Soil fertility impact on plant photosynthetic strategies: from global scale to Maple-dominated forests to Sugar Maple individuals

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Understanding how soil fertility promotes the productivity of terrestrial ecosystems is currently under hot debate. Ecosystem productivity depends on the functional strategies that compose the ecosystem as well as their assembly within the community. Among important strategies, the ability of plants to alternatively use water (H2O) or nitrogen (N) resources for achieving a given leaf photosynthetic rate, has important theoretical impact to predict ecosystem productivity. However, photosynthetic functional strategies have been overlooked along spatial gradient of soils, which deliver most of the H2O and N resources to plants. In addition, the extent to which the adoption of an optimal photosynthetic strategy (maximizing carbon gain at the leaf scale) endangered confers dominance to species at the community scale, is essential but virtually unexplored in order to link functional strategies with ecosystem productivity.My recent research has demonstrated that soil pH is determinant over more classical soil fertility variables to understand the global patterns in leaf nutrition and H2O utilization. However, the mechanisms underlying these spatial patterns are poorly understood.In this proposal, I plan to determine how soil fertility, through its pH values, modulates the distribution of photosynthetic strategies between and within Maple-dominated forests. This ecosystem is of strong ecological, cultural and economic importance to Eastern North America but is endangered due to previous acidic atmospheric depositions.First we will define the mechanisms by which soil pH influences the optimal combination of functional traits that species adopt to capture, transport, use N and H2O resources and maximize carbon gain. Second we will determine how this optimal trait combination defines a community attractive point toward which species would converge in order to dominate. Then we will determine how soil pH defines the variance of functional strategies around this attractive point.Soil pH is strongly influenced by climate and it is important to spatially decouple its study. We will work at three complementary scales: (i) at the global scale using a global trait dataset; (ii) within a given climatic and vegetation envelope through a natural soil pH gradient caused by the underlying geology; (iii) at the individual tree level through a long-term liming treatment on a historically acidified soil.Coupling functional with community ecology, we will shed light on the role of soil fertility on the prediction of the optimal functional strategy between communities, the distribution of functional strategies within community and ultimately the ecosystem productivity. Central to this program, six highly qualified personnel will learn specialized research technologies, as well as using a multidisciplinary approach in order to leverage knowledge acquisition.