Chapter 19
Ecosystem
Essentials
Robert W. Christopherson
Charlie Thomsen
Biosphere
The space on Earth where life exist forms a
sphere which extends from ocean floor to
~8km altitude into the atmosphere.
Ecosystem: A self-sustaining association of
living plants, animals and microbes and their
nonliving physical environment.
1) Natural ecosystems are open systems with respect to energy and
matter.
2) Ecosystem boundaries often function as transition zone, not sharp
demarcations.
3) Natural ecosystems can varying significantly in size
Ecology
Ecology is the study of the relationship
between organisms (human beings, plants,
animals, microbes) and their environment
and among the various
a) the living organisms have impacts on the environment.
lichens/mosses grow on rocks soils
growth of trees add litter to soils more fertile soil
wolfs eat deer reduce deer population
b) through altering the environment, their impacts also have feedbacks
to themselves.
lichens/mosses grow on rocks soils higher plants to grow lichens/mosses compete out
Wolfs eat deer reduce deer population less food for wolf Humans as Most Agents
Deforestation:
timber economic gains better life more people
more space for agriculture more food more people
loss of other lives loss of resources
soil erosion land degradation less food
Agriculture
more food more people
expansion loss of other land (grass, forest, wetland …)
fertilization/pesticide more food pollution disease
Urban expansion
better living more people
expansion loss of other lands
Fossil fuel use
better living more people
global warming/pollution Ecosystem Essentials
Ecosystem Components and Cycles
Biotic Ecosystem Operations
Ecosystems, Evolution, and Succession
Ecosystem Components
Like any system in general, it is made up of several
components, each function independently yet in
concert.
biotic
individuals population Communities
producers (plants), consumers (animals), decomposers
Abiotic Ecosystem Components
soils, light, heat (temperature), water, air
As ecosystems are open systems, there are constant flow of
energy and matter through the system to keep the system
alive.
Biotic and Abiotic Components
Figure 19.2
Small Leaves do the Big Job: Photosynthesis
roplast
6CO 2 + 6H 2 O light/Chlo

→ C6 H12 O 6 + 6O 2 ↑
CO2
Underside
H2O
stoma
Losing water is the price to pay for gaining CO2
Plants also keep cool with transpiration
Concepts
Net Photosynthesis
Plants consume energy and release CO2 during the process of
photosynthesis. Because photosynthesis only happens during the
day time, we call this respiration as day respiration (note: this is
not part of the autotrophic respiration). The net carbohydrate the
photosynthesis produce is called net photosynthesis.
Compensation Point
The point when the day respiration and photosynthesis break
even: CO2 compensation point vs. light compensation point
Light Saturation Point
The point when increase of light energy on the leaves will not
lead to the increase in photosynthesis rate.
Stomatal Regulation
1. Stoma opens when light shine on the leaf, thus opens during the day to
absorb CO2 and closes during night to prevent unnecessary water loss.
2. Stoma closes when there is limited water in the soil.
3. Stoma closes when the air is too dry, i.e. high vapor pressure deficit.
4. Stoma closes to save water when CO2 concentration is high in the air.
Gross Primary Production and Respiration
GPP: Gross Primary Production, the amount of carbohydrate
(C6H12O6) produced is called gross primary production.
Plant Respiration: All living organism needs energy to stay
alive. Plants do too. Plants use about 50% of GPP they
produce to stay alive. The respiration is the opposite process
of photosynthesis. We call this respiration as autotrophic
respiration (Ra).
C6 H12O 6 + O 2 
→ CO 2 + H 2O + Energy
Autotrophic respiration is use for two purpose:
(1) to keep living tissues alive, called maintenance respiration.
(2) To realize growth, call growth respiration.
Note: Energy is not heat energy as said in the textbook, but energy in the
form plant can use, ATP (Adenosine Triphosphate)
Net Primary Production
NPP: Net Primary Production is the balance of GPP after plant
respiration (autotrophic respiration) is taken away.
NPP = GPP – Ra
NPP is the part of photosynthesis product that can be used for
growth, including
Leaves
Branches
Stems
Roots
Part of NPP become food resources available for the
consumers ( herbivores, carnivores, humans)
Photosynthesis and Respiration
Figure 19.5
Energy Budget of the Biosphere
Herbivore consumption
Energy Received
but not fixed
Biomass Remaining
Net Primary Production
Figure 19.6
Biomass vs. Net Primary Production
Biomass
The dry weight of the living organisms. e.g. the total dry weight
of leaves, branches, stems, and roots would be the biomass of a
tree, not including the dead leaves or stems on the floor.
For plants, Biomass is the accumulated NPP that stays as part
of the living organism. Due to litter fall and mortality, Biomass
is less than the annual NPP added up. Biomass is a cumulative
figure, NPP is an annual figure.
For forests, the biomass eventually levels off as the addition of
growth from NPP breaks even with loss of biomass due to litter
fall and mortality.
Net Primary Productivity
Figure 19.7
Global NPP
b
ta
is
Th
le
o
is
ut
d!
te
da
This Table is confused between Biomass and NPP. We do not have an reliable figure for
global biomass. The annual NPP on land is approximately ~56 Billion tons Carbon/year, and
annual NPP in the oceans is approximately 49 billion tons Carbon/year.
Net Ecosystem Production (NEP)
NPP: Tells us how much CO2 plants suck from the
atmosphere, offsetting CO2 released by fossil fuel burning.
Ecosystems also releases carbon into the atmosphere:
Autotrophic Respiration (Ra)
Heterotrophic Respiration (Rh)
Rh: Carbon released into to atmosphere by microbes
(decomposers) decomposing the detritus materials.
NEP= NPP- Rh
Carbon Sink: Taking CO2 away from the atmosphere
Carbon Source: Adding CO2 into the atmosphere
Net Ecosystem Production
Kyoto Protocol (signed in Kyoto, Japan in 1997):
Developed countries reduce their CO2 emission by 5% at the
1990 level during 2008-2012 period.
No-plan post 2012: Copenhagen will not have a binding
Protocol as it was announced in APEC meeting.
Carbon absorbed by forests established after 1990 can be used
to offset carbon emission. These forests were later called
Kyoto Forests.
Potential problems with Kyoto Forests:
Abiotic Factors
Light
Temperature
Water
Nutrients
Air
Abiotic Factors: Light
Light provides energy for photosynthesis
Plants use visible light (photosynthetically active radiation,
PAR) in photosynthesis.
latitudinal adaptation of plants to daily sun
shine hours (photoperiod):
Plants that need long photoperiod to flowering
Plants that need short photoperiod to flowering
Abiotic Factos: Temperature and Precipitation
Water is a raw
material for
photosynthesis.
Water can cool off
leaves through
transpiration.
Water influences
plants to regulate
its stomatal
opening, thus its
ability to absorb
the other raw
material.
PSN is a complex biochemical
process. It requires a special
enzyme (RuBP) to complete the
carbon fixation process. The
enzyme activity is a function of
temperature.
Figure 19.8
Abiotic Factors: Nutrients
Plant need more than 20 elements in addition to C, H, O as
seen in C6H12O6.: N, P, K, S, Ca, Mg, …
The most needed elements is N as it is a key elements in
protein.
NO-3(Nitrate) and NH+4 (Ammonium) are the only form N plants can
use. Therefore, even 78% of air is N2, plants cannot use it directly.
Plants reabsorb N released from the detritus materials decomposed
Plants transfer N not needed from old leaves to new leaves.
Plants form symbiotic association with bacteria/algae or mycorrhizal
fungi.
N availability to plants in natural world depends on soil types and its
organic matter content.
Abiotic Factors: Air
Plants need air to breath to stay alive.
Plants breath in O2 for respiration.
Plants breath in CO2 for photosynthesis
For many plants two much water in the soil can
suffocate plants due to lack of air in the soil.
Some plants develop special mechanisms to provide
O2 for roots, such as prop roots in mangrove forests.
Life Zones
Figure 19.9
Element Cycles
If consider the Earth ecosystem as a whole, it
is a closed system in terms of matter. But the
flow of matter in the system never ceases.
Elements cycle in the system so they can be
used and reused …
•Carbon
• Oxygen
• Nitrogen (Phosphate, Sulfur, …)
• Water
Figure 19.10
Carbon Cycle and Balance
Input: 6.3 (fossil) + 1.6 (landuse)=7.9
Output: 1.4 +1.7 =3.1
Balance: 7.9-3.1 = 5.8
Actual increase seen: 3.2
Missing 2.2 C in the atmosphere: missing sink
Figure 19.10
The Nitrogen Cycle in the Ecosystem
Lighting/biological fixation
NH3
decomposition
Ecosystem
NH+4
NO
NO
N 2O
nitrification
N 2O
denitrification
N2
NO-3
NH3: ammonia
NH+4: ammonium
NO-3: Nitrate
NO: Nitric Oxide
N2O: Nitrous Oxide
Figure 19.11
Global Nitrogen Cycle
Figure 19.11
Global Industrial Nitrogen Fixation
Industrial Nitrogen fixation:
N is the most needed nutrients in the natural
environment for plant growth. So is it true for crops.
Since 1970, industrial nitrogen fixation in fertilizers
exceeded the natural fixation (140 million metric
tones).
Extra N into the streams and oceans cause algal bloom,
depleting surface water O2, killing aquatic lives.
Figure 19.11
The Gulf Coast Dead Zone
Figure 19.2.1
Energy/Matter Flow in Ecosystems
Producers, Consumers, and Decomposers
Producers: Plants on land
Phytoplankton in oceans
Consumers: Primary (herbivores), secondary
(carnivores), tertiary (carnivores),
omnivores
Decomposers: bacteria and fungi
Energy, Nutrient,
and
Food Pathways
Figure 19.13
Food Chains
Figure 19.14
Food Webs
Figure 19.15
Temperate Forest Food Web
Figure 19.16
Energy and
Nutrient
Flows
Figure 19.19
Biomass Consumption and Efficiency
Figure 19.17