Soil types differ in the temporal response of the priming effect to nitrogen addition: a study on microbial mechanisms

Understanding how nitrogen (N) fertilisation influences the priming effect (PE) in soils is imperative to predict the carbon loss and subsequent impact on climate. Three contrasting soil types with low mineral N, Vertosol, Calcarosol, and Chromosol, were treated for 4 weeks with the single supplement of N ranging from 0 to 300 mg kg −1 and weekly addition of 13 C-glucose. Nitrogen addition did not affect the PE in the clay Vertosol. In contrast, the addition of N to the sandy loam Calcarosol above 10 mg N kg −1 suppressed the PE by 14% in week 1, but increased by 20% at 120 mg N kg −1 in week 4. In the silty loam Chromosol, the addition of 40 and 120 mg N kg −1 increased the PE by 78% in week 4. Nitrogen addition increased the abundance of functional genes for decomposing chitin and recalcitrant phenolic compounds particularly in the Calcarosol which had a high proportion of recalcitrant soil C; the predicted pathways for the degradation of microbial necromass and recalcitrant compounds were also positively related to the PE in this soil. These functions concurred with an increase in the abundance of resource-acquisition strategists such as Microbacteriaceae , Lysobacter , and Sphingomonadaceae over time and under N addition. In the Chromosol rich in labile C, the PE was positively correlated with the predicted pathways for the microbial biosynthesis of diverse metabolites and compounds for growth and enzyme production, corresponding to the rise of Micrococcaceae (high-yield strategists) under N addition. In the Vertosol, although the abundances of C-relevant functional genes were stimulated by N addition, the greater clay content might protect the soil organic C from being further primed. Overall, N-induced alternation of PE is likely dependent of the microbial metabolisation on soil organic C sources which vary among soils, but this N effect may be defective under soil physical protection.