Infectivity and community composition of arbuscular mycorrhizal fungi from different soil depths in intensively managed agricultural ecosystems

Arbuscular mycorrhizal (AM) fungi represent a functionally important component of soil microbial communities. It is critical to achieve an improved understanding of the community structure of the indigenous AM fungi if we are to use this group of fungi either as indicators of ecosystem health or to enhance the sustainability of agricultural systems. In the present study, we assessed the impact of land use and soil depth on the number and community composition of infective AM fungal propagules in high-input agricultural ecosystems. Three different agricultural land use systems with high management intensity were selected, i.e., vegetable greenhouses, arable land, and open vegetable fields. Soil samples were collected from different soil depths (0-30, 30-60, and 60-90 cm) of three replicated (triplicate) land-use types at two sites in north China. The modified mean infection percentage (MIP) method was used to determine the inoculum potential of each soil sample. The community composition of AM fungi was analyzed using PCR, cloning, and sequencing techniques. Land use and soil depth greatly influenced the development of root-associated AM fungi and also edaphic properties. MIPs and species richness were lower in the top (0-30 cm) of soil profile in the vegetable greenhouses than in the nearby open vegetable fields or arable fields. Moreover, AM fungal distribution in the soil profile varied with land use. The MIPs and species richness decreased with increasing soil depth in the arable land and open vegetable fields. By contrast, in the greenhouse vegetable soils, the highest richness was found in the deepest soil depth (60-90 cm). The presence and prevalence of AM fungi also varied with land-use type and soil depth. Of the 13 total phylotypes investigated, Glo 6, Div 1, and Glo 1 accounted for 82.8 % of AM fungal clones analyzed and were present in each land-use type and soil depth. There were some observed phylotypes that were only found below 30 cm depth (Glo 4, Glo 5, Div 3, and Div 4). AM fungal infectivity and richness were not always lower in the deeper soil profiles in the greenhouse than in the agricultural fields. High land-use intensity was correlated with a preferential persist of some AM fungi in the deeper soil layers to escape from the adverse conditions caused by intensive farming practices.