COS 110-7: Bridging the gap: The role of mycorrhizal symbiosis in plant uptake of organic nitrogen
Jenny Talbot, University of California Irvine
Mycorrhizal plants from a variety of ecosystems have the capacity to take up organic forms of nitrogen, yet the fraction of plant nitrogen demand met by organic N (ON) uptake remains unclear. The gap in our understanding of ON uptake by mycorrhizal plants is perpetuated by a conceptual distinction between studies of plant ON uptake and studies of ON uptake by mycorrhizal fungi. Here I synthesize concepts from each body of research and evaluate the role of symbiosis in structuring realistic patterns of ON uptake by mycorrhizal plants. Many mycorrhizal fungi can decompose and assimilate ON compounds from a range of ON substrates commonly found in soils. However, C availability is a major control over the capacity for mycorrhizal fungi to access ON. Symbiotic mycorrhizal plants tend to have greater capacity to mobilize and take up ON than when plants and fungi are grown as isolates. Thus, patterns of ON uptake in ecosystems are likely structured by factors that affect the exchange of carbon and N between plant and fungal symbionts. In contrast to a “phytocentric” or “mycocentric” view of ON acquisition, this synthesis supports a new “symbiosis-centric” model of ON uptake by mycorrhizal plants.