Toward Forest Growth: Understanding Nitrogen in Soils
Forests in the Northeastern United States—and other northern, temperate, boreal regions—need nitrogen to expand, but there’s a problem: access to it. Plants can’t retrieve the nitrogen stored in soils. Carmen Enid Martínez, Integrative Plant Science, and Christine Goodale, Ecology and Evolutionary Biology, are uncovering why.
Nitrogen is the nutrient most often limiting forest growth, and this limitation is a primary constraint to future terrestrial strategies for reducing carbon dioxide. The limitation exists despite enormous stores of fixed nitrogen in soils that are typically an order of magnitude larger than the nitrogen stored in trees. The ability of plants to acquire this nitrogen may depend in part on its form in soil organic matter, the activity of soil microbes and other soil organisms, the type and activity of plant mycorrhizal associations, and the ability of plants to enhance this mineralization activity. The exact mechanisms by which this large soil nitrogen pool accumulates also remains uncertain.
In this project, funded by the Agriculture and Food Research Initiative Foundational Program, Martínez and Goodale leverage a long-term nitrogen-15 tracer study. They conduct a series of laboratory incubation experiments and molecular analyses to substantially improve understanding of how soils retain nitrogen. These studies trace the fate of added nitrogen over a range of environmental conditions and timescales and examine the form of nitrogen retained in soil as well as the long-term potential for redistribution of this nitrogen to plants. Ultimately, Martínez and Goodale investigate the fundamental structure and function of plant-soil interactions in forest ecosystems. Because the research addresses fundamental processes, the results also translate to a variety of terrestrial ecosystems. The research has broad applications to the effects of nitrogen retention and to plant nutrition and environmental quality. This work also provides foundational research for improved process-based models of forest ecosystem function.