Lecture 4: Plant Physiology Notes
These are my notes from lecture on Sept 21. They combine key points from the slides and Prof. Currie's comments. Hope they're helpful!
Overview
- Energy of a landscape from all autotrophs equates to primary production
- Wetlands are of the most production ecosystems in world because water is not limiting
- Water and temperature are the most limiting resources to organisms, not just nutrients
Controls in primary production
- Light and CO2 are necessary for photosynthesis
- Temperature limits what type of vegetation can be in an area which affects primary production
- Water is necessary for carrying dissolved nutrients through plants, and helping to cool the leaves during photosynthesis
- Nutrients (including Nitrogen, and Phosphorous to power the enzymes involved in photosynthesis) limit plant production; plants often evolve ways to use them efficiently in their areas
Photosynthesis
- Photosynthetically active region is part of the visible light, longer wavelength
- Pigments interest different wavelengths of PAR
- PAR only extends so far into water; this is why photosynthesis can't occur at deep ocean depths
- Pigments that don't get absorbed get reflected
Light Reactions
- Light energy is captured and splits water molecules to O2, H+, and e-
- Energy, H+, e- are stored in short-term intermediate compounds
- O2 is waste product
- ATP and NADHP store energy and are cyclical from light —> dark —> light
Dark Reactions (Light-Independent Reactions)
- Don't require light
- CO2 substrate
- long-term energy storage, CH2O (sugar)
- Goes through process in the Calvin cycle
C3 Plants: most common, have 3 carbons in their energy storage
- Mostly trees, shrubs and forbs
- less water use efficiency and grow when water isn't limiting
- Dark reaction/calvin cycle takes place in the same place and same time as photosynthesis
- Ribisco enzyme bonds RuBP and CO2
- Water loss is a major issue for C3 plants
- Stomates are on the underside of leaves
- Transpiration: water vapor out of leaf, carrying away latent heat
- So the plant is able to lose extra heat, but in the process loses water it needs
- Diffusion of water vapor from leaf to outside. CO2 has higher concentration on the outside of the leaf but this process is slower than the water diffusion
- Photorespiration occurs in C3 as well: consumes O2 and produces CO2 (the 'undoing' of CO2 fixation)
C4 and CAM
- They both start with C3 and build on it
- It changes the transport of CO2 into the reaction
- Reduces water loss and reduce photorespiration
- C4: malic acid shuttles the CO2 fixation to the bundle-sheath cell (where the calvin cycle occurs)
- more limiting water than C3, better water use efficiency, grasses use this
- This is different from C3: if we higher temperatures or more/water, the competition will be altered toward C3 or C4
- CAM: Get CO2 (through open stomates) at night and fixes the CO2 in malic acid and wait until the daytime for the calvin cycle
- lower rates of photosynthesis, very high water use efficiency, most succulents
Aquatic Light
- visible light is absorbed, function of sun angle
- water has a low albedo of 10% or less
- transmission and scattered
- plants in photic zone can respire and photosynthesis
- CO2 dissolves in water
- causes an acid
- dissociates into CO2 and HCO3-
- C3 and C4 occurs in water
Factors controlling primary production
- Plants respire CO2 just like animals do
- Scientists can measure net CO2 fixation and O2 production for individual leaves
- Gross photosynthesis - autotrophic respiration = NPP
- In aquatics, measure O2 uptake
- Leaves on the same plant have different compensation points based on canopy positions
- Gross photosynthesis and respiration are sensitive to temperature
Nutrients
- Nitrogen and phosphorus are 2 most commonly limiting nutrients
- Nitrogen is important because enzymes are a key component in life processes
- Phosphorus is a part of ATP, phospholipids, etc
- Liebig's law of minimization: growth is controlled not by the total of resources available, but by the scarcest resource
- Colimitation is when two nutrients equally limit growth
- nutrient use efficiency: how much dry matter production as a function of assimilation
- forests with lower productivity tend to exhibit higher nutrient-use efficiency
Soils
- Texture: distribution of size particles
- Clay (small particles, more surface area so water does adhere) -> Silt -> Sand (bigger particles, less surface area, more productive)
- Plants draw water from soil
- osmosis: gets it into roots
- transpiration stream: pulled up the rest of the way
- Terrestrial plants pull water up against soil tension and gravity; this is possible because of strong hydrogen bonds in water (fine soil holds more water so has more tension)(only able to move water a short distance, evapotranspiration needed thereafter)
- Wilting point: water held too tightly by the soil
- Field capacity: not enough water
- Between the wilting point and the field capacity is the available water for a plant
page revision: 10, last edited: 09 Oct 2010 19:12