III.10Peter M. Vitousek and Pamela A. Matson
Nutrient Cycling and Biogeochemistry
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.
|1. ||Element cycles in terrestrial ecosystems|
|2. ||Global element cycles|
|3. ||Illustration: Nutrient cycling in practice|
GLOSSARYbiological 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
|• ||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|
Questia, a part of Gale, Cengage Learning. www.questia.com
Book title: The Princeton Guide to Ecology.
Contributors: Simon A. Levin - Editor.
Publisher: Princeton University Press.
Place of publication: Princeton, NJ.
Publication year: 2012.
Page number: 330.
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