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 more abundant on
monocultures, due to greater numbers of squash flowers, than polycultures. Despite this, I found that
increasing non-squash floral resource diversity in polycultures supports a greater abundance of squash
bees. On-farm diversification may be an important refuge for specialist bees that are vulnerable in
landscapes dominated by agriculture.
The second part of my dissertation sought to more closely characterize mechanisms that enhancepollination services critical to promoting food security. While aboveground floral visitors provide
pollination services to plants, belowground AMF could enhance the quality of floral resources (pollen
and nectar). Yet, the effect of the AMF community composition on pollination is still unclear because
existing studies consist of a single AMF species or disregard the interacting effect of soil nutrient
availability. Therefore, in a controlled greenhouse and field experiment, I investigated how different
levels of AMF diversity and nutrient availability impacted floral resources and pollinator visitation.
Our results demonstrate that greater AMF diversity, regardless of nutrient availability, has the largest
positive effect on floral resource quality and pollinator visitation, an indicator of pollination services.
Altogether, this dissertation points to the effects of crop diversity on belowground and abovegroundbiodiversity that could bolster ecosystem functions. By working directly with small-scale farmers of
color, this research also outlines potential pathways that farmers can take towards harnessing beneficial
ecosystem functions. Importantly, the results demonstrate that crop diversification could help to
recover biodiversity from below- to above-ground even in the intensively managed region in
California’s San Joaquin Valley.