The effects of living roots and arbuscular mycorrhiza fungi (AMF) on soil N2O emissions

Living roots and arbuscular mycorrhiza fungi (AMF) are widespread in most terrestrial ecosystems and play an important role in ecosystem nitrogen (N) cycling. However, the influence of living roots and AMF on soil N₂O emissions remains poorly understood. In this study, we conducted a pot experiment with ryegrass (Lolium perenne) growing in a greenhouse for three months with three factors: root and AMF presence (None or unplanted, Root or with roots, and Root+AMF or with roots colonized by AMF), two N addition levels (N0 and N1 with 0 and 50 mg N kg^-1 soil) and two P addition levels (P0 and P1, with 0 and 20 mg P kg^-1 soil).

 

Our results showed that N addition didn’t have significant effect on N₂O emission, however, we detected significant effects of Root and Root+AMF, particularly under P addition. Though the colonization of AMF didn’t significantly influence N₂O emission, the presence of roots (Root and AMF+Root treatments) deceased N₂O emission by 58%-67% compared with the None treatment. P addition increased (+134%) N₂O emission from unplanted soil but decreased (74%-98%) N₂O emission under planted soil regardless of AMF colonization. Moreover, there were no significant relationship between N₂O emission and soil pH, NH₄⁺-N and net N mineralization. The lower N₂O emission from rooted treatments were mainly due to the lower soil NO₃^--N (and MBN) content which might be immobilized by plant biomass, while the higher N₂O emission from unplanted soil under P addition was attributed to increased soil available (r=0.760, P<0.01) and total (r=0.654, P<0.01) phosphorus content. We conclude that root presence and P addition played an important role in regulating N₂O emission from P-limited soils.