Investigating the effects and interactions of zinc and the arbuscular mycorrhizal symbiosis on crops in urban soils

By 2050 the global population is expected to reach 9.8 billion, 70% of whom are predicted to live in urban areas. An increase in food production of 70% is required however agricultural land is currently being lost. There is an urgent need to find new solutions to diversify food production. Urban greenspaces have the potential to contribute to food security; however, they often possess elevated levels of zinc the effects of which on food production in these soils are unclear. Arbuscular mycorrhizal (AM) fungi, form associations with many crops and can enhance nutrient uptake and improve stress tolerance.

I first used radioisotope tracing to study the effects of zinc soil concentrations relevant to urban horticultural soils on nutrient exchange between peas and AM fungi. When zinc soil levels were increased to 250 mg kg-1, phosphorus transfer was lost but carbon allocation was maintained. However, at 400 mg kg-1 both carbon and phosphorus exchange were greatly reduced.
I then carried out a stress assay in three commonly grown crop species, peas, potato and lettuce, grown with and without AM fungi to investigate species-specific effects of Zn concentration and AM on plant performance. The interactions were highly context dependent with AM having various effects on the parameters measured.
Finally, I used global proteomics on peas to identify mechanisms behind the previously observed responses. In shoots the proteome was conserved by AM whereas in roots there was considerable variation. Affected proteins included those involved in oxidative stress response, photosynthesis and P transport.

This work examines the effect of the AM symbiosis in a context that has thus far been largely neglected, however may become vital to diversifying food production. Future work should investigate the other distinct characteristics of urban soils and how they can affect the potential of food production in urban areas.