Gross NO Production Process, Not Consumption, Determines the Temperature Sensitivity of Net NO Emission in Arable Soil Subject to Different Long-Term Fertilization Practices.

Chronic amendment of agricultural soil with synthetic nitrogen fertilization and/or livestock manure has been demonstrated to enhance the feedback intensity of net NO emission to temperature variation (i.e., temperature sensitivity, TS). Yet few studies have explored the relevance of changes in underlying gross NO production and consumption processes toward explaining this phenomenon, in particular for the latter. Furthermore, the microbe-based mechanisms associated with the variation of NO consumption process remain largely unexplored. To address this knowledge gap, a temperature- (15, 25, and 35°C) and moisture-controlled (50% water holding capacity) microcosm incubation experiment was established using an arable soil subject to long-term addition of synthetic fertilizer (NPK), a mixture of synthetic fertilizer with livestock manure (MNPK), or with no fertilizer treatment (CT). Over the incubation time period, the CH inhibition method was adopted to monitor reaction rates of gross NO production and consumption; the population sizes and community structures of I- and II-NO reducers were analyzed using quantitative PCR (Q-PCR) and terminal restriction fragment length polymorphism (T-RFLP). The results indicated that only NPK significantly increased the TS of net NO emission, and gross NO consumption process consistently occurred under all treatment combinations (temperature and fertilization) at each sampling time point. The responses of gross NO production and consumption processes to temperature elevation exhibited fertilization- and sampling time-dependent pattern, and the higher net NO production TS in the NPK treatment was underlain by its higher TS of gross production process and insensitivity of gross consumption process to temperature. The size and structure of II-NO reducers, as well as the community structure of I-NO reducers, were positively correlated with variation of gross NO production and consumption rates across all fertilization regimes. II-NO reducer abundance was less responsive to temperature change, and its community structure less susceptible to fertilization, as compared with I-NO reducers. Overall, our results demonstrate that the TS of the gross NO production process, not gross consumption, is the key step regulating the TS of net NO production, and both I- and II-NO clades are likely active NO reducers in the tested soil.