Theme E Flashcards
- Geological history of atmospere, permafrost, adaptations, C cycling , high lat events
What can be used to examine the relationship between C02 and temperature in various ecosystems over time?
- Phytoplankton:
- changes in C02 affect growth rates - Liverworts
- plants sensitive to environmental change - Leaf Gas exchange
- affected by both C02 and temp - Stomatal frequencies
- High C02= reduced stomatal density - Carbon isotopes
- can indicate type of photosynthetic pathway plants use
How can we use knowledge of how C02 has varied over time to provide context for the climate crisis?
- We can compare our warming with past events (which have been 4-10x slower)
- Can observe through fossils etc how life was effected
- In past climate warming events there has been a crash in the abundance and diversity of phytoplankton
- Can observe sedimentation and isotope ratio to see the source of C02 - is it the same?
How can geological data be used to test the sensitivity of climate models to C02?
- We know climate isn’t in equilibrium with Ghg emissions
- We know there will be a re-scale response, due to heat stored in the ocean etc.
- When paris set on 1.5-20 it was set at an attempt to avoid some of the worst ‘tipping cascades’ and positive feedbacks
- Proxies can be used to compare models and give future scenarios so it was used to state that to double C02 from pre-industrial times we would have to have a 3.40 warming
What have we predicted regarding sea level rise in response to different climate scenarios?
- 2-3 degree warming could lead to 17m sea levels rise
-Dramatic change in sea levels associated with the C02 3 million years ago (last warming)
How does geological date demonstrate the central role of life in the Earth System?
Some of the major fluctuations in C02 over time have been driven by innovation of life e.g. plants going on land
Photosynthesis responsible for oxygen in atmosphere
What was the ‘green Sahara’?
- Sahara was wet and could accommodate plants
- Occurred during the holocene and the pleistocene
Why do phenomenon’s like ‘hothouse earth’ and ‘snowball earth’ provide hope for our climate crisis?
- life persisted when the earth was frozen solid
- Shows past environments have been radically different to todays and life has adapted and found a way
What is the faint young sun paradox?
- Sun was 30% less bright when the earth was first forming
- decrease solar output means earth should have been frozen but it wasnt
- enhanced greenhouse effect stopped the earth from being frozen
What were the first photosynthetic organisms?
- Prokaryotic cyanobacteria which evolved ONCE 2.45bya (as in the oxygen-producing process)
How can we see when oxygenation of the atmosphere occured?
Through sulphur isotopes in ancient rocks
- Oxygenation caused ozone layer formation and meant UV rays stopped formation of sulphur MIF isotopes (can be tracked)
What caused ‘snowball earth’?
- Oxygen destroyed earths methane gas
- Causes snowball earth on three occasions:
1. Huronian
2. Stuartian
3. Marinoan - Volcanic C02 thawed the snowball each time
What is endosymbiosis?
one organism lives inside another organism in a mutually beneficial relationship
- Endosymbiosis gave rise to all other eukaryotic algae and plants from cyanobacteria
Give some characteristics of the Boreal Forest
- Freezing temps for much of the year, winter period is majority of the year
- Characterised by coniferous forest which reach a max height of 5m
- 11.5% of terrestrial land
- 20% of world carbon uptake
- Low diversity due to harsh conditions
Give some characteristics of the Arctic Tundra
- The land that is beyond the northern limit on the tree line because its too cold
- Only 5.5% of terrestrial land surface
- Winter dominant season
- Grasses and shrubs dominate landscape
- slow nutrient cycling
What is GPP?
Total amount of carbon thats taken up by photosynthesis by plants in the ecosystem, called primary production because its related to the primary producers- the plants
What is NPP?
Looking at the loss of carbon through respiration too so its GPP- carbon lost from respiration
What is R(eco)?
Total amount of respiration from soil and plants
What is NEE?
Net ecosystem change and is the Net carbon uptake in total from the ecosystem so its the GPP- plant respiration - soil respiration
What is Net Biome Production?
Used when looking at big areas and big time scales
net amount of carbon stored in a biome over a given period after accounting for all carbon inputs and outputs
How poor is Boreal and Tundra forest NPP?
Boreal = 1/5th of the productivity of tropical
Tundra = 1/10th of the productivity of tropical
HOWEVER
C has a long residence time
How much C is in the soil compared to plants in Boreal and Tundra ecosystems?
Boreal has 2-3 times more C in soil than plant biomass
Tundra has 5 times more C in soil than plant biomass
Why is biomass increasing in tundra and boreal forests?
- increasing temps- 20% increase in biomass
- Warmer conditions for growth, snow melts earlier so there’s longer, warmer ‘summers’
What is causing boreal tree decline and how can we tell?
- trees are advancing on to tundra
- Looked at age structure of the trees and the seedlings coming in
- As you move through the systems you find younger trees with a bigger proportion of seedlings implying it is a new system
What is shrubification (tundra)
More deciduous shrubs in the tundra
Happening to a considerable extent and is termed the ‘Greening of the Arctic’
Major shrub expansion in places like Alaska
Why is causing the concerns of carbon loss in high lat ecosystems?
Priming of decomposition:
- deciduous trees which are nutrient demanding as they invest carbon in enzymes and inorganic acids, break down organic matter in the soil which releases carbon. So the load of carbon in the soil will be released through microbial breakdown
Why is an intermediate level of warming good for high lat ecosystems?
With a little bit of climate change it might make this better because bit of plant productivity is good, but too much climate change is bad because soil C being depleted from plants and warmer soil= more respiration and more C release
How was rubisco formed?
- Evolved in heterotrophic anaerobic methanogenic archaea
- Rubisco was later recruited into photosynthetic CO2-fixation in bacteria
What problems did rising 02 bring to photosynthetic organisms?
- Oxygenation competes with carboxylation- lowering the enzyme’s efficiency
- Oxygenation generates a toxic product- 2-PGA
What strategies did photosynthetic organisms evolve to deal with this?
- Photorespiration which gets rid of 2-PGA but needs ATP and releases C02
- Carbon concentrating mechanisms to concentrate C02 at rubisco active site to minimise oxygenation
What does the carboxylation:oxygenation ratio depend on?
the partial pressure of the two gasses
What have the concentrations of atmospheric C02 and 02 been like in a phanerozoic context?
- Past 540 million years
- C02 gradually declined but has been the lowest in the last 30 million years
- O2 has gradually increased over time
How are the problems of rubisco worse at high temperatures?
- Photorespiration today can release 40% of fixed carbon at high temps
- C02 relative to 02 goes down at high temps due to differential solubility effects
- Rubisco ‘specificity’ goes down as temp goes up meaning its less able to grab onto the right molecule (C02/02)
How are problems of rubisco worse in aquatic habitats?
- Diffusion of C02 is 100x slower in water than air
- Carbon is stuck in bicarbonate
- Total organic carbon conc. is sensitive to pH as its less abundant in acidic conditions
What is meant by Parallel evolution of CCMs in two lineages?
- Cyanobacteria and Plants both independently evolved CCMs in permo-carboniferous (cold) regions to optimize photosynthesis
How do Cyanobacteria/ C02 fixing bacteria utilize C02 during photosynthesis?
- Bicarbonate is transported into the cell
- Bicarbonate accumulates in the cytoplasm
- Bicarbonate converted back to CO₂.
- High concentration of CO₂ in the carboxysomes allows Rubisco to efficiently fix CO₂ into organic molecules
(bicarbonate more soluble and easily stored in the cell)
Which eukaryotic organisms do not have a CCM?
- organisms that live in fast running water or the intertidal zone
What is the difference between C4 and CAM photosynthesis?
C4:
- Carbon fixation and the Calvin cycle are separated as they occur in different cells
- Operates continuously during the day
CAM:
- Perform carbon fixation and calvin cycle at different times of the day: open stomata at night for carbon fixation and close stomata during day to break down organic acids for calvin cycle
- Helps survive in limited water environments
What are the two major intervals of low C02, high 02, glaciation and dry climates?
- Permocarboniferous (300mya)
- Oligocene (30mya to now)
Give some characteristics of C4 photosynthesis?
- Evolved 70+ times
- Mostly present in grasses and tropical savannas
- Carboxylation > oxygenation
- Minimises photorespiration
- Saturates rubisco with C02
- Requires energy
What were the ecological conditions associated with C4 evolution?
- Only evolved from the start of the oligocene period to today in a dry cold world
- tropical climate regions
- enabled greater water use efficiency of N and water use through lower stomatal conductance and less rubisco for N use efficiency
Give some characteristics of CAM photosynthesis
- Photosynthesis
- Evolved as water conservation mechanism in low c02 world
- Closely associated with succlene
- Though to evolve in deserts (cacti, ice plants)
- Have all diversified in the past 8my
- Thought to have occurred by the expansion of desert habitats
Why is increased fire in tundra a problem?
- Not natural like it is in boreal
- Fire frequency and severity increasing
- Less recovery period due to increased frequency
- Greater release of C, losing just 3x from burning the top 4cm of soil
- Reduces ability to sequester carbon
Why is Tundra fires increasing?
- Increasing due to lighting strikes hitting ground which is drier due to climate change
Why are herbivore outbreaks an issue and how?
- varying temps = different herbivore outbreaks
- Operophtera brumata and epirrita autumnata
- typical outbreaks 9-10 years but less cold means less eggs being killed by extreme temps
- defoliate trees and grass
How are pathogen outbreaks in high lat ecosystems an issue?
- Arwidsson empetri is a fungal pathogen on empetrum shrubs
- Prefer warmer conditions and longer snow lay as there is more nutrient cycling under snow
How much faster is arctic warming to global and what does it mean?
4x
Means more extreme events in the winter rather than the summer
What happens in extreme winter warming in high lat regions?
- Rise in air temp can happen in 24 hrs, snow melts, ecosystem below get warmed up
- Ecosystem then exposed to extreme winter cold as snow has gone and theres a sudden change
- Max temps could be 4-12 degrees for 5-12 days when usually it would be -20
- 50% loss of life plant biomass
What happens to the plants in extreme winter warming in high lat regions?
Plants think they should do a spring bud burst
They lose their freeze tolerance
When cold comes back they die because they have no freeze tolerance
What is freeze drought?
- Canopies of plants exposed in winter so they transpire and lose water
- Frozen roots so they cant get more water
- Plant dies
- Huge reduction in C sink strength
What is Icing?
- Ice encasement of vegetation
- Liquid precipitation falls on snow freezes around vegetation when the snow melts a bit
- Also if snow doesnt fully melt and then refreezes you get ice
LESS NEE
How much land does permafrost occupy in the northern hemisphere?
24%, mostly high lat
How does permafrost store carbon?
- as peat and soil organic matter and methane
How much carbon is in permafrost and what is happening to it?
- 1300 Gt (2x as much than atmosphere)
- PERMAFROST IS THAWING NOT MELTING
- Releasing C
What is the active layer of permafrost?
- Surface that thaws each summer so that life can form - refreezes in the winter
- Active layer getting progressively deeper and thicker
- Permafrost is the bit below the active layer which never thaws but as the active layer gets deeper, more permafrost is exposed to decay for C02 release
- Positive feedback to climate
What are the ecosystem controls of active layer thickness?
- Evergreen > deciduous trees for permafrost freeze as they keep snow (which acts as an insulating cover) off the ground by trapping in its canopy
- Moss as winter/summer heat transfer - good for protecting permafrost as it keeps the ground cold when it’s wet and also doesnt let the ground heat up as much in the summer
- Organic soils act in the same way as moss to protect the permafrost
- Dry soils good in summer as cant conduct heat
What did the research regarding the active layer in the boreal forest in Canada show?
- aiming to detangle all the controls on ALT
- At each site, lots of ecosystem characteristics were measured as well as the depth of the active layer to correlate the variables
- The bigger evergreen trees has the smallest ALT layer (best protection) and burnt areas had the biggest ALT
- Fire deepend ALT by 1m
What did the Canada research find was the most important ALT ecosystem factors?
Moss layer thickness
Organic layer thickness
Tree canopy LAI
Surface moisture
(Fire has biggest negative effect understandably as it removes all of these characteristics)
How do factors such as a steep slope and wet conditions effect the ALT?
- A steep slope means no influence of organic layer thickness because there is good drainage and dry soil, so it isn’t needed
- In wet conditions, having more tree canopy helps to reduce ALT, in v dry conditions having more and more tree canopy doesn’t protect the permafrost
What is thermokarst?
- Permafrost thaws
- Ice within soil melts causing ground to collapse/susbside
- These structures may then fill with water/create ponds or wetlands which then further heat the ground/produce methane(feedback)
How are thermokarst wetlands studied?
- Want to look at when the methane was released by looking at emissions from the edge/centre of the woodland
- More methane emissions in summer when wetland is thawed
- Study sampled methane in different parts of the wetland then radioactively studies the carbon in the methane to see how old it is (its usually modern)
