8
DAVID M. GATES
during transient states. During steady-state conditions the rate a t
which energy is stored or lost from storage is zero and the organism
surface temperature adjusts to them streams of energy flow until the
total energy entering the eurface is balanced by the total energy leaving
the surface.
IV. COUPLING FACTORS BETWEEN PLANT AND ENVIRONMENT
Each environmental factor of significance transfers energy to or from
a plant according to the strength with which it is coupled to the plant
surface. Radiation is coupled to the plant by the absorptivity of the
surface. Air temperature is coupled to the plant by the convection
coefficient, and the water vapor pressure of the air by the diffusion
resistance of the transpiration pathway. The exchanges of oxygen and
carbon dioxide between the plant and the environment tire also controlled by diffusion resistances which act as coupling factors. In the
following discussion each coupling factor is identified explicitly and
must be known for a plant if its interaction with the environment is
to be understood.
A. RADIATION ABSORPTIVITY
The amount of radiation absorbed by the organism is the sum of all
incident fluxes on various exposed surfaces each having a specific
absorptivity. Hence,
A Qabs = aiA1S + a&# + a d d s + 8 ) + aJ4Ri1 + a J $ g
(2)
where A is the total surface area of the organimi and the Al’s are
respectively the surface areas presented to the incident fluxes of direct
sunlight, 8; of scattered skylight, 8 ; of reflected sunlight and skylight,
r(S + a); of infrared thermal radiation from the atmosphere, R,; and
of infrared thermal radiation from the ground and nearby surfaces, Rg.
The ul’a are the average (over wavelength or frequency) absorptivities
of the organism surface to the incident fluxes of radiation. The reflectivity of the underlying ground surface to sunlight and skylight is r.
For the one environmental factor, e.g. radiation, one sees here precisely
the coupling factors between the organism and the incident fluxes of
radiation. The coupling factors are the al’s Al’s. Both the absorptivities
and the surface areas exposed vary enormously from organism to
organism. The absorptivities are functions of the wavelength or of the
fiequency or wavenumber of the incident radiation. Their averages are
given in the following manner:
(3)
I d 4 8 ”
$8(N d
- - ; eta
; a, =
j44 S(4 dh
= J&h) dh
DAVID M. GATES
during transient states. During steady-state conditions the rate a t
which energy is stored or lost from storage is zero and the organism
surface temperature adjusts to them streams of energy flow until the
total energy entering the eurface is balanced by the total energy leaving
the surface.
IV. COUPLING FACTORS BETWEEN PLANT AND ENVIRONMENT
Each environmental factor of significance transfers energy to or from
a plant according to the strength with which it is coupled to the plant
surface. Radiation is coupled to the plant by the absorptivity of the
surface. Air temperature is coupled to the plant by the convection
coefficient, and the water vapor pressure of the air by the diffusion
resistance of the transpiration pathway. The exchanges of oxygen and
carbon dioxide between the plant and the environment tire also controlled by diffusion resistances which act as coupling factors. In the
following discussion each coupling factor is identified explicitly and
must be known for a plant if its interaction with the environment is
to be understood.
A. RADIATION ABSORPTIVITY
The amount of radiation absorbed by the organism is the sum of all
incident fluxes on various exposed surfaces each having a specific
absorptivity. Hence,
A Qabs = aiA1S + a&# + a d d s + 8 ) + aJ4Ri1 + a J $ g
(2)
where A is the total surface area of the organimi and the Al’s are
respectively the surface areas presented to the incident fluxes of direct
sunlight, 8; of scattered skylight, 8 ; of reflected sunlight and skylight,
r(S + a); of infrared thermal radiation from the atmosphere, R,; and
of infrared thermal radiation from the ground and nearby surfaces, Rg.
The ul’a are the average (over wavelength or frequency) absorptivities
of the organism surface to the incident fluxes of radiation. The reflectivity of the underlying ground surface to sunlight and skylight is r.
For the one environmental factor, e.g. radiation, one sees here precisely
the coupling factors between the organism and the incident fluxes of
radiation. The coupling factors are the al’s Al’s. Both the absorptivities
and the surface areas exposed vary enormously from organism to
organism. The absorptivities are functions of the wavelength or of the
fiequency or wavenumber of the incident radiation. Their averages are
given in the following manner:
(3)
I d 4 8 ”
$8(N d
- - ; eta
; a, =
j44 S(4 dh
= J&h) dh