Abstract
Most plants obtain nitrogen through nitrogen-fixing bacteria and microbial decomposition of plant and animal material. Most vascular plants are able to form close symbiotic associations with endophytic fungi. Metarhizium is a common plant endophyte found in a large number of ecosystems. This abundant soil fungus is also a pathogen to a large number of insects, a source of nitrogen. It is possible that endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of nitrogen transfer to plant hosts via fungal mycelia. In this study we used soil microcosms to test the ability of M. robertsii to translocate insect-derived nitrogen to plants. Insects were injected with 15N-labelled nitrogen, and we tracked the incorporation of 15N into amino acids in two plant species, haricot bean (Phaseolus vulgaris) and switchgrass (Panicum virgatum), in the presence of M. robertsii. These findings are evidence that active nitrogen acquisition by plants in this tripartite interaction may play a larger role in soil nitrogen cycling than previously thought.