Lecture 16: Plant Ecophysiology Flashcards
sessile
fixed in one place; little scope for behaviour
What nutrients are needed for growth
(NPK) Phosphorus, potassium, nitrogen
What does photosynthesis use and what does it produce?
CO2 and H2O with light produce carbohydrates and O2 which is consumed in cellular respiration to produce ATP
Carbon balance
Plants must acquire more carbon through photosynthesis than they lose through respiration
What are the tradeoffs of large leaf size?
Good for harvesting sunlight and gas exchange, but a larger leaf is more prone to overheating (enzymes that facilitate photosynthesis need to be at an ok temperature) and transpiration.
C3 photosynthesis
85% of Earth’s plants are C3. Carbon accepted by enzyme Rubisco. At high temperatures, Rubisco accepts oxygen accidentally.
ex. peanuts, cotton, tobacco, soybeans, spinach, most trees, and lawn grasses.
Photorespiration
When plants accidentally give off CO2 and take up O2. Affects carbon balance, no glucose is made. Results in crop loss every year.
Plants with large leaves combat overheating by…
- growing in shady habitats
- evaporative cooling by opening stomata
How does evaporative cooling work?
Essentially, water molecules on the surface of a warm body will evaporate off the surface. Water molecules on the surface of something have a certain kinetic energy. If the kinetic energy is high enough, the hydrogen bonds keeping the water together will break and the water will vaporize (thus taking the kinetic energy with it). Energy is continually transferred from the body to the water thus the body cools down.
Why is evaporative cooling only helpful to an extent?
Works only as long as there is enough water
How do plants prevent water loss?
Closing stomata. This in turn cuts off gas exchange and plant growth stops. Overheating is a problem when stomata close.
Important thing to understand about desert plants
No plant lives in the desert because it functions best in that habitat. It only lives there because the desert hasn’t killed it yet. Take any desert plant out of the desert and it will grow better there because it has better access to water and lower heat.
Palo verde
Name means green stick. They are drought deciduous meaning in a drought they will drop their leaves. Photosynthesis can occur in the branches and bark without incurring heat load and water loss through leaves.
Where will you find large leaves and tiny leaves respectively?
Large leaves will be found in tropical rainforests and small leaves in the desert. Rainforests have a lot of water (duh) so overheating can be combatted with evaporative cooling but in a desert there is negative water so leaves must be tiny.
What is microphylly taken to extremes??
No leaves at all (prickly pear cactus rotates towards setting sun to have maximum surface area towards light (plant behaviour??))
C4
Carbon intermediate is a four carbon molecule instead of three. Common photosynthesis system in plants existing in hot climates. Pep carboxylase accepts CO2 first to give rubisco and is much more discriminatory (does not not accept O2). Very energetically expensive though so you won’t see this adaptation in cooler climates. Examples include crabgrass, sugarcane, corn.
CAM
Crassulacean acid metabolism photosynthesis—named for the family Crassulacae where it was first discovered—involves plants only opening their stomata at night. CO2 comes in, is stored as an organic acid until light energy can be harvested the next day. Prevents water loss and photorespiration.
Saguaro Cactus
Adapted to low rain in Arizona, uses CAM photosynthesis, very extensive shallow roots, has accordion pleated trunk to absorb water when it does rain (can absorb hundreds of litres)
Why do both tropical trees and cacti have shallow extensive root systems if their environment differs so much?
Tropical rainforests have a shallow layer of nutrient-rich soil so trees have an extensive shallow root system to absorb maximum nutrients while cacti have shallow roots to absorb water from surface as soon as it rains (no deep water sources).
What is a split root experiment and what does it show?
Shows that roots forage for nutrients and grow more when nutrients like NPK or symbionts (N fixing bacteria) are present/stored. Plants respond dynamically to their environment!!
How does being deciduous help plants?
Allows them to avoid stress (dry or cold seasons). Dry tropical forests in Costa Rica do this.
HOw do sun and shade leaves from same tree differ?
Shade leaves don’t have much need for cooling so they are smoother. Leaves exposed to sun are pointy and lobed (dissected outlines) so that airflow over them is turbulent.
Nurse tree effect
Saguaro seedling can be sheltered by Palo Verde
Can plants be water stressed—that is, lack water—even in rainforests?
Yes, if they are epiphytes (meaning they grow on trees and aren’t actually able to put their roots in the soil). Epiphytes can have water and nutrient shortages.
Epiphytes
Grows on surface of another plant and derives nutrients and water from air. Have water “tanks”
Fun facts about orchids
- epiphytes
- don’t make nectar but they make pollen which is dispersed by bees (DONT get nectar but they use orchid scent to use to attract mates)
