Photosynthesis, tree growth and water transport

For the new engine. I have been designing a genome model for the biosphere. This is the set of genes that describe any plant that can grow in Earthsim’s biosphere. Each gene has a specific function in the plant.

To do this well I needed to have a good idea of the model that the trees and plants would be growing inside.

Once you have a good understanding of the model. You can know what genes to put in a plant description so it can optimise itself for growing in the environment.

Below is the model for how water can move around on the land.

The land simulator manages this water for us, so we will know exactly how much water we have in any of these components.

This water availability is used by the Biosphere simulation to know where and how trees can grow.

Here is the summary design of the plant/tree model that works with the above.

A few interesting points to note about this model. (When I mention a tree it also applies to any plant)

1. Trees can self shadow, so sections of a tree can be less efficient and can die away. So a tree can grow and change shape over time.
2. Trees and plants have a few interesting dilemmas they need to solve with their different genetic makeups.
   1. When they want to photosynthesize, they have to open their pores. But when they open their pores, if the air is hot, the can loose much more water to the air than they would want. Trees that can manage when they open or close their pores can survive better in arid climates.
   2. Tree’s that have leaves that can be damaged by the cold have to decide when to drop and when to grow their leaves.
   3. Tree’s that have seed/fruit that can be damaged by the cold. or that can require much more water and energy to grow also have to manage their timings.
   4. Tree canopies heat up from sunlight, but you can still photo synthesize from indirect illumination. Hence different canopy and leaf configurations offer different competitive factors for optimization.

The critical thing about all this is that it lets us know how much new water vapor and C02 is added to the atmosphere by a forest. And we can model what happens to the atmosphere as we change the forest.

Here is the diagram of the top level model that these pieces fit into.