Lecture 5

Question 1

Organisms obtain energy from _______, from inorganic chemical compounds, or through
the consumption of organic compounds.

Answer 1

Organisms obtain energy from sunlight, from
inorganic chemical compounds, or through
the consumption of organic compounds.

Question 2

autotrophs

Answer 2

photosynthesis; chemosynthesis

energy is converted into chemical energy stored in C-C bonds of organic molecules

Question 3

most autotrophs obtain energy through ______

Answer 3

photosynhesis

Question 4

sunlight provides energy to take up carbon dioxide and synthesize organic compounds

Answer 4

photosynthesis

Question 5

Energy in ecosystems originates with _______ by _____

Answer 5

primary production by autotrophs

Question 6

Energy assimilated by autotrophs is stored as ______ _____ in plant tissue

Answer 6

carbon compounds

Question 7

the currency used for the

measurement of primary production

Answer 7

Carbon

Question 8

_______ is the rate of

primary production.

Answer 8

primary productivity

Question 9

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

Answer 9

Gross Primary Production (GPP)

Question 10

LAI varies among biomes:

Answer 10

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.

Question 11

Net primary production (NPP)

Answer 11

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.

Question 12

Measuring belowground NPP is more

difficult.

Answer 12

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.

Question 13

Harvesting plant biomass is impractical for

large or biologically diverse ecosystems.

Answer 13

Solution: measure chlorophyll concentrations using satelitte

Question 14

NDVI (normalized difference vegetation

index) uses

Answer 14

the difference between
visible light (VIS) and near-infrared
(NIR) reflectance to estimate the
absorption of light by chlorophyll

NDVI = (NIR - VIS)/(NIR + VIS)

Question 15

NEE (net ecosystem exchange)

Answer 15

NEE = GPP – Ecosystem respiration

Question 16

Eddy covariance method:

Answer 16

measures changes in CO2
concentrations between plant
canopies and the atmosphere
above; estimates NEE.

Question 17

Phytoplankton turn over much more

rapidly than terrestrial plants, so

Answer 17

biomass at any given time is low
compared with NPP; harvest techniques
are not used.

Question 18

Photosynthesis and respiration are measured
in water samples collected and incubated at
the site with light (for photosynthesis) and
without light (for respiration).

Answer 18

The difference in the rates is equal to NPP.

Question 19

Global patterns of net primary production

reflect climatic controls and biome types.

Answer 19

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

Question 20

Net primary productivity is constrained by
both _____ and _____ environmental
factors.

Answer 20

physical and biotic

Question 21

The results of several experiments
indicate that nutrients, particularly
_______, control NPP in terrestrial
ecosystems.

Answer 21

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).

Question 22

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.

Answer 22

phosphorus availability

Question 23

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.

Answer 23

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.

Question 24

Dead zones are

The bacterial decomposition of
algae from the blooms
depletes the dissolved
oxygen in the water.

Answer 24

areas of low
oxygen, and high fish and
zooplankton mortality.

Question 25

Limiting nutrients vary in marine

ecosystems.

Answer 25

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.”

Question 26

In the open ocean, NPP is mainly

from phytoplankton.

Answer 26

Picoplankton (cells < 1 um)
contribute as much as 50% of
the total marine NPP.

Floating seaweeds such as
Sargassum also contribute to
NPP.

Question 27

In coastal areas, kelp forests
may have leaf area indices
and rates of NPP as high as
those of tropical forests.

Answer 27

“Meadows” of seagrasses such 
as eelgrass (genus Zostera) 
are also important nearshore 
zones.

Question 28

In the open ocean, NPP is mostly limited

by nitrogen.

Answer 28

But NPP in the equatorial Pacific Ocean
appears to be limited by iron (Martin et
al. 1994). P. 422-423

Question 29

Variation in NPP among terrestrial
biomes is associated mostly with
differences in leaf area index and length
of growing season.

Answer 29

Variation in NPP among aquatic
ecosystems is primarily related to
variation in inputs of nutrients.