Perennial biofuel crop identity and management alter abundance and activity of soil organisms
In response to the 2007 U.S. Energy Independence and Security Act which mandates production of 16 billion gallons of cellulosic ethanol by 2022, many farmers are considering growing warm season perennial grasses such as switchgrass (Panicum virgatum) and miscanthus (Miscanthus × giganteus) for cellulose feedstock, especially on marginal lands. These perennial grasslands can support greater biodiversity and provide more ecosystem services than annual crops. However, management considerations, such as what crop to plant and levels of fertilizer inputs, may alter ecosystem services provided by these grasslands, especially those influenced by belowground organisms. Our objective in this study was to evaluate the effects of crop identity and fertilization on arbuscular mycorrhizal fungal (AMF) activity and soil nematodes in ongoing experiments associated with the Great Lakes Biofuels Research Center (GLBRC) at the Kellogg Biological Station (KBS) in Michigan, USA. In May 2014, we collected soils from fields planted in either miscanthus or switchgrass (cave-in-rock variety), and which had been either been left unfertilized or fertilized at a rate of 72 kgN/ha for the past five years. We quantified crop AMF root colonization, AMF extra-radical hyphal length, and plant-parasitic nematode abundance in each field.
Our results showed that switchgrass had twice as dense AMF root colonization and extra-radical hyphal production compared to miscanthus. Fertilization tripled plant-parasitic nematode abundance in both crops, and tended to increase AMF hyphal production, possibly due to increased root biomass. These results indicate that switchgrass may enhance soil carbon storage compared to miscanthus by increasing AMF activity belowground. More work needs to be done to evaluate crop and fertilizer effects on AMF and nematode community diversity, and how these soil organisms may feedback to influence crop yield and associated ecosystem services.