Intraradical and extraradical communities of AM fungi associated with alfalfa respond differently to long-term phosphorus fertilization.

• P addition significantly decreased AM fungal colonization rates at high soil P level. • The effects of P addition on intraradical and extraradical AM fungal communities are different. • P addition has significant effects on AM fungal community in roots but not in soil. • pH and soil organic matter structured roots and soil mycorrhizal communities, respectively. To investigate the responses of alfalfa root-/ soil-associated arbuscular mycorrhizal (AM) fungal communities to phosphorus (P) addition, we examined the intraradical and extraradical mycorrhizal communities in an alfalfa (Medicago sativa) field being fertilized with four levels of P for 9 years. We found that AM fungal colonization declined significantly at the highest P level and was negatively related to soil available phosphorus, suggesting a decreased reliance on AM fungi at this high P level. A total of 22 operational taxonomic units (OTUs) from three families were detected in roots and 25 in soil. Both AM fungal OTU richness and diversity in soil were higher than that in roots. The AM fungal diversity in roots declined significantly when P was the highest. The indicator species in roots increased in relative abundance in the P1 treatment (75 kg P 2 O 5 ha−1 a−1). Although P addition had no significant effect on OTU richness or AM fungal community composition in soil, we found that pH and soil organic matter structured roots and soil mycorrhizal communities, respectively. In conclusion, P addition affected root and soil AM fungal communities differently. Further research is needed to determine how individual AM fungal species may respond to P fertilization, and how this may impact plant productivity. [ABSTRACT FROM AUTHOR]