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Decline of arbuscular mycorrhizal fungi in northern hardwood forests exposed to chronic nitrogen additions
- van Diepen, Linda T.A., Lilleskov, Erik A., Pregitzer, Kurt S., Miller, R. Michael
- The new phytologist 2007 v.176 no.1 pp. 175-183
- Acer, aboveground biomass, carbon, correlation, energy, fatty acids, hardwood forests, mycorrhizal fungi, nitrogen, phospholipids, roots, soil, vesicular arbuscular mycorrhizae
- Arbuscular mycorrhizal (AM) fungi are important below-ground carbon (C) sinks that can be sensitive to increased nitrogen (N) availability. The abundance of AM fungi (AMF) was estimated in maple (Acer spp.) fine roots following more than a decade of experimental additions of N designed to simulate chronic atmospheric N deposition. Abundance of AMF was measured by staining and ocular estimation, as well as by analyzing for the AMF indicator fatty acid 16:1ω5c in phospholipid (biomass indicator) and neutral lipid (lipid storage indicator) fractions. Arbuscular mycorrhizal fungal biomass, storage structures and lipid storage declined in response to N addition measured by both methods. This pattern was found when AM response was characterized as colonization intensity, on an areal basis and in proportion to maple above-ground biomass. The phospholipid fraction of the fatty acid 16:1ω5c was positively correlated with total AMF colonization and the neutral lipid fraction with vesicle colonization. Decreased AMF abundance with simulated N deposition suggests reduced C allocation to these fungi or a direct soil N-mediated decline. The fatty acid (phospholipid and neutral lipid fractions) 16:1ω5c was found to be a good indicator for AMF active biomass and stored energy, respectively.