BIOB50H3 Chapter Notes - Chapter L#20: Silt, Rhizobia, 2-Step Garage
LECTURE #20, pages: 449-455, 494-498, 502-504, 507-508
CHAPTER 20: PRODUCTION
-Ecosystem: all the components of an ecological system, biotic or abiotic, that influence
the flow of energy and elements
Elements = nutrients, but also pollutants
PRIMARY PRODUCTION (20.1)
-Primary production: the fixation of carbon during photo/chemo synthesis
Is the conversion of light energy from the sun into chemical energy
Carbon © is the currency used for the measurement of primary production the
rate of primary production is called primary productivity
Gross primary production is total ecosystem photosynthesis
-Gross primary production: equivalent to the total of all plant photosynthesis is
controlled by climate and by the leaf area of the plants above ground (called the leaf
area index, which has no units)
Leaf area index varies among biomes (0.1 in tundra, 12 in tropics)
More leaves = more shading shading of leaves below the upper most layer
increases w/ each new leaf layer so the incremental gain in photosynthesis for each
lead layer added decreases
Plants match their LAI w/ climate for maximize carbon gain
- Plants use 50% of carbon for biosynthesis and cellular respiration
Plants that have a large portion of non-photosynthetic stem tissue (eg.
Trees/shrubs) tend to have higher overall respiratory rates than herbaceous plants
Plant respiration increases w/ increasing temp respiratory carbons losses are
higher in the tropics than the tundra
Net primary production is the energy remaining after respiratory losses
-NPP = GPP – respiration
- the NPP of a terrestrial ecosystem is the amount of energy captured by autotrophs that
resulted in an increase in living plant matter (biomass) NPP reps. The total net input
of carbon into ecosystems
- plants allocate carbon for growth/reproduction/storage/defense, there are trade-offs
eg. Plants in deserts may allocate more of their NPP to root growth relative to the
growth of shoots, than plants growing in ecosystems w/ higher soil water and
nutrient availability
eg. Allocating NPP to storage compoudns (eg. Starchs) provides insurance if they
lose osme tissues to herbivory others may allocate 20% of NPP for biological
defenses against herbivory
find more resources at oneclass.com
find more resources at oneclass.com
NPP changes during ecosystem development
-disturbance and succession influence gains
or losses of CO2 from ecosystems
- most ecosystems have their highest NPP at
mid-successional stages
b/c: lots of photosynthetic tissues, plant
diversity, and nutrient supply are highest
at this state
decrease in NPP in grass land ecosystems
is less pronounced than in forest
ecosystems
NPP can be estimate by a number of
methods
a) TERRESTRIAL
ECOSYSTEMS
- Are the best developed ones
- Measure increase in plant
biomass during the growth
season by harvesting plant
tissues in experimental plots at
start of growing season and
then again when the plant
biomass reaches its maximum the difference in plant biomass between the 2
harvests is used as an estimate of NPP
- NPP in roots is more difficult roots born/die faster than
shoots, and they may also release carbon into the soil or
to their bacteria/fungi symbionts
- Use minihizotrons (underground cameras) to better
understand the below ground production
- It’s hard to measure NPP over large/biodiverse ecosystems
Thus some measures use remote sensing and
athmopsheric CO2
- [chlorophyll] in plant canopy provides proxy for
photosynthetic biomass that can be used to measure GPP
and NPP
indicators of NPP based on [chlorophyll] can
overestimate NPP if the vegetation is not
physiologically active, but remote sensing generally
provides the best estimate for NPP at regional/global scale
find more resources at oneclass.com
find more resources at oneclass.com
- can also measure NPP from GPP and plan respiration measures the change of CO2 in
an closed system (eg. Enclose a stand of trees inside a 200m^2 x 20m tall clear plastic
“tent” the change inside this
ecosystem (b/c the respiratory
uptake of CO2 from atmosphere
results in a net change in CO2)
net ecosystem exchange: the net
change in CO2 inside the system
results from the balance
between GPP and total
respiratory release by the plants
and the heterotrophs
heterotrophic respiration must
be substracted from NEE to
obtain NPP NEE provides a
more refined estimate of
ecosystem carbon storage than
NPP (b/c soil
leeching/disturbances change change NPP carbon estimates)
- another approach: eddy covariance/eddy correlation uses the CO2 gradient between
the plant canopy and the atmosphere that
develops b/c photosynthesis and respiration
during day, CO2 is lower in the plant
canopy than in the air above the plant
canopy // CO2 is higher at night (b/c no
photosynthesis)
PG: 494-498
CHAPTER 22: NTURIENT SUPPLY AND CYCLING
-biogeochemistry: the study of the physical, chemical, and biological factors that
influence the movements and transformations of elements
-nutrients: the chemical elements an org. requires for its metabolism and growth
must be present in certain chemical forms to be available forms to be uptaken
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Ecosystem: all the components of an ecological system, biotic or abiotic, that influence the flow of energy and elements. Primary production: the fixation of carbon during photo/chemo synthesis. Is the conversion of light energy from the sun into chemical energy. Carbon is the currency used for the measurement of primary production the rate of primary production is called primary productivity. Gross primary production: equivalent to the total of all plant photosynthesis is controlled by climate and by the leaf area of the plants above ground (called the leaf area index, which has no units) Leaf area index varies among biomes (0. 1 in tundra, 12 in tropics) More leaves = more shading shading of leaves below the upper most layer increases w/ each new leaf layer so the incremental gain in photosynthesis for each lead layer added decreases. Plants match their lai w/ climate for maximize carbon gain. Plants use 50% of carbon for biosynthesis and cellular respiration.
