Linking above and below-ground interactions in agro-ecosystems : an ecological network approach

Abstract

Belowground microbial communities, such as arbuscular mycorrhizal fungi (AMF), may modify plant reproductive traits, although little is known about how this might then influence pollinator behaviour. This is important as pollinators provide an ecosystem service by contributing towards agricultural production. AMF also provide an ecosystem service by assisting plants with increased access to nutrients and water resources, thereby influencing yields. However, few studies have examined the combined effects of how AMF interact with crop cultivars to alter plant reproductive traits, pollination processes, and ultimately crop yield. Furthermore, the importance of both AMF and pollinators for human perceived crop quality has not been investigated. In this thesis, I examine the influence of manipulating AMF communities on plant-pollinator interactions, and the role of crop cultivars in mediating these effects, by growing three strawberry (Fragaria × ananassa) cultivars inoculated with four AMF communities, and measuring strawberry yield and quality (determined through human taste tests) in two 2-year experiments. The first experiment was conducted under greenhouse conditions and I found that pollen foraging visits by bumblebees (Bombus terrestris Audax) were influenced by both AMF community and strawberry cultivar, whereas nectar foraging visits were only influenced by AMF community. AMF community influenced strawberry yield, without any changes in fruit quality, and effects were consistent across each strawberry cultivar, while AMF community and strawberry cultivar interacted to influence strawberry appearance. The second experiment was similar to the greenhouse experiment but repeated under field conditions to examine the effects on the naturally occurring pollinator community. Here, I found that while AMF community may influence the visitation of some pollinator taxa, the wild pollinator community provided a high degree of functional redundancy, and strawberry yield was influenced in the same manner as in the greenhouse experiment when plants were exposed to the highly efficient pollinators used in commercial production. The potential to utilise the above and below-ground interaction data to improve yields relies on the opinions of end users. I conducted a socio-economic analysis of growers’ and scientists’ iv perceptions, which showed that key stakeholders believe that interactions between above- and below-ground organisms should be harnessed to improve crop production. These results show that manipulating a below-ground mutualistic community has effects that cascade through the network to influence plant-pollinator interactions, and alters strawberry yield without loss in quality, with largely predictable outcomes across multiple strawberry cultivars. The interdisciplinary nature of this research revealed that stakeholders believe AMF should be used to improve strawberry production. Understanding the dynamics of these interactions may form part of a toolset for sustainable increases in food security, as well as helping to gain a deeper understanding of the underlying biology that influences ecological networks.