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71 Cards in this Set
- Front
- Back
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gross primary productivity (GPP)
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total energy captured in photosynthesis
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efficiencies
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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* |
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to be efficient in ecological sense...
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when you make being efficient competitive
the organism must be efficient for the MOST LIMITING RESOURCES to persist in an ecological system |
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trade offs in availability of essential resources cause..
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changes in the most limiting resource
.... & controls what plant speices will win out in competition |
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generalized pathway for photosynthesis is
THE CALVIN CYCLE |
uses the enzyme "Rubisco"
to shove carbon dioxide onto RuBP |
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problems with the calvin cycle & carbon dioxide affinity
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the enzyme rubisco has a low affinity for carbon dioxide
SO -uptake inefficient when carbon dioxide levels are low --causes plants to load up on the enzyme |
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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)
--->PHOTORESPIRATION!! -can reduce efficiency & defeats purpose of the enzyme |
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the improvement of c4 plants
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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! |
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whats really different about the enzymes in c4 plants and the improvement?
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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!! |
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cost of the improvement of c4 plants?
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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] |
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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..) |
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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 |
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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 |
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CAM plants
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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 |
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advantages of CAM plants
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carbon dioxide is harvested when
-there's no comp with other plants -water loss is low |
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CAM plants are found in
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-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 |
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CAM plants are most water efficient
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1 g biomass / 80 g h2o
*most efficient.. but not winning strategy in most enviros |
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Leaf Area Index (LAI)
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sq meters of leaves / sq meters of ground
mathematical description of LIGHT ABSORBANCE -absorbance constant (k) is characteristic of ecosystem |
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leaf angle
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-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 |
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water limitation and leaf angle
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in water limited systems (like GRASSLANDS)
--> low leaf angle -dilutes some of the sunlight |
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photosynthesis
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process by which carbon and chemical energy enter ecosystems
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controls over photosynthesis
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availability of
light energy , co2 (reactants) temperature (governs reaction rates) nitrogen (needed to produce photosynthetic enzymes) |
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gross primary production (GPP)
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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 |
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photosynthesis uses light energy...
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to reduce co2 and produce carbon containing organic compounds
(carbon containing organic compounds is transferred along ecosystem and eventually released by respiration or combustion |
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two groups of reactions in photosynthesis
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LIGHT HARVESTING REACTIONS
-transform light energy into temporary chemical energy CARBON-FIXATION REACTIONS -use products of light harvesting to convert co2 into sugars (more permanent chemical energy) -- can be stored , transported, metabolized. |
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limiting factor of carbon-fixation reactions?
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the reaction of a 5 carbon sugar with co2 forming two 3carbon sugars
-"C3 photosynthesis!" |
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net photosynthesis
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net rate of carbon gain measured by ind. leaves
-balance between co2 fixation and leaf respiration |
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decomposition
term |
physical and chemical breakdown of detritus (dead plant / animal / microbial material)
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mineralization
term |
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 |
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immobilization
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removal of inorganic nutrients from available pool by microbes and chemical fixation
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co2 response curve
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compensation point where leaf shows + net photosynthesis
(when photosynthesis is greater than respiration... carbon gain) |
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consequences of high WUE
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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* |
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C3 plants steps
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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) |
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rubisco is carboxylase
& oxygenase |
carboxylase - starts fixation reaction
oxygenase - starts photorespiration between RuBP & oxygen (breaks down sugars to CO2 & chemical energy) |
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problems w c3
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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 |
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c4 steps
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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 |
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c4 improvements
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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!) |
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c3 outcompetes c4
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when high co2
in low light low temp in high N |
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after leaf is past light saturation point
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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 |
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x intercept for amt of sunlight needed for + energy gain differs among plant species
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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 |
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NPP
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total carbon gain to ecosystem MINUS plant respiration
*OVER TIME* (GPP - plant resp) AET good estimate |
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Rgrowth
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requires synthesis of compounds (compounds made into more complex products)
-atp needed for synthesis -most expensive :: proteins lignins tannins |
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Rmaint
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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 |
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Rion
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ion transport across membranes
get nutrients |
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NPP indirect global patterns
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NPP increases with temp and moisture
(though directly depends on availability of below ground resources) |
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plants deliberately throw away leaves
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- 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.. |
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NEP
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net accumulation of carbon by ecosystem
GPP - heterotrophic resp!!! (NOT PLANT RESP) -represent amt of stored carbon |
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NEP is 0 when..
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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 |
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NEE
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net ecosystem exchange
GPP - (plant resp + hetero resp) + NEE when photosynthesis greater than resp (carbon gain more than carbon losses) |
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N hemisphere more seasonal changes in atmospheric CO2 concentrations than S hemisphere
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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 |
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3 factors controlling decomposition rate
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1. climate
2. quality of dead organic matter 3. abundance activity and comp of microbes & soil species |
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"decomposition"
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the breakdown of dead organic matter to inorganic nutrients and co2
thru fragmentation chemical alteration and leaching |
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mineralization
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conversion of organic matter to inorganic nutrients available for uptake of plants
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immobilization
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the uptake of inorganic nutrients by microbial uptake and chemical fixation
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3 factors controlling rate of decomp
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1. climate
2 quality of dead organic matter 3. activity / abundance / comp of micrabes & soil animals |
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climate affecting decomp rate
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more moisture (not enough for o2 depletion)
higher temp = higher decomp rate |
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quality of dead organic matter
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1.
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 |
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how can things be decomposed but no minerals returned to enviro?
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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
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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 |
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resorption
& 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 |
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where get nutrients if decomposing CHO?
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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) |
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small molecules higher quality
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bc they can pass thru the microbial membrane
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energy gain less when eat a big molecule?
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you must secrete exoenzymes which sometimes take more energy to make than you'll receieve from its products
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exoenzyme
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enzyme secreted into the enviro
dangerous 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 |
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decomposition rate not determined by AET
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decomposition is sensitive to soil moisture (unlike NPP)
-too much soil moisture restricts oxygen water acts as barrier to oxygen supply |
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why's lignin recalcitrant?
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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 |
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lignin -> humus addition of N
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lignin degraded
compounds converted to quinones (highly reactive) quinones react w soil compounds (esp amine groups that have a N) forms humus |
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decay estimate of recalcitrant stuff
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lignin : N
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decay in tropics faster w regard to plant production
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-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 |
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avg decomp rate
equation |
k = litterfall / litterpool
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anaerobic decomp
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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 |
