Abstract Detail

Symbioses: Plant, Animal, and Microbe Interactions

Hawkins, Barbara J. [1], Kranabetter, J. Marty [2], Jones, Melanie D. [3], Li, Tao [4].

Evidence for adaptation of ectomycorrhizae to nitrogen form availability.

Nitrogen (N) availability is hypothesized to be a strong abiotic filter for ectomycorrhizal (ECM) fungi, directly affecting the composition and diversity of ECM communities. N-related functional trait differences among ECM fungal species may therefore be a key adaptation for both the fungal and plant partners in the symbiosis. We investigated if uptake of ammonium and nitrate differed among the suites of ectomycorrhizae found on Douglas-fir (Pseudotsuga menziesii) roots from sites of contrasting fertility and N form availability in spring and autumn. Root sections of 45-year-old Douglas-fir trees of one provenance were randomly sampled from three sites with contrasting N-availability (~0.09 – 0.28% N) and proportions of inorganic and organic N (~10 - 65% inorganic N). Roots were sampled in May/June and again in September/October. Net fluxes of ammonium, nitrate and protons were measured on root tips colonized by representative ECM fungi and on non-mycorrhizal roots using a microelectrode ion flux measurement system (MIFE^TM) (n = 13 – 20 roots per site). ECM fungal species measured with the MIFE then were identified by DNA sequencing. The suite of ECM fungal species identified varied among sites. Root tips from the high-N site were more frequently associated with Tomentella species, while the low-N site roots were commonly associated with Cortinarius and Piloderma species. ECM root tips had up to five times greater rates of ammonium uptake than non-mycorrhizal roots. Ammonium uptake was greater than nitrate uptake for most ectomycorrhizae. Ammonium uptake was greatest in the spring, while nitrate uptake rates were greatest in the autumn. Ammonium uptake rates were greatest in the ECM root tips from the high-N site and lowest in ECM roots from the low-N site. Nitrate uptake did not differ significantly among sites. Proton efflux, indicating acidification of the rhizosphere, was observed for most root tips and was greatest in roots from the high-N site and lowest for the low-N site. Results suggest that ammonium uptake capacity may be a particularly important functional trait differentiating the niche of ECM associations, and likely defines an essential belowground adaptation in conifer nutrition.

1 - University of Victoria, Centre for Forest Biology, Department of Biology, 3800 Finnerty Road, Victoria, British Columbia, V8P 5C2, Canada
2 - BC Ministry of Forests, Lands and Natural Resource Operations, , P.O. Box 9536, STN PROV GOVT, Victoria, BC, V8W 9C4, Canada
3 - UBC Okanagan, Biology Department, Sci-385, 1177 Research Road, Kelowna, BC, V4V 1V7, Canada
4 - Yunnan University, Laboratory of Conservation and Utilization for Bioresources, Kunming, China

Keywords:
ectomycorrhizae
nitrogen
ammonium uptake
nitrate uptake
Pseudotsuga menziesii
ion flux measurement
nutritional niche.

Presentation Type: Oral Paper:Papers for Topics
Session: 36
Location: Salon 5/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 10:15 AM
Number: 36009
Abstract ID:459
Candidate for Awards:None