Soil nitrogen (N) availability is determined by microbial gross N mineralisation (GNM) and immobilisation, where net N mineralisation (NNM) represents their balance. Plants provide a substantial amount of their photosynthesized C belowground into the soil as rhizodeposition, which can stimulate microbial activity affecting GNM and NNM, but this activity also depends on soil N and phosphorus (P) availability. We examined how N (25 and 100 kg N ha⁻¹ or 44 and 177 mg N pot⁻¹) and P (10 and 40 kg P ha⁻¹, or 18 and 71 mg P pot⁻¹) fertilisation affected microbial N mineralisation in soil planted with two wheat genotypes (Suntop and 249) varying in root biomass and rhizodeposition. We used a continuous ¹³CO₂ labelling method to track plant C rhizodeposition and a ¹⁵N pool dilution technique to investigate GNM. We further assessed NNM by comparing N pools in plant and soil at the start and end of the experiment. We observed increased GNM with increased P fertilisation, likely because of P-induced N limitation stimulating microbial mining for N, particularly at the low level of N fertilisation. N fertilisation did not affect GNM but the higher level of N fertilisation reduced NNM, likely because of increased microbial immobilisation of fertiliser N. Our results suggest that GNM was more sensitive to soil N and P availability than to rhizodeposition between wheat genotypes, although at high N fertilisation, rhizodeposition contributed to reduced NNM, likely because rhizodeposition enhanced microbial N immobilisation. We conclude that the relative availability of N and P in soil should be considered for managing GNM and NNM in soil.

土壤氮 (N) 可用性由微生物总氮矿化 (GNM) 和固定化决定，其中净氮矿化 (NNM) 代表它们的平衡。植物在地下将大量光合作用碳以根际沉积的形式提供到土壤中，这可以刺激影响 GNM 和 NNM 的微生物活动，但这种活动也取决于土壤 N 和磷 (P) 的有效性。我们研究了施肥N（25 和 100 kg N ha ^-1或 44 和 177 mg N pot ^-1）和 P（10 和 40 kg P ha ^-1或 18 和 71 mg P pot ^-1）如何影响微生物 N 矿化在种植了两种小麦基因型（Suntop 和 249）的土壤中，根系生物量和根系沉积不同。我们使用了连续的¹³ CO₂标记方法跟踪植物 C 根际沉积和¹⁵研究 GNM 的 N 池稀释技术。我们通过在实验开始和结束时比较植物和土壤中的氮库来进一步评估 NNM。我们观察到随着 P 施肥的增加，GNM 增加，这可能是因为 P 诱导的 N 限制刺激了微生物对 N 的挖掘，特别是在低水平的 N 施肥下。施氮不影响 GNM，但较高的施氮水平会降低 NNM，这可能是因为肥料 N 的微生物固定增加了。 N 施肥、根际沉积有助于减少 NNM，可能是因为根际沉积增强了微生物 N 的固定。