Complexity and Patchy Stomatal Conductance

In collaboration with Dr. David Peak (Physics Department, USU), this project investigates the dynamics of stomatal networks in leaves as a possible example of computation in a multicellular, non-neuronal biological system. Stomata are tiny pores on the surfaces of leaves that regulate the exchange of gases between the plant and the atmosphere. By continually adjusting stomatal aperture a plant solves the problem of maximizing CO2 uptake while minimizing H2O loss. Stomatal systems are formally similar to networks of distributed computational elements that process and share information only locally. Simulations of such networks show that computation involving the entire network can emerge from local processing when the elements are correctly “wired” together. Stomata have been shown to exhibit complex collective behavior, and we hypothesize that this behavior implies that the plant solves its CO2/H2O constrained optimization problem by distributed, emergent computation.

It is found, however, that even when environmental conditions are uniform, collections of tens to thousands of stomata can have similar conductances, different from those of surrounding stomata. This is the phenomenon of "stomatal patchiness."

Stomatal patchiness can be visualized in images of chlorophyll fluorescence such as in the image to the right. In this image, light intensity and gas concentrations are uniform over the leaf surface shown (2.5 cm x 2.5 cm).

Sometimes stomatal patchiness can be remarkably dynamic. The movie below demonstrates long, dynamic patchy episodes.

Fluorescence movie of patchy stomatal conductance

In the two movies below, thermal images (right) are compared with fluorescence (left). Variations in temperature are directly related to water evaporation and, therefore, directly to stomatal aperture. The close similarity of these movies demonstrates that chlorophyll fluorescence is a good representation of stomatal aperture.

Thermal and Fluorescence Movie 1

Thermal and Fluorescence Movie 2