Heterogeneous row-crop soil environments to harbor diverse, system-stabilizing mycorrhizal fungi

Background/Question/Methods

Row crop agriculture in the US Corn Belt is under the dual pressures of an increasingly variable climate and a need to improve regional environmental quality.  Arbuscular mycorrhizal fungal (AMF) provide plant- and ecosystem-benefitting services that could help agriculture face these pressures.  AMF communities in intensively-managed agroecosystems, however, generally are considered to be low-diversity and low-functioning.  This phenomenon is attributed to the major land management choices of monocropping, tillage, and broadcast fertilization, which all have the same effect of homogenizing the soil environment at the sub-20cm scale.  Recent evidence suggests that niche partitioning and competitive exclusion play a major role in structuring AMF communities.  Therefore, re-introducing heterogeneity to the soil environment through a tilling management class called precision zonal management (PZM) could restore the beneficial services that AMF provide.  We hypothesize that PZM-induced soil heterogeneity diversifies the composition of surface AMF communities in corn and soybean fields in southern Minnesota and central Illinois.  We further predict that subsurface communities will act as a pool of diversity that restores surface community composition and function. 

Results/Conclusions

Initial results support our hypotheses.  Differences (Bray-Curtis dissimilarity) between ridge and furrow communities in PZM systems for both bacterial (r² = 0.387) and fungal (r² = 0.564) communities increases as fields age, while nonmetric multidimensional scaling shows fungal communities in Minnesota cluster by PZM or chisel plow management.  Additionally, T-RFLP analysis shows multiple AMF taxa as deep as 40-60 cm that could potentially colonize surface environments.