**1. Introduction**

318 Thermodynamics – Interaction Studies – Solids, Liquids and Gases

Yonetani, T., Park, S. I., Tsuneshige, A., Imai, K.&Kanaori, K. (2002). Global allostery model

of hemoglobin. Modulation of O(2) affinity, cooperativity, and Bohr effect by heterotropic allosteric effectors. *J. Biol. Chem.,* 277, 37, pp. 34508-34520, 0021-9258

> Now ecologists feel necessary to construct the theoretical building of system ecology, to break strong reductionistic tradition of ecology and to include the use of thermodynamics in a new holistic approach to study ecosystems, their structure, functioning and natural history. We tried to present here the current state of thermodynamic view on ecosystems.

> The first law of thermodynamics proclaims constancy of the total energy of isolated system for all changes, taking place in this system: energy cannot be created or destroyed. According to the second law of thermodynamics in isolated system entropy is always increasing or remaining constant. All processes in the Universe are oriented to the equilibrium state. Nevertheless, biological systems, and, consequently, ecological systems create order from disorder, they create and support chemical and physical non-equilibrium state – the basis they live on.

> In this chapter the general overview of ecosystem as thermodynamic system is given and the concept of Eco-Exergy is introduced. The use of this concept in ecology is demonstrated to be very fruitful. To make it easy for other researchers to use the Eco-Exergy the procedure of exergy evaluation for ecosystems is followed with special attention to dimensions used. The main applications of exergy in modern ecology are reviewed with special focus on practical use of Eco-Exergy, exergy index, and structural exergy for real ecosystem assessment and estimation of their health and disturbance.

> Another application of irreversible thermodynamics (Prigogine's inventions) is discussed. The theory of hypercycles, developed for cycles of autocatalytic reactions and widely accepted in biochemistry and molecular biology can also be applied for ecological systems. The model of conjugated hypercycles, applied to ecological systems explains many aspects of their non-linear dynamics and can be used for analysis of oscillating processes in ecological systems.
