Microbial Contributions to Carbon Sequestration Potential in Response to Perenniality.

Perennial cropping systems have shown marked potential to build soil carbon (C) pools in comparison to annual field crops, yet the role of microbial processes remains virtually unknown. Through evaluating microbial contributions to C sequestration in soil, we can begin to understand how newly incorporated C provides opportunity to enhance soil health and CO₂ mitigation over the long-term. A field experiment established in 2009 at the Kellogg Biological Station to evaluate novel perennial grain types compared to annual wheat has shown plant species effects on soil chemical and biological factors. A perennial plant type was associated with four-fold higher root biomass and a moderate but significant increase in CO₂ respiration and the size of the permanganate oxidizable C pool. This field experiment affords a unique opportunity to examine the effect of perennial traits through comparison of annual wheat (Triticum aestivum) with perennial wheat (hybrid of Triticum and Thinopyrum that has undergone cycles of backcrossing to Triticum with selection for perenniality). Our objective was to assess soil C building potential of perennial root quality and quantity of inputs, to evaluate microbial controls on carbon cycling using an incubation experiment. We added 1X and 5X amounts of C3 annual wheat and perennial wheat roots to a C4 residue enriched soil/sand background to assess the effect of carbon quality (equal amounts of annual vs. perennial wheat roots) and quantity (1X versus 5X) of newly added root inputs. Bacterial and fungal community composition and abundance along with CO₂ respiration measurements were monitored throughout the incubation experiment. It was expected that similar to field observations, plant type will strongly influence microbial community composition and this effect will contribute, in part, to shifts in processing newly added C inputs. Our work provides a key component to understanding microbial mechanisms involved in processing new plant inputs.