Survival of a commercial AM fungal inoculant and its impact on indigenous AM fungal communities in field soils

Abstract

Arbuscular mycorrhizal fungi (AMF) are being promoted as commercial biofertilizers (bioinoculants) for sustainable agriculture. However, little is known about the survival of AMF inoculants in soil and their impacts on indigenous AMF communities under multiple cropping conditions. A three-year study was conducted at four field-sites across semiarid to subhumid climate zones in the Saskatchewan prairie, Canada. A commercial AMF inoculant containing Rhizophagus irregularis was applied at seeding in the first year of the study in 2011 to the host crop pea (Pisum sativum), grown in open-ended soil cores. The persistence of the inoculant and subsequent phylogenetic changes in the community of the indigenous AMF taxa were assessed for three consecutive cropping seasons (2011–2013), during which wheat (Triticum aestivum) was grown in year two and pea in year three. At harvest of each year, the AMF community was assessed using 18S rRNA gene pyrosequencing of AMF trap roots. A total of 131 AMF OTUs (year 1: 54, year 2: 28, year 3: 49 OTUs, respectively), representing eight genera (Glomus, Funneliformis, Claroideoglomus, Diversispora, Paraglomus, Rhizophagus, Septoglomus, and Archaeospora) was detected. Phylogenetic analysis showed the inoculant could be detected to the end of third cropping season (i.e., 27-month after inoculation) at the Swift Current and Outlook field-sites, but was only detected at the Scott and Melfort field-sites to the end of the first (3-month) and second (15-month) growing seasons, respectively. The commercial inoculant caused alterations (taxa suppression, stimulation, and exclusion) of specific members of the indigenous AMF (abundance and diversity) after the first crop season at Swift Current and after all three seasons at Outlook, Scott, and Melfort sites. Multivariate statistical analysis revealed the survival of the commercial inoculant, and the subsequent changes in the indigenous AMF taxa were dependent on soil environments.