Turf contains living assemblages of not only grass plants, but also a plethora of microorganisms that may play critical roles in plant health through interactions such as predation, mutualism, and resource competition. Little is known about the turf microbiome and how it might change in response to renovations such as new sod installation or overseeding. In this work, we survey bacteria inhabiting the rhizosphere of mature and recently renovated turf stands at the United States National Mall in Washington, DC. We contrasted these data with the microbiomes of sod soon to be planted at the National Mall, and from the lawn of a nearby government facility. The soil‐inhabiting microbiome was quantified through high‐throughput next generation sequencing of the 16S ribosomal DNA. Over 1600 operational taxonomic units were identified from 9.2 million sequence reads, of which 751 could be diagnosed at the genus level. Over 50% of the 751 identifiable bacterial taxa were members of the phylum Proteobacteria, predominately in the genusRhodoplanes. Phenotypic mapping of predicted microbial function on the basis of taxonomy showed all four locations were diverse and, in general, contained an abundance of Gram‐negative, aerobic, free‐living thermophilic organisms. Ordination plots showed clustering of samples according to location. However, this pattern of differentiation between locations was not recapitulated using hierarchical clustering analysis, α diversity measurements, or analysis of similarities (ANOSIM), with no significant differences between locations identified. Given the commonality of bacterial communities between locations, these data suggest that the resident National Mall microbiome may not experience appreciable change due to the renovation process.

Creeping bentgrass (Agrostis stolonifera) is widely used in golf course settings for its desirable playing surface characteristics; however, it is highly susceptible to diseases that can disrupt surface integrity and cause significant losses despite preventative management. Understanding the influence of early plant growth and basic management practices on microbiome communities are crucial first steps to developing future efforts to harness the microbiome for plant health. This study investigated bacterial and fungal communities of creeping bentgrass foliage and rhizosphere through 6 months postemergence under a controlled environment to elucidate microbiome community dynamics in response to plant age. We hypothesized that plant compartments will host distinct community structures and exhibit different responses to plant age. Our results showed that predominant bacterial phyla and fungal classes remain consistent across time and plant compartment. However, genus-level classification revealed that bacterial taxa differed across plant compartment while fungal taxa remained consistent. Host influence over the microbiome manifests quickly, with the largest shift in both microbial communities occurring between emergence and 2 months postemergence. For example, Burkholderia and Penicillium spp. were present at high relative abundance at emergence but, by 2 months postemergence, both taxa decreased significantly. Bacterial communities continued to experience significant fluctuation in rare taxa from 2 months postemergence onward, while fungal community structure was driven by the fluctuation of the most common taxa. These results highlight the connection between plant age and microbial community structure in creeping bentgrass in addition to underscoring future research efforts in creeping bentgrass microbiome manipulation for plant health. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Fungicides are frequently applied on golf course putting greens to combat the myriad of diseases that can affect them; however, it is unknown how these fungicides may affect microbial populations. Plant-associated microbial communities are intimately involved with plant development and soil biological processes. This two-year study was designed to evaluate the impact of five selected fungicides on culturable actinomycetes, fungi, general bacteria, and fluorescent pseudomonads residing in the turfgrass phyllosphere. Fungicides were applied at label rates on a 14-day interval. Four samples, consisting of five individual turf plants, were taken five days post-application. Samples were homogenized in 1 ml sterile deionized water and serial diluted to 10⁻³ and 10⁻⁵. Each dilution was then plated onto four different media (actinomycete isolation agar, acidified potato dextrose agar, nutrient agar + 1% sucrose, and King’s B) for enumeration of microbial populations. Fungicides had both positive and negative impacts on the culturable microbes tested, although population shifts across all treatments were observed with the prevailing weather conditions. These results show that while response to repeated fungicide application appears to be organism dependent, microbes are not completely removed from the environment.

Characterization of the plant microbiome may allow for the development of diagnostic tools or improvements in plant health. To that end, this project sought to determine the influence that resident seed and soil microbiota exert on the developing creeping bentgrass (Agrostis stolonifera L. cv. 007) microbiome. A sterile growth environment was created in a laminar flow hood. Sterile 50 ml conical tubes were filled with autoclaved or non‐autoclaved soil (85% sand and 15% peat) and seeded with 007 creeping bentgrass. Foliage and rhizosphere samples were taken at emergence, 2, 4, and 6 wk post‐emergence, and soil samples were taken at the conclusion of the experiment. Amplicon sequencing libraries were generated from extracted environmental DNA, sequenced using an Illumina MiSeq, and analyzed in R. After quality control 3.32 × 10⁷ sequences were grouped into 2,273 bacterial and 303 fungal amplicon sequence variants (ASVs). Bacterial and fungal ASVs were predominantly members of the Proteobacteria and Eurotiomycetes, respectively. Over the 6‐wk sampling period the microbial communities were stable, with taxonomic shifts occurring mainly in low relative abundant taxa. Ordination of Bray‐Curtis distance matrices revealed significant differences in community centroids between grass planted in autoclaved and non‐autoclaved soil. However, taxonomic profiling showed these differences were due to shifts in taxa present at low relative abundances <.5%). Data show that the microbiota originating from the seed exerts only a minimal influence over the microbiome of developing creeping bentgrass compared to the soil microbiome.

Bacterial etiolation, caused by Acidovorax avenae, is a widespread problem in creeping bentgrass putting green turf. The symptoms normally appear as abnormally elongated turfgrass stems and leaves. Observations at multiple field sites suggest the involvement of plant growth regulators (i.e., GA-biosynthesis inhibitors) commonly applied to turf, alluding to a phytohormone imbalance caused by the bacterium. A 2-year field study examined the effects of trinexapac-ethyl, flurprimidol, and paclobutrazol on bacterial etiolation severity caused by A. avenae. Trinexapac-ethyl applied at 0.05 kg a.i. ha⁻¹ every 7 days and 0.10 kg ha⁻¹ every 14 days increased etiolation compared with all other treatments in both years. Flurprimidol and paclobutrazol were not different from the control but high-rate applications caused phytotoxicity that lowered turf quality early in 2014. When the etiolated turfgrass was removed with mowing, turfgrass treated with trinexapac-ethyl exhibited the highest turfgrass quality on most rating dates. Results from this work illustrate that using plant growth regulator materials with different modes of action is a solution to managing creeping bentgrass growth while limiting the potential for bacterial etiolation outbreaks.