Live roots can stimulate microbial soil organic matter (SOM) decomposition and nutrient cycling, which is termed as the rhizosphere priming effect (RPE). Compared to nitrogen (N) availability, fewer studies have focused on the effect of phosphorus (P) availability on the RPE. Here we investigated the RPEs of ryegrass (Lolium perenne) and clover (Trifolium repens) with and without P fertilization (4 g P m⁻²) at three sampling times (Day 30, Day 44, and Day 58 after planting). A continuous ¹³C–CO₂ labeling method was used to separate soil-derived CO₂ from root-derived CO₂. A nutrient budget method was applied to evaluate the rhizosphere effect on net soil N and P release for plant uptake. We found that ryegrass and clover induced positive RPEs in most plant-soil combinations, ranging from −1% to 134%. Ryegrass exhibited a larger RPE than clover by Day 30, but clover exhibited a larger RPE than ryegrass by Day 44 and Day 58, possibly due to larger shoot biomass regrowth rates, root activity, and rhizodeposition during the later stages. P fertilization significantly decreased the RPE of ryegrass by Day 44 and Day 58, but did not change the RPE of ryegrass by Day 30 and clover at all three sampling times. The reduced RPE of ryegrass with P fertilization was associated with increased microbial biomass N, more root-derived microbial C, and less shoot biomass and root-derived CO₂. These findings suggest that P fertilization coupled with C supply from root exudates induced more microbial N immobilization, which reduced the RPE of ryegrass during later stages when soil N limitation negatively impacted plant growth. However, P-induced microbial N immobilization did not affect clover as much because its biological N fixation, on average 37% of total plant N, may have alleviated soil N limitation. We further observed significant positive relationships between excess net soil N and P release and the RPE by Day 58 across all planted treatments, indicating that soil N and P release by plants can be directly linked to rhizosphere C mineralization. Overall, our results demonstrate the importance of C–N–P interactions for understanding the RPE, which have significant implications for P cycling in plant-soil systems.

活根可以刺激微生物土壤有机质（SOM）分解和养分循环，这被称为根际启动作用（RPE）。与氮（N）的可用性相比，很少有研究集中在磷（P）的可用性对RPE的影响上。在这里，我们在三个采样时间（种植后第30天，第44天和第58天）研究了有无磷肥（4 g P m ^-2）的黑麦草（黑麦草）和三叶草（三叶草）的RPE。连续的¹³ C–CO ₂标记方法用于将土壤来源的CO ₂与根来源的CO _2分离。应用营养预算法评估根际对植物吸收氮和磷净释放的影响。我们发现，在大多数植物-土壤组合中，黑麦草和三叶草会诱导阳性RPE，范围为-1％至134％。在第30天，黑麦草的RPE比三叶草大，但在第44天和第58天，三叶草的RPE比黑麦草大。施肥到第44天和第58天均显着降低了黑麦草的RPE，但在所有三个采样时间均未改变第30天和三叶草的黑麦草的RPE。P施肥使黑麦草的RPE降低与微生物量氮增加，根系微生物C增加，芽生物量和根系CO _{2减少有关}。这些发现表明，磷肥和根系分泌物的碳供应诱导了更多的微生物氮固定化，这在后期土壤氮限制对植物生长产生负面影响的过程中降低了黑麦草的RPE。然而，磷诱导的微生物氮固定化对三叶草的影响不大，因为其生物固氮（平均占植物总氮的37％）可能减轻了土壤氮的限制。我们还观察到，在所有种植处理中，到第58天，土壤净氮和磷的过量释放与RPE之间都存在显着的正相关关系，这表明植物释放的土壤氮和磷可以直接与根际C的矿化作用相关。总体而言，我们的结果证明了C–N–P相互作用对于理解RPE的重要性，这对植物-土壤系统中的P循环具有重要意义。