Garden with Insight v1.0 Help: Plant drawing next day functions: meristem next day

A meristem can be vegetative or reproductive. A vegetative meristem accumulates biomass to make an internode and leaves, and a reproductive meristem accumulates biomass to make an inflorescence.

The amount of biomass needed for an internode and leaves is the optimal biomass for the internodes and leaves multiplied by the minimum fraction needed for creation (usually 10%). When the vegetative meristem has enough biomass, it creates one internode and one or two leaves (one if the plant has an alternate leaf pattern, two if the leaf pattern is opposite). However, since phosphorus is necessary for shoot growth, the internode and leaves can be stunted if the plant is highly phosphorus stressed on the day they are created. If the P growth constraint is less than 0.5 (zero being worst), the biomass given to the new internode and leaves is reduced using a linear function from zero biomass at a P growth constraint of zero (worst) to normal biomass at a P growth constraint of 0.5. Whatever biomass is lost from the new internode and leaves because of P stress goes back into an unallocated pool in the drawing plant to be redistributed tomorrow. The meristem gives its accumulated biomass (minus the P stress adjustment) to the internode and leaves, and then its biomass goes back to zero. If the meristem is still active it starts work on another set of structures.

Along with an internode and one or more leaves, the meristem also creates one or two axillary meristems. Axillary meristems are buds found in the angles between the stem and the leaf stalk. These angles are called axils. If axillary meristems develop, they create new branches. Usually most of the axillary meristems on a plant are inactive and do not branch. The reason they don't branch is that the meristem at the tip of the branch, the apical meristem, puts out a plant hormone that diffuses back down the branch. The hormone inhibits the development of the axillary buds and so they do not develop. This phenomenon is called apical dominance because the apex of the branch dominates the axillary meristems. As the hormone diffuses down the branch it gets less concentrated (it has a gradient), so the further away from the apex an axillary bud is, the greater the chance that it will develop. If you look at a plant that has branches, the branches usually come out of the main stem near the bottom of the stem. That is because of apical dominance.

In this simulation apical dominance is modeled very simply. Each day all axillary meristems decide if they ought to develop based on a probability of branching, which is a plant parameter. But if the axillary meristem is within a certain number of nodes distance from the apex of its branch (the branching distance, another parameter), the axillary meristem cannot branch. This is a stepped hormonal gradient -- all or none. When an axillary meristem decides to develop, it turns into an apical meristem (at the apex of the new branch) and begins creating new internodes, leaves, and axillary meristems.

On getting a signal from the model plant that reproductive allocation has started, the meristem checks its determinate probability (described in the starting reproduction section) to see if it should make an inflorescence. If so, the meristem immediately switches over any accumulated biomass it has to the creation of an inflorescence. When the required amount of biomass has been accumulated, the meristem creates one inflorescence, gives the biomass to the inflorescence, and stops demanding biomass forever. In the same way that P stress reduces the size of the internode and leaves, water stress influences the size of the inflorescence. (It is possible that P stress also reduces the size of inflorescences too, but we haven't put that in.)

calculation of phosphorus stress, starting reproduction
More on the biomass partitioning submodel
Model contents