Transcript Vodní režim rostlin

Plant water regime
• Transpiration
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Leaf energy balance
Fick laws
Boundary layer
Cuticle
Stomata
Leaf energy balance
• Energy sources:
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– shortwave sun radiation
– longwave radiation emitted by sky and surrounding
Solar radiation might be reflected, absorbed or transmitted (according to wave
length)
• Energy balance:
• SRnet + LRnet + C + E + M = 0
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SRnet, LRnet - absorbed short-wave or long-wave radiation, C - heat transport
(sensible heat flow), E - heat used for vaporization (latent heat flow),
M - energy consumption or production by metabolism
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Bowen ratio = C/E
Effect of plant on energy balance
Absorbance, reflectance and transmittance is affected by leaf area, orientation in
space, quality of leaf surface, leaf anatomy
Latent heat flow by transpiration
Penman-Montheith equation
s Rnet + c (es-e)/ra
E =

s +  (ra+rs)/ra
E - latent heat flow
s - change of water vapour pressure
with temperature,
Rnet - absorbed radiation,
 - density,
c - specific heat,
es - e – difference between saturated
and actual water vapour pressure,
 - psychrometric constant,
ra - boundary layer resistance,
rs - stomatal resistance
• 1st Fick law:
• Jv = -D (dc / dx)
Fick laws
• 2nd Fick law:
• dc / dt = - dJv / dx = D (d2c / dx2)
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Jv - transport rate, D - diffusion coefficient, dc/dx - gradient of concentration,
t - time
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sub-stomatal cavities, stomata, boundary layer
Transpiration rate
• E = gl c
• E - transpiration rate mmol m-2 s-1 or g m-2 s-1
• gl - leaf conductance (gl = -D) mol m-2 s-1 or m s-1
• c - difference in water vapour concentration between ambient air and
air in sub-stomatal cavities (dc/dx) mmol mol-1
• gl = gs + gc
• 1/gl = 1/ga + 1/gs + 1/gi
• gs - stomatal conductance, gc - cuticular conductance,
• ga - boundary layer conductance, gi - conductance in intercellular
spaces
• g = 1/r, r - resistance
Transpiration stomatal (Es), cuticular (Ecu) and peristomatal (Ep)
Water vapour concentration in substomatal cavity and
boundary layer
cl = cs ew(Vw/RT)
cl - water vapour concentration in
sub-stomatal cavity,
cs - saturated concentration,
w - leaf water potential
Vw - molar volume of water
R - gas constant
T - temperature
Boundary layer
• Thickness (da) is dependent on
wind speed, leaf shape,
roughness of his surface,
presence of trichomes
• ( 0.01 - 1 mm)
• da = 4 L/v
• L - leaf length in the direction
of air flow, v - wind speed
• Relationship between
transpiration rate and stomatal
conductance is affected by
boundary layer thickness (wind
speed)
Cuticle
• Cuticle - adaptation to drought
• Structure and composition: upper layer of the cell wall is impregnated
by cutin and waxes (endocuticular or epicuticular waxes)
• Cuticular conductance for water is 1.7 - 28.6 % of stomatal
conductance
• Cuticular conductance for CO2 is only 6 % of that for water
• Cuticular conductance has higher importance when stomata are
partially or completely closed
• Cuticular conductance is dependent on plant species, age and
conditions. It is very low in species adapted to dry conditions, in
contrast, it is high in plants in vitro. Usually it increases during leaf
ontogeny and decreases during dehydration.
Leaf epidermis structure
Cuticle matrix
Arrangement of cuticular waxes on leaf surface
Effect of air humidity on permeability of cuticle in different plant
species
Stomata
Area of apeture of all stomata is about 1 % of leaf area, nevertheless,
water vapour efflux corresponds to that from free water
Two types: kidney-shaped and dumbbell shaped
Development during leaf ontogeny
Stomatal density 20 - 2 000 mm-2, different size
Amfistomatic and hypostomatic leaves, adaxial/abaxial ratio, e.g.:
wheat 33/14, maize 48/52, oat - 25/23, sunflower 85/156,
tomato 12/130, apple tree 0/235
Sun/shade leaves : beech 113/416, hornbeam 170/365
Heterogeneity on one leaf area
Stomatal patchiness
Stomatal heterogeneity on leaf area of Commelina communis
Stomatal patchiness in Nicotiana tabacum
Methods
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1) Gravimetric methods
2) Transpiration curves (water loss by detached leaves) enable to differentiate
stomatal and cuticular transpiration
3) Determination of transpiration rate from the changes in air humidity in leaf
chamber
4) Calculation of transpiration rate from measurements of water flow in xylem
5) Calculation of evapotranspiration from energy balance
Methods
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1) Cuticular conductance
a) transport HTO or fluorescent dyes in isolated cuticle
b) measurement of water efflux from epidermis without stomata or with closed
stomata
2) Microscopic methods for determination of stomatal density, shape, size and
aperture
a) in situ
b) microrelief (replica) methods
3) Determination of stomatal conductance
a) diffusion porometers
b) mass flow porometers
c) calculation from transpiration rate