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71 Cards in this Set

  • Front
  • Back
gross primary productivity (GPP)
total energy captured in photosynthesis
are ratios!!!

product / cost

(grams of carbon fixed / gram of leaf) == production efficiency of carbon

(g of carbon fixed / unit water transpired) == water use efficiency

(g of carbon fixed / unit N required) === n use efficiency

(g of carbon fixed / unit light) == light efficiency

*to be very efficient at full sunlight prob means low efficiency at low sunlight*
to be efficient in ecological sense...
when you make being efficient competitive

the organism must be efficient for the MOST LIMITING RESOURCES
to persist in an ecological system
trade offs in availability of essential resources cause..
changes in the most limiting resource

.... & controls what plant speices will win out in competition
generalized pathway for photosynthesis is

uses the enzyme "Rubisco"
to shove carbon dioxide onto
problems with the calvin cycle & carbon dioxide affinity
the enzyme rubisco has a low affinity for carbon dioxide
-uptake inefficient when carbon dioxide levels are low
--causes plants to load up on the enzyme
problem with the calvin cycle when
-leaf temp is high
-carbon dioxide is low
-& in presence of oxygen
the enzyme oxidizes some of the RuBp rather than adds co2 to them (fixes them)

-can reduce efficiency
& defeats purpose of the enzyme
the improvement of c4 plants
evolutionary step occured where -high temp -lots of oxygen -low co2

-the photosynthetic cycle in limited to bundle sheath cells (doesn't occur in all cells)
-mesophyll cells surround the bundle sheath cells
-inside the mesophyll cells is "PEP carboxylase"
-"PEP carboxylase" is an enzyme that combine with a carbon to produce a 4carbon acid
-this c4 compound is then moved to the bundle sheath cell
-the bundle sheath cell converts the c4 compound to a c3 compound and carbon dioxide
--Which is then captured like before!
whats really different about the enzymes in c4 plants and the improvement?
PEP carboxylase has a high affinity for what its on (its substrate)
-& a higher v-max than ribisco
--carbon dioxide higher concentration in the bundle sheath cells than the c3 plants have
--->Photorespiration is eliminated!!
cost of the improvement of c4 plants?
energy yield

-2 more atp used to reduce one carbon dioxide molecule
-->light use efficiency is lower [only seen at low temps tho bc photorespiration of c3 plants occurs at high temps]
C3 v C4 plants:

carbon dioxide concentrations
higher co2 levels favor c3 plants over c4

(our increasing co2 in the atmosphere should star favoring c3 plants..)
C3 v C4 plants:

water use efficiency
c4 plants have higher water use efficiency

c4: 1 g biomass / 300 g water

c3: 1 g biomass / 700 g water
C3 v C4 plants:

nitrogen use efficiency
c4 plants have less rubisco
-rubisco is loaded w nitrogen
-c4 plants can have less nitrogen concentration

but c4 plants can have higher carbon fixation rates .. so can suggest that c4 plants have higher N use efficiencies
CAM plants
modification to c4 plants

-same pathway of c4 plants for photosynthesis (but a temporal seperation of enzymes.. not spatial)

-stomata opens at night -- co2 fixed into c4 acid
-during day material fed into c3 pathway -- & carbon is fixed
advantages of CAM plants
carbon dioxide is harvested when
-there's no comp with other plants
-water loss is low
CAM plants are found in
-succulents in desert

-epiphytes in tropics

-in some aquatic plants

*in all places surrounding co2 is not readily available or is only available at high costs
CAM plants are most water efficient
1 g biomass / 80 g h2o

*most efficient.. but not winning strategy in most enviros
Leaf Area Index (LAI)
sq meters of leaves / sq meters of ground

mathematical description of LIGHT ABSORBANCE

-absorbance constant (k) is characteristic of ecosystem
leaf angle
-goal: saturate enzyme system w/o heat overload

controls solar input
-cal/area = cosine of leaf angle (from horizontal)

--->100% for flat leaf -> 0% for leaf pointing at sun
water limitation and leaf angle
in water limited systems (like GRASSLANDS)
--> low leaf angle
-dilutes some of the sunlight
process by which carbon and chemical energy enter ecosystems
controls over photosynthesis
availability of
light energy , co2 (reactants)
temperature (governs reaction rates)
nitrogen (needed to produce photosynthetic enzymes)
gross primary production (GPP)
photosynthesis at scale of ecosystems

-varies in response to light temp and N (seasonal controls)

-difference in amt of leaf area and length of time leaf is photosynthetically active (yearly difference)
--->these are dependent on availability of soil resources, climate, & time since last disturbance
photosynthesis uses light energy...
to reduce co2 and produce carbon containing organic compounds

(carbon containing organic compounds is transferred along ecosystem and eventually released by respiration or combustion
two groups of reactions in photosynthesis
-transform light energy into temporary chemical energy

-use products of light harvesting to convert co2 into sugars (more permanent chemical energy) -- can be stored , transported, metabolized.
limiting factor of carbon-fixation reactions?
the reaction of a 5 carbon sugar with co2 forming two 3carbon sugars

-"C3 photosynthesis!"
net photosynthesis
net rate of carbon gain measured by ind. leaves

-balance between co2 fixation and leaf respiration

physical and chemical breakdown of detritus (dead plant / animal / microbial material)

conversion of carbon and nutrients from organic form to inorganic form

caused by breakdown of litter and SOM

gross mineralization = total amounts of nutrients released via mineralization

net mineralization = net accumulation of inorganic nutrients in soil solution over time
removal of inorganic nutrients from available pool by microbes and chemical fixation
co2 response curve
compensation point where leaf shows + net photosynthesis
(when photosynthesis is greater than respiration... carbon gain)
consequences of high WUE
high WUE means stomata is more closed
-which decreases amt of co2 coming in
-but since water diffuses faster than co2... changes in stomata have greater effect on water loss than carbon gain

*water declines to greater extent than co2 absorption declines*
C3 plants steps
after light converted to chemical energy (ATP & NADPH)

the chemical energy used for fixation reaction

Rubisco starts reaction of 5 carbon sugar to from 2 3 carbon sugars (fixation)
rubisco is carboxylase
carboxylase - starts fixation reaction

oxygenase - starts photorespiration between RuBP & oxygen
(breaks down sugars to CO2 & chemical energy)
problems w c3
rubisco has low affinity for co2 (uptake not good if co2 is low)
-rubisco requires a lot of N
-rubisco is oxygenase which causes photorespiration between RuBP and oxygen

*bad at getting carbon and looses a lot of it right away
c4 steps
photosynthesis only in sheath cells
surrounded by mesophyll cells that have PEP carboxylase (not rubisco) which makes 4carbon acid

4carbon acid goes to sheath cells where its decarboxylated then co2 released into normal path
c4 improvements
PEP carboxylase = higher affinity for CO2

-bc carbon is carboxylased then decarboxilated at rubisco site co2 is more concentrated so you need less rubisco and thus less N

-there is less O2 and more CO2 so there is no photorespiration!!

-can absorb more co2 with more closed stomata bc PEP can draw down CO2 to increase gradiant (LESS WATER LOSS!)
c3 outcompetes c4
when high co2

in low light

low temp

in high N
after leaf is past light saturation point
photosynthesis no longer responds to changes in light supply
-light harvesting reactions have limited capacity to capture light
--light's converted less efficiently into sugars
x intercept for amt of sunlight needed for + energy gain differs among plant species
sun species
-need more light for + energy gain (greater x int)
--- bc more proteins and higher respiration

shade species
-need less light to have + energy gain bc
-less proteins and less respiration
(have more + carbon balance under low light)

*x intercept can vary for different leaves of same plant due to differences in leaf angle
total carbon gain to ecosystem MINUS plant respiration

(GPP - plant resp)

AET good estimate
requires synthesis of compounds (compounds made into more complex products)

-atp needed for synthesis

-most expensive :: proteins lignins tannins
energy needed to maintain ion gradiants and to replace proteins

-greatest in systems with high tissue N (bc turnover of proteins part of maintenence)

*accounts for 1/2 of plant respiration
-enviro stresses = more maint. respiration
= less allocation to growth
ion transport across membranes

get nutrients
NPP indirect global patterns
NPP increases with temp and moisture

(though directly depends on availability of below ground resources)
plants deliberately throw away leaves
- when resources below level needed to maintain current leaves

-senescence (programmed breakdown of tissues)
--allows leaves in low qual light to go and new ones grow in high qual light at canopy top
--in seasonal changes (when resource gain less than maintanence cost)
---can shed parasites..
net accumulation of carbon by ecosystem

GPP - heterotrophic resp!!!

-represent amt of stored carbon
NEP is 0 when..
gpp is equal to heterotrophic resp

-bc NPP provides organic material to fuel hetero resp and hetero resp provides mineral that support NPP
THEN ecosystem in steady state can be at 0
net ecosystem exchange

GPP - (plant resp + hetero resp)

+ NEE when photosynthesis greater than resp
(carbon gain more than carbon losses)
N hemisphere more seasonal changes in atmospheric CO2 concentrations than S hemisphere
bc NEE differs more seasonally in N hemisphere

-warm summer = more photosynthesis than resp (+)
-cold winter = less photosynthesis than resp (-)

in S hemisphere oceans don't change co2 as much bc carbon exchange more determined by wind / temp and physical factors which don't vary as much seasonally
3 factors controlling decomposition rate
1. climate
2. quality of dead organic matter
3. abundance activity and comp of microbes & soil species
the breakdown of dead organic matter to inorganic nutrients and co2
thru fragmentation chemical alteration and leaching
conversion of organic matter to inorganic nutrients available for uptake of plants
the uptake of inorganic nutrients by microbial uptake and chemical fixation
3 factors controlling rate of decomp
1. climate
2 quality of dead organic matter
3. activity / abundance / comp of micrabes & soil animals
climate affecting decomp rate
more moisture (not enough for o2 depletion)
higher temp
= higher decomp rate
quality of dead organic matter
2. bonds (single easier faster to break)
-some give more energy -- decomposers want these
3. molecule
---the smaller the better
----the simpler the better (don't want complex ones or irregular ones that wont fit the active enzyme site)

3. nutrient qual of dead organic matter
-lots of nutrients = high quality
how can things be decomposed but no minerals returned to enviro?
during decomp its possible for the decomposers not to mineralize nitrogen (not realease back as a mineral) and instead they're immobilized and taken up by the microbe
fauna (animals that eat microbes and detritus)
speed up decomposition but only respire ~5% of litter carbon
the N and phosphorous the animals acquire is usually more than they need for growth / reproduction so they excrete these nutrients & they become available for plant uptake

*fauna speed up decomposition by increasing fragmentation allowing for more decomposition by microbes

& its effects on litter
resorption is when senescence occurs in leaf tissue
-& the compounds in the leaf are broken down and transported to other plant parts

-the leaf has lost some nutrients that went back to the plant

-when leaf falls resorption is still occuring so there are many soluble products that can be easily leached ... increasing ease to which bacteria esp can get them
where get nutrients if decomposing CHO?
they break down cho (sugars, lignin) for energy
then use this energy to get nutrients from more recalicitrant substrate such as humus

(esp since humus forms due to the partial decomp of lignin)
small molecules higher quality
bc they can pass thru the microbial membrane
energy gain less when eat a big molecule?
you must secrete exoenzymes which sometimes take more energy to make than you'll receieve from its products
enzyme secreted into the enviro

microbe doessn't have control over
-substrate availability
-delivery of enzymes
-efficient use of breakdown products

enzyme can get lost
--gets stuck on organic goo
--microbe gets eaten by predator
decomposition rate not determined by AET
decomposition is sensitive to soil moisture (unlike NPP)

-too much soil moisture restricts oxygen
water acts as barrier to oxygen supply
why's lignin recalcitrant?
it has irregular structure
can't bind easily to active enzyme site
fungi can do it but will only produce these enzyme when easier labile substrates aren't available
*oxygen required to make the enzymes
lignin -> humus addition of N
lignin degraded
compounds converted to quinones
(highly reactive)
quinones react w soil compounds (esp amine groups that have a N)
forms humus
decay estimate of recalcitrant stuff
lignin : N
decay in tropics faster w regard to plant production
-productive plants produce high qual litter (more labile carbon & lots of microbes) --- easily decomposed

-recalcitrant materials easier to decompose in high temps bc temp alters 3d structure

-tropic organisms are larger than the same species toward poles so tropic org. have greater effect on decomp thru fragmentation
avg decomp rate
k = litterfall / litterpool
anaerobic decomp
oxygen unavailable so organisms use other electron accepter to get energy from organic matter

when oxygen depleted --
denitrifiers have advantage
(nitrate = electron acceptor)

when nitrate depleted

-sulfate used where available

-carbon dioxide electron acceptor when sulfate unavailable
--waste product = methane