The Princeton Guide to Ecology

By Simon A. Levin | Go to book overview

III.10
Nutrient Cycling and Biogeochemistry
Peter M. Vitousek and Pamela A. Matson
OUTLINE
1. Element cycles in terrestrial ecosystems
2. Global element cycles
3. Illustration: Nutrient cycling in practice
Studies of nutrient cycles involve integrating information from very fine spatial and temporal scales (the dynamics of enzymes in the neighborhood of microbes) to very coarse scales (the global biogeochemical cycles); they involve integrating the dynamics of organisms with those of the environment that they inhabit and help to shape. Some of the finest-scale, most biological of processes (e.g., the growth of microbial populations on chemically recalcitrant plant litter) control important aspects of the Earth system (e.g., the persistence of nitrogen limitation to primary production, as in the example above). Nutrient cycles cannot be studied effectively in isolation, whether that means isolation from a consideration of both biological and geochemical processes or isolation from understanding the substantial and increasing influence of human activity on the Earth system.
GLOSSARY
biological nitrogen fixation. The enzyme-mediated reduction of atmospheric dinitrogen (N2) to chemical forms that can be used by most organisms.eutrophication. Overenrichment of ecosystems resulting from excessive additions of nutrients; eutrophication may create anaerobic conditions (“dead zones”) in aquatic ecosystems.mineralization. With reference to phosphorus and nitrogen, mineralization is the microbially mediated conversion of organically bound nutrients to soluble, biologically available inorganic forms.mycorrhizae. Mycorrhizae are a symbiosis between the roots of most higher plants and several groups of fungi, in which the fungal partner typically derives energy from the plant and the plant receives nutrients from the fungus.nitrification. The biologically mediated oxidation of ammonium (NH4) to nitrate (NO3); specialized microorganisms derive their energy from this transformation.nutrient limitation. Nutrient limitation occurs where the rate of a biological process like productivity or decomposition is constrained by a low supply of one or more biologically essential elements.weathering. The breakdown of rocks and minerals, at least partly into soluble and biologically available components.within-system cycle. Transfers of nutrients among plants, animals, microorganisms, and soil and/or solution, within the boundaries of an ecosystem.We define a “nutrient” as an element that is required for the growth of some or all organisms—and one that plants typically acquire from soil or solution (as opposed to the uptake of carbon from gaseous forms). The cycles of nutrients are interesting to ecologists for many reasons, including the following:
A low supply of a nutrient can constrain the growth and populations of organisms and the productivity, biomass, diversity, and dynamics of entire ecosystems.
Losses of nutrients from terrestrial ecosystems represent inputs to aquatic systems and to the atmosphere. In the atmosphere, reactive nitrogen gases influence atmospheric chemistry and climate; in freshwater and marine systems, inputs of N and P can drive eutrophication (overenrichment). Element losses thus represent a useful currency for evaluating land–water and landatmosphere interactions.
The cycles of multiple elements are altered on regional and global scales by human activity. Much research in this area has focused on the global cycle of carbon, in part because of the importance of CO2 in the climate system, but

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