Understanding the links between soil, plants, and pollinators

David, Thomas and Stevens, Carly and Storkey, Jonathan (2020) Understanding the links between soil, plants, and pollinators. PhD thesis, Lancaster Environment Centre.

Text (2020DavidPhD)
ThomasDavid_CorrectedThesis_2020.pdf - Published Version
Available under License Creative Commons Attribution-NonCommercial-NoDerivs.
Download (5MB)

Abstract

Global nitrogen (N) deposition has risen steeply since the mid-19th Century and is forecasted to rise further. This increased flux of N to ecosystems is increasingly considered as a worldwide driver of environmental change. Impacts to botanical communities have been shown across a range of ecosystems and regions, but evidence on consequential impacts to further trophic levels is currently limited. Our understanding of how N affects plant-pollinator interactions is relatively poor. Declining trends in pollinating insects have been widely reported during recent decades and a key factor in this is losses of floral resources. The research chapters presented in this thesis seek to address the wide knowledge gap of how N affects pollinators by investigating how soil N affects 1) the composition of floral functional traits in a plant community, 2) intra-specific variation in key floral functional traits: phenology and nectar, and 3) the potential impacts to plant-pollinator interaction networks. This research was undertaken using the Park Grass Long-term Experiment (PGE) at Rothamsted Research, UK, a long-term nutrient-enrichment experiment. The study found extensive impacts of N on the provision of floral resources. Floral resources were lost with N-enrichment, with morphologically specialised floral units particularly threatened. Flowering phenology of plant species was influenced by N-enrichment with a notable contrast between early-season species, which had an extended flowering duration, and peak-season species that had a reduced flowering duration. Responses of nectar traits varied across species but were shown to respond to N applications. The observed pollinator visitation networks were impacted by the soil treatments; N additions typically led to Diptera-dominant communities and networks that were potentially less robust to stochastic events. The research project provided evidence that soil N can act as an underlying driver of plant-pollinator networks and should be considered as a factor in pollinator ecology and trends.