climate change 1 Flashcards
role of carbon dioxide in plants (25 cards)
atmospheric CO2 through geological time
increased CO2 in atmosphere drives climate change
CO2 historically has been much higher and has dropped causing plants to adapt
historic CO2 is variable
history of Co2 reconstructed through deep sea sediment, ice cores
less CO2 in ice ages
currently 425 ppm CO2
atmospheric Co2 in recent geological time
Co2 is largest driver of anthropological climate change
levels were stable at 270-285 ppm for the last 2000 years
increase from 1750- post industrial fossil fuel and chnage in land use
other climate gases in recent geological time
increasing methane concentration
double methane concentration now compared to pre-industrial levels
methane traps 28x more heat than the equivalent mass of CO2
N2O also increasing global warming
atmospheric CO2 over past 50 years
measures at Muana Loa Observatory
increases at an increasing rate
increase is not constant, CO2 lowers in summer when plants photosynthesise more
seasonal cycle of carbon from atmospheric to biomass store
global variation in Co2 sequestration
more forest in Northern hemisphere
when Northern hemisphere has more sun, more CO2 is absorbed
photosynthesis in plants
Co2 enters through stomatal pores
uses enzyme rubisco to fix it
Calvin cycle
rubisco characteristic
dual catalytic nature of rubisco
rubisco uses Co2 and RuBP as a substrate to make 3 phosphoglycerate
rubisco uses O2 as a substrate as well
carboxylation or oxygenation is dependent on CO2/O2 ratio
if fixes oxygen it produces 2-phosphoglycolate which is toxic to the plant and must be converted to phosphoglycerate
photorespiration
CO2 release which only occurs when there is light
change in net photosynthesis with changing CO2 conc
CO2 is a substrate so is a limiting factor of photosynthesis
main driver on if fix is fixed or respires is ratio of CO2 to oxygen inside chloroplast due to dual catalytic nature of rubisco
C3 plant
fix carbon dioxide directly in the Calvin cycle using RUBISCO
generally adapted to cooler, wetter weather
more than two mesophyll cells between neighbouring vascular bundles
C4 plant
first fix carbon to a 4C molecule before releasing it to the Calvin cycle
have Kranz anatomy leaves to help concentrate CO2
adapted for warm dry environments bc photosynthesise effectively even in low CO2 levels with closed stomata
effect of temperature on carboxylation or oxygenation of rubsico
higher temp causes more oxygenation
faster molecule movement makes it harder to distinguish between CO2 and O2
at what point is CO2 concentration no longer increasing carbon fixation in plants
approx. 400 ppm (current atmospheric levels)
C4 photosynthesis
can occur at higher CO2 levels
some cells fix CO2, some cells increase CO2 levels inside cells
bundle sheath tissues: regulate water movement from vascular structure to mesophyll
bundle sheath tissues: C4 plants
regulate water movement from vascular structure to mesophyll
surrounded by gas impermeable cell wall
mesophyll tissue in C4 plants
fixes carbon dioxide to oxalate (C4 acid)
which is transferred into the bundle sheath where a carbon pump occurs then to C3 acid which returns to mesophyll
the process in the bundle sheath makes CO2 conc 10x higher in than in the mesophyll
CO2 response of C3 plants vs C4 plant
at low CO2 conc C4 plants can assimilate much more CO2 by supressing photorespiration
C4 max out CO2 much sooner than C3 due to the energy needed for the carbon pump
limiting factor in C3 vs C4 plant CO2 assimilation
C3 plant limiting factor: CO2 conc
C4 plant limiting factor: energy? idk bro
increase atmospheric CO2 would have different reaction for C3 compared to C4 plants
above 500ppm CO2 C3 plants are better than C4 plants
temperatures impacting C3 vs C4 plants
C4: inc temp, in CO2 assimilation across all temp
do not benefit as much from extra CO2 at low temp
C3: increase in temp increase in CO2 assimilation across all temp
relationship between photorespiration and temperature
gain from reducing photorespiration (C3) is temp dependent
the detriment of photorespiration is higher at high temperatures
hence C4 plants are more found at high temps where photorespiration is often high
CO2 delivery into chloroplast
stomata respond to a variety of environmental signals (temp, water, light intensity, CO2 conc)
close to prevent water loss when plant has sufficient CO2
at high CO2 stomata close
difference in C3 and C4 plant response to stomatal opening
C4 plants close stomata more than C3 plants at the same CO2 conc
due to carbon concentration mechanism in C4 plants
impacts carbon the plants gain and water the plants lose
role of nitrogen in carbon dioxide absorption
in absence of N, growth is relatively insensitive to rising CO2
N is needed for proteins and plant material to process carbon
nitrogen source
nitrogen fixing organism are the main source of N for ecosystem
principle source is root nodules of higher plants 9e.g. legumes and alders), blue-green algae and tropical grasses
dependent on carbon status of plant (if plant has a lot of C, lots C given to N fixer, plant gains more N)
therefore N fixing plants gain more from high CO2 e.g. gorse
