Mycorrhizal fungi-mediated uptake of tree-derived nutrients by crops - the role of tree-maintained versus crop-associated fungal mycelia

Arbuscular mycorrhizal (AM) fungi translocate nutrients within agroforestry systems but the role of common mycorrhizal fungal networks (CMNs) is unclear. We compared AM fungi-mediated nutrient transfer from mango versus faidherbia trees to maize plants to understand how to foster the AM symbiosis for enhanced agroecosystem sustainability. In mesocosms we applied 15N and 33P tracers via tree stem injection or root-free soil labeling compartments to test tree-to-maize versus soil-to-maize nutrient transfer via AM fungi. Maize plants grew in large in-growth cores with intact versus broken mycelia. Soil-to-maize transfer was assessed with and without trees to compare nutrient transfer via tree-maintained AM fungi i.e. CMNs versus maize-associated AM fungi. Tracer application via stem injection neither corroborated nor falsified our hypothesis of tree-to-maize nitrogen and phosphorus transfer. Soil-to-maize nutrient transfer occurred but was not enhanced by the presence of mango or faidherbia trees. Competition with maize plants for nitrogen but not phosphorus was greater with mango than faidherbia trees. Results from our experimental set-up provide neither evidence nor disproval for CMNs between two-year-old trees and ten-week-old maize plants. In the absence of trees and tree-maintained AM fungal mycelia maize plants developed their own AM fungal mycelia that mediated uptake of nutrients from beyond the maize plants' rooting zones.