Shift of microbial turnover time and metabolic efficiency strongly regulates rhizosphere priming effect under nitrogen fertilization in paddy soil

Microbial turnover and the decomposition of soil organic matter can be stimulated by living roots in a phenomenon known as the rhizosphere priming effect (RPE). Both the microbial turnover time (MTT) and metabolic efficiency are closely related to RPE. However, changes in MTT, metabolic efficiency and RPE in response to nitrogen (N) fertilization at different levels and the associations between these factors during plant growth are unknown. The effects of N fertilization at different levels (0, 150 and 300 kg N ha −1 ) on RPE and the underlying mechanisms were investigated in maize ( Zea mays L.) grown in paddy soil using a 13 Carbon (C) natural abundance method. The RPE varied from −1.49 to 15.93 mg C kg −1 soil day −1, with significant effects at different levels of N fertilization, growth stages and interactions between these factors. Nitrogen fertilization reduced microbial C:N imbalance and soil pH. During the plant growth periods, the RPE was initially low because the microbes preferentially utilized plant-derived C, but later increased due to trade-offs between microbial N acquisition and acidity stress alleviation under N fertilization. The soil microbes altered their MTT and metabolic efficiency with changes in the microbial community structure to maintain stoichiometric homeostasis and adapt to acidity stress. RPE was lowest whereas MTT and metabolic efficiency were highest with N fertilization at 150 kg N ha −1. Changes in MTT and metabolic efficiency explained 84.5% of the variations in the RPE, and the latter had greater impact (55.8%) than the former (28.7%). Changes in MTT and metabolic efficiency to cope with microbial resource acquisition and acidity stress under N fertilization represent an important pathway for RPE regulation in paddy soil. These findings highlight the significance of MTT and metabolic efficiency in RPE regulation for optimization of the N fertilization level to mitigate soil C losses.