Abstract:
According to the second law of thermodynamics, no process can be 100%
efficient and all processes must increase the total entropy of the system they
occupy. Therefore, living systems require a constant influx of low-entropy energy
to survive, giving an evolutionary advantage to those that produce less waste.
Odum suggested that ecosystems would therefore develop mechanisms for
reducing entropy production per unit biomass, as they matured.
Isothermal calorimetry allows the direct measurement of waste heat emitted from
any system, including soils and the life within them. However, upon review it
became apparent that current methods employed in the analysis of soil microbial
communities via isothermal calorimetry are outdated and in need of review. An
experiment was conducted to troubleshoot the method and appropriate
modifications were made. A second experiment was conducted to test the
microbial community response to pre-incubation prior to calorimetric analysis at
20°C, concluding that samples should be pre-incubated for ten to sixteen days
prior to analysis at 20°C.
Subsequently, experiments were carried out to establish how much waste heat
was produced by soil microbial communities in the context of various ecological
gradients, following glucose amendment. Results for enthalpy efficiency (ηeff)
proved inconclusive, whereas results for substrate induced heat production
(SIHP), where heat output is expressed per unit biomass, indicated that soil
microbial communities produced significantly more waste heat when subjected to long-term metals induced stress and short-term copper-induced stress. In
addition, a reduction in the production of waste heat generated by soil microbial
communities associated with primary succession along a glacier foreland was
observed. This provides evidence that living systems do indeed evolve towards
greater thermodynamic efficiency, manifest via the reduction of energetic waste.
