Page 122 - PC2019 Program & Proceedings

PLANT CANADA 2019

S29. Nutrient deposition modifies how arbuscular mycorrhizal fungi influences competitive
interactions in plants
Hicks, K.; H. Maherali
University of Guelph

Arbuscular mycorrhizal (AM) fungi increase plant access to phosphorous in exchange for sugars from
photosynthesis and can provide a competitive advantage to highly responsive species in low nutrient soils.
Increased phosphorus deposition may change the composition of AM fungal communities in soil, which
in turn can influence competitive interactions among plant species. The aim of this study is to examine
how phosphorous fertilizer and soil biota influence fungal effects on plant growth and competitive
interactions between species that differ in their response to AM fungi using Andropogon gerardii, a highly
responsive species native to tallgrass prairies, and Bromus inermis, a less responsive species that invades
and competes with A. gerardii. Soil inoculum from three sites varying in phosphorous levels was applied
along with low and high phosphorous fertilizer treatments in an additive replacement series competition
experiment. Mycorrhizal fungi from soils with a history of low phosphorus inputs had more positive
effects on plant growth than fungi from soils with high phosphorus input. For A. gerardii, we found that
interspecific competition was either stronger or equal to intraspecific competition when grown with more
beneficial soil biota. Our study can improve our understanding of how nutrient deposition can affect the
mutualistic efficiency of AM fungal communities and imply the likelihood that non-native species could
invade during the establishment phases of tallgrass prairie restoration efforts with A. gerardii.

Kelsey Hicks (hicksk@uoguelph.ca)

S30. Nitrogen fixing plant evolution: the interactive effect of elevating CO2 and herbivores on
nitrogen fixing plants
*
Chen, H. ; J. Markham
University of Manitoba

Nitrogen fixing plants evolved during the late Cretaceous period when atmospheric CO2 was ca. 800-
1600 ppm. The current CO2 level is around 400 ppm and it is predicted to increase up to 800 ppm by
2100. Little is known about how nitrogen fixing and non-fixing plants respond to both changing CO2
condition and herbivores. Speckled alder (Alnus incana ssp. rugosa) were grown in growth chambers and
inoculated with the symbiont Frankia or not. Plants were grown at one of three atmospheric CO2 levels:
400, 800, 1600 ppm, representing ambient, future and Cretaceous era atmospheric levels, respectively.
After growing for three months, they were exposed to white-marked tussock caterpillar (Orgyia
leucostigma) for 5 days. A choice experiment showed herbivores preferred nitrogen fixing plants.
Nodulated plant biomass, leaf C:N ratio and plant total phenolic compounds were increased under
elevated CO2. Specific nodule activity and nodule allocation were decreased under elevated CO2.
Nodulated plants synthesized more total phenolic compounds to defend against herbivores damage. This
suggests that nitrogen-fixing plants are likely to exhibit higher level of chemical defenses in the future in
response to herbivore damage. Nitrogen fixing plants failed to balance C:N ratio suggesting increased
carbon availability cannot be balanced by symbiotic nitrogen fixation.

Haoran Chen (Chenh318@myumanitoba.ca)

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