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Garden with Insight v1.0 Help: Plant next day functions: allocate new biomass among shoots, roots, fruits

Allocation of new plant biomass is to four plant compartments: shoots, roots, fruits and storage organ. The fruit and storage organ components are not in the EPIC plant model.

The different parts of the plant demand biomass as follows.

gif/20000000.gif Reproductive biomass demand works by attempting to maintain a ratio of reproductive to total plant biomass that follows a linear increase from the start of reproductive allocation (just after floral inititation is complete) until maturity (at heat unit index = 1.0). The proportion of total plant biomass devoted to reproductive structures at maturity is determined by a plant parameter. For example, if the parameter "Biomass allocation to flowers and fruits at maturity" is set at 0.5, the plant will attempt to reach a reproductive/total biomass ration of 50% at maturity. Reproductive demand takes precedence over all other demands.
gif/20000000.gif Root biomass demand attempts to maintain a root/total biomass fraction that follows a linear progression based on two proportions of total plant biomass: at emergence (just after germination) and at maturity. Usually the root biomass fraction decreases as the plant ages. However, root biomass demand is secondary to reproductive demand. The root will only demand biomass after reproductive demand has been met. In fact, root biomass can be removed from the root and moved (remobilized) to the reproductive portion of the plant if there is inadequate new biomass to meet reproductive demand. Remobilization is limited to one percent of the total root biomass in any one day.
gif/20000000.gif Shoot biomass works in nearly the same way as does root biomass, but it uses the inverse linear function from the root biomass function. For example, if roots are to take up 40% of the total plant biomass at emergence, shoot biomass will demand enough biomass to take up 60% of the total plant biomass. As with roots, shoot biomass defers its allocation to reproductive demand, and shoot biomass can be remobilized to meet reproductive demand.
gif/20000000.gif The storage "organ", which is really any area in which sugars are stored in the plant, works in two ways: it can be explicitly filled if the storage organ is harvested (as in a carrot or potato), and it can be used to temporarily store photosynthate that particular plant parts aren't ready to use yet. When demands increase, the stored material can be moved to any of the other biomass divisions. Explicit allocation to the storage organ works in the same way as reproductive demand: with a storage/total biomass fraction at maturity and a heat unit index when storage organ allocation should start.

You may have noticed that these demands could add up to more than one hundred percent. If this happens the available biomass is allocated to the competing demands proportionately.

After allocation to the major biomass compartments is complete, root biomass is partitioned to each of the soil layers by the water use in that soil layer. Remember that when water use was calculated we said that the root growth constraint for each soil layer affected water use, and that water use affected the growth of roots in the layer. This is where the water use affects the root biomass in each layer.

calculation of actual new biomass, root growth constraint
More on the biomass partitioning submodel
Model contents

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Updated: March 10, 1999. Questions/comments on site to
Copyright © 1998, 1999 Paul D. Fernhout & Cynthia F. Kurtz.