Microbial energy and matter transformation in agricultural soils

Low bioavailability of organic carbon (C) and energy are key constraints to microbial biomass and activity. Microbial biomass, biodiversity and activity are all involved in regulating soil ecosystem services such as plant productivity, nutrient cycling and greenhouse gas emissions. A number of agricultural practices, of which tillage and fertiliser application are two examples, can increase the availability of soil organic C (SOC). Such practices often lead to reductions in soil aggregation and increases in SOC loss and greenhouse gas emissions. This review focuses on how the bioavailability of SOC and energy influence the ecology and functioning of microorganisms in agricultural soils. Firstly we consider how management practices affect the bioavailability of SOC and energy at the ecosystem level. Secondly we consider the interaction between SOC bioavailability and ecological principles that shape microbial community composition and function in agricultural systems. Lastly, we discuss and compare several examples of physiological differences that underlie how microbial species respond to C availability and management practices. We present evidence whereby management practices that increase the bioavailability of SOC alter community structure and function to favour microbial species likely to be associated with increased rates of SOC loss compared to natural ecosystems. We argue that efforts to restore stabilised, sequestered SOC stocks and improve ecosystem services in agricultural systems should be directed toward the manipulation of the microbial community composition and function to favour species associated with reduced rates of SOC loss. We conclude with several suggestions regarding where improvements in multi-disciplinary approaches concerning soil microbiology can be made to improve the sustainability of agricultural systems