UC Davis

Arbuscular mycorrhizal (AM) fungi are well-known microbial symbionts that support nutrient and water uptake, soil structure, and ecosystem resilience. Although research across diverse cropping systems has advanced our understanding of AM fungi, their dynamics across environmental gradients, phenological stages, and management practices remain poorly understood in perennial woody crops such as grapevines. This dissertation employs amplicon sequencing and microscopy to evaluate AM fungal colonization, diversity, and community composition in western U.S. vineyards. The first chapter surveyed 11 vineyards spanning a broad edaphoclimatic gradient from Oregon to California’s Central Coast, comparing AM fungal communities across regions, rootstocks, and scions. Our findings suggest that AM fungal communities in grapevines are structured at multiple scales, where broad environmental gradients establish baseline differences in community composition and plant-level traits may refine patterns of taxon abundance. The second chapter investigated AM fungal colonization and community composition across five phenological stages (bud break, bloom, veraison, harvest, and dormancy) in two vineyard sites cultivating different scion-rootstock combinations. AM fungal colonization and community composition varied across phenological stages and between scion-rootstock combinations, with patterns likely driven by host physiological responses to site conditions and phenological development. The third chapter evaluated the short-term effects of regenerative agriculture practices, including no-till, compost application, and sheep grazing on AM fungal colonization, diversity, and community composition in the same vineyard sites as chapter two. Site characteristics, including soil physicochemical properties and scion-rootstock identity, were stronger drivers of AM fungal communities than the practices themselves, with treatment responses varying between sites. Overall, these studies illustrate the importance of considering site-level characteristics and scion-rootstock identity in shaping AM fungal symbiosis, advancing our understanding of the factors that shape these communities in commercial vineyards.