SVERIGES LANTBRUKSUNIVERSITET - Epsilon Open Archive - SLU

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model can be used as a research too l to lead to new ideas for
experimentation, and to provide a link between plant physiol­
ogy in the laboratory and problems in the field. Thirdly, the
model could be used by researchers in analyzing their own
field data. Being simple to use, the models are suitable for
those who have not time to develop their own models and/or
are not experienced in using simulation modeIs. The main
emphasis has been to develop so called interactive computer
programs, which are easy to use, include various type of
help facilities and have possibility to show results in
graphical form.
Water movement in Soil-Plant-Atmosphere-Continuum
Water movement in the plant can be considered to be
driven by differences in water potential and flow is restric­
ted by some resistances within the system. Water will flow
from a point of high water potential to the direction of
decreasing water potential. In the soil-plant-atmosphere
system the water potential in a well-watered soil may be on
the order of -0.01 MPa (equivalent to -100 cm or pF 2). In
plant leaves midday values of the water potential are gene-
rally around -0.5 ... -2.5 MPa (-5000 ... -25000 cm). In the air
the water potential is very low (-30 ... -100 MPa depending on
vapour pressure deficit of the air). Comparison of these
potentials show that general ly there is a continuous stream
of water from the soil to the plant and from plant to the
atmosphere. The magnitude of flow is influenced by resistan­
ces at various parts (see Fig. 1): from the soil to the plant
roots, from the roots to the leaves (plant resistance), from
the intercellular spaces to the atmosphere (stomataI and
boundary layer resistances) .
Description of the computer programs
Various type of computer programs have been developed
mainly to be used as research and educational tooIs. The
value of mathematical models depends on the nature of the
problem. Some points of general significance are given
below:
. modeling can stimulate new ideas and experimental
approaches