Jane:

Increasing minimum temperature will have an impact on DSSAT 3.5
SOYGRO.  And if you increase Tmin but not Tmax, the effect may not
necessarily be negative.

Crop respiration (and phenology driver, also pod addition and seed growth)
use hourly temperature based on Tmax and Tmin (sine wave during day, and
decay function at night), so they will respond to Tmin.

If you are using the leaf-level photosynthesis option (L option in File X),
the model decreases daytime photosynthesis in two ways from lower Tmin (one
is because the hourly daytime temperature driving leaf photosynthesis moves
from Tmin to Tmax and partway back down, and secondly, there is a direct
(inhibitory) effect of Tmin on the photosynthetic rate the next day, if
Tmin is less than 19 C).  See two lines on species file dealing with leaf
response to temperature.

For the daily version (C option), the model uses only daytime temperature
(effective average), but not night time temperature.  So it could be less
responsive.  It has its own separate temperature line in species file.

Lastly, nighttime respiration is sort of a red hering.  The real problem is
because increasing temperature speeds up rate of individual seed fill
(shorter duration, lower yield) and affects reproductiveness giving smaller
seed (also interactive with daylength).  But, yes, we increase crop
respiration with increasing temperature, using the function mentioned.

Good luck with it,
Ken Boote


At 03:43 PM 3/22/01 -0500, you wrote:
>A quick question:
>
>Given much of the climate change debates specifically looks at how minimum
>temperatures increase greater than maximum daily temperatures I was
>wondering to what degree (if any) the role of minimum temperatures and
>nighttime respiration is incorporated within the DSSAT 3.5 SOYGRO model.
>
>thanks for your help
>
>sincerely
>
>Jane Southworth
>Indiana University