Chapter 10 - Thermodynamics of vegetation

Abstract

This chapter analyses the photosynthesis thermodynamically. When the total biomass of the system stops increasing, the amount of exergy captured will be the maximum, but ecosystems can continue the development beyond this limit. Ecosystems have three growth forms: growth by increase of the biomass, growth by increasing the network, and growth by increase of the information content. Only the first growth form is associated with exergy destruction, because more biomass requires more exergy for maintenance, but the exergy destruction per unit of biomass is the same. A complex network is able to utilize the exergy of the solar radiation better, and increased information means increased exergy but not increased exergy consumption for maintenance. The thermodynamic examination of photosynthesis in this chapter introduces two important efficiency coefficients—the radiation efficiency is defined as the ratio of the amount of energy used for the photosynthesis to the radiation, and the exergy efficiency is the increment of information exergy relative to the total amount of energy coming from the solar radiation. Maintenance of the biological structure requires a major exergy input, including the coverage of evapotranspiration. It implies a high production of entropy, but the entropy is transferred continuously from the ecosystem to the environment, whereby the temperature is maintained within the range suitable for life processes.