A look at the diversity of rhizosphere bacteria in USGA putting greens

The soil environment immediately around a root frequently has a larger number of microorganisms compared to soil just a few millimeters away from a root. This zone of influence is called the rhizosphere (Rovira, 1991), which is composed of many groups of organisms that are capable of affecting plant health beneficially and deleteriously (Schippers et al., 1987). Putting greens are artificially constructed soils, built from a predetermined mixture usually composed of sand and organic matter (USGA Green Section staff, 1993). In the Southeastern U.S., newly built putting greens are often fumigated before planted. However, previous research shows microbial populations present before fumigation rebound quickly after fumigation (Elliott and Des Jardin, 2001; Elliott et al., 2004). Additionally, as the putting greens mature, thatch, root and shoot production will cause significant increases in organic matter (Gaussoin et al., 2006), which will promote microbial growth. Natural materials, organic materials and microbial inoculants are used by the golf course industry because there's an assumption few microbes are present in the turfgrass system or the "wrong" microbes are present. However, recent studies indicate turfgrass systems have extensive microbial populations (e.g., Bigelow et al., 2002; Elliott and Des Jardin, 1999; Elliott et al., 2004; Feng et al., 2002; Mercier, 2006) and diverse microbial communities (e.g., Mueller and Kussow, 2005; Sigler et al., 2001; Yao et al., 2006). Also, it's unclear whether introduced bacteria can influence bacterial populations in the phyllosphere, thatch, rhizosphere soil or bulk soil (Hodges et al., 1993; Lynch, 2002; Mercier, 2006; Mueller and Kussow, 2005; Sigler et al., 2001). The emphasis of the project described herein was on culturable bacteria because it's culturable bacteria that are being exploited by the golf course industry. In other words, if you can't grow bacteria in large quantities (by a company or directly on the golf course in fermentation tanks), they aren't useful as products. While we know there's a diverse microbial community present in turfgrass root systems, it's not known which culturable fluorescent pseudomonad species or culturable bacilli species are present. A joint project was undertaken by Auburn University, Clemson University and the University of Florida to examine bacterial populations and diversity in USGA putting greens during a three-year period after the greens were established. We've reported on the flux of the extensive bacterial populations present in putting greens (Elliott et al., 2004), the