Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Whiteside, Matthew D. [1], Smith, Joshua M. [2], Durall, Daniel M. [3], Jones, Melanie D. [4].

I just don’t know who to send it to: Transfer of nitrogen and phosphorus between an ectomycorrhizal fungus and two symbiotic pine seedlings varying in nutrient supply.

Most commercially important conifers in northern temperate forests form ectomycorrhizal symbioses on their roots. In these symbioses, the fungal symbiont accesses soil nutrients that are less available to non-mycorrhizal roots, such as those sequestered in complex organic forms, and transfers some portion to the tree. The mycelia of some ectomycorrhizal fungi colonize the roots of many adjacent trees, thereby forming extensive mycorrhizal networks. Mycorrhizal networks are important sources of fungal inoculum to establishing seedlings and transport signalling molecules between trees. Little is known, however, about the factors that influence nutrient allocation by the fungus among hosts in a mycorrhizal network. We ran two experiments in which pairs of lodgepole pine seedlings were grown in a microcosm where they were colonized by the same ectomycorrhizal fungal mycelium (Suillus tomentosus). In each experiment, one of the two seedlings received a foliar application of nutrient (P in one experiment and N in the other). The second seedling received an application of water to the foliage. After several days, labelled N (¹⁵N as NH₄ or glycine) or P (³²P as phosphate or phosphoserine) was added to a well that hyphae, but not roots, could access. In both experiments, we predicted that the fungus would direct less labelled nutrient to the seedling that had just received foliar nutrients. For P, this was indeed the case when P was supplied to hyphae in organic form, but not when applied as phosphate. For N, ¹⁵N-enrichment was generally low and no effect of foliar N application could be detected. Instead, surprisingly, we found evidence that N moved from seedlings to the fungus (i.e., the opposite direction to normal) when the fungus was supplied with nutrients in the hyphal well. We speculate that exposure to nutrients after a period of nutrient starvation, stimulated the fungus not only to retain the nutrients supplied, but also to trigger transfer of N from the seedlings to the fungus at the host-fungus interface. Overall, factors governing transfer rates, and even the direction of nutrient transfer among symbionts in mycorrhizal networks, are complex and will require considerable study to establish general principles.

1 - Vrije Universiteit , Department of Ecological Sciences, Amsterdam, The Netherlands
2 - University of British Columbia Okanagan campus, Biology, 1177 Research Road, Kelowna, BC, V1V 1V7, Canada
3 - University of British Columbia Okanagan campus, Biology, 1177 Research Road
4 - UBC Okanagan, Biology Department, Sci-385, 1177 Research Road, Kelowna, BC, V4V 1V7, Canada

Keywords:
ectomycorrhizae
nitrogen
mycorrhizal networks
phosphorus
Plant nutrition
symbiosis.

Presentation Type: Oral Paper:Papers for Topics
Session: 36
Location: Salon 5/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 11:15 AM
Number: 36013
Abstract ID:530
Candidate for Awards:None