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Date of Award

Spring 2023

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Science

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Bauman, Jenise

Second Advisor

Bunn, Rebecca

Third Advisor

Poppe, Katrina L.


Lupine (Lupinus rivularis) is used in the revegetation of coarse sediments surrounding the Elwha basin in Washington State due to its ability to improve soil conditions. Previous research illustrated that seeding lupine with conifers increased growth and foliar nitrogen, however, decreased ectomycorrhizal (ECM) root colonization, an important symbiosis for conifers used in restoration. We hypothesized the observed decrease in ECM may be due to lupine increasing soil nitrogen, negating the need for a fungal symbiont. To investigate this, we explored the interaction between lupine and ECM colonization of grand fir (Abies grandis) in both a field and greenhouse experiment. In the field we surveyed for a correlation between lupine and conifer growth and ECM colonization. No correlation between lupine cover and conifer growth was detected, however, ECM colonization was negatively correlated with lupine cover (P<0.05). In the greenhouse we investigated growth and ECM colonization of grand fir under the following treatments: 1) synthetic nitrogen, 2) N-fixing lupine, 3) non-N fixing forbs, and 4) a control. We found that growth did not differ among treatments, however, ECM colonization decreased within the nitrogen treatment (P<0.05) but not the lupine treatment. Additionally, conifers growing within the lupine and competition treatments had more foliar nitrogen than in the nitrogen or control treatments (P<0.05). The greenhouse study illustrated that N fertilizer reduced ECM colonization, not lupine, which may indicate other factors influencing fungal colonization in the field. Our results show that fertilizer may negatively impact ECM and companion plantings with native species help with the retention of N in coarse soils.




companion planting, nutrient retention, restoration, vegetation


Western Washington University

OCLC Number


Subject – LCSH

Riverbank lupine--Washington (State)--Elwha Basin; Abies grandis--Washington (State)--Elwha Basin; Ectomycorrhizas--Washington (State)--Elwha Basin; Soils--Nitrogen content--Washington (State)--Elwha Basin

Geographic Coverage

Elwha Basin (Wash.)




masters theses




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Creative Commons License

Creative Commons License
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