Current major research themes and questions in the Grogan lab:
ARCTIC research
Role of phosphorus as well as nitrogen in tundra plant community structure and responses to climate
change
P as a plant growth regulator – Do the Daring Lake results indicating N P co-limitation of
deciduous shrub (and graminoid) growth apply across the low arctic? (pan-Arctic N:P ratio study;
N P addition study at Umiujaq)
What can we learn by comparing low level with high level N and P addition effects on mesic
tundra plant communities, and what are the implications in terms of potential climate change
responses?
What is the mechanistic nature of the NP co-limitation, given that birch (at least) responds to
high level N only additions, but not to low level N only additions?
Soil P availability to plants – What is the relative importance of microbial and abiotic processes
and the impact of climate change on P as compared to N?
Transfers to downslope ecosystems – Are there significant movements of N and P in snowmelt
water to downslope ecosystems? Is P (or N) deposition on snow (in dust and/or biota) a
significant P input to tundra ecosystems?
What is the influence of factorial N and P fertilisation (and greenhouse warming) on mesic
tundra soil bacterial and fungal community structure (Fierer)?
Tundra plant community responses to summer warming
Is the relatively strong greenhouse warming response of evergreen compared to deciduous
shrubs at Daring Lake a widespread phenomenon?
Is it a short-term response that will eventually switch to deciduous shrub dominance?
Is the evergreen shrub response explained by the microbial N uptake ‘sponge saturation’
hypothesis coupled with the concept of superior evergreen capacity for nutrient uptake in
nutrient-limiting environments?
Coupled to the above question, what is the outcome of tundra plant-soil microbial competition
for ambient and climatically realistic, slow and moderate increases in nutrient availability over a
5-10 year time scale (low level N and P addition plots, the one-year only high N addition plots,
Abisko (Michelsen) and Daring 15N plots)?
Are our very recent data suggesting declining impacts of greenhouse warming on annual plant
growth a climate anomaly (cold early July) or a result of depleting labile soil organic matter pools
(short term decomposition response to warming hypothesis)?
Are we being oversimplistic in focussing on N (and lately P) availability as drivers of plant
community change – What are the impacts of experimental warming on potential plant growth
limitation by the availabilities of Mg, K, S, Ca, Fe, Mn, Zn, B, Cu and Mo?
What will happen the graminoids? Is herbivory the primary constraint on their potential
response to warming? Graminoid response to N+P is greater than for N or P alone, and is also
very noticeable as tall grass (Calamagrostis?) patches in the N+P areas within exclosure plots,
and over buried caribou carcass. Graminoid shoot biomass is doubled in the greenhouses.
The potential for low to tall shrub tundra vegetation transition – How, When, Where, Which?
Do dendrochronological analyses of shrub growth rates at warming and relatively stable sites
(Umiujaq and Daring Lake respectively) match climate trends?
Why is it that Birch seems to be the most responsive to warming in Eastern Canada, while Alder
seems to dominate responses in W. Canada and Alaska?
Are the scattered trees (black spruce) in the Daring region providing viable seed that could
facilitate the predicted treeline expansion from its current position about 75 km to the south
into this area over the next 100 years?
Soil microbial community and nutrient cycling dynamics between winter and summer
Are there discrete ‘critical times’ – the snowmelt water percolation thaw-freeze hypothesis; the
microbial crash at complete snowmelt
Are fungi and bacterial communities similarly affected?
What is the significance of these microbial dynamics for nutrient availability to plants, nutrient
flushes downslope, and denitrification?
Deepened snow in tundra
Does it impact plant nutrient acquisition and growth (Shrub-snow hypothesis)?
How are leaf litter decomposition rates affected over multiple years, and within the winter and
shoulder seasons?
Is there a follow-on effect of deepened snow on ecosystem and soil respiration in the following
summer, and if so, what is the cause (the depleted labile carbon hypothesis)?
Soil microbial community (fungi and bacteria) structural patterns down the active layer and into the
permafrost
Are there distinct depth-specific communities all the way down into the permafrost, and can we
infer functional impacts of a climate-warming induced deepened active layer?
What biogeochemical and physical factors determine the composition and structure of depthspecific communities in the active layer and permafrost?
Are the answers to the above two questions influenced by the overlying vegetation-type?
Is variation in community structure with depth greater or less than variation across surface soil
horizontal space? (ADAPT trans-Canada cores)
Do the fundamental differences between prokaryotes and eukaryotes results in different panArctic biogeographical community patterns for soil bacteria as compared to soil fungi? (Prieme)?
TEMPERATE FOREST research
Has the recent history of high deer browsing resulted in an alternative stable state in Ontario temperate
forests?
Does abundant sedge cover in the understory inhibit growth of other plant species?
What are the primary controls on maple seedling production and progression to the sapling stage?
TEMPERATE GRASSLANDS research
Will increased atmospheric nitrogen deposition significantly alter plant species diversity (richness and
evenness) and primary production (above and below-ground)?
What is the relative importance of bottom up (water and/or nutrient availability) compared to top-down
(deer herbivory) on plant community structure and productivity?
What are the likely impacts of decreased summer precipitation on these grasslands as climate changes
over the next 100 years?