Unexpectedly high diversity of arbuscular mycorrhizal fungi in fertile Chernozem croplands in Central Europe

Abstract

Highly fertile soils are considered to harbor low diversity of arbuscular mycorrhizal fungi (AMF), since plants might not depend on the mycorrhizal symbiosis to efficiently assimilate soil nutrients. ‘Black steppe soils’ classified as Chernozems are counted among the soil types with highest natural fertility and productivity. However, information on AMF diversity from highly productive Chernozems used as croplands are extremely rare to non-existent. Our objective was to study the impact of soil tillage and fertilization intensity on AMF communities in a long-term field trial established on a silty-loamy Calcic Chernozem in the Magdeburger Börde (Central Europe). Samples were taken at harvest of maize that grew in a rotation with winter wheat, winter barley, winter oil seed rape and again winter wheat. AMF species were characterized by spore morphology. Astonishingly high spore densities (up to 41 spores g−1 soil) and species richness (19–33 species) of AMF were found in this highly productive Chernozem cropland, even under high-input conditions, which were, however, higher in reduced tillage than in regularly ploughed plots. AMF diversity decreased with increasing fertilizer input concerning N and P. These findings might re-stimulate the discussion about the significance of AM fungi in highly productive croplands, which was so far thought to be low. Several indicator AMF species were identified for reduced tillage (e.g. Ambispora fennica and Dominikia bernensis) or reduced fertilizer inputs (e.g. Dominikia aurea) or both (e.g. Diversispora celata and Scutellospora calospora), but only a few for tillage (e.g. Funneliformis fragilistratus and Pacispora dominikii). AMF indicators have to be, however, identified for each soil type and climatic condition separately, as they should be completely different from those species for instance in nutrient-poor or in acidic soils, in warmer or colder as well as in more humid or arid climates.