Jean Ridriguez Ramos | ALES Graduate Seminar

Date(s) - 06/01/2021
2:00 pm - 3:00 pm

A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES PhD Final Exam Seminar by Jean Rodriguez Ramos.

Supervisors: Dr. Nadir Erbilgin and Dr. Justine Karst

This seminar is open to the general public to attend via Zoom (link below).

Thesis Title:  Characterization, restoration, and assembly of fungal communities in lodgepole pine forests impacted by disturbances

Seminar Abstract:

Novel disturbance regimes have altered community dynamics in the Canadian boreal forest with unknown consequences for belowground communities and underlying ecological processes. Soil fungi are an integral component of belowground communities and particularly sensitive to such disturbances. In the Canadian boreal forest, common overstory pine trees, such as lodgepole pine (Pinus contorta var. latifolia), form mutualisms with ectomycorrhizal (EcM) fungi, while most understory plants in boreal coniferous forests tend to associate with arbuscular mycorrhizal (AM) fungi. These fungal symbionts influence the establishment and growth of their host by mediating nutrient availability while also interact with saprotrophic and pathogenic fungal guilds. The response of different fungal guilds to individual disturbances and the response of seedlings to such changes is poorly understood. Furthermore, it is less clear what processes underlie EcM fungal community assembly and whether different disturbances affect the relative contribution of neutral and deterministic assembly processes. The objectives of this thesis are to (1) characterize soil fungal communities in lodgepole pine forests following a bark beetle outbreak, wildfire, clear-cut logging, and salvage-logging, (2) test whether the disruption of the soil organic matter is one of the drivers structuring the communities of fungal guilds, (3) determine whether soil transfers from intact (control) lodgepole pine forests into regenerating conspecific forests amend soil fungal communities and, in turn, affect the performance of pine seedlings, (4) examine whether root-associated EcM fungi assemble at fine spatial scales based on neutral or deterministic processes across disturbances.

Examination of fungal communities from control and disturbed forests revealed that stand replacing disturbances changed the community composition of EcM fungi and shifted the dominance from EcM to saprotrophic fungi compared to control forests. The disruption of the soil organic layer with disturbances correlated with the decline of EcM and the increase of AM fungi. In addition, wildfire changed the community composition of pathogenic fungi but did not affect their proportion or diversity. Fungal biomass declined with stand replacing disturbances that also disrupt the soil organic layer. Furthermore, the use of soil transfers did not result in changes in the fungal community. Instead, we found that the effects of disturbances override the effects of soil inoculations as variation in the EcM fungal community of pine roots was explained largely by disturbance type. Consequently, inoculations did not affect seedling survival or performance. For EcM fungi colonizing roots of seedlings grown in the different disturbances, a neutral model that uses species abundance in the soil metacommunity to predict their occurrence on roots predicted the abundance of approximately 60% or more root-associated EcM fungal taxa. This finding suggests that neutral processes dominate the fine-scale assembly of EcM fungi regardless of disturbance type. I also found that the fungal communities of taxa assigned as neutral or deterministic were similar across the disturbance types. Traits, including host-specificity of EcM fungi, large production of resistant spores, and uncertain ecological roles of taxa commonly identified as EcM fungi could explain their deviations from neutrality. Collectively, these results suggest that while disturbances alter the community composition and abundance of soil fungal guilds and root EcM fungi under the studied disturbance regimes, lodgepole pine seedlings can be relatively insensitive to the in-situ variation in fungal communities across disturbances that assemble in roots largely by dispersal from soil.

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