Soil microbial communities under model biofuel cropping systems in southern Wisconsin, USA: Impact of crop species and soil properties

Abstract

Biofuel-induced landscape change will have an enormous impact on terrestrial ecosystems in the near future due to globally escalating energy demands, but investigations into the biological properties of soil under potential biofuel crops have not been well documented. The soil microbiota plays a significant role in ecosystem services and especially their regulation of carbon and nutrient cycles. To improve our knowledge about the structure of soil microbial community and the factors that influence it, we analyzed microbial lipids and various soil physicochemical factors under model biofuel cropping systems of corn, switchgrass and mixed prairie in southern Wisconsin, USA. Principal component analysis of lipid biomarkers from soil microbial communities indicated that there were consistent differences among the crop species. Microbial biomass was significantly lower in corn than prairie soils, with switchgrass intermediate to these systems. An increase in fungi to bacteria ratio was coinciding with a net growth in fungal biomass when converting conventionally managed corn system to perennial systems, which indicates the microbial community change could be affected by the creation or expansion of niches for certain functional groups, rather than rebalancing of competitive interactions among these groups. The soil microbial community structure under corn was distinct from the perennial systems with markers indicative of greater in situ stress in annual corn sites and a reduced proportional abundance of arbuscular mycorrhizal fungi and an increased of gram-positive bacteria. Redundancy analysis (RDA) using 21 lipid biomarkers concurrently with 17 physicochemical indices showed that these properties correlated with different subsets of the microbial communities. We conclude that the cropping system shifted the microbial community composition at this regional scale, which may also affect the microbial processes associated with these differing communities. This may be significant when scaled up from regional to national, continental or global scales.