Hedin Lab

Research in my laboratory centers on ecosystem analysis, with emphasis on the emergence and maintenance of geographically broad patterns in cycling of nutrients and greenhouse trace gases. Postdoctoral, graduate, and undergraduate students work on diverse topics that range from local-scale microbial processes to global-scale controls on ecosystem structure and function. Our current interests fall in three general areas: 1) Broad controls on nutrient cycles in temperate and tropical forests; 2) Emergence of macroscopic properties (e.g., stoichiometric ratios and ecosystem functions) from Darwinian selection; and 3) Biophysical controls on soil-atmosphere exchange of the greenhouse gas methane.

I am particularly interested in understanding how biogeochemical cycles are changing globally in response to large-scale modern human activities, and how such changes influence evolutionary environments of plants and microbes. While it is difficult to find ecosystems that are entirely free of human disturbances, we have for over a decade studied remote forests in southern Chile and Argentina that are historically free from atmospheric pollution, cutting, and other major human influences. These studies offer a "baseline" for how forests function naturally as biogeochemical systems, against which mechanisms and extents of human impacts can be better understood. We are presently expanding these studies to include tropical forests across the Hawaiian archipelago, the Amazon basin, Panama, and locations in Africa.

From an evolutionary perspective we seek to understand why macroscopic patterns in nutrient cycles emerge despite the complex interplay of myriad biotic and abiotic elements, and despite the propensity for evolution to alter organism-nutrient relations over time. We are developing a series of models to explore how plant and microbial functional properties are magnified through Darwinian selection on strategies such as competition, cooperative maximization, but also Nash-type interactions that appear dilutive at the ecosystem level.

We also seek tounderstand the biogeochemical function of microbial communities from a thermodynamic perspective. Our current efforts focus on microbial transformations of methane, a powerful heat-trapping gas that influences the Earth's climate system. We have recently developed a new 13CH4 isotope pool-dilution technique that permits us to separate the central and competing microbial processes of methane production and consumption, and to understand how these processes depend on biophysical factors within and across soils. We are particularly interested in whether rates of methane transformations follow fractal self-similarity scaling laws.

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