Open Collections

Neumann, Sarah

University of British Columbia

Most conifer trees exist in symbiosis with ectomycorrhizal (ECM) fungi. Mycorrhizal networks (MNs) form when hyphae from the same fungus connect two or more root systems. In ECM forests, soil nutrients, including nitrogen (N), are taken up by hyphae and translocated to roots, but it is unclear what factors affect the allocation of N to individual plant hosts within an MN. One such factor may be plant nutrient status. Although movement of N is generally understood to occur strictly from fungus to plant, it’s possible that N could be allocated from plant to fungus. Petri plate microcosms were constructed containing two Pinus contorta seedlings connected by a Suillus tomentosus mycelium. Foliar treatments consisting of: (i) a homogeneous treatment where both seedlings in the microcosm received urea, (ii) a homogeneous treatment where both seedlings in the microcosm received H₂O, or (iii) a heterogeneous treatment where one seedling in the microcosm received urea and the other received H₂O, were applied. After 72 h, N or H₂O was supplied to hyphae, and manual severing of hyphae served as a control. In some cases, foliar treatments contained ¹⁵N-labelled urea to detect movement of N from shoots to roots. In other microcosms, ¹⁵NH₄Cl or ¹⁵N-labelled glycine was supplied to hyphae to follow the fungal distribution of N within the MN. I found that movement of ¹⁵N from foliage to roots was common; however, hyphal severing and hyphal treatment had no effect on this movement indicating that it occurred independently of the fungus. Based on a small number of successfully labelled seedlings when ¹⁵N was supplied to hyphae, I found seedlings that received foliar treatments of urea had higher atm% ¹⁵N excess values than those that received foliar treatments of H₂O, but only when the ¹⁵N was supplied to hyphae as glycine. These results suggest that the partitioning of fungal N to plant symbionts in an MN may be affected by both the nutrient status of the plant, and the form of N assimilated by the ECM fungus. Here, special emphasis is given toward optimizing microcosm experimental design, as several methodological issues arose throughout my experiments.

Text

2022-10-05

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82819

Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/