Over 18 million hectares of Bermudagrass (Cynodon spp.) is cultivated in the US. However, bermudagrass cultivation is linked with several pressing issues such as eutrophication of aquatic systems. In response to concerns over environmental and economic costs of turfgrass management, breeders are developing lower-input genotypes. While breeding programs focus on improving aboveground biomass and disease resistance, belowground microbial symbioses such as arbuscular mycorrhizal (AM) fungi are generally not considered. However, AM symbioses can efficiently improve plant nutrient and water uptake, potentially subsidizing commercial fertilization and irrigation.
We conducted complementary field and greenhouse experiments to evaluate the responsiveness of bermudagrass genotypes on AM fungi for nutrient uptake. We examined soil collected in the rhizosphere of 24 genotypes growing in field production trials to determine AM fungal biomass (neutral lipid fatty acid biomarkers). Based on this assessment, we conducted a greenhouse study assessing 12 representative genotypes, grown across three P-fertilizer amendments (10, 20, or 30 mg kg-1), with or without AM fungi. This allowed for calculations of AM-responsiveness, a measure of host-plant growth attributed to AM symbioses. We also measured root morphology, aboveground tissue quality, and associated AM fungal taxa (molecular quantification) to determine the mechanisms and consequences of differential host-plant responsiveness.
Results/Conclusions
We found AM fungal biomass differed significantly between bermudagrass genotypes, ranging from 5.78 - 32.45 nmol g-1 soil. Our findings indicate 5 of the 24 genotypes assessed were associated with relatively high AM fungal biomass, similar to that observed in native grasslands, while associated AM biomass of 19 genotypes was significantly lower. Preliminary greenhouse analyses show a significant influence of AM fungi on bermudagrass P-uptake, with substantial impact on productivity and tissue quality. Additionally, assessment of AM fungal taxa indicates more phylogenetically clustered taxa in low plant-available P soil and over-dispersed taxa in high plant-available P soil. We propose phylogenetically clustered taxa represent more nutritionally beneficial symbionts. Genotypes that are more responsive to AM fungi may improve not only nutrient use efficiency, but also drought resilience and soil stability. We propose bermudagrass cultivation can be more sustainable if breeders are able to identify traits that reduce fertilizer and water requirements, while maintaining or increasing productivity, quality, and performance. Our research suggests benefits provided by AM fungi can be enhanced through selective breeding, particularly under low-input conditions, and provides an important foundational step toward sustainable bermudagrass management.