Apportionment study of calcium nutrition of boreal tree species

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The goal of this research is to assess the role of calcium (Ca) nutrition on tree growth in boreal forests. Intense forest harvesting practices may favor increased exports of Ca from the ecosystem to a point that Ca may become limiting to trees before nitrogen. Increased air pollution with a concomitant increase in rain acidity and leaching of Ca will only exacerbate its export. It has therefore been suggested that foliar Ca deficiencies and subsequent health problems/growth declines will occur in air polluted and/or commercial boreal forests if Ca exports are in excess of those added naturally or by fertilization. These forests grow on coarse-textured acidic soils that slowly release Ca from soil mineral weathering and thus, the paradigm that the Ca in trees are those mobilized into the soil solution from weathering is being challenged by studies showing that contributions of atmospherically derived Ca to the trees in some ecosystems is very large and that the trees are almost fully decoupled from Ca coming from deeper soil sources. The next five years will therefore aim at determining the capacity of Canadian and Scandinavian boreal tree species with different functional traits to promote soil mineral weathering and make use of the released Ca when availability is low and/or being intensely competed for (deficient). The applicant's plan is to investigate Ca nutrition by using alkali earth element ratios and strontium isotopes as tracers. Tree species will be studied in growth chambers and in the field along gradients of soil fertility, plant competition, and productivity. The results will then be used to find the best indicators of Ca supply and tree growth and implement them in landscape productivity models with permanent site variables (e.g., climate and drainage) and nitrogen as driver variables. These indicators are important from a forest management perspective as they will allow scientists and forest managers to better forecast growth rates of forest stands and therefore, make better planning of forest utilization. In the long term, this research will help identify if some stands are sensitive to exports in Ca and whether the integrity of these forests is jeopardized by harvesting.