Reducing environmental and economic costs of turfgrass management through mycorrhizal symbiosis

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Elizabeth Haymaker, Natural Resources Ecology & Mangement, Oklahoma State University, Stillwater, OK, Adam Cobb and Gail Wilson, Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK, Yanqi Q. Wu, Plant and Soil, Oklahoma State University, Stillwater, OK

Background/Question/Methods
Bermudagrass (Cynodon spp.) is a highly desirable turfgrass with ~18 million hectares cultivated throughout the United States. Bermudagrass is frequently managed with abundant commercial fertilizers, resulting in downstream ecosystem damage. This is leading breeders to target development of genotypes requiring fewer nutrient inputs and reducing economic costs. Historically, breeding programs focused on aboveground performance traits, while belowground attributes, such as root architecture and arbuscular mycorrhizal (AM) symbiosis, received less attention. It has been well-established that AM symbioses improve plant nutrient uptake, suggesting a reduction in commercial fertilizer amendments may be achieved if bermudagrass is selectively bred to improve nutritional benefits received from AM fungi.

We evaluated 12 bermudagrass genotypes, including experimental varieties developed at Oklahoma State University. Genotypes were planted in 5 kg native grassland soil, with or without AM fungi. Plants were amended with 10, 20, or 30 mg g-1 plant-available P, maintained in a greenhouse, with five replicates. We measured aboveground growth rates, final above- and belowground biomass production, root architecture (WinRhizo), and aboveground tissue quality as measures of host-plant benefits attributed to AM symbioses. Our research provides a foundation for improved in turfgrass management through selective breeding that includes optimization of AM fungal benefits.
Results/Conclusions
We found significant differences in shoot biomass between genotypes, indicating genetic mediation of AM benefits can be targeted in future selective breeding efforts. Increasing plant-available P typically reduced AM growth responses (difference between mycorrhizal and nonmycorrhizal plant production), and in some cases shifted these responses from positive to negative (beneficial to parasitic). Root biomass production also differed significantly between genotypes. For example, elimination of AM fungi resulted in a 15% root dry weight reduction for genotype ‘Celebration’ but a 158% increase for genotype ‘MS-Choice,’ as compared to mycorrhizal plants. AM fungi substantially influenced root architecture, as average root length and root branching significantly decreased when AM fungi were present. Shoot P uptake was less variable across genotypes, as compared to differences resulting from P fertilization.
Genotypes that are more dependent on AM fungi may improve turfgrass nutrient use-efficiency, as well as drought resilience and soil stability. We propose bermudagrass management can be more environmentally sustainable if AM fungal responsiveness is included in breeding programs and managed as natural biofertilizers, thereby reducing fertilizer requirements while maintaining or increasing turfgrass productivity, quality, and performance.