Synthetic soil crusts against green-desert transitions: A spatial model: Synthetic ecosystems' terraformation

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.This study was supported by an European Research Council Advanced Grant (SYNCOM), by the Botin Foundation (Banco Santander through its Santander Universities Global Division), the PR01018-EC-H2020-FET-Open MADONNA project, by the FIS2015-67616-P grant, and by the Santa Fe Institute. This work has also received the support of Secretaria d’Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya. J.S. has been funded by a ‘Ramón y Cajal’ contract RYC-2017-22243, and by the MINECO grant no. MTM2015-71509-C2-1-R and the Spain’s ‘Agencia Estatal de Investigación’ grant no. RTI2018-098322-B-I00, as well as by the CERCA Programme of the Generalitat de Catalunya