LECTURE 16: PLANT ECOPHYSIOLOGY

Question 1

Plants can’t evade stresses like animals do…but…

Answer 1

They can make food!!!

- Through photosynthesis, they get an input of sunlight, carbon dioxide as well as water

Question 2

The parts of the plant that are adapted to their environment

Answer 2

• roots, stems and leaves

Question 3

Physiological Ecology is different for plants than animals because plants are…

Answer 3

SESSILE
- they can’t move to evade their stresses so they develop adaptations to tolerate them
AUTOTROPHS
- they make their own food through photosynthesis and thus many of the adaptations are aimed to make them effective at searching for nutrients that enable them to make their food

Question 4

Photosynthesis: A quick refresher

Answer 4

CO2 + water + light = oxygen and glucose

• plants need to bring together water, CO2 and light in their photosynthetic tissues
• enzymes also need an OK temperatures
• for growth, plants need to acquire more carbon through photosynthesis than they lose to respiration

Question 5

Photosynthetic Structures

Answer 5

Plant leaves

- They take in CO2 through their stomata and this is also where they harvest the light that they need for photosynthesis

Question 6

SA: V ratio in plants

Answer 6

SA:V Ratios are really important in plants as well due to the fact that they must balance the ratio for both thermoregulation as well as water conservation

Question 7

Benefits and Costs of Having a big surface area to volume ratios

Answer 7

Benefit: Big surface area to volume ratios ensure that there is sufficient surface area to harvest sun and carbon dioxide
Cost: too much surface area causes concern for overheating and excess water loss through transpiration an effort to cool the plant

Question 8

The main form of photosynthesis in plants

Answer 8

C3 photosynthesis

• the enzyme rubisco accepts the carbon from the environment and then fixes it into a 3 carbon intermediate which is then passed down through the photosynthetic pathway
• when the plant leaf becomes too hot, rubisco starts to accept oxygen rather than carbon dioxide which cause for a very hazardous process - photorespiration

Question 9

How do plants deal with water loss and overheating: 2 Types of Photosynthesis

Answer 9

C4 Photosynthesis
- PEP carboxylase intakes the carbon instead and fixes it into a 4 carbon intermediate and then passes it down to rubisco so that photosynthesis can occur
CAM photosynthesis
- close the stomata during the day which prevents the loss of water
- open the stomata during the night so that CO2 can be taken in without extreme exposure to the sun
- photosynthesis needs sunlight so the CO2 is stored as malate until the sun shines and photosynthesis is possible

Question 10

Other ways plants cope with overheating and water loss

Answer 10

• plants grow in the shade

- evaporative cooling by opening the stomata

Question 11

Evaporative cooling is not always an option where there isn’t water available: trade-off

Answer 11

• In places that are not abundant with water, plants close their stomata which stops CO2 from getting in the plants which turn off photosynthesis
• this is a trade-off between water conservation and rapid growth
• this is most obvious in desert plants

Question 12

Palo Verde

Answer 12

• green stick plant whose tactic to prevent water loss as well as overheating is to have a photosynthetic barks

Question 13

Leaves in tropical rainforests versus deserts

Answer 13

Tropical rainforests: leaves that are the size of umbrellas

Deserts: extreme tiny microphylly

Question 14

Microphylly in Santa Clarita prickly pears

Answer 14

• don’t have any leaves
• the spines are non-photosynthetic but rather are used as a defense mechanism
• at sunset, they use their stems to intake the carbon dioxide that is necessary for their photosynthesis

Question 15

Episodic Rainfalls and Saguaro Cacti

Answer 15

• In the sonoran desert, it is extremely dry for the majority of the year
• there are brief episodic rainfalls where an abundance of rain falls
• saguaro cacti make the most of these episodic rainfall periods

Question 16

David Grundman

Answer 16

-killed by a saguaro cactus that fell on top of him

Question 17

Shallow Roots of Cacti

Answer 17

Extensive and shallow roots to make the most of episodic rainfall

Question 18

Tropical Plants have shallow roots for different reasons

Answer 18

• only small layer of the dirt has an abundance of resources for these plants so thus they have shallow but extensive roots to make sure they get optimal root nutrition

Question 19

Root-Foraging

Answer 19

• roots will forage for the most nutrients
• split root experiment; put the roots of the same into two different nitrogen conditions and saw that the roots wanted to travel to the area with the most nutrients
• ROOTS FORAGE FOR BOTH SYMBIONTS AND NITROGEN

Question 20

Animals can evade stresses through their behavior - how do plants do this

Answer 20

• in deciduous forests, plants drop their leaves during cold or dry seasons to prevent tissue damage or water loss

Question 21

Turbulence

Answer 21

Aids in convective cooling because it breaks up the laminar air layer which enables the leaf to effectively cool itself through evaporative cooling

Question 22

Recursive digression

Answer 22

Convective cooling aided by turbulence

Question 23

Nurse Tree Effect

Answer 23

• palo verde shades saguaro cactus
• cactus benefits because limited exposure to the sun
• this is optimal when the cacti is a seedling so they don’t compete for resources
• when the cactus grows, it might outcompete the palo verde for nutrients

Question 24

Can plants in the rainforest become waterlogged?

Answer 24

Yes if they’re epiphytes

• epiphytes grow atop other plants and obtain their nutrients from high above the atmosphere
• they also don’t have roots so they become nutrient deficient as well as water stressed