creates a repeating series of counts from 1 to 24 to correspond to the hours in
the day, and
Day night switch ¼ IF Daily cycle <¼ 6 OR Daily cycle >¼ 19 THEN 0 ELSE 1:
ð20:2Þ
These parameters generate a daily accumulation of assimilates. Assimilates are
allocated among the plant parts according to standard percentages found in the
literature [1]. Also included is carbon allocation to respiration of the roots and
shoot. The rate and magnitude of allocation are controlled by switches, which also
incorporate randomness during the growing season. Such randomness accounts for
variations in plant development that may arise due to differences in soil water
status, growing degree-days, and other environmental variables. A major feedback
in the model is the accumulation of leaf area over the season and the subsequent rise
in photosynthesis.
Senescence has two components. The initial component is a small loss of leaf
mass occurring early in the season due to self-shading and loss of leaf area deep in
the canopy. The larger component occurs later in the season as the plant matures.
The timing of the senescence components also incorporates randomness. The sum
of all the plant components feeds into soybean growth over the season.
Using this model, we are able to grow a single, small plant into a mature soybean
under alternative environmental conditions. Under current atmospheric conditions,
we assume a specific leaf area (SLA) ¼ 0.0270 (area/mass) and the following initial
values:
Assimilates ¼ 0 g
Leaf ¼ .09 g
Root ¼ 0 g
Seed ¼ 0 g
Stem ¼ .1 g
The leaf assimilation rate, which is a key determinant of CO 2 uptake, is shown in
Fig. 20.2.
Figure 20.3 demonstrates that there is a daily increase in the assimilated carbon
that is subsequently exported at night to the various plant organs (Fig. 20.4). There
is no build up of soluble carbon from 1 day to the next, which is consistent with
actual total soluble carbohydrate measurements.
Let us now modify the model by incorporating elevated CO 2 concentrations.
Growth in elevated CO 2 results in higher leaf assimilation rates and decreased SLA.
Decreases in SLA are common in plants exposed to elevated CO 2 and reflect altered
carbon contents. Photoinhibition also decreases in elevated CO 2 . The greater final
biomass of soybeans grown in elevated CO 2 reflects the beneficial decrease in
photoinhibition.
The results are shown in Fig. 20.5, where we assume the same parameters as
under current ambient conditions except that now Photoinhibition ¼ 0.03,
SLA ¼ 0.023, and the Leaf Assimilation Rate CO 2 is as specified in Fig. 20.6 and
20.1 Soybean Plant Model
159
the day, and
Day night switch ¼ IF Daily cycle <¼ 6 OR Daily cycle >¼ 19 THEN 0 ELSE 1:
ð20:2Þ
These parameters generate a daily accumulation of assimilates. Assimilates are
allocated among the plant parts according to standard percentages found in the
literature [1]. Also included is carbon allocation to respiration of the roots and
shoot. The rate and magnitude of allocation are controlled by switches, which also
incorporate randomness during the growing season. Such randomness accounts for
variations in plant development that may arise due to differences in soil water
status, growing degree-days, and other environmental variables. A major feedback
in the model is the accumulation of leaf area over the season and the subsequent rise
in photosynthesis.
Senescence has two components. The initial component is a small loss of leaf
mass occurring early in the season due to self-shading and loss of leaf area deep in
the canopy. The larger component occurs later in the season as the plant matures.
The timing of the senescence components also incorporates randomness. The sum
of all the plant components feeds into soybean growth over the season.
Using this model, we are able to grow a single, small plant into a mature soybean
under alternative environmental conditions. Under current atmospheric conditions,
we assume a specific leaf area (SLA) ¼ 0.0270 (area/mass) and the following initial
values:
Assimilates ¼ 0 g
Leaf ¼ .09 g
Root ¼ 0 g
Seed ¼ 0 g
Stem ¼ .1 g
The leaf assimilation rate, which is a key determinant of CO 2 uptake, is shown in
Fig. 20.2.
Figure 20.3 demonstrates that there is a daily increase in the assimilated carbon
that is subsequently exported at night to the various plant organs (Fig. 20.4). There
is no build up of soluble carbon from 1 day to the next, which is consistent with
actual total soluble carbohydrate measurements.
Let us now modify the model by incorporating elevated CO 2 concentrations.
Growth in elevated CO 2 results in higher leaf assimilation rates and decreased SLA.
Decreases in SLA are common in plants exposed to elevated CO 2 and reflect altered
carbon contents. Photoinhibition also decreases in elevated CO 2 . The greater final
biomass of soybeans grown in elevated CO 2 reflects the beneficial decrease in
photoinhibition.
The results are shown in Fig. 20.5, where we assume the same parameters as
under current ambient conditions except that now Photoinhibition ¼ 0.03,
SLA ¼ 0.023, and the Leaf Assimilation Rate CO 2 is as specified in Fig. 20.6 and
20.1 Soybean Plant Model
159