Suzanne Simard

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
Kin-selected signal transfer through mycorrhizal networks in Douglas-fir (2017)

Mycorrhizal networks create pathways for movement of resources and information molecules belowground. A mycorrhizal network is formed when two or more plants are linked by the same mycorrhizal fungus. Experiments have demonstrated movement of carbon and nitrogen between Douglas-fir and neighboring plants in response to source-sink dynamics, seasonality, and differences in age of linked plants. Furthermore, the network appears to act a conduit for information chemicals, where defense chemicals are transferred in response to herbivory or pathogen attack. Because of recent evidence implying the capacity for Douglas-fir to recognize kin, as well as differential colonization of Douglas-fir by ectomycorrhizas based on tree relatedness, this thesis aimed to determine whether Douglas-fir would preferentially transfer carbon and/or nitrogen through mycorrhizal networks to kin over strangers in response to herbivory treatment. Using seedlings with and without access to a mycorrhizal network (restricted or permitted via mesh pore size), stable isotope probing was used to track carbon and nitrogen in the system. One seedling of a pair was designated as the 'donor' and defoliated immediately prior to photosynthesizing with 99%-¹³C-CO₂ as well as pulse-labelling with 99%-¹⁵N ammonium nitrate. Both a greenhouse and field experiments were performed to corroborate results. Transfer was determined by measuring δ¹³C and δ¹³N in tissues (needle, stem, root) of kin and stranger seedlings. Data was analyzed using linear mixed effects models. Significantly more carbon was transferred to kin than strangers, and through the mycorrhizal network than when the mycorrhizal network was blocked. Furthermore, herbivory (in the form of western spruce budworm defoliation as well as manual defoliation) induced transfer of carbon to kin over strangers. Douglas-fir families differed in their tendency to transfer carbon and nitrogen to kin. Molecules potentially involved in defense signaling were identified using liquid chromatography coupled with mass spectroscopy. Ectomycorrhizal fungi that can form mycorrhizal networks were found on all seedlings. We conclude that preferential carbon transfer through mycorrhizal networks occurs between kin in Douglas-fir and is amplified by herbivory stress. Herbivory is not necessary for transfer, as some transfer also occurred in the no-herbivory treatment.

View record

Mycorrhizal fungi : unlocking their ecology and role in the establishment and growth performance of different conifer species in nutrient-poor coastal forests (2016)

This thesis explored the fungal communities of arbuscular mycorrhizal-dominated Cedar-Hemlock (CH) and ectomycorrhizal-dominated Hemlock-Amabilis fir (HA) forests on northern Vancouver Island, British Columbia, Canada and examined the role of mycorrhizal inoculum potential for conifer seedling productivity. Objectives of this research project were to: (1) examine the mycorrhizal fungal communities and infer the inoculum potential of CH and HA forests, (2) determine whether understory plants in CH and HA forest clearcuts share compatible mycorrhizal fungi with either western redcedar (Thuja plicata) or western hemlock (Tsuga heterophylla), (3) test whether differences in mycorrhizal inoculum potential between forest types influence attributes of seedling performance during reforestation and (4) test effectiveness of providing appropriate mycorrhizal inoculum at the time of planting on conifer seedling performance. Molecular and phylogenetic techniques were utilized to compare mycorrhizal fungal diversity between forest types and to identify mycorrhizal fungal associates of the plant species occurring in clearcuts. In a field trial utilizing seedling bioassays, the role of mycorrhization of western redcedar and western hemlock on seedling growth was evaluated; reciprocal forest floor transfers from uncut forests were incorporated into the project design as inoculation treatments. Though diversity was similar, ectomycorrhizal and saprophytic fungal community composition significantly differed between CH and HA forests; arbuscular mycorrhizae were widespread in CH forests, but rare in HA forests. There was high similarity of arbuscular mycorrhizal fungi to those found in western redcedar among the dominant plant species colonizing CH clearcuts, including the ericoid plant Gaultheria shallon and in Blechnum spicant growing sparsely in HA clearcuts. No alternative ectomycorrhizal host species were detected. Mycorrhization greatly influenced productivity of western redcedar seedlings; without mycorrhizal inoculum, redcedar did not achieve its full growth potential in HA clearcuts. Mycorrhization of western hemlock seedlings did not differ between forest clearcut type or treatment group; however, an inhibitory effect of forest floor collected under mature western redcedar trees on the growth of western hemlock seedlings was unexpectedly detected. These results have implications for sustainable forest management practices, including retention of legacy trees and plants with timber harvesting and inoculation of seedlings with mycorrhizal fungi at the time of planting.

View record

Vascular plant response to slashburning and clearcutting in central British Columbia : a 20 year study of plant functional type resilience (2014)

How resilience is understood and measured has become increasingly challenging for ecologists, particularly as terrestrial ecosystems are undergoing radical change as climate changes. This body of work proposes a specific approach to studying resilience and applied it to Interior Cedar-Hemlock (ICH), Sub-Boreal Spruce (SBS) and Engelmann Spruce-Subalpine Fir (ESSF) forests extending across central British Columbia, Canada. Repeated measurements (% cover and height) of vascular plants were collected between 1981 and 2008 (1, 2, 3, 5, 10 and 20 years after clearcutting and slashburning) in permanent research installations. Individual species sensitive to the forestry treatment (recorded exclusively pre-burn) included Rhododendron albiflorum, Menziesia ferruginea and Prosartes hookeri in the ICH; Rubus pedatus in the SBS; and Orthilia secunda, Listera cordata and Moneses uniflora in the ESSF. Post-burn shifts in species dominance consisted of substantial loss of Abies lasiocarpa, Oplopanax horridus and Listera cordata, and increases in Alnus spp., Salix spp., Epilobium spp. and Calamagrostis spp., indicating possible transition from conifer forest to mixed forest or open meadow ecosystems at several study sites.To overcome the difficulty of evaluating ecosystem resilience from measurements of 183 individual species recorded in experimental plots, I created plant functional types (PFTs) based on 15 common plant traits. PFTs were determined by grouping together plants that behave in similar ways or produce similar outcomes despite having different physical characteristics or evolutionary paths. PFT models of abundance and richness along gradients of soil nitrogen and fire severity over time indicated linear and non-linear response trends, and lasting and temporary effects. Structural equation modeling (SEM) was used to measure the relative importance of factors driving the responses observed. The SEM indicated that mean annual precipitation (MAP) negatively influenced fire severity; mean annual temperature (MAT) positively influenced fire severity and soil nutrients; and MAP and MAT directly and/or indirectly influenced most PFTs. My research suggests that clearcutting and slashburning do not alone alter the diversity or function of mesic ESSF, SBS and ICH forests; however, past and future anthropogenic disturbances combined with non-historical climate and interrelated edaphic factors may place long-term stability of these ecosystems at risk.

View record

Juvenile growth of subalpine fir (Abies Iasiocarpa) in the Montane Spruce ecological zone of British Columbia Canada (2013)

No abstract available.

The complex socio-spatial architecture of Rhizopogon spp. mycorrhizal networks in xeric and mesic old-growth interior Douglas-fir forest plots (2012)

Mycorrhizal networks (MNs) can influence tree establishment and resource competition but little is known regarding their underlying architecture in situ. This study examined the socio-spatial architecture of MNs between Rhizopogon spp. genets and interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) trees in an old-growth forest. MN features were contrasted between plots with xeric versus mesic soil moisture regimes as a proxy for changes in site water stress anticipated with climate change. My objectives were to: (1) describe the fine-scale spatial patterns and autecological traits of R. vesiculosus and R. vinicolor mycelia systems and compare these between xeric and mesic plots; (2) describe the spatial patterns and architecture of Rhizopogon spp. MNs at the forest stand scale; (3) contrast MN architectures between phytocentric and mycocentric perspectives and between xeric and mesic plots, and identify critical determinants of MN architectures. Rhizopogon vesiculosus mycelia occurred deeper, were more spatially prolific, and colonized more tree roots than R. vinicolor mycelia. Both species were associated with moist microsites within plots, and had more prolific mycelia in mesic compared to xeric plots. The occurrence of R. vesiculosus shifted in the presence of R. vinicolor towards deeper soil horizons, suggesting competition and foraging strategy are important for niche partitioning between these species. At the forest stand scale, Rhizopogon spp. genets spanned tens of metres and colonized up to 19 trees, but R. vesiculosus genets were larger and linked more trees than R. vinicolor genets. Multiple tree cohorts were linked, with saplings and mature trees sharing the same fungal genets. Across all plots, the physical size of individual trees or fungal genets was positively related to their MN connectivity. This together with size asymmetries among different genets and trees resulted in the self-organization of complex, hierarchical scale-free MN architectures. The MNs appear robust to random perturbations but susceptible to the loss of large trees or fungal genets. No MN structural differences were found between phytocentric and mycocentric models or between xeric versus mesic plots. The pervasive mycelia and extensive MNs formed by these Rhizopogon spp. could influence interior Douglas-fir stand dynamics and resistance to water stress.

View record

Natural Regeneration Potential of Douglas-Fir Following Wildfire and Clearcut Harvesting (2011)

No abstract available.

The role of ectomycorrhizal networks in plant-to-plant facilitation across climatic moisture gradients (2011)

Common ectomycorrhizal (EM) networks are expected to facilitate conifer regeneration under abiotic stress, such as drought exacerbated by climate change. This study examined effects of climate, CO₂ concentration ([CO₂]), and EM networks on Douglas-fir seedling establishment. My objectives were (1) to determine the effects of regional climate (represented by a drought index) on EM network facilitation of Douglas-fir seedling establishment; (2) to separate genotypic effects from climatic effects; (3) to compare the importance of EM networks to 3-year-old outplanted nursery seedlings versus 1st year seedlings germinated in the field; (4) to parse the competitive from facilitative effects of residual Douglas-fir trees on small seedlings; and (5) to determine the interaction between soil water and [CO₂], in their effects on EM network-facilitated seedling establishment and C-transfer between different sized Douglas-fir seedlings. Survival was maximized when seedlings were able to form an EM network in the absence of root competition, both in growth chambers and in the field for the medium moisture provenance. When drought conditions were greatest, growth of these same seedlings increased when they could form an EM network with nearby trees in the absence of root competition, but it was reduced when they were unable to form a network. Overall, survival was greatest for these seedlings relative to those from the wet or dry provenances, but decreased with summer heat:moisture index more rapidly. I found no evidence of C transfer between seedlings through growth chamber ¹³CO₂ labeling, but D₂O labeling and natural abundance H₂¹⁸O measurements are suggestive of increasing water transfer from donor to receiver seedlings as receiver water deficiency increased.

View record

Carbon, plant and microbial dynamics in Low-Arctic tundra (2010)

Anthropogenic climate change threatens the stability of Arctic C stores. Soil microbes are central to the C balance of ecosystems as decomposers of soil organic matter and as determinants of plant diversity. In four experiments in the tundra, I address critical gaps in our understanding of the role of soil microbial communities in the response of an Arctic ecosystem to climate change. My objectives were 1) to asses the role of mycorrhizal networks (MN) in plant-plant interactions; 2) to determine the effects of warming and fertilization on the ectomycorrhizal (ECM) community of Betula nana; 3) to determine the effect of warming on soil fungi and bacteria over time; 4) to assess the role of the mycorrhizal symbiosis in C-allocation to rhizosphere organisms. I show that MNs exist in tundra and facilitate transfer of C among Betula nana individuals, but not among the other plants examined. C-transfer among Betula nana pairs through MNs represented 5.5 ± 2.2% of photosynthesis, total belowground transfer of C was 10.7 ± 2.1%. My results suggest that C-transfer through MNs may alter plant interactions, increasing competition by Betula nana, and that this will be enhanced with warming. I show that warming leads to a significant increase of fungi with proteolytic capacity, particularly Cortinarius spp., and a reduction of fungi with high affinities for labile N, especially Russula spp. My findings suggest that warming will alter the ECM community and nutrient cycling, which may facilitate Betula nana in tundra. I show that warming leads to a 28% and 22% reduction in the richness of soil fungi and bacteria in tundra, respectively, as well as corresponding declines in diversity. My data agree with reductions in plant community richness with warming at this site, and suggest that warming will reduce total community diversity in tundra. I show that Gram-negative bacteria and a species-specific community of mycorrhizal fungi are the primary consumers of rhizodeposit C among tundra shrubs. Together, these results strongly suggest that soil microbes play a critical role in plant community dynamics and C-cycling in Arctic tundra, and that this role will become increasingly important as climate warms.

View record

Effects of nurse tree species on growth environment and physiology of underplanted Toona ciliata Roemer in subtropical Argentinean plantations (2009)

Toona ciliata Roem. plantations require a nurse-tree overstorey to minimize damage from drought and frost in north-eastern Argentina. Nurse-species vary in their facilitative and competitive abilities, thus influencing trade-offs among T. ciliata establishment success, stem quality and productivity, and ultimately stand revenues. The first objective was to quantify the influence of nurse species (G. robusta A. Cunn., Pinus elliottii Englm. x Pinus caribaea Morelet, P. taeda L.) and thinning density on mortality, stem morphology and growth of under-planted T. ciliata. Trade-offs among performance traits were considered in developing recommendations for nurse species selection and density management. The second objective was to examine interspecific interaction mechanisms by determining the effects of nurse species and thinning intensities on light, soil water and nutrient availability to T. ciliata. The final objective was to link T. ciliata establishment success and early growth to soil water availability, by calibrating the two-dimensional forest hydrology model, ForWaDy. To develop a stand management tool for guiding establishment of T. ciliata plantations it was found that T. ciliata responded more to nurse species identity than density. G. robusta was less competitive with T. ciliata for soil nutrients and soil water than either of the pine species: P. elliottii x P. caribaea was an strong competitor for water while P. taeda was a strong competitor for nutrients. G. robusta, by contrast, increased water and phosphorus availability to T. ciliata. Density effects varied with nurse species and performance traits. ForWaDy had good predictive capability for early T. ciliata performance, and was especially discriminatory among nurse species effects. This study shows that nurse species and thinning effects depend on management objectives, but that nurse species choice can be more important than thinning for increasing early T. ciliata performance. Future research employing a greater range of overstorey species, thinning densities, tree ages and environmental conditions will improve predictions of mixed stand productivity under a broader range of conditions. The study contributes to a better understanding of competitive and facilitative interactions in nurse tree plantations and emphasize the need for long-term empirical and modeling studies of mixed species stand dynamics.

View record

Interacting effects of soil nitrogen supply and light availability on understory sapling growth and foliar attributes (2008)

Light availability in forest understories is a well recognized constraint on sapling growth, but limitations in soil nitrogen (N) availability, and the link to foliar photosynthetic capacity, typically receive less consideration in describing stand dynamics. My primary hypothesis is that light and soil N availability have species-specific effects on photosynthetic activity and growth, and that together these resources will better define understory development in complex forests. To test these relationships, I examined 1) soil N indices and the tradeoffs between soil fertility and light attenuation in old-growth forest understories; 2) the effects of light and N constraints on understory sapling foliar N concentration (N%), N per unit area (Na), and natural abundance of ¹³C; 3) the effects of light and soil N supply on species growth and photosynthetic activity in a factorial field experiment; and 4) the mechanisms responsible for the stagnation of understory saplings. Soil N indices incorporating dissolved inorganic N and organic N were useful in characterizing differences in N supply among contrasting sites. Understory light availability declined with increasing soil N supply, while understory Abies lasiocarpa had strong correlations between foliar N% and soil N availability, despite shading effects. In partial-cut forests, understory Tsuga heterophylla and Picea glauca x sitchensis had consistent foliar N% across gradients of light availability; in contrast, foliar N% of Betula papyrifera and Thuja plicata declined with increasing shade, which would distort assessments of soil fertility and perhaps contribute to increased mortality of these species in deep shade. Strong correlations between foliar Na and ¹³C or growth increment suggest foliar N per unit area is the simplest integration of light availability and N nutrition on leaf photosynthetic activity. Ontogenic interactions that occur among foliar attributes and tree size in forest understories, especially for saplings
View record

Master's Student Supervision (2010-2017)
Forest canopy gap size affects regeneration potential of interior Douglas-fir (2016)

There is growing concern about the long term productivity of forests in British Columbia due to changing climatic conditions. Interior Douglas-fir, an economically and culturally valuable conifer species, has recently had inconsistent regeneration success in the dry climatic regions of its distribution due to high summer soil surface temperatures, drought and growing season frost. Seeds of interior Douglas-fir germinate after mixed severity disturbances, but their survival appears to depend on the size of disturbance gaps, environmental resources and conditions, and colonization by mycorrhizal fungal symbionts. In two separate experiments that differed in climate (very dry, hot and dry, cool Interior Douglas-fir (IDF) subzones), and disturbance agent (natural and harvested), I sowed interior Douglas-fir seed into different sized forest canopy gaps. In both experiments, I tested the effects of canopy gap size and access to mycorrhizal networks on seedling performance (establishment, growth, water use efficiency, foliar nutrition, mycorrhizal colonization) and environmental resources and conditions (light, temperature, soil moisture). In the first experiment, regeneration failed in all canopy gap sizes and network treatments due to the harsh climatic conditions. There, neither protection in small gaps nor access to mycorrhizal networks were sufficient to create favourable regeneration conditions. In the second experiment, where the climate was cooler and wetter, seedling survival reached 74% in harvested gaps that were 80 – 300 m² in area, corresponding with greater soil moisture availability. Gaps of 20 – 80 m² were too small to initiate gap-phase regeneration, however, as indicated by low seed emergence and slow height growth rates. Gaps >300 m² resulted in high emergence but low survival (26 %) due to low soil moisture availability. Access to mycorrhizal networks had minor effects on mycorrhizal colonization and water use efficiency. My study shows that regeneration potential of interior Douglas-fir is severely limited by the very dry, hot climate in the low elevation IDF forests, but can be increased in wetter, cooler climates with forest harvesting practices that create moderately sized canopy gaps.

View record

Networks of communication : defense-related signal transfer between tree seedlings via mycorrhizal networks and an educational mycorrhizal-focused video game (2016)

The majority of terrestrial plants associate with fungi in symbiotic resource-exchange relationships called mycorrhizae. Mycorrhizal networks (MNs) arise when the same fungus is connected to multiple plants, allowing for interplant resource transfer and impacting ecosystem functions. Recent work suggests MNs also transfer defense-related information from pathogen-, herbivore-, or mechanically-damaged plants to unharmed neighbors. I investigated the defense pathways involved in defense-related signal transfer in ectomycorrhizal systems. Paired Douglas-fir seedlings were grown with varying levels of belowground connectivity (soil water only; soil water and MNs; soil water, MNs, and roots), and a defense response was stimulated in donor seedlings by methyl jasmonate. After 24 and 48 hrs, I measured expression of two regulatory genes on the jasmonate and ethylene pathways. Receiver response was unrelated to hormone treatment of donors in either gene, but the jasmonate response of donor and receiver pairs was correlated across treatments. Positive expression of both genes across donors and receivers and pervasive presence of spider mites suggested signal transfer may either have not occurred or been masked by already ongoing defensive responses. Results indicate the complexity of these systems, and further work is needed to better characterize defense signal transfer via ectomycorrhizal networks. Because of the importance of these mycorrhizal systems to ecosystem functioning, it is crucial that resource managers and scientists have a good understanding of mycorrhizal ecology. However, lower student interest in plants and fungi combined with difficulties visualizing belowground processes present challenges for teaching and learning mycorrhizal concepts. To address this, I co-created the digital plant-centric action-based game Shroomroot for use in lower level postsecondary settings. I conducted a pre-test/post-test evaluation of Shroomroot in a 2nd year postsecondary Introduction to Soil Science course. Students’ knowledge of mycorrhizal ecology increased after playing Shroomroot, and engagement with mycorrhizal content tended to increase after gameplay. These exploratory results suggest positive potential for action-based plant-oriented digital games in the higher education classrooms. Both studies focus on improving our understanding of mycorrhizae and mycorrhizal networks, ecologically and pedagogically. Greater understanding of mycorrhizae has the potential to improve our multi-faceted relationships with the ecosystems upon which we depend.

View record

Interspecific Interactions in Mixed Stands of Douglas fir and paper birch (2015)

No abstract available.

Mycorrhizal facilitation of kin recogniation in interior Douglas-fir (2013)

No abstract available.

Current Students & Alumni

This is a small sample of students and/or alumni that have been supervised by this researcher. It is not meant as a comprehensive list.
 

Membership Status

Member of G+PS

Program Affiliations

 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.