Transition from abstract thermodynamic concepts to perceivable ecological indicators

Abstract

Entropy and exergy are the central concepts in thermodynamics, and many researchers have used them to characterize ecosystem development. However, these concepts are very abstract to outsiders. Direct measurements of the indicators related to entropy and exergy are difficult and involve large errors. Schneider and Kay (1994) bridged thermodynamic concepts, i.e., entropy and exergy, with perceivable ecological indicators, i.e., canopy surface temperature (Tsurf) and net radiation (Rn) in their maximum exergy destruction principle. However, the connection between entropy and exergy with Tsurf and Rn was based on the similarity between the ecosystem and the Bénard cell, and not on thermodynamic reasoning. Considering the coherence of entropy production and exergy destruction, we analyzed the relationship between entropy production and Tsurf and Rn, based on the first and second laws of thermodynamics, and verified it using long-term monitoring data of a tropical seasonal rain forest. We demonstrated that total entropy production (exergy destruction) linearly increased with increasing Rn and decreasing Tsurf theoretically. Empirical data showed that the total entropy production increased, whereas specific entropy production decreased during the growing season. This indicates that plant growth can enhance exergy conversion efficiency. Rn, Tsurf, and related indicators can be used as surrogates for thermodynamic indicators to measure ecosystem status and development. The bridge between thermodynamic concepts and measurable ecological indicators will improve the application of thermodynamics in ecology studies and the understanding of thermodynamic processes in ecosystem.