Principles of terrestrial ecosystem ecology.pdf

376 Glossary
Alfisol. Soil order that develops beneath temperate
and subtropical forests, characterized
by less leaching than spodosol.
Allocation. Proportional distribution of photosynthetic
products or newly acquired nutrients
among different organs or functions in a
plant.
Allochthonous input. Input of energy and
nutrients from outside the ecosystem; synonymous
with subsidy.
Allometric relationship. Regression relationship
that describes the biomass of some part
of an organism as a function of some easily
measured parameter (e.g., plant biomass as a
function of stem diameter and height).
Ammonification. Conversion of organic nitrogen
to ammonium due to the breakdown of
litter and soil organic matter; synonymous
with nitrogen mineralization.
Amorphous minerals. Minerals with no
regular arrangements of atoms.
Anadromous. Life cycle in which reproduction
occurs in lakes, streams, or rivers while the
adult phase occurs primarily in the ocean.
Anaerobic. Occurring in the absence of
oxygen.
Andisol. Soil order characterized by young
soils on volcanic substrates.
Angular momentum. Force possessed by a
rotating body.
Anion. Negatively charged ion.
Anion exchange capacity. Capacity of a soil to
hold exchangeable anions on positively
charged sites at the surface of soil minerals
and organic matter.
Anthropocene. Geologic epoch characterized
by human impacts, initiated with the
Industrial Revolution.
Anthropogenic. Resulting from or caused by
people.
Arbuscular mycorrhizae. Mycorrhizae that
exchange carbohydrates between plant roots
and fungal hyphae via arbuscules; also
termed vesicular arbuscular mycorrhizae or
endomycorrhizae.
Arbuscules. Exchange organs between plant
and mycorrhizal fungus that occur within
plant cells.
Aridisol. Soil order that develops in arid
climates.
Aspect. Compass direction in which a slope
faces.
Assimilation. Incorporation of an inorganic
resource (e.g., CO2 or NH4 + ) into organic
compounds; transfer of digested food
from the intestine to the bloodstream of
an animal.
Assimilation efficiency. Proportion of ingested
energy that is assimilated into the bloodstream
of an animal.
Assimilatory nitrate reduction. Conversion of
nitrate to amino acids by soil microbes.
Autochthonous production. Production occurring
within the ecosystem.
Autotroph. Organism that produces organic
matter from CO2 and environmental energy
rather than by consuming organic matter
produced by other organisms. Most produce
organic matter by photosynthesis; synonymous
with primary producer.
Available energy. Absorbed energy that is not
stored or conducted into the ground; it is the
energy available for turbulent exchange with
the atmosphere.
B horizon. Soil horizon with maximum accumulation
of iron and aluminum oxides and
clays.
Backscatter. Reflection from small particles.
Base cations. Nonhydrogen, nonaluminum
cations.
Base flow. Background stream flow from
groundwater input in the absence of recent
storm events.
Base saturation. Percentage of the total
exchangeable cation pool that is accounted
for by base cations.
Benthic. Associated with aquatic sediments.
Biofilm. Microbial community embedded in
a matrix of polysaccharides secreted by
bacteria.
Biogenic. Biologically produced.
Biogeochemical cycling. Biologically mediated
cycling of materials in ecosystems.
Biogeochemistry. Biologically influenced
chemical processes in ecosystems.
Biological pump. Flux of carbon and nutrients
in feces and dead organisms from the
euphotic zone to deeper waters and the
sediments of the ocean.