Kinetic and Thermodynamic Characteristics of Soil Enzymes in Pure and Mixed Forest Samples on the Loess Plateau of China

Background

Soil enzymes are key to predicting nutrient availability and forest fertility.

Aims

We aimed to evaluate the influence of forest type on the kinetic and thermodynamic characteristics of soil enzymes.

Methods

Soils were sampled at 0–10 and 10–20 cm depth from two pure forests (Pinus tabulaeformis [PTF] and Quercus acutissima [QAF]) and a mixed forest of PTF and QAF (MF) on the Chinese Loess Plateau. Kinetic parameters (maximum enzyme activity [V_max], half-saturation constant [K_m], and enzyme efficiency [K_cat]) and thermodynamic parameters (temperature coefficient [Q₁₀] and activation energy [E_a]) of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), l-leucine aminopeptidase (LAP), and alkaline phosphatase (AP) were determined.

Results

Forest type exerted significant influence on soil enzyme kinetic parameters. The V_max and K_cat values of BG, NAG, and AP in PTF of 0–10 cm soil depth were 42.54% and 59.22%, 77.18% and 23.08%, and 62.82% and 58.21% higher than that in MF, respectively. The V_max of AP and K_cat of NAG in PTF of 10–20 cm depth were 34.61% and 39.90% higher than that in MF. The soil enzyme thermodynamic parameters were significantly influenced by forest type and soil depth. At 0–10 cm depth, low values of Q₁₀–V_max and Q₁₀–K_m of BG, Q₁₀–V_max and Q₁₀–K_cat of NAG, and E_a of BG and NAG were found in PTF. At 10–20 cm depth, low values of Q₁₀–V_max, Q₁₀–K_cat, and E_a of BG and NAG were found in MF.

Conclusions

PTF was more effective in promoting soil enzymatic reactions, especially in surface soil. MF improved subsoil enzyme thermal stability and reduced temperature sensitivity. The study showed that pure and mixed forests affect soil enzyme characteristics differently, with soil depth as a key factor.