A synthetic microbial Daisyworld: planetary regulation in the test tube

The idea that the Earth system self-regulates in a habitable state was proposed in the 1970s by James Lovelock, who conjectured that life plays a self-regulatory role on a planetary-level scale. A formal approach to such hypothesis was presented afterwards under a toy model known as the Daisyworld. The model showed how such life-geosphere homeostasis was an emergent property of the system, where two species with different properties adjusted their populations to the changing external environment. So far, this ideal world exists only as a mathematical or computational construct, but it would be desirable to have a real, biological implementation of Lovelock's picture beyond our one biosphere. Inspired by the exploration of synthetic ecosystems using genetic engineering and recent cell factory designs, here we propose a possible implementation for a microbial Daisyworld. This includes: (i) an explicit proposal for an engineered design of a two-strain consortia, using pH as the external, abiotic control parameter and (ii) several theoretical and computational case studies including two, three and multiple species assemblies. The special alternative implementations and their implications in other synthetic biology scenarios, including ecosystem engineering, are outlined.

Soil Carbon Dioxide Planetary Thermostat

Biological regulation of planetary temperature has been explained with the Daisyworld model, in which reflective-cooling white daises balance absorbing-warming black daisies. This article advances the proposition that cooling "daisies" of Daisyworld represent carbon sequestration and consumption by productive soils and ecosystems, such as grasslands expanding into deserts and tropical forests migrating toward the poles. On the other hand, warming "daisies" represent continued CO₂ emissions from volcanoes and springs allowed by unproductive frigid and desert ecosystems. Greenhouse spikes of CO₂ in deep time from large perturbations, such as flood basalt eruptions and asteroid impacts, did not continue as lethal runaway greenhouses, such as Venus, nor did low CO₂ of ice ages decline to a sterile global snowball, such as Mars. These hypotheses are quantified and tested by new global soil maps derived from paleosols of the last extremes of atmospheric CO₂: middle Miocene (16 Ma) and last glacial maximum (20 ka), when CO₂ levels were 588 ± 72 and 180 ppm, respectively. Observed expansion of productive soils curbed large atmospheric injections of CO₂ in deep time and observed expansion of unproductive soils during ice ages of low CO₂ was thwarted by continued metamorphic and volcanic degassing. This short-term Soilworld thermostat of biogeographic redistribution of ecosystems supplemented long-term evolution of terrestrial carbon sequestration curbing solar radiation increases over billions of years. Similar agricultural management of ecosystems has potential for short-term carbon sequestration.

Robustness and Contingent History: From Prisoner's Dilemma to Gaia Theory

In both social systems and ecosystems there is a need to resolve potential conflicts between the interests of individuals and the collective interest of the community. The collective interests need to survive the turbulent dynamics of social and ecological interactions. To see how different systems with different sets of interactions have different degrees of robustness, we need to look at their different contingent histories. We analyze abstract artificial life models of such systems, and note that some prominent examples rely on explicitly ahistorical frameworks; we point out where analyses that ignore a contingent historical context can be fatally flawed. The mathematical foundations of Gaia theory are presented in a form whose very basic and general assumptions point to wide applicability across complex dynamical systems. This highlights surprising connections between robustness and accumulated contingent happenstance, regardless of whether Darwinian evolution is or is not implicated. Real-life studies highlight the role of history, and artificial life studies should do likewise.

Global warming description using Daisyworld model with greenhouse gases

Daisyworld is an archetypal model of the earth that is able to describe the global regulation that can emerge from the interaction between life and environment. This article proposes a model based on the original Daisyworld considering greenhouse gases emission and absorption, allowing the description of the global warming phenomenon. Global and local analyses are discussed evaluating the influence of greenhouse gases in the planet dynamics. Numerical simulations are carried out showing the general qualitative behavior of the Daisyworld for different scenarios that includes solar luminosity variations and greenhouse gases effect. Nonlinear dynamics perspective is of concern discussing a way that helps the comprehension of the global warming phenomenon.