L11 - Mediterranean Vegetation Types Flashcards
Give three points on the climate and plant diversity of the Mediterranean
- Wet winters and hot, dry summers
- Highly disturbed habitat, often fires
- Predominated by stress tolerant, scrubby forest: Macchia.
- Rich floristic diversity
What does a Kilmadiagramm plot?
What can the relative curve heights tell you?
- Scaled monthly temperature and precipitation.
- Where temperature curve is above monthly precipitation, evaporation dominates - dry season.
Name and describe the 3 major plant types in the Mediterranean climate.
Sclerophylls (resprouters):
- Tough, leathery leaves that crack when folded
- Evergreen, forming canopy
- Re-sprout from lignotubers after fire
- E.g. Olea europea (olive)
Malacophylls (seeders):
- Soft-leaved
- Semi-deciduous
- Regrow from seeds after fire
- E.g Rosmarinus
Geophytes:
- Avoid drought as underground corms or bulbs
- E.g. Narcissus bulbocodium (hoop daffodil)
How can solute potential at full hydration be measured and why is this a useful parameter?
Sketch the relevant diagram
Who came up with this as a marker of drought tolerance?
- Important marker of intrinsic drought tolerance.
Measurement:
1) Measure water potential across time, using pressure bomb, as tissue is progressively dehydrated
2) Weigh each time and plot graph of -1/Ψw against 100-RWC.
3) Beyond the turgor loss point (TLP) graph becomes linear as water is reduced for finite solute content.
4) Extrapolate this line to y-axis for solute potential at full hydration.
- Diagram on pg 37
- Megan Bartlett et al (2012) - solute potential easier that TLP to measure.
How does solute potential at full hydration predict drought tolerance?
- Plants with more negate solute potential at full hydration (pi0) tend to be more drought tolerant.
What is our interest in Sclerophylls and Malacophylls related to?
- Both groups have contrasting strategies for surviving in drought and fire prone regions.
- Different strategies defined by their water relation parameters which we will explore.
Give the 3 parameters over which we will explore the different strategies of Sclerophylls and Malacophylls.
What paper outlined these findings?
1) Solute potential at full hydration
2) Hydraulic conductance
3) Leaf gas exchange ( to calculate IWUE)
- Vilagrosa et al. (2014)
How does solute potential at full hydration vary between Sclerophylls and Malacophylls?
- Ψp more negative in sclerophylls
- Sclerophylls have a higher capacity for osmotic adjustment.
How does hydraulic conductance compare between Sclerophylls and Malacopylls?
- Higher hydraulic conductance in Malacophylls
- Narrower xylem in Malacophylls but greater number/density of vessels cause this
- Narrower xylem reduce cavitation risk posed by high flow rate and growth + flowering in summer
Define intrinsic water use efficiency (IWUE)
How do Sclerophylls and Malacophylls compare in leaf gas exchange and IWUE
How do their leaf gas exchange parameters vary with drought?
- IWUE = A/gs
(C assimilation/stomatal conductance - proxy for water lost via tranpiration) - Malacophylls have higher total A and gs
- But Sclerophylls have higher IWUE
- Sclerophylls considered conservative water “savers” , Malacophylls considered “spenders” of water.
For increasing drought stress:
- Malacophylls start with high A and gs but show rapid decline with water stress.
- Sclerophylls start w/ lower A and gs but maintain photosynthesis for longer into drought (more gradual decline)
Summarise the different strategies of Sclerophylls vs Malacophylls given the comparison of parameters.
- Seeders spend water when available, require xylem to withstand higher risk of cavitation.
- Re-sprouters have lower demand for water and sap flow rates, reducing cavitation risks. Can have larger diameter xylem.
- Re-sprouters have higher solute conc. can function for longer during drought
- Seeders more competitive + grow faster when water available. Seeders plod on for longer when drought hits. “Hare” and “Tortoise” strategies, both competitive.
Compare the growth timings of Sclerophylls and Malacophylls.
Detail the study that shows this
- Malacophylls only grow for very short part of the year.
- Sclerophylls grow throughout the year.
Fontanella (1992)
-Quercus ilex (holly oak) leaves out + flowers in early summer, then no new growth till Oct.
- Cistus monspeliensis grows leaves throughout year. Flowers + seeds across long summer period.
- Quercus has high water deficits, Cistus recovers water status each night.
What impact does climate have on plant species distribution?
How is this shown with Mediterranean-type ecosystems?
- Climate filters for plant form + strategies that allow plants to survive that region.
- Mediterranean-type ecosystems worldwide dominated by broadleaf, evergreen, high LMA sclerophyll shrubs.
How has the flora of the Mediterranean changed and why?
- Mediterranean basin warmer and wetter in Eocene (56 - 33Mya) and Pliocene.
- Widespread laurel forest of thermo-hygrophilous laurophylls dominated.
- Laurophylls still seen in Pliocene (5-2.5Mya)
- Northern hemisphere glaciation caused colder, drier conditions = modern Mediterranean climate (drought)
- Most laurophylls squeezed to western refuges e.g. Canary Islands due to drought.
- Laurus persisted in Med. as requires less water and less sensitive to cold temp. + better cavitation recovery (Salleo et al. 2004).
