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

Semiarid ecosystems are threatened by global warming due to longer
dehydration times and increasing soil degradation. Mounting evidences
indicate 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 i.e., 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 change the location 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.