Responses of soil heterotrophic respiration to changes in soil temperature and moisture in a Stipa krylovii grassland in Nei Mongol

Aims Due to concurrent variations of multiple factors influencing soil heterotrophic respiration (Rh), it is difficult to determine the responses of Rh to changes in individual factors and their interactive effects under field conditions. In this study, we conducted a laboratory incubation experiment with controlled temperature and water levels to determine the responses of Rh to changes in soil temperature and moisture using soil samples collected from an Stipa krylovii (Stipa sareptana var. krylovii) grassland in Nei Mongol.
Methods The incubation experiment consisted of five temperature treatments (9, 14, 22, 30, and 40 °C) and five water treatments (20%, 40%, 60%, 80%, and 100% of water holding capacity (WHC)), with a full factorial arrangement. We measured Rh at an interval varying from every two days to once a week, and soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) at an 18-day interval during the 71 days of incubation period.
Important findings The results showed that Rh differed significantly among different temperature treatments (p < 0.001) and was positively related to temperature (p = 0.001); the temperature sensitivity of Rh (Q₁₀) also increased with increasing moisture level. The relationship between Rh and water was best fitted using quadratic equations, and the optimal moisture condition increased when temperature rose. There existed significant interactions between soil temperature and moisture (p < 0.001) and their interactions could be best fitted using the function lnRh = 0.914 + 0.098T + 0.046M + 0.001TM - 0.002T² - 0.001M², it suggested that the models in additive form could explain the Rh response better than those in multiple form. Our results also showed that the relationship between Rh and MBC varied during incubation, and DOC was not significantly related to Rh (except for the 20th incubation day), suggesting that microbial turnover and community transformation could lead to the changes of gross microbial activity.