Soil N2O emissions are more sensitive to phosphorus addition and plant presence than to nitrogen addition and arbuscular mycorrhizal fungal inoculation

Although phosphorus (P) addition and arbuscular mycorrhizal fungal (AMF) colonization have potential for mitigating soil N2O emission, the effects and mechanisms remain unresolved. We conducted a pot experiment with ryegrass (Lolium perenne) growing in a growth chamber for 80 days with three factors: Plant and AMF presence (unplanted, with plants, with plants colonized by AMF), two nitrogen (N) addition levels (0 and 50 mg N kg−1 soil) and two P addition levels (0 and 20 mg P kg−1 soil). Our results showed that N addition and AMF colonization had insignificant effects on soil N2O emission. However, the presence of plants decreased soil N2O emission by 90%–99% (planted vs. unplanted) under P addition. Moreover, P addition increased (+134%) N2O emission from unplanted soil, but decreased (74%–98%) it from planted soil. Further analysis showed that soil N2O emission was controlled by soil available P, soil NO3−-N, plant biomass P and N across all treatments. The lower N2O emissions from planted soils were mainly due to the lower soil NO3−-N content which might be immobilized by plant biomass, while the higher N2O emissions from unplanted soils under P addition were attributed to the increased soil available P content. Furthermore, we found an antagonistic effect between AMF inoculation and P addition on soil N2O emission because sufficient soil P may inhibit AMF colonization and activity. Taken together, we conclude that plant presence combined with P addition can effectively reduce N2O emission from P-limited soils.