PARENT SESSION
Oral Session #2: Thermodynamics and Complexity. Presiding: T. Allen.
Monday, August 6, 2001. 8:00 AM to 11:45 AM. Madison Ballroom D.

Ecosystem thermodynamics:Testing complexity with small-scale vegetation models.

Vullings, Nicole ¹, Allen, T.F.H.¹, Havlicek, Tanya ¹, Norman, John¹, ¹

ABSTRACT- As complex highly ordered entities, ecosystems seem to defy the second law of thermodynamics. Schneider and Kay reformulate the second law: complex systems form in response to imposed gradients. This applies to terrestrial ecosystems on a gradient of incoming solar energy. Plants dissipate this energy using the latent heat of vaporization of water through evapotranspiration. It follows that systems under stress and not functioning at maximum capacity are able to dissipate less energy. To test how stress affects thermodynamic functionality of terrestrial ecosystems we constructed two model plant ecosystems using single genotypic seed stock of soybean (Glycines max). Plants grew in chambers at different wind speeds (0.3 m/s and 1.8 m/s), but with controlled inputs of energy, nutrients, and water. We measured stress as canopy infrared temperature, a result of whole plant capacity to dissipate heat energy by evapotranspiration, which is known to have a simple relationship to growth. Plants showed stress when exposed to wind speeds different from rearing conditions. The slow group was warmest (stressed) when exposed to fast wind speeds. Fast group plants were warmest (stressed) at a range of slower wind speeds. The results show thermodynamic function (the ability to dissipate energy) of the system is impaired when the conditions under which it developed are altered. With this measurable definition of functionality, new classes of experimentation can independently address several pressing issues, including diversity and adaptation.

KEY WORDS: thermodynamics, ecosystems, wind-speed, stress