From Soil Fungi to Bees: Fertile Grounds for Agroecology in California’s San Joaquin Valley

All the ecological components of a farm are tightly interlinked – influencing each other, negatively orpositively, through multiple divergent pathways. Belowground, roots can form a well-developed network with arbuscular mycorrhizal fungi (AMF) for greater nutrient uptake. Aboveground, floral resources (pollen and nectar) influence bee visitation needed for crop pollination. In this way, AMF could positively influence crop pollination through improving nutrient uptake. However, agricultural intensification, characterized by high nutrient inputs, low crop diversity, and high tillage frequency, have been linked to biodiversity loss, negatively impacting multiple species interactions. While diversifying crops could help to promote these beneficial ecological interactions, it is poorly understood how changes in crop diversity impact bees that specialize on limited floral resources or mycorrhizal fungi that exhibit preferential host associations. By partnering with small-scale farmers of color, my dissertation focused on understanding the mechanisms in which crop diversity influences below- and above-ground interactions, and their connections (AMF to pollination).The first part of my dissertation examined how crop diversity (monoculture versus polycultures)affected AMF and pollinator communities in the intensively managed agricultural region in California’s San Joaquin Valley. I examined how crop diversity influences several aspects of AMF communities: (1) richness and diversity, (2) composition, and (3) colonization. I demonstrate that crop diversity enriches AMF communities, counteracting the negative effects of agricultural intensification, providing the potential to increase agroecosystem functioning and sustainability. Next, to investigate the impact of on-farm diversification on pollinator communities, I focused on how specialist squash bees (Peponapis genera) responded to crop diversity (monoculture versus polyculture) using squash (Cucurbita pepo) as the focal crop. I hypothesized that squash bees would be ...