Objective  The Spen Pleurotus ostreatus mushroom substrate could be utilized as a plant growth substrate and soil improvement agent, and its application could affect soil enzyme activities and greenhouse gas emissions which are also adjusted by the soil moisture. This study aimed to reveal the effects of spent mushroom substrate on soil enzyme activities and greenhouse gas emissions under different soil water holding capacities and to clarify the comprehensive relationship among spent mushroom substrate application dosage, greenhouse gas emissions, and soil enzyme activities.

  Method  The spent mushroom substrate was applied to the soil under different soil moisture contents, and the β-glucosidase, urease and chitinase actives and CO_2, N₂O and CH₄ emissions were also quantified. The application rates of spent mushroom substrates were 0.0%, 2.5%, 5.0%, 10.0%, respectively, and soil moistures were 60% WHC, 75% WHC, and 90% WHC, respectively.

  Result  The result showed that urease, β-glucosidase, and chitinase activities were positively correlated with the application rates of the spent mushroom substrate. Under the condition of 10% spent mushroom substrate application, the highest enzyme activity was observed, but there was no significant differences among different water holding capacities. There was a positive correlation between the amount of CO₂ emission and the amount of spent mushroom substrates. The highest amount of CO₂ emission was observed following 10% spent mushroom substrate application. The N₂O emission was positively correlated with soil moisture when the spent mushroom substrate was applied at 0.0% and 2.5%. Meanwhile, the N₂O emission was negatively correlated with spent mushroom substrate application at 90% WHC. There was no significant difference in CH₄ emission among the treatments with different spent mushroom substrate applications. The soil enzyme activities were significant positively correlated with the CO₂ average emission. A significant negative correlation between the soil enzyme activities and N₂O average emissions were observed.

  Conclusion  Applications of the spent mushroom substrate will present a double-edged sword effect. Although the applications of the spent mushroom substrate could improve soil enzyme activities, but they could increase global warming potential. The application rate of 2.5% was an optimal application rate of returning to the filed. The results of this study could provide technical support for improving soil enzyme activities and controlling greenhouse gas emissions with spent mushroom substrate. The current study also provided theoretical support for resource utilization of mushroom residue, which would promote the sustainable development of the mushroom industry.