Maximum entropy production and plant optimization theories

Photosynthetic membrane sacs (thylakoids) of plants form granal stacks interconnected by nonstacked thylakoids, thereby being able to fine-tune (i) photosynthesis, (ii) photoprotection and (iii) acclimation to the environment. Growth in low light leads to the formation of large grana, which sometimes contain as many as 160 thylakoids. The net surface charge of thylakoid membranes is negative, even in low-light-grown plants; so an attractive force is required to overcome the electrostatic repulsion. The theoretical van der Waals attraction is, however, at least 20-fold too small to play the role. We determined the enthalpy change, in the spontaneous stacking of previously unstacked thylakoids in the dark on addition of Mg 2þ , to be zero or marginally positive (endothermic). The Gibbs free-energy change for the spontaneous process is necessarily negative, a requirement that can be met only by an increase in entropy for an endothermic process. We conclude that the dominant attractive force in thylakoid stacking is entropy-driven. Several mechanisms for increasing entropy upon stacking of thylakoid membranes in the dark, particularly in low-light plants, are discussed. In the light, which drives the chloroplast far away from equilibrium, granal stacking accelerates non-cyclic photophosphorylation, possibly enhancing the rate at which entropy is produced.

Section: In the Light Granal Stacking Accelerates Non-cyclic Atp Synmentioning

confidence: 99%

Acclimation of leaves to low light produces large grana: the origin of the predominant attractive force at work

Jia

Liggins

Chow

2012

“…The last six papers deal with various aspects of biotic organisms, ranging from the scale of bacteria (Ž upanović et al 2010) to plants (Dewar 2010) to food webs (Meysman & Bruers 2010;Vallino 2010) and ecosystems (Holdaway et al 2010;Schymanski et al 2010). Ž upanović et al (2010) take a thermodynamic view of bacterial chemotaxis-the ability of some bacteria to direct their movement towards certain chemicals such as glucose.…”

Section: Contents Of This Issuementioning

confidence: 99%

Maximum entropy production in environmental and ecological systems

Kleidon

Malhi

Cox

2010

151

107

The coupled biosphere -atmosphere system entails a vast range of processes at different scales, from ecosystem exchange fluxes of energy, water and carbon to the processes that drive global biogeochemical cycles, atmospheric composition and, ultimately, the planetary energy balance. These processes are generally complex with numerous interactions and feedbacks, and they are irreversible in their nature, thereby producing entropy. The proposed principle of maximum entropy production (MEP), based on statistical mechanics and information theory, states that thermodynamic processes far from thermodynamic equilibrium will adapt to steady states at which they dissipate energy and produce entropy at the maximum possible rate. This issue focuses on the latest development of applications of MEP to the biosphere -atmosphere system including aspects of the atmospheric circulation, the role of clouds, hydrology, vegetation effects, ecosystem exchange of energy and mass, biogeochemical interactions and the Gaia hypothesis. The examples shown in this special issue demonstrate the potential of MEP to contribute to improved understanding and modelling of the biosphere and the wider Earth system, and also explore limitations and constraints to the application of the MEP principle.Keywords: thermodynamics; interactions; Earth system science; ecosystems THERMODYNAMICS AND ENVIRONMENTAL AND ECOLOGICAL SYSTEMSThermodynamics has long been recognized as critical for understanding complex systems ranging from the living cell to planet Earth (Boltzmann 1886;Schrö dinger 1944;Lovelock 1965). Boltzmann already noted in 1886 that:. . . the general struggle for existence of animate beings is not a struggle for raw materials-these, for organisms, are air, water and soil, all abundantly available, nor for energy which exists in plenty in any body in the form of heat, but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold Earth.Schrö dinger (1944) extended this perspective in his seminal book What is life? in which he suggested that the living cell maintains its organized structure in a state of thermodynamic disequilibrium by depleting sources of free energy and exporting high entropy waste. At the planetary scale, Lovelock (1965) recognized that the Earth's atmospheric composition is maintained in a state far from thermodynamic equilibrium, and he attributed this unique thermodynamic state to the profound effect that life has on its environment.Taken together, these examples suggest that in order to better understand Earth's environmental and ecological systems and their couplings, we need to view these as coupled thermodynamic systems that are organized in a state far from thermodynamic equilibrium. Central to thermodynamics is the concept of 'entropy' as a measure of 'disorder' or 'randomness'. While the use of 'entropy' is often surrounded with ambiguity, it can nevertheless be used in purely quantitative terms to measure the distance of a given state from thermodynamic equilibriu...

“…In their introduction they say that there are 'many ways in which 'maximization' can be interpreted, and there are different ways in which the 'entropy production rate' is defined (depending on which processes one accounts for). ' Dewar (2010), in his fascinating paper that examines entropy production across three scales of plant systems, focuses on chemical entropy production, but ignores radiative exchange, water transport, liquid water evaporation, and other 'potential contributions' to entropy production. He does not justify this choice.…”

Section: Entropy-how You Produce It T Volk and O Pauluis 1319mentioning

confidence: 99%

It is not the entropy you produce, rather, how you produce it

Volk

Pauluis

2010

The principle of maximum entropy production (MEP) seeks to better understand a large variety of the Earth's environmental and ecological systems by postulating that processes far from thermodynamic equilibrium will 'adapt to steady states at which they dissipate energy and produce entropy at the maximum possible rate'. Our aim in this 'outside view', invited by Axel Kleidon, is to focus on what we think is an outstanding challenge for MEP and for irreversible thermodynamics in general: making specific predictions about the relative contribution of individual processes to entropy production. Using studies that compared entropy production in the atmosphere of a dry versus humid Earth, we show that two systems might have the same entropy production rate but very different internal dynamics of dissipation. Using the results of several of the papers in this special issue and a thought experiment, we show that components of life-containing systems can evolve to either lower or raise the entropy production rate. Our analysis makes explicit fundamental questions for MEP that should be brought into focus: can MEP predict not just the overall state of entropy production of a system but also the details of the sub-systems of dissipaters within the system? Which fluxes of the system are those that are most likely to be maximized? How it is possible for MEP theory to be so domain-neutral that it can claim to apply equally to both purely physicalchemical systems and also systems governed by the 'laws' of biological evolution? We conclude that the principle of MEP needs to take on the issue of exactly how entropy is produced.