Hi Derek

I agree with you, that temperature and
solar radiation are not the only factors
influencing development. However, these
other influences are taking place on time scales
and levels of organization which are small
enough to make them unintersting for practical
modelling purposes, so far. Despite, they will
not override the paramount importance of
light and temperature in determining crop
development.

We share your experience with the influence
of water stress on anthesis date of wheat. Yet, we
are talking here about a time span of a week
or so, which is small compared to the entire
life-cycle of the crop, which lasts for several
months.

Water stress also has a large influence on the
physiological performance of the plant such as
the shoot/root ratio and many other characteristic
(DSSAT handels them with the SWDFx coefficients).
However, the underlying processes have to be
clearly distinguished from the process of plant
development. While growth performance is event
driven, development is a pre-defined genetic
characteristic.

Plants have been taken to space, deep into the
earth and to the poles to fool their inner clock,
but it wasn't possible. It only became a "little
slower" or a "little faster", but never went out
of the range of about a  24 hour cycle. Despite
being of endogenic origin, the "clock" relies on
an external timer, which sends synchronizing signals
in a periodical fashion. The only two signals which
have these characteristic are light and temperature.
(Nataraj, in respect to your question, it is intersting
to note that rises in temperature don't cause significant
rises in "clock speed".). Since plants have this
independantly functioning watch, they are able to
adjust their activities to external environmental cycles.


Cheers

Matthias


--
Matthias Langensiepen, PhD
Hannover , Germany

Internet : www.langensiepen.net
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