Page 209 - PC2019 Program & Proceedings

PLANT CANADA 2019

S203. The effects of nutrient enrichment on the community composition of arbuscular mycorrhizal
fungi: a meta-analysis of fertilization studies
MacColl, K.; H. Maherali
University of Guelph

Nutrient deposition from human sources has the potential to decouple nutrient-exchange mutualisms
between plants and below-ground fungi. In the widespread mutualism between plants and arbuscular
mycorrhizal (AM) fungi, plants decrease their interactions with AM fungi when resources are abundant
because the cost of association exceeds the benefits. Thus, AM fungal biomass is consistently reduced by
nutrient enrichment, but effects on community composition are less clear because results are variable
across study systems. To address this, we used a meta-analysis to determine overall patterns across
studies, while accounting for experimental factors that could introduce variability between experiments.
We found that fertilization reduced the species richness of AM fungal communities but did not affect
species diversity. Nitrogen (N) fertilization had the greatest negative effects on species richness, and these
effects were more negative at higher dosages of fertilizer. Synthetic fertilizers had stronger negative
effects on species richness than organic fertilizers. Phosphorus (P) addition or simultaneous fertilization
with both N and P did not affect AM fungal species richness or diversity. Nutrient deposition increased
the abundance of AM fungal genera with faster growth rates that specialize on disturbed environments but
decreased the abundance of slow-growing AM fungal genera. This meta-analysis provides evidence that
AM fungal communities are simplified by nutrient loading in favour of more ruderal species.

Kevin MacColl (kmaccoll@uoguelph.ca)

S204. Endophytic bacteria: nitrogen-source for lodgepole pine trees on disturbed sites?
*
Padda, K.P. ; A. Puri; C. Chanway University of British Columbia

Unreclaimed gravel mining pits located in the central interior of British Columbia have limited soil
nitrogen-levels due to gravelly-textured soils, no organic forest floor and low atmospheric nitrogen-inputs
through precipitation. However, lodgepole pine (Pinus contorta) trees have been growing well at these
pits with tissue nitrogen-content and growth-rate unaffected by extremely low soil nitrogen-levels,
indicating that pine trees can meet their nitrogen-requirements from an unknown source. We hypothesized
that biological nitrogen fixation by endophytic bacteria could be a potential nitrogen-source for pine trees.
Testing this hypothesis, we isolated 77 endophytic bacteria from needle, stem, and root tissues of pine
trees. Of these, 14 bacteria that showed consistently positive results for nitrogenase enzyme activity were
selected for a yearlong greenhouse study to quantify the amount of nitrogen-fixed and plant-growth-
promoted by each bacterium in planta. After one year, bacteria-inoculated seedlings had significantly
higher biomass (100-311%) and length (31-64%) than non-inoculated control seedlings and fulfilled 23-
53% of their nitrogen-requirements through biological nitrogen fixation. Notably, Pseudomonas
migulae AR1r and Pseudomonas lini SN1r inoculated seedlings accumulated 4-fold higher biomass than
control seedlings and fixed about half of their nitrogen from the atmosphere. Thus, endophytic nitrogen-
fixing bacteria naturally harboured by pine trees at these unreclaimed gravel pits are capable of providing
fixed nitrogen to their host and could potentially be used for effective reclamation of such highly
disturbed sites in a sustainable manner.

Kiran Preet Padda (kiranpreet.padda@alumni.ubc.ca)

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