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Mycorrhizas and root traits of the riparian tree species Populus fremontii

  • Author / Creator
    Schaefer, Elena A.
  • In hot and arid environments, trees may be particularly carbon-limited. In addition to supporting their own growth and activities, trees also lose carbon to associate with mycorrhizal fungi. Most trees form associations with either ecto- or arbuscular mycorrhizal fungi, and these fungi can have distinct effects on quantities of carbon released from fine roots and other root traits. Forests in arid regions are not uncommon, however trees in these areas must budget carbon as a limited resource, suggesting variation in carbon allocation to roots and mycorrhizal fungi could be important for overall tree fitness. Populus fremontii occurs in the southwest United States, a region that has experienced more droughts with climate change. Increasing aridity throughout its range means P. fremontii’s future will be progressively more carbon-limited. Moreover, unlike most other plant species, this species simultaneously associates with both ecto- and arbuscular mycorrhizal fungi, thus making it possible to decouple the effects of mycorrhizal type from tree species identity.
    I tested the influence of mycorrhizal type on root traits, including fine root carbon flux, using provenances of P. fremontii known to vary in dominance of the two mycorrhizal types. In both a field study and greenhouse experiment, I confirmed not only that P. fremontii forms ecto- and arbuscular mycorrhizas simultaneously, but depending on provenance and environment, individuals also preferentially associate with one mycorrhizal type over the other. While I did not measure carbon allocation from P. fremontii to each mycorrhizal type, high colonization rates of both mycorrhizal types suggests carbon is transferred from trees to support these fungi. Mycorrhizal type, however, did not affect fine root carbon flux in either experiment, and overall, I measured extremely low fine root carbon-flux rates. In addition, root traits were variable and disconnected from mycorrhizal type, revealing highly context-dependent patterns. These results suggest that P. fremontii minimizes exudation of carbon across a range of environments, and the distinct effects of mycorrhizal type on root traits are nuanced. Compared with other tree species in wetter environments, P. fremontii is a conservative species in regard to fine root flux, with no indication that mycorrhizal fungi moderate this belowground process. As aridity increases in regions with historically wetter environments, P. fremontii could signal how other tree species under increasing carbon-limitation, might modify root traits including fine-root carbon flux and how this could influence belowground processes such as carbon cycling.

  • Subjects / Keywords
  • Graduation date
    Fall 2022
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-71yd-se07
  • License
    This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.