ABSTRACT

Unlike agricultural ecosystems that rely almost exclusively on an external supply of nutrients through fertilizer application, most natural, land-based ecosystems, like forests, prairies, and tundra, rely almost exclusively on internally recycled nutrients to support plant growth. In these natural ecosystems, the supplies of nutrients like nitrogen and phosphorus from weathering bedrock and deposition in rain and dust are so slow that less than 5% of the annual plant productivity can be met from these external sources. Instead, these ecosystems accumulate nutrients over thousands of years and reuse and recycle them via internal nutrient cycles. This almost exclusive dependence on internally recycled nutrients means that the response of these ecosystems to a changing environment or to disturbance has to rely on a redistribution of nutrients already in the ecosystem, at least for the first few decades. Over hundreds of years, these responses depend on the ability of the ecosystem to retain and recycle more nutrients. This project will compare and contrast various types of ecosystems, from grassland to forest, from tropical to arctic, and develop a general model to describe how these ecosystems accumulate nutrients over time and how their dependence on recycled nutrients affects their responses to a varying climate, elevated carbon dioxide, and disturbances like wildfire, biomass harvest, or storm damage. The study promises to make an important contribution to our understanding of general ecosystem function, which will be valuable to increase understanding of how ecosystems around the world are regulated, how they respond to climate and disturbance, and how they can be managed as a sink for carbon dioxide in the future. It will also increase understanding of how and why ecosystems differ in their stability, resilience to disturbance. Researchers also will develop a teaching module for use in undergraduate courses to allow students to explore nutrient regulation of ecosystems. The model and associated data will be available to researchers and educators on the web and will also serve to link both research and educational programs at the Marine Biological Laboratory. This project will support one full-time post-doctoral scholar and a masters-level research assistant.

This project builds on a theory of resource optimization and element interactions within ecosystems as formulated in the Multiple Element Limitation model, which simulates the optimization of resource acquisition by vegetation and soil microbes, the synchronization of nutrient cycles within ecosystems, and the coupling of these nutrient cycles with energy, carbon, and water fluxes through ecosystems. Through synthesis of existing data and the implementation and analysis of a model of the interactions among carbon, nitrogen, phosphorus, and water in terrestrial ecosystems, this project will examine biogeochemical constraints on responses to climate and disturbance and the consequent effects on carbon sequestration and ecosystem nutrient capital. Resource optimization describes how plants and microbes regulate the acquisition of vital resources to both maintain their metabolic balance and maximize growth. It is through this optimization and the balanced interactions between plants and soil microbes that ecosystems can accumulate vital nutrients and recycle them internally, which in turn allows higher production and carbon sequestration than would otherwise be possible. By comparing and contrasting responses to climate and recovery from disturbance in several different types of terrestrial ecosystem, this project will further advance the theory of resource optimization and element interactions in ecosystems, assess the mechanisms by which tight within-ecosystem nutrient cycles are synchronized, and evaluate the potentials of carbon and nutrient sequestration or loss across the globe.

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