Interactive impacts of earthworms (Eisenia fetida) and arbuscular mycorrhizal fungi (Funneliformis mosseae) on the bioavailability of calcium phosphates

The positive interactive impacts of arbuscular mycorrhizal fungi (Funneliformis mosseae) and earthworms (Eisenia fetida) on increasing calcium phosphate availability, AM hyphal contribution to maize (Zea mays L.) P uptake and utilization efficiency of calcium phosphate-P by maize were studied in the Organization for Economic Co-operation and Development (OECD) artificial soil (non-phosphorus active soil). Treatments included maize plants inoculated vs. not inoculated with AM fungi and treated with or without earthworms. Root colonization, maize shoot and root biomass, shoot and root N, P, K contents, soil available P, soil microbial biomass P, available P, and the Shannon-Wiener index (H) for the bacterial communities from T-RFLP profiles were measured at harvest. The results indicated that mycorrhizal colonization increased markedly in maize inoculated with AM fungi, which was further enhanced by the addition of earthworms. Earthworms decreased the soil pH and increased available soil P and soil microbial biomass P, as well as the abundance of Flavobacteriaceae and Betaproteobacteria. The addition of AM fungi to soils promoted soil bacterial diversity and soil microbial biomass P. The earthworm and AM fungi interaction increased maize shoot and root N, P, and K contents and shoot and root biomass, as well as enhanced the microbial biomass P and utilization efficiency of calcium phosphate-P (Ca-P), leading to greater nutrient uptake and AM hyphal contribution to plant P uptake. Earthworms and AM fungi could interactively promote maize to absorb the free phosphate ions released from calcium phosphate.