Greater cover crop diversity supports soil microbial community diversity and carbon storage

Bronte M Sone, Soil & Water Systems, University of Idaho, Moscow, ID, Jane Lucas, Department of Soil & Water Systems, University of Idaho, Moscow, ID and Michael S Strickland, Soil and Water Systems, University of Idaho, Moscow, ID

Background/Question/Methods
A fundamental ecological principle states that with increasing biodiversity there is a corresponding increase in ecosystem function. For example, grasslands with greater aboveground diversity have higher soil carbon (C) levels, which promotes soil fertility, structure, and water holding capacity. This in turn strengthens the system and provides resiliency to climate extremes. Whether these positive plant diversity effects hold for agroecosystems, especially given the short timeframe in which plant diversity can be increased, is unknown. One effort to increase diversity in agroecosystems is the application of cover crops. However, little is known about the effect of diverse cover crops on soil microbial communities, which are intrinsic to soil processes- in particular soil C sequestration. Here we test that 1) increasing cover crop diversity leads to an increase in bacterial and fungal community diversity; and 2) that higher microbial diversity results in greater microbial biomass and soil C stores. Using a replicated random-block design, we tested how cover crop functional and species diversity affected soil microbial composition and soil C storage. We used 16S and ITS amplicon sequencing techniques to analyze microbial communities, and analyzed soil C fractions (particulate organic matter and mineral-associated organic matter) including microbial biomass C and dissolved organic C.

Results/Conclusions
After three months of crop growth, cover crop treatment altered bacterial and fungal community diversity compared to the fallow control. We also found increased microbial biomass C and respiration with increasing cover crop diversity (0 to 6 spp.). Microbial biomass C is an indicator of long-term carbon storage, yet greater respiration may indicate less C is being retained within the soil. Generally, our results indicate both cover crop diversity levels and composition can influence microbial communities and soil C stores. This suggests that biodiversity in agroecosystems can increase soil function. The information gained through this research will not only inform soil management practices but will also fill knowledge gaps in the complex processes underlying C cycling.