plant limitations cont Flashcards
nitrogen importance?
Nitrogen is in plant proteins and enzymes and is the foundation of energy molecules thus
allocation is important
increase N =?
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
N trade off?
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
short vs long term response to water limit
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)
What is the optimal temp range for photosynthesis
emperature: 15-25 degrees
Tropical: 30-35 degrees
how is low temp limiting? high?
Low temperature is limited by rate of chemical
reactions
High temperature creates enzyme inactivation and
destruction of photosynthetic pigments
how do plants adjust for CO2
Plants physiologically and morphologically adjust so that CO2 diffusion and biochemical
limitations on photosynthesis are equal
principles of limiting factors? look at graph
a) Photosynthesis à process limited by >1 factor
b) Rate of governed by most limiting factor
c) Other factors will adjust to match
higher co2 and temp increase?
rate of photosynth
what limiting traits exist for carbon gain
hick, long-lived leaves (decrease of biomass)
- Low leaf nitrogen
- Low stomatal conductance
- Low photosynthetic capacity
what ample traits influence photosynth
- Thin leaves, high turnover (increase of biomass)
- High leaf nitrogen
- High stomatal conductance
- Low photosynthetic capacit
why are plants central to the carbon cycle
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%.
how are plant interactions measured
Measured in productivity of leaves: Allocation and structure of leaves (photosynthesis structures)
– leaf area index`
what do canopy processes increase?
Canopy processes increases range of light intensities over which LUE curve continues to
increase
what do canopy processes increase?
Canopy processes increases range of light intensities over which LUE curve continues to
increase
higher vs lower canopy radiation usage
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
what is NPP calculated by?
Net primary productivity (NPP) – NPP = GPP – RR
-Difference between energy fixed and respiration rate
GPP functions as? how does it vary?
Energy store during photosynthesis
-Varies diurnally and seasonally in response to proximate controls: light, water, nitrogen,
temperature, carbon dioxide
what determines variation in GPP
- Quantity of photosynthetic tissue (leaf-area)
- Duration of tissue activity (season length)
where is GPP highest and when
Croplands and deciduous forests have the highest GPP within the growing season of
April to August
what is LAI
Leaf Area Index (LAI) –one half of the total amount of leaf material in a canopy
compared to ground area
what dos LAI affect
Affects light (PAR) penetration through canopy
- Main driving force of net primary production, water and nutrient use
and carbon balance
how is PAR absorption allocated
Canopy absorbs 79% of PAR, low vegetation absorbs 2% of PAR,
middle absorbed 7% of PAR
- Boreal forest reflects 10% of PAR
why is NPP less than GPP
NPP is about half of GPP because most ecosystems have similar efficiencies converting
photosynthate to NPP
