plant limitations cont

Question 1

nitrogen importance?

Answer 1

Nitrogen is in plant proteins and enzymes and is the foundation of energy molecules thus
allocation is important

Question 2

increase N =?

Answer 2

ncrease N in leaf (allocated to photo structures) = Increase NPP
Increase N = Increase photosynthetic rate b/c used to make enzymes or other photosynthesis
structures

Question 3

N trade off?

Answer 3

Trade off -> stomata used to exchange CO2
- Less precipitation = closed stomata b/c risk of desiccation even at the
cost of photosynthesis
- As N increases = Stomata conductance increases (rate of gas exchange
and transpiration determined by the physical structure of stomata)
- More N = Open stomata more = Higher photosynthesis and
transpiration

Question 4

short vs long term response to water limit

Answer 4

Short term responses:
1. Reduce stomatal conductance (tradeoff between photosynthesis and water loss)
2. Wilting, shedding leaves
Long-term responses:
1. Reduce leaf area (transpiration)

Question 5

What is the optimal temp range for photosynthesis

Answer 5

emperature: 15-25 degrees
Tropical: 30-35 degrees

Question 6

how is low temp limiting? high?

Answer 6

Low temperature is limited by rate of chemical
reactions
High temperature creates enzyme inactivation and
destruction of photosynthetic pigments

Question 7

how do plants adjust for CO2

Answer 7

Plants physiologically and morphologically adjust so that CO2 diffusion and biochemical
limitations on photosynthesis are equal

Question 8

principles of limiting factors? look at graph

Answer 8

a) Photosynthesis à process limited by >1 factor
b) Rate of governed by most limiting factor
c) Other factors will adjust to match

Question 9

higher co2 and temp increase?

Answer 9

rate of photosynth

Question 10

what limiting traits exist for carbon gain

Answer 10

hick, long-lived leaves (decrease of biomass)
- Low leaf nitrogen
- Low stomatal conductance
- Low photosynthetic capacity

Question 11

what ample traits influence photosynth

Answer 11

• Thin leaves, high turnover (increase of biomass)
• High leaf nitrogen
• High stomatal conductance
• Low photosynthetic capacit

Question 12

why are plants central to the carbon cycle

Answer 12

pllants are central to carbon cycle because with the emergence of plants they changed the
atmosphere and change the oxygen levels from 15%to 21%.

Question 13

how are plant interactions measured

Answer 13

Measured in productivity of leaves: Allocation and structure of leaves (photosynthesis structures)
– leaf area index`

Question 14

what do canopy processes increase?

Answer 14

Canopy processes increases range of light intensities over which LUE curve continues to
increase

Question 15

what do canopy processes increase?

Answer 15

Canopy processes increases range of light intensities over which LUE curve continues to
increase

Question 16

higher vs lower canopy radiation usage

Answer 16

Sunlit leaves (higher canopy) – basic curve until a certain level of the
photosynthesis decreases because of breakdown of structures (enzymes) by the
intense sun
Shade leaves (bottom layer of canopy) – as a whole they contribute to whole
primary productivity more than sunlit

Question 17

what is NPP calculated by?

Answer 17

Net primary productivity (NPP) – NPP = GPP – RR
-Difference between energy fixed and respiration rate

Question 18

GPP functions as? how does it vary?

Answer 18

Energy store during photosynthesis
-Varies diurnally and seasonally in response to proximate controls: light, water, nitrogen,
temperature, carbon dioxide

Question 19

what determines variation in GPP

Answer 19

1. Quantity of photosynthetic tissue (leaf-area)
2. Duration of tissue activity (season length)

Question 20

where is GPP highest and when

Answer 20

Croplands and deciduous forests have the highest GPP within the growing season of
April to August

Question 21

what is LAI

Answer 21

Leaf Area Index (LAI) –one half of the total amount of leaf material in a canopy
compared to ground area

Question 22

what dos LAI affect

Answer 22

Affects light (PAR) penetration through canopy
- Main driving force of net primary production, water and nutrient use
and carbon balance

Question 23

how is PAR absorption allocated

Answer 23

Canopy absorbs 79% of PAR, low vegetation absorbs 2% of PAR,
middle absorbed 7% of PAR
- Boreal forest reflects 10% of PAR

Question 24

why is NPP less than GPP

Answer 24

NPP is about half of GPP because most ecosystems have similar efficiencies converting
photosynthate to NPP

Question 25

what does respiration provide? how is it calculated? what does each component involve?

Answer 25

provides energy for plants to grow and maintain biomass and acquire nutrients
R plants = R growth + R maintenance + R ion
Each component involves oxidation of carbohydrates to make ATP

Question 26

3 functions of resp/ that require it?

Answer 26

1. Growth – cellulose and lignin are important compounds made by biosynthesis and
   contribute to the standing carbon pool
2. Maintenance – Energy for replacing proteins, membranes, and other tissues; increase
   temp=increase tissue turnover; accounts for 50% of total plant respiration
3. Ion transport – gradient required for nutrient uptake

Question 27

what is compensation point?

Answer 27

Compensation point – where light intensity is at the point where the rate of photosynthesis is
equal to the rate of respiration