Synthetic soil crusts against green-desert transitions: a spatial model

Abstract

Semiarid ecosystems are threatened by global warming due to longer dehydration times and increasing soil degradation. Mounting evidence indicates that, given the current trends, drylands are likely to expand and possibly experience catastrophic shifts from vegetated to desert states. Here, we explore a recent suggestion based on the concept of ecosystem terraformation, where a synthetic organism is used to counterbalance some of the nonlinear effects causing the presence of such tipping points. Using an explicit spatial model incorporating facilitation and considering a simplification of states found in semiarid ecosystems including vegetation, fertile and desert soil, we investigate how engineered microorganisms can shape the fate of these ecosystems. Specifically, two different, but complementary, terraformation strategies are proposed: Cooperation -based: C -terraformation; and Dispersion -based: D -terraformation. The first strategy involves the use of soil synthetic microorganisms to introduce cooperative loops (facilitation) with the vegetation. The second one involves the introduction of engineered microorganisms improving their dispersal capacity, thus facilitating the transition from desert to fertile soil. We show that small modifications enhancing cooperative loops can effectively modify the aridity level of the critical transition found at increasing soil degradation rates, also identifying a stronger protection against soil degradation by using the D -terraformation strategy. The same results are found in a mean-field model providing insights into the transitions and dynamics tied to these terraformation strategies. The potential consequences and extensions of these models are discussed.

Ecological complexity and the biosphere: the next 30 years

“…It is now well known that some dynamical systems close to catastrophic shifts can exhibit extremely long delays before they jump into collapse. This is the case for example of green-desert transitions [ 97 , 98 ] in drylands models, where vegetation cover might persist long after crossing the tipping point. Since a species can live in this transient configuration, it might appear healthy when in fact collapse is inevitable.…”

“…In this context, some ecological interaction motifs [ 123 ] and network-level constraints [ 124 ] act as firewalls to the spread of synthetic microbes. An example of this view is the potential of terraforming for drylands [ 97 , 98 , 125 ]. In this case, species that play a key role in maintaining soil integrity and organic carbon levels, such as cyanobacteria ( figure 2 k ), would be used as engineering targets.…”

Environmental Galenics: large-scale fortification of extant microbiomes with engineered bioremediation agents

“…Under this perspective, the repertoire of biological agents that can be engineered includes not only specialized strains and communities of the type discussed above but also spreaders of DNA sequences bearing beneficial properties by means of programmed HGT. Obviously, the technical question of how to disseminate live agents and/or fostering transmission of selected genes at a very high level turns around the traditional pursuit of biological and genetic containment 4 for a somewhat opposite quest of securing persistence and promoting DNA propagation [129,146].…”

“…3 For a thorough review of possible strategies of C capture in the oceans see http://nap.edu/26278. 4 For a compilation of containment strategies see https://standardsinsynbio.eu/biocontainment-finder/.…”

“…The ongoing climate change and the ensuing prospect of a massive extinction is the result of the interplay between the innate geochemical and planetary dynamics of Earth with the impact of anthropogenic activities (in particular industrial/urban emissions and land use) on a large number of otherwise balanced ecosystems [ 1 ]. A growing volume of data supports the notions coming from theoretical ecology that human pressure on natural environments often follows a nonlinear threshold-dependent dynamics [ 2 – 4 ] with catastrophic fold bifurcations [ 5 ]. Under this scenario, stress may push the corresponding systems to reach a tipping point followed by irreversibly running into the complete shift of regime ( figure 1 ).…”