Nutrient Manipulations in Terrestrial Ecosystems

Abstract

Abstract: Nutrient addition experiments can be used to address a variety of questions, including the role of nutrients in mediating ecosystem processes, nutrient effects on plant and microbial community dynamics, the limitations on plant growth and ecosystem production, and the response of ecosystems to increased atmospheric deposition of nutrients. When designing a nutrient addition experiment, it is critical to minimize the impact of the fertilizer additions on soil pH, salt toxicity, and the supply of other potentially limiting nutrients that are not being tested (e.g., S, Ca). It is also important to understand whether a lack of response to fertilization is due to the absence of limitation for that nutrient, or the failure of the nutrient additions to become available to plants. This is especially important when comparing responses of plant growth to nutrient additions across sites, where factors controlling fertilizer availability could differ substantially. Isotopes are an invaluable tool for attaining a mechanistic understanding of the fate and dynamics of nutrient additions. They can be used to test how much of the fertilizer becomes available to plants, elucidate mechanisms of nutrient retention and loss, detect changes in soil nutrient dynamics, and trace competitive uptake between different plant species and microbial groups. The incorporation of isotope methods into nutrient addition experiments should solidify our understanding of the controls of nutrients over all aspects of the ecosystem.