Lecture 3: Ecosystems & Energy Flashcards
potential energy
energy available to do work because of position or chemical bond
kinetic energy
energy associated with motion
1st Law of Thermodynamics
(conservation of energy)
can be transformed from one form to another (X created/destroyed)
2nd Law of Thermodynamics
(law of entropy)
amount of disorder in universe is always increasing (no energy transformation is completely efficient)
Odum & Barrett
Ecosystems are open, non-equilibrium thermodynamic systems that continually exchange energy and matter with the environment to decrease internal entropy but increase external entropy
Primary productivity - incoming solar energy
- 1% of solar energy captured by photosynthesis (GPP)
- 60% of GPP respired
- 40% of GPP used for producer growth and reproduction (NPP)
Why do higher latitudes receive less solar energy?
- solar radiation has longer to travel through the atmosphere
- @ Earth’s surface. same incoming radiation is spread over greater ground area
Primary productivity
rate @ which solar/chemical energy is captured + converted –> chemical bonds (photosynthesis/chemosynthesis)
Standing crop
biomass of producers present in a given area of an ecosystem at a particular moment in time
Gross Primary Productivity (GPP)
rate @ which energy captured + assimilated by producers in area
Net Primary Productivity (NPP)
rate of energy assimilated by producers + converted into producer biomass in an area (including all energy X respired)
NPP = GPP - Respiration
Photosynthesis equation
6CO2 + 6H2O + light energy –> C6H12O6 + 6O2
Light-dependent reactions
- transforms energy from visible light –> temp forms of NADPH + ATP
- oxygen waste product
Carbon-fixation reactions
- use energy from light-dependent reactions to reduce CO2 –> sugars
- photosynthetic enzymes require lots of N
- photorespiration immediately uses 20-40% of fixed carbon (psotosyn less efficient for net C production –> more efficient when CO2 higher)
- plants in hot + dry evolved ways to reduce photosyn losses
C4 plants - in dry conditions/excessive heat
- reduces ocygenase behavior of rubisco + improves efficiency of photosynthesis @ cost of of ATP/more CO2
Respiration
C6H12O6 +6O2–> 6CO2 + 6H2O+ 36ATPs
NPP and Photosynthesis Capacities
- high protein = high respiration
- trade-off between capacity to photosynthesize @ high light vs. performance @ low light (defines light compensation point)
Trade-offs in photosynthetic abilities on diverse growth forms
- increased overall growth may be due to high competition + efficient use of light energy (high tree shade, leaf patterns)
- shift in biomes for competitions for light (evergreen forest) to competition for water (tropical desert)
Ultimate (long-term) controls
- biota
- time
- parent material
- climate
Interactive (intermediate) controls
- plant functional types
- soil resources
Short-term (direct) controls
- leaf area
- N
- season length
- temperature
- light
- CO2
Ratio of NPP to GPP
- carbon use efficiency - fraction of C absorbed by ecosystem that is allocated to plant biomass production
- often similar across different biomes
- suggests that ecosystems organize to max C allocation to growth
Possible issues w/ biomass-based estimates of NPP?
- researchers typically only harvest above-ground plant growth
1) below-ground growth can be substantial
2) fine roots frequently die + replaced –> X accounted for
3) energy sent to mycorrhizal fungi
4) loss to herbivores
Variation in annual primary production
1) Quantity of photosyn tissue
2) Duration of activity
* light avail
* water avail
* material/nutrients avail
Measuring NPP
- small-scale
1) bottle-leaf: measure uptake of CO2 in light vs. dark
2) aquatic: measure O2 uptake - larger-scale
1) sample CO2 concentrations @ different heights above ground (within forest vs. atmosphere) - remote sensing
1) chlorophyll pigments absorb wavelengths in red + blue range, reflect green
