Which fungal friend is the best to trees at nutrient highs and lows?

Lydia Peterson*, Emel Kangi, and Edward Brzostek

Department of Biology, West Virginia University, Morgantown, WV 26505

Presentation Category: Agricultural & Environmental Sciences (Poster Presentation #57)

Student’s Major: Horticulture

Most trees form symbiotic relationships with mycorrhizal fungi to increase their ability to take up nutrients. However, it remains unknown the extent to which the growth benefit of mycorrhizal fungi differs between the two main types: arbuscular mycorrhizae (AM) vs. ectomycorrhizae (ECM). As such, our central research question was to determine under which nutrient conditions AM or ECM fungi were most beneficial to poplar trees. We used poplar trees (Populus grandidenta) because, unlike most plants, poplar uses both ECM and AM fungi allowing us to isolate mycorrhizal effects. To answer our question, we grew poplar seedlings in the greenhouse and varied the mycorrhizae (i.e., AM, ECM, or none) and the levels of nitrogen (N) and phosphorus (P). After eleven weeks, we harvested the seedlings and weighed the dry mass of leaves, wood, and roots. At high N and P, we found that the trees with no mycorrhizal fungi had the most growth. It was only at low P levels that mycorrhizae were beneficial, with both ECM and AM stimulating growth. Finally, at low N and low P levels, seedlings with ECM fungi had the greatest growth rates. Collectively, our results suggest that at high nutrient levels the cost of mycorrhizae outweighs their benefit with mycorrhizae only beneficial to plant growth when the nutrient return on investment stimulated growth.

Funding: Department of Energy

Program/mechanism supporting research/creative efforts: Other, First2 Network