The quality and quantity of exogenous organic carbon input control microbial NO3- immobilization: A meta-analysis

The accumulation of NOT in the soil has resulted in increased nitrogen (N) loss through runoff, leaching, and gaseous emissions. Microbial immobilization of NOT as an important process in reducing soil NOT accumulation has been for a long time neglected due to the predominant viewpoint that microbes preferentially immobilize NHS4+-N. Microbial NOT immobilization is generally carbon (C)-limited, and thus exogenous organic C input may enhance microbial NOT immobilization. However, the effect of the quality and quantity of exogenous organic C input on soil microbial NOT immobilization is poorly understood, and a synthetic assessment on such an effect is lacking. We thus assessed the impact of exogenous organic C type, the application rate of simple organic C (glucose and acetate), complex organic C type (animal manure, plant residue) and the C/N ratio of complex organic C on soil microbial NOT immobilization rate using a meta-analysis. We found that the quality and quantity of exogenous C input affect soil microbial NOT immobilization: microbial NOT immobilization was enhanced with the addition of simple organic C at rates >500 mg C kg(-1), or complex organic C with C/N ratios >18. Furthermore, a positive relationship between the natural log of response ratio of soil microbial NOT and NH4+ immobilization indicates the simultaneous utilization of NHS and NOT under elevated C availability. We conclude that specific exogenous organic C input at a high rate or with a high C/N ratio can enhance microbial NOT immobilization and reduce soil NOT accumulation. (C) 2017 Elsevier Ltd. All rights reserved.