Putting greens are often portrayed as a monoculture environment with limited microbial diversity. This idea likely developed as a byproduct of the intensive management associated with putting greens coupled with the fact that putting green mixes were often fumigated before seeding or sprigging (this was especially true in the southeastern United States).
So, until fairly recently, there was a common perception that turfgrass microbial communities might have few microbes, or that they might be the “wrong” microbes. In an effort to get better information, in the late 1990s, a team of researchers from Clemson, Florida and Auburn set out to both quantify and identify microbial community diversity in creeping bentgrass and hybrid bermudagrass putting greens through the southeastern United States.
Four locations were used for the study — either newly constructed sand-based putting greens on golf courses (Crenshaw creeping bentgrass in North Carolina and Tifdwarf hybrid bermudagrass in South Carolina) or newly constructed sand-based, small-scale putting greens at research facilities (Crenshaw in Alabama and Tifdwarf in Florida).
Methyl bromide was used to fumigate at every location, with Tifdwarf sprigs used in Florida and South Carolina, Crenshaw seed in North Carolina, and washed Crenshaw sod laid in Alabama. Samples (cores of roots and soil) were collected four times a year (every three months) from the replicated greens, with samples taken to a depth of 4 inches (10 centimeters).
All the samples were washed, with the roots and rhizosphere (the area immediately surrounding the root, as compared with just bulk soil) washed, diluted and spread onto selective media. Isolates were then identified via gas chromatography for analysis of fatty acid methyl ester profiles (GC-FAME). In all, 10,000 bacterial isolates were selected for identification over the three years of this study.
And what was found?
Even with that initial fumigation, considerable taxonomic diversity was found in the putting greens. Five genera comprised at least 1% of all the isolates at each site: Bacillus, Clavibacter, Flavobacterium, Microbacterium and Pseudomonas. Of these, populations of Bacillus were twice as high in bermudagrass sites (around 11% to 19% of all isolates in Florida and South Carolina), whereas in bentgrass, populations of Pseudomonas were either higher than (19% in North Carolina) or equal to (14% in Alabama) levels of Bacillus. A total of 76 bacterial genera were identified in bermudagrass, with 50 common to both locations, and 59 were identified in bentgrass, with 47 common to both locations. In all, 40 bacterial genera were common to all locations.
Although a wide diversity of bacterial populations was identified, it should be noted that the largest group of bacterial isolates could not be identified. Of all the selected isolates, 32% (North Carolina) to 50% (Florida) had no match in the GC-FAME system. Although this percentage of unidentified bacterial genera may seem surprising, it was actually fairly similar to that found in other agricultural studies of other crops. The ability to identify the bacteria was a function of the “bacteria library” that was used to provide identification, and, as the authors noted, “Any database is only as good as the data.”
This indicates that bacterial diversity in putting greens is even greater than documented in this work. Newer research methods developed since this study will only continue to quantify and demonstrate the wide diversity of microbial species in turfgrass systems.
Source: Elliott, M.L., J.A. McInroy, K. Xiong, J.H. Kim, H.D. Skipper and E.A. Guertal. 2008. Taxonomic diversity of rhizosphere bacteria in golf course putting greens at representative sites in the southeastern United States. HortScience 43:514-518.
Editor’s note: Read all of Beth Guertal’s recent Verdure columns.
Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the 2019 president of the Crop Science Society of America. She is a 21-year member of GCSAA.