Microbial regulation of net N mineralisation is driven by C, N, P content and stoichiometry

Soil net nitrogen mineralisation (Nt) is crucial for nitrogen availability and ecosystem productivity. However, the patterns and drivers of Nt remain unclear under different management practices. We examined the biotic and abiotic determinants of Nt, using 11 treatments in Northern China fluvo-aquic soil under wheat-maize rotation. Biotic properties, for example, soil microbial community, were determined based on phospholipid fatty acid (PLFA) together with high-throughput sequencing technologies. Abiotic properties were characterised by the content and stoichiometric ratios of soil nutrients. Animal manure applications (HNM, NM, M, FM) significantly increased the Nt (1.80-3.40 mg kg(-1)) and available phosphorus (Olsen-P) (46.3-199.3 mg kg(-1)), compared with treatments with plant residues (NG, NS) incorporation. Fallow with animal manure (FM) had the highest Gram-negative bacteria (G-, 29.3 nmol g(-1)), arbuscular mycorrhizal fungi (AMF, 4.57 nmol g(-1)) abundance, which was also significantly higher than that of the NG and NS. Structural Equation Modelling revealed that the content of total nutrient, including soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) rather than biotic properties, such as microbial community (lambda = -0.26) and enzyme activities (lambda = -0.16), had the strongest direct effect on Nt (lambda = 0.85). Stoichiometric ratios of C, N, and P controlled Nt indirectly by mediating enzyme activities. Specifically, high Nt was associated with low Dothideomycetes, Tectomicrobia abundance that negatively correlated with SOC, TN, TP, Olsen-P, and BG activity. Random forest model indicated that SOC and Olsen-P contents were top-rated determinants of Nt. Our result indicated that the content and stoichiometric ratios of SOC and N, P directly drive Nt or via microbial ways. Our study highlighted the importance of P to improve Nt: animal manure was thus recommended for nitrogen availability. Highlights Animal manure significantly enhanced Nt rather than plant residue incorporation Nt is negatively correlated with the AN:Olsen-P ratio and Dothideomycetes abundance Stoichiometric ratios of nutrients associated with enzymes activities regulate Nt SOC and Olsen-P affected Nt as key factors under N enrichment conditions