Impact of agricultural management on arbuscular mycorrhizal fungal communities in Kenyan ferralsol

Arbuscular mycorrhizal fungi (AMF) represent a functionally important component of soil microbial community, being of particular significance for plant mineral nutrition in tropical agroecosystems. The effects of crop rotation of maize (Zea mays L.) with crotalaria (Crotalaria grahamiana Wight & Arn.) versus continuous maize and phosphorus (P) fertilization on AMF spore community composition and diversity were studied in a long term field experiment in western Kenya. The spores were isolated from the soil, identified according to their morphologies, and enumerated. Trap pots using soil from the maize-crotalaria rotation were sown with four different plant species, sunflower (Helianthus annuus (L.) Merill.), leek (Allium porrum L.), maize, and crotalaria. The spores isolated from the traps were identified according to their morphology and by sequencing of their large ribosomal subunits (LSU). Ten AMF species were isolated from the field soil and 16 species from the traps. Altogether, 18 species were recorded in the field site. The spore communities in the field soil were dominated by Scutellospora and Acaulospora species. The species diversity of AMF spores in the soil was affected neither by crop rotation nor by P fertilization. However, the composition (relative species abundances) of AMF spore communities was significantly affected by crop rotation. The abundance of Acaulospora scrobiculata and Scutellospora verrucosa spores was significantly higher in soil under maize-crotalaria rotation than under continuous maize. Both the composition and diversity of spore communities, as well as spore densities in the traps were strongly affected by species identity of the host plant, whereas the P fertilization history of the soil only affected diversity of the spore communities. Functional consequences of changing composition of AMF communities through agricultural management practices are discussed.