Lecture 5 Flashcards
Organisms obtain energy from _______, from inorganic chemical compounds, or through
the consumption of organic compounds.
Organisms obtain energy from sunlight, from
inorganic chemical compounds, or through
the consumption of organic compounds.
autotrophs
photosynthesis; chemosynthesis
energy is converted into chemical energy stored in C-C bonds of organic molecules
most autotrophs obtain energy through ______
photosynhesis
sunlight provides energy to take up carbon dioxide and synthesize organic compounds
photosynthesis
Energy in ecosystems originates with _______ by _____
primary production by autotrophs
Energy assimilated by autotrophs is stored as ______ _____ in plant tissue
carbon compounds
the currency used for the
measurement of primary production
Carbon
_______ is the rate of
primary production.
primary productivity
total amount of carbon fixed by autotrophs in an ecosystem
depends on the influence of climate on photosynthetic rate and leaf index (LAI) - lear area per unit of ground area
Gross Primary Production (GPP)
LAI varies among biomes:
Less than 0.1 in Arctic tundra (less than 10% of the
ground surface has leaf cover).
12 in boreal and tropical forests (on average, there
are 12 layers of leaves between the canopy and the
ground).
LAI = 1 means that 100% of the ground is
covered by leaves.
Net primary production (NPP)
NPP = GPP – respiration
NPP represents the biomass gained by the
plant.
NPP is the energy left over for plant growth,
reproduction and consumption by detritivores
and herbivores.
NPP allocated as carbon in plants (i.e. leaves,
stems, roots) and represents storage of carbon
in ecosystems.
Measuring belowground NPP is more
difficult.
Roots turn over more quickly than shoots;
that is, more roots are “born” and die
during the growing season.
Roots may exude a significant amount of
carbon into the soil, or transfer carbon to
mycorrhizal or bacterial symbionts.
Harvesting plant biomass is impractical for
large or biologically diverse ecosystems.
Solution: measure chlorophyll concentrations using satelitte
NDVI (normalized difference vegetation
index) uses
the difference between
visible light (VIS) and near-infrared
(NIR) reflectance to estimate the
absorption of light by chlorophyll
NDVI = (NIR - VIS)/(NIR + VIS)
NEE (net ecosystem exchange)
NEE = GPP – Ecosystem respiration
Eddy covariance method:
measures changes in CO2
concentrations between plant
canopies and the atmosphere
above; estimates NEE.
Phytoplankton turn over much more
rapidly than terrestrial plants, so
biomass at any given time is low
compared with NPP; harvest techniques
are not used.
Photosynthesis and respiration are measured
in water samples collected and incubated at
the site with light (for photosynthesis) and
without light (for respiration).
The difference in the rates is equal to NPP.
Global patterns of net primary production
reflect climatic controls and biome types.
Global NPP has been estimated to be 105
petagrams (1 Pg = 1015 g) of carbon per
year.
54% of this carbon is taken up by
terrestrial ecosystems, 46% by primary
producers in the oceans
Net primary productivity is constrained by
both _____ and _____ environmental
factors.
physical and biotic
The results of several experiments
indicate that nutrients, particularly
_______, control NPP in terrestrial
ecosystems.
nitrogen
In a fertilization experiment in two alpine
communities—dry and wet meadows—
N, P, and N+P were added to different
plots (Bowman et al. 1993).
NPP in lake ecosystems is often limited
by ________.
Many lake experiments use enclosures
called “limnocorrals”—clear containers
with open tops to which nutrients can be
added.
NPP is measured by change in
chlorophyll concentrations or number of
phytoplankton cells.
phosphorus availability
Whole-lake fertilization experiments have also been
done at the Experimental Lakes Area in Ontario.
Declining water quality in the 1960s motivated David
Schindler to do experiments to determine whether
inputs of nutrients in wastewater were causing the
dramatic increases in the growth of phytoplankton.
Nitrogen, carbon, and phosphorus were
added to all or half of several lakes.
Results showed that P was the limiting
nutrient.
P addition resulted in massive increases
in cyanobacteria.
Dead zones are
The bacterial decomposition of
algae from the blooms
depletes the dissolved
oxygen in the water.
areas of low
oxygen, and high fish and
zooplankton mortality.
Limiting nutrients vary in marine
ecosystems.
Estuaries are usually nutrient-rich;
variation in NPP is correlated with N
inputs from rivers.
N from agricultural and industrial
practices can result in blooms of algae
and “dead zones.”
In the open ocean, NPP is mainly
from phytoplankton.
Picoplankton (cells < 1 um)
contribute as much as 50% of
the total marine NPP.
Floating seaweeds such as
Sargassum also contribute to
NPP.
In coastal areas, kelp forests
may have leaf area indices
and rates of NPP as high as
those of tropical forests.
“Meadows” of seagrasses such as eelgrass (genus Zostera) are also important nearshore zones.
In the open ocean, NPP is mostly limited
by nitrogen.
But NPP in the equatorial Pacific Ocean
appears to be limited by iron (Martin et
al. 1994). P. 422-423
Variation in NPP among terrestrial
biomes is associated mostly with
differences in leaf area index and length
of growing season.
Variation in NPP among aquatic
ecosystems is primarily related to
variation in inputs of nutrients.
