Modeling Transpiration of Leaves

air temperature (C)

15.85

wind speed (m/s)

1.5

leaf length (m)

0.1

incident radiation (W

-2

m

)

750

albedo (-)

0.15

atmospheric pressure (kPa)

100

symbol
leaf temperature (ºC)	20.9	17.9	16.2	15.6
E mmol -2 m -1 s 	2.7	6.6	11.3	14.7
leaf water vapor (mol/mol)	0.025	0.02	0.018	0.018
air water vapor (mol/mol)	0.007	0.007	0.007	0.007
air vapor pressure deficit (kPa)	1.1	1.1	1.1	1.1
conductance mol -2 m -1 s 	0.154	0.5	1.	1.4

E (mmol

-2

m

-1

s

)

Transpiration is the transport of water vapor through plant stomatal apertures. This water loss is a necessary requirement for vascular plants as they take up carbon dioxide for photosynthesis. The two main factors that determine transpiration are the conductance of water vapor from inside the leaf to the atmosphere and the gradient of water vapor from inside to outside the leaf. It is generally assumed that the water vapor in the leaf is saturating, thus the gradient is determined by the leaf temperature and water vapor concentration in air. Here, relative humidity is used to determine the atmospheric water vapor (

y

axis), and leaf conductance to water vapor (

x

axis) represents all diffusive conductances associated with the leaf. Transpiration is modeled based on leaf energy budget and a Fick's law analogy.