Box 2: Rewilding microbes to boost carbon cycling
Soil microbes are key drivers of the global cycling of Soil Organic
Carbon (SOC). They both deplete SOC through respiration and accumulate
SOC through growth and by stabilizing soil aggregates (Anthony et
al. , 2020). Ecto- and endo- mycorrhizal fungi are particularly
important for the accumulation of SOC as their hyphae stabilize soil
aggregates, making SOC inaccessible for other microbes and limiting
respiration (Wei et al. , 2019). Restoration of the natural carbon
cycle in revegetated areas is therefore highly dependent on the return
of soil microbiota. Although some soil communities in restoration areas
track towards remnant sites (Barber et al. , 2017), soil microbes
differ in their dispersal capabilities according to the presence or
absence of traits needed to survive during airborne dispersal such as
spore formation and pigment production (Choudoir et al. , 2018).
Consequently, dispersal distances vary greatly between species, with
some fungi exhibiting effective dispersal ranges of only
~1 km (Peay, Garbelotto and Bruns, 2010).
Like invertebrates, the return of soil microbes and the functions they
provide to revegetated “habitat islands” on degraded farmlands is
often assumed to occur passively (Box 1). However, restoration projects
may benefit from actively rewilding soil microbes. This could both
overcome dispersal constraints and tailor the reconstructed microbe
community to a desired trajectory. Local paddock trees are often the
last remaining remnant trees on degraded farms. They are potential
reservoirs of soil carbon cycling taxa as they contain mycorrhizal fungi
and bacterial species adapted to competitive dynamics within local
conditions (Wood, Tang and Franks, 2018). This provides a competitive
advantage over communities already established in revegetated areas and
increases the likelihood of rewilded communities overcoming the biotic
barrier.
Rewilding soil microbial communities would entail moving soil from the
rhizosphere (area of soil in contact with roots) of a local paddock tree
and scattering this around the base of revegetated plants (Figure 4).
Local paddock trees may be particularly useful in highly modified
systems where remnant patches are non-existent and could contain the
last locally adapted source of remnant microbial communities.