L9 - Leaf Economic Spectrum Flashcards
What does leaf economics describe?
- The investment in photosynthesis within a leaf and the return generated as photosynthates over the leaf’s lifespan.
Name the six features that LES describes.
Name the initial study that analysed these traits
1) Photosynthetic CO2 assimilation rate
2) Dark respiration rate
3) Leaf mass per area (LMA) (or inverse = Specific Leaf Area - SLA)
4) Leaf Nitrogen
5) Leaf Phosphorous
6) Leaf lifespan
- Reich et al (1997)
Class the 6 LES traits into groups.
Investment for a leaf:
- Leaf mass per area
- Leaf Nitrogen
- Leaf Phosphorous
(contribute to photosynthetic proteins etc…)
Return on Investment:
- CO2 assimilation
- Lifespan (defines how long the return will keep coming in for)
Maintenance costs of photosynthesis:
- Dark respiration (expenditure of photosynthates)
How is CO2 assimilation rate measured?
Give the relevant equation
- Leaf enclosed in a gas exchange cuvette and CO2 concentration of air entering and leaving measured.
Net CO2 uptake = (CO2 entering - CO2 leaving) *flow rate / leaf area or mass
Describe how photosynthetic capacity correlates with leaf lifespan and leaf age?
Draw the relevant diagram
- Negative correlation between leaf lifespan and maximum photosynthetic rate.
- Max. photosynthesis rate declines with the age of a specific leaf.
- Ageing rate enhanced in sun leafs due to self shading and re-allocation of resources.
(Diagram on pg 17 comparing ageing rate in sun vs shade leaves)
Describe the relationship between leaf thickness and photosynthetic capacity.
Describe the relationship between Leaf Nitrogen and photosynthetic capacity.
What does this imply?
- Strong positive correlation between Specific Leaf Area (SLA) and max. photosynthesis rate. (thinner = higher rate)
- Positive correlation between Leaf Nitrogen and max. photosynthesis rate.
- Implies trade offs between rate, leaf N and SLA - all factors co-vary (limited N means thick, high N content leaf not possible)
Why does Leaf Nitrogen influence photosynthesis rate?
How does the shape of the relationship between increased N supply and net photosynthesis vary between plants?
Give an example.
- Photosynthesis requires N for chlorophyll and amino acids for proteins involved e.g Rubisco.
- Long-lived trees have a slow response to N.
- Fast-growing pioneers have a fast response
- E.g Same amount of N produces higher rate increase in Vismia compared to Picea.
Explain the intercorrelation of the LES traits
Give the two general leaf strategies.
Explain why these occur.
- Leaf traits strongly intercorrelated - single axis can be used to explain variation.
- Co-variation accounts for 72% of total trait variation
Leafs can make:
1) Thin, short-lived leaves w/ high nutrient content and high photosynthesis rate.
2) Thick, long-lived leaves w/ low nutrient content and low photosynthesis rate.
Constraints such as nutrient levels, within leaf shading, herbivory, restrict thick, long lived high photosynthesis rate leaves.
How do leaf traits vary between climates?
Explain these differences
Arid and Semi-Arid regions = generally higher LMA (thicker)
- Differences are modest and large variation between co-existing species seen.
Leaf longevity shorter (at given LMA) where rainfall is lower
- High temp. means stomata more closed. So leaf invests in more N to produce more mesophyll cells, assisting transpiration for CO2.
- Mesophyll cells aren’t bio-mechanically strong, giving lower longevity.
Give two physiological mechanisms that link LES relationships
- Stomatal conductance determines Amax via control over CO2 diffusion into leaves
- Rubisco controls Amax via control over carboxylation capacity as it’s the rate limiting enzyme of the Calvin Cycle
Outline how stomatal conductance for CO2 can be calculated
1) Measure net water release as previously described.
2) Find stomatal conductance to H20 (gs) via: net water release = gs*(H20in - H20out) where H20out (concentration out of leaf) is measured and H20in is calculated from leaf temp, assuming 100% humidity
3) gs (CO2) = gs (H20)/1.6
How is Maximum Rubisco Activity calculated?
1) Calculate CO2 conc. inside leaf intercellular airspace (Ci) via:
Ci = Ca - A/gs (CO2)
2) Plot A/Ci curve and calculate Vcmax from this
Outline the relation between LES traits and these physiological traits.
Who was the study by?
- Long leaf span (high LMA) comes from greater physical strength in cell walls - requires more and thicker walls, requiring more N invested in cell walls
- A trade off exists between N invested in cell walls vs N invested in Rubisco. Therefore high LMA reduces photosynthetic efficiency from less N in proteins/Rubisco
- Photosynthesis less limited by CO2 diffusion in low LMA leaf. Therefore high LMA also reduces photosynthetic efficiency due to greater resistance to CO2 diffusion.
- Onoda et al. (2017)
