Nutrient cycling and limitation in soils of higher latitude ecosystems

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Phosphorus (P) and nitrogen (N) often limit or co-limit plant growth in terrestrial ecosystems. Many studies have suggested that the availability of these two nutrients differs during soil development. While plant growth during early stages of soil development is mostly N-limited, it becomes increasingly P-limited on older soils. Most soils in Canada are relatively young on a geological timescale, because they have developed since the last glaciation approximately 12,000 years ago. For this reason, it is generally assumed that plant growth in most Canadian ecosystems is N-limited. The combustion of fossil fuels and the volatilization of N-fertilizers have substantially increased the atmospheric deposition of N in the northern hemisphere. Many natural ecosystems in Canada might therefore have shifted from being primarily N-limited to being P-limited or P co-limited, with unknown consequences to for primary productivity, plant and microbial community structures, net ecosystem exchange of CO2 and ecosystem stability and resilience. My research program therefore aims to elucidate how a changing supply of N affects the biogeochemical cycling and availability of P in soils of non-agricultural ecosystems in higher latitudes. Both laboratory and field experiments will be carried out to answer research questions ranging from the molecular to the ecosystem scale. Field experiments will be conducted in forest and wetland ecosystems, specifically in a temperate mixed deciduous and coniferous forest on Mont Saint Hilaire, QC, in an ombrotrophic bog in Mer Bleue, ON, and in a boreal forest in the Experimental Lakes Area, ON. The effect of increasing supply of N on the bioavailability of P in soils of these ecosystems will be investigated by measuring enzyme activities, changes in concentration of geochemical soil P-pools and by quantifying atmospheric P inputs to nutrient poor organic soils. A special focus will be on the use of oxygen isotopes in phosphates to trace sources, sinks and biogeochemical processes in the environmental P-cycle. If necessary, new laboratory methods will be developed to address specific questions dealing with P-cycling in soils with high organic content, for example peatland soils and boreal forest soils. In summary, this research program will give new and fundamental insights into the cycling, limitation and fluxes of P and N in terrestrial ecosystems in Canada and elsewhere, as these ecosystems adapt to anthropogenic impacts and global change.