Measurements of ecosystem broad function and specialized function
The basal microbial respiration (mSR) was selected as a broad function in this study, because it widely existed in almost all micro-organisms and had been considered as a proxy of total biological activity without environmental limitation (Campbell et al. 2003; Delgado-Baquerizo et al. 2016a). The mSR was measured by quantifying the carbon dioxide (CO2) from the equivalent dry-weight fresh soil in ideal incubation environment. The details were described in previous studies (Qiao et al. 2014; Zhang et al. 2016).
The specialized functions (i.e. net nitrification rate, NR and potential nitrification rate, PNR) were measured, because they were a key microbial driven process in the N cycle and characterized by the oxidation of ammonia to nitrate via nitrite. Microbes holding the gene encoding ammonia monooxygenase (AMO) are the first and rate-limiting step of nitrification process (Hatzenpichler 2012; Trivedi et al.2019b; Jia et al. 2020). The NR and PNR were measured with the soil samples incubating in field and a standard environment (25 ℃ and 60% of the water saturation holding content) during a 14-day periods, respectively. The NR was calculated as the difference of NO3--N concentrations at the beginning and the end of the incubation periods.