Responses of arbuscular mycorrhizal fungi to nitrogen addition: a meta-analysis

Arbuscular mycorrhizal (AM) fungi play many important roles in terrestrial ecosystems. The effects of increasing nitrogen (N) deposition on AM fungi will inevitably affect many important ecosystem processes. However, our quantitative understanding on the generalizable patterns of how N deposition affects AM fungi at the global scale remains unclear.

We conducted a meta-analysis of 431 observations from 111 publications to investigate the responses of AM fungi to N addition, including abundance, richness and diversity, and explored the mechanisms of N addition affecting AM fungi by trait-based guilds method.

Results showed that N addition had strong negative effects on AM fungal abundance and richness, and different AM fungal guilds showed different responses to N addition: the rhizophilic guild significantly decreased under N addition, while the edaphophilic guild increased (but with much variability) under N addition. Further analysis showed that N addition affects AM fungi mainly by causing soil acidification and increasing soil available N. Specifically, soil acidification had a negative effect on both the rhizophilic and edaphophilic AM fungi and increased soil available N mainly negatively affect the edaphophilic AM fungi. Moreover, the response of AM fungi to N addition was also affected by the shifts in plant carbon (C) allocation caused by soil phosphorus (P) availability.

This synthesis highlights that trait-based AM fungal guilds as well as taking soil P and C from host plants into consideration can improve our understanding of dynamics of AM fungal communities under increasing N deposition. This would further enable better predictions of the functional consequences of changes in AM fungal communities such as impacts on soil organic C dynamics, plant P uptake and plant diversity.