Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/1998
Publication Date: N/A
Citation: Interpretive Summary: Switchgrass, Panicum virgatum, was one of the dominant grasses of the tall- grass prairie and is used in warm-season pastures and has potential use as a biomass fuel. The objective of this study was to evaluate the effectiveness of arbuscular mycorrhizal fungi (AMF) and associated rhizosphere microflora indigenous to the rhizosphere or soil environment of switchgrass in enhancing switchgrass growth. Switchgrass roots and rhizosphere soil was collected from native and seeded stands at 14 sites in six states. The effectiveness of the soil microflora including mycorrhizal populations in these soils to enhance switchgrass growth and nutrient uptake was evaluated in greenhouse studies. In the greenhouse in pots containing only sand and fertilized with a nutrient solution, the rhizosphere populations significantly improved switchgrass growth and nutrient (N and P) utilization of four different cultivars demonstrating that switchgrass is a micorrhizae dependent species. The most effective microflora sources came from old fields of switchgrass rather than from native prairies.
Technical Abstract: The objective of this study was to evaluate the effectiveness of arbuscular mycorrhizal fungi (AMF) and associated rhizosphere microflora indigenous to the rhizosphere of switchgrass (Panicum virgatum L.) plants for enhancing switchgrass yield and nutrient uptake. Switchgrass roots and rhizosphere soil were collected from native prairies and seeded stands in Nebraska, Kansas, Iowa, Missouri, Virginia and North Carolina. Seedlings of four switchgrass cultivars were inoculated with roots and rhizosphere soil from each collection, fertilized with a nutrient solution and grown in steamed sand for 12 wk in a greenhouse. Seedlings inoculated with AMF and associated rhizosphere microflora produced up to 15-fold greater shoot and root yields, and recovered up to six-fold more N and 36-fold more P than seedlings inoculated with rhizosphere bacteria only. These responses were consistent for all four switchgrass cultivars. Switchgrass rhizosphere populations were highly variable in their ability to recover N and P and stimulate shoot and root yields. However, rhizosphere populations that stimulated the greatest N-uptake differed from populations that resulted in the greatest P-uptake. Seedlings inoculated with rhizosphere populations from seeded switchgrass stands averaged 1.5-fold greater shoot and root yields than seedlings inoculated with rhizosphere populations from native prairies. Highly effective microbial populations appear to develop in the rhizosphere of long-term seeded switchgrass stands.