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Trinity Term 1 > To hunger or to thirst: plant water-use and photosynthesis > Flashcards

To hunger or to thirst: plant water-use and photosynthesis Flashcards

1
Q

Stomata are

A

the main site of H2O loss and CO2 uptake by plants

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2
Q

Give the equation for water potential in the vapour phase

A

psiWV = (RT/Vw) x (lnRH(%) / 100)

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3
Q

Describe RT/Vw

A

135MPa at 20 degrees

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4
Q

What is the relative humidity inside lead air spaces

A
  • 100%
  • 0.00MPa psiWV
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5
Q

vpd

A

vapour pressure deficit
- depends very strongly on ambient temperature

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6
Q

Describe the relationship between CWV(sat.) in molm-3 against air temperatures in degrees C

A
  • positive
  • non-linear
  • exhibits vpd
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7
Q

CWV(sat.)

A

saturation water vapour concentration

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8
Q

Describe the importance of stomata in regulating transpirational water loss

A
  • boundary layer adjacent to leaf surface determines transpirational flux
  • transpiration largely controlled by stomatal aperture when boundary layer effects are small
  • not when boundary layer is large
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9
Q

when are boundary layer effects small?

A

in moving, turbulent air

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10
Q

when is the boundary layer large

A

in still air

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11
Q

Describe the relationship between transpirational flux (grams water vapour per cm2 leaf surface per second) against stomatal aperture (micrometers)

A

much more positive in moving air

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12
Q

Rate of CO2 influx and photosynthesis depend on

A
  • physical resistances
  • biochemical ‘resistance’
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13
Q

Describe physical resistance in the leaf

A

boundary layer, stomata, diffusion in liquid phase to chloroplast

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14
Q

Describe biochemical resistance in the leaf

A

activity of the Calvin cycle

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15
Q

Describe TR

A

= H2O lost/CO2 fixed; approx. 500 to 700

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16
Q

TR

A
  • transpiration radio
  • defined on either molar or mass basis
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17
Q

Describe WUE

A

= CO2 fixed/H2O lost; 0.0020 to 0.0014

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18
Q

WUE

A
  • water-use efficiency
  • defined as either molar or mass basis
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19
Q

List some stomatal feedforward loops

A
  • direct humidity effect
  • direct light effect
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20
Q

List some stomatal feedback loops

A
  • hydro passive
  • hydro active
  • CO2
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21
Q

How to optimise photosynthesis and transpiration rates

A

dE/dA = lambda; constant

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22
Q

Describe the relationship between transpiration, E (mmolm-2s-1) against photosynthesis, A (micromolm-2s-1)

A
  • at the bottom end, too little photosynthesis
  • at the top end, too much transpiration
  • optimum found in the middle
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23
Q

Optimal stomatal behaviour in terms of changes in conductance appears to be that which

A

maintains the marginal cost (H2O lost) equal to the marginal benefit (CO2 gained)

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24
Q

Constancy of λ leads to:

A
  • maximal amount of CO2 fixation for a given amount of water transpired
  • minimal amount of water transpired for a given amount of CO2 fixation
  • maximal WUE
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25
Q

Describe the midday depression of photosynthesis

A
  • an example of the optimisation theory in practice
  • in seasonally arid, Mediterranean-type ecosystems
  • e.g. in Quercus suber (cork oak)
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26
Q

Describe stomatal responsiveness to stimuli

A
  • high sensitivity to CO2 (eudicots)
  • high ABA sensitivity + active stomatal control (seed plants)
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27
Q

ABA

A
  • abscisic acid
  • stress hormone
28
Q

Where were stomata innovated?

A

before the mosses

29
Q

Describe the evolution of the Tracheophytes

A
  • Late Silurian/ Early Devonian (430Mya): Cooksonia, small
  • Early Devonian (410Mya): Rhynia, 15-20cm
  • Late Devonian (380Mya): Archaeopteris, Cordaites, Lepidodendron; trees to 35m
30
Q

Describe the evolution of planate leaves

A
31
Q

Describe microphylls

A
  • Early Devonian (400Mya)
  • CO2 c.3000 p.p.m. low stomatal density
32
Q

Describe megaphylls

A
  • Late Devonian (360Mya) / Carboniferous
  • CO2 c.300 p.p.m. high stomatal density
33
Q

What are megaphylls

A

large planate leaves

34
Q

Describe the evolution of megaphylls

A

First Embryophytes in the early Devonian (430–400Mya) had axial form and microphylls
- laminate, planate leaves did not evolve for another 40Ma or so

35
Q

Did low atmospheric CO2 concentrations and transpirational cooling permit the evolution of megaphylls?

A
  • dramatic decline in [CO2]atm started during the Devonian
  • well-established inverse relationship between [CO2]atm and stomatal density
  • higher transpiration rates would have become possible and evaporative cooling of the leaves more effective
  • permitted the evolution of megaphylls without tissue temperatures reaching lethal values
36
Q

Plant survival in water-limited environments is mediated by

A

Functional traits and drought tolerance mechanisms

37
Q

List some drought tolerance mechanisms and functional traits that allow plant survival in water-limited environments

A
  • life-history strategies
  • morphological adaptations
  • biochemical mechanisms
38
Q

Describe plant life history strategies and drought tolerance

A
  • leaf deciduousness
  • short life cycle
  • dormancy (drought escape)
39
Q

Describe plant morphological adaptations for drought tolerance

A
  • small leaves
  • surface characteristics (leaf hairs; cuticle)
  • stomata (number; topography; regulation)
  • extensive or deep root systems
40
Q

Describe some plant biochemical mechanisms for drought tolerance

A
  • turgor maintenance (solute accumulation)
  • protective (compatible) solutes in cytoplasm
41
Q

List some drought-tolerant lineages

A
  • cactus shrubs
  • mangrove vegetation on littoral fringes
  • thorn woodland or semi-deciduous thicket
42
Q

List habitat water reliance in lowlands of Trinidad and NE Venezuela

A
  • cactus shrub
  • thorn woodland
  • deciduous seasonal forest
  • semi-evergreen seasonal forest
  • evergreen seasonal forest
43
Q

Describe coastal cactus shrub

A

terrestrial and epiphytic succulents (bromeliads, orchids, cacti)

44
Q

Describe thorn woodland or semi-deciduous thicket

A

many drought-tolerant woody shrubs and small trees

45
Q

‘Tropical rain forest’ aka

A
  • lowland rain forest
  • evergreen broadleaf forest
46
Q

Describe the understory of a tropical rainforest

A

sparse vegetation; low light levels

47
Q

Describe the lower montane rainforest

A
  • more open canopy
  • abundant epiphytes on tree limbs
48
Q

Describe the upper montane forest

A
  • lower canopy
  • steeper slopes
  • open aspect
  • more profuse undergrowth
49
Q

Describe the dwarf montane forest

A
  • aka elfin forest
  • low canopy (~2m) of stunted trees
  • due to exposure, high wind speeds, and thin nutrient-poor soils
50
Q

PAR

A
  • Photosynthetically Active Radiation (400–700nm)
  • only a part of the whole solar radiation spectrum
51
Q

Describe leaf radiation balance

A
  • the energy budget equation
  • energy into leaf – energy out of leaf = energy stored by leaf
52
Q

List the energies that enter a leaf

A
  • absorbed solar irradiation
  • absorbed infrared irradiation from surroundings
53
Q

List the energies that leave a leaf

A
  • emitted infrared (long-wavelength) radiation
  • heat loss by conduction and convection
  • heat loss by water evaporation
    (i.e. latent heat loss by transpiration)
54
Q

Heat loss by conduction and convection

A

sensible heat loss

55
Q

Describe the energy stored by a leaf

A
  • photosynthesis and other metabolism
  • leaf temperature changes
56
Q

Describe leaf and stem absorptance

A
  • inverse of reflectance
  • α
  • reduced by surface covering of hairs, cuticular waxes and spines (e.g. desert shrubs - Encelia farinosa [Asteraceae], Sonoran Desert, California, USA)
  • = 0.8 in spring, 0.3 in late summer
  • reduces energy input to the leaf by irradiation
  • phenotypic plasticity
57
Q

In hot, water-limited environments, small, finely dissected leaves have…

A
  • low boundary layer resistance
  • efficient sensible heat exchange by conduction and convection (because of high SA:V ratio)
  • leaves do not heat up too much above ambient temperature
  • e.g. Acacia sp. (Fabaceae), Madagascar
58
Q

Transpiration (latent heat loss) can cool leaves of some desert plants to … ambient air temperature.

A

15°C below

59
Q

Without transpirational cooling, some leaves could be up to … ambient, exceeding lethal temperature for photosynthesis.

A

20°C above

60
Q

Describe Death Valley, California, USA

A
  • light: ~ 2000 μmol m−2 s−1
  • air temperature: > 50 °C (max.)
  • soil temperature: >70°C
  • humidity: < 5% RH (min.)
  • water potential: < −10MPa
  • soil salinity: >3x seawater
61
Q

Give an example of an halophytic plant

A

Atriplex hymenelytra (Amaranthaceae, Chenopodiaceae)

62
Q

Hairs

A
  • enhance reflectivity at visible and near IR wavelengths (0.4–1.6 μm)
  • at longer, mid-IR wavelengths (> 8 μm), act as an antireflection layer, enhance emissivity, helping to dissipate heat
63
Q

The paradox of high-altitude giant rosette plants…

A
  • close to the snow line on tropical mountains (3500–5000 m)
  • can be explained by leaf radiation balance
  • large mass and nyctinastic leaf movements serve to maintain central meristematic tissues above ambient temperature during the night, so preventing freezing of cellular water
64
Q

Describe the ‘cushion’ or ‘rosette’ habit in arctic- and alpine-type environments

A
  • maximize energy input by irradiation during the day
  • create high boundary-layer resistance to energy loss during the night
65
Q

large mass has large

A

heat capacity

Trinity Term 1 (38 decks)

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