Fish, forests, fungi : soils in the ‘salmon forests’ of British Columbia

In this thesis, I examine the effects of returning salmon on riparian soils in Heiltsuk traditional territory, near the community of Bella Bella on the Central Coast of British Columbia, Canada. My main objectives were to: 1) quantify how salmon affect forest soil chemistry; 2) use nitrogen stable isotopes to measure salmon contributions to fungi, soil, and litter nitrogen metabolism; 3) quantify how salmon affect soil fungal communities; 4) quantify how salmon affect soil bacterial communities; and 5) test the role of fungi in plant ammonium uptake by disrupting fungal metabolism. To achieve objectives 1 through 4, I used two observational approaches: the first examined watersheds along a natural gradient of salmon density; and the second used sites where waterfalls block salmon migration, allowing for within-watershed comparisons above and below these barriers. To achieve objective 5, I employed a nitrogen stable-isotope addition experiment. I found that salmon affected soil chemistry, with impacts on concentrations of nitrogenous compounds, exchangeable cations, phosphorus, and metals, as well as differences in pH. I found that δ15N was greater in sporocarps when salmon were present, and interpreted this as evidence fungi acquire salmon nutrients. Using next-generation environmental sequencing, I found salmon inputs impact fungal relative abundance, soil fungal β- and α- diversity, but did not affect phylogenetic dispersion. In general, symbiotrophic fungi were affected by salmon inputs more than saprotrophs. Soil bacterial communities had fewer correlations with salmon inputs. Finally, I found that disruption of fungal metabolism slowed the uptake of ammonium by riparian shrubs. These results show that salmon are important in structuring riparian soil chemistry and microbial ecology, and support the hypothesis that fungi play an important role in salmon nutrient uptake by plants.Forestry, Faculty ofGraduat