene was added to the volumetric flask (for as long as it could completely wet the soil sample) and it was left for 15 min; then, 10 mL of 10% urea solution and 20 mL of citric acid buffer (pH \(\approx\) 6.7) were added, and the result was mixed carefully and shaken well. The volumetric flask was then placed in a thermostat at 37 \({}^{\circ}\)C and incubated for 24 h. At the end of the incubation period, the suspension was diluted with purified water heated to 37 \({}^{\circ}\)C, shaken carefully, and then filtered through a triangular flask using quantitative filter paper. A total of 3 mL of filtrate was pipetted into a 50 mLvolumetric flask, 10 mL of distilled water was added, it was shaken well, then 4 mL of sodium phenol was added; this was then mixed carefully, before adding 3 mL of sodium hypochlorite, shaking well, leaving to stand for 20 min, diluting with water to scale, and then the solution showed the blue color of indophenol. The color-developed solution was colorimetrically determined at 578 nm within 1 h using a spectrophotometer. (3) Phosphatase: disodium phosphate colorimetric method [19; 22]. Using 5% disodium phosphate as the hydrolysis substrate, 1 g of air-dried soil sample was put into a 50 mL conical flask, toluene was used to pretreat the soil, 20 mL of 0.5% disodium phosphate was added, and the sample was filtered at 37 \({}^{\circ}\)C for 24 h in the incubator. A total of 1 mL of the filtrate was taken into a 50 mL colorimetric tube, and 5 mL of borate buffer, 0.5 mL of 8% potassium ferricyanide, and 0.5 mL of 2% 4-aminoamino aminostilbene were added to it. Then, it was shaken well, the color development was fixed for 25 min, and the absorbance value was measured at 510 nm with a spectrophotometer. The control group was treated with distilled water instead of substrate, and 3 groups of parallel samples were set up. The results were expressed as the mass of phenol produced by 1 g of soil incubated at 37 \({}^{\circ}\)C for 1 h.  
(4) Measurement of soil extracellular enzyme activity: BG, NAG, and sucrose activities were determined by fluorescence assay using 96 microtiter enzyme labeling plates [19; 22]. A total of 2.75 g of fresh soil sample was weighed in a triangular vial, 91 mL of buffer (pH adjusted according to the measured soil samples) was added, and then it was shaken on a shaker at 200 r min\({}^{-1}\) for 30 min. A total of 250 uL of fluorescently labeled C, N, and P substrate solution at a concentration of 200 umol L\({}^{-1}\) was inoculated into a deep-well plate as a substrate plate. We then inoculate 250 uL of 4-methylumbelliferone at different concentrations into the deep-well plate as a marker plate, and pipette 800 uL of soil suspension into a 96-well plate, seal the deep-well plate with self-adhesive sealing film after all the samples have been added, and invert the deep-well plate repeatedly to shake and mix. The plates were incubated in an incubator at 25 \({}^{\circ}\)C for 4 h. After incubation, the plates were centrifuged at 4 \({}^{\circ}\)C for 3 min at 4800 r min\({}^{-1}\) and 200 uL of supernatant was aspirated.