Abstract
Trees within farmers' fields can enhance systems' longer-term productivity e.g., via nutrient amelioration, which is indispensable to attain sustainable agroecosystems. While arbuscular mycorrhizal fungi (AMF) are known to improve plant access to soil nutrients, the potential of AMF to mediate nutrient uptake of tree-derived N by crops from beyond the crops' rooting zones is unclear. We hypothesized that AMF quantitatively contribute to the crop uptake of tree-derived N. We set up root and AMF exclusion and control plots around faidherbia trees (Faidherbia albida) and used the (15)N natural abundance technique to determine the magnitude of AMF-mediated uptake of tree-derived N by maize from beyond its rooting zone in smallholder fields. We further tested whether AMF-mediated N uptake decreases with distance-from-tree. We show that within one cropping season, maize obtained approximately 35 kg biologically fixed N ha(-1) from faidherbia. One third of tree-derived N in maize leaves was attributed to AMF-mediated N uptake from beyond the maize rooting zone and two thirds to N from tree leaf litter, regardless of distance-from-tree. As hypothesized, maize grown close (1 m) to faidherbia obtained significantly more tree-derived N than at further distances (4 and 5 m). Thus, the faidherbia-AMF association can enhance agroecosystem functioning.