The value of biodiversity to agriculture is being increasingly recognised, such as the role of below-ground organisms to healthy soils, and the contribution of insect pollination to crops. There is growing recognition that what happens below-ground can have impacts on how plants respond above-ground and vice versa. We do not yet fully understand how below-ground soil animal communities might be indirectly affecting above-ground pollinator communities. This has important implications not only for the maintenance of biodiversity, but also for the healthy functioning of agricultural systems.
This study investigates how soil biodiversity might alter plant traits and in turn affect pollinator behaviour. A soil biodiversity gradient was created using the dilution-to-extinction approach, and experimental microcosms created using the annual plant Phacelia tanacetifolia Benth. The effects of soil biodiversity loss were explored by measuring above and below-ground plant traits, floral signals and rewards. A pollinator choice experiment was carried out to investigate the preference of a key group of pollinators, bumblebees (Bombus terrestris L.), for one plant treatment over another in a semi-field setting using pollinator cages.
This study is one of the first to investigate soil-plant-pollinator interactions (i) in a multispecies setting and (ii) incorporate the plant root system.
Results/Conclusions
Soil biodiversity affected a variety of different plant traits. Phacelia plant biomass decreased with soil biodiversity loss, while the number of branches and leaves increased. Plant height, floral signals such as total flower number and biomass were not affected. Bumblebees showed no preference for plants of any treatment in terms of what plant was chosen to be visited first. This would suggest that soil biodiversity loss may not affect the plants ability to attract pollinators initially. This is supported by the nectar sugar concentration range (% brix) remaining unaltered. Additional floral reward data on the chemical composition of the nectar as well as bee behaviour data such as visitation rate and time spent drinking nectar and collecting pollen are used to explore any direct or indirect effects.
Although soil biodiversity is crucial for functioning of terrestrial ecosystems, this study shows that although soil biodiversity loss effects some plant traits there was no measurable knock-on effects on floral choice by bumblebees. These findings, and more, are discussed in light of additional data such as the effects on below-ground root biomass and the presence of a key taxa, arbuscular mycorrhizal fungi (AMF).
