2.2 Microbial restoration: moving beyond interactions with plants
Like invertebrates, it is generally assumed that microbial diversity and function in revegetated areas will naturally attain the level maintained in remnant sites. However, communities of microbes are monitored the least of any organism group post-restoration (5% of projects) (Kollmannet al. , 2016). For microbes, targeted reintroductions aimed at improving plant health are the focus: inoculation of single species of non-native Arbuscular Mycorrhizal Fungi (AMF) is a common restoration practice (Asmelash, Bekele and Birhane, 2016). Non-native AMF are used to help revegetated plants establish and grow, but this practice ignores all other components of soil biota. Indeed, it has been argued that AMF inoculations could be improved by incorporating whole native communities rather than using single non-native species (Asmelash, Bekele and Birhane, 2016), and this hypothesis is now being tested through field trials (Lance et al. , 2019). There are analogous developments in fields that use cyanobacteria to improve soil processes. Emerging studies examining the efficacy of whole community transfer of cyanobacteria (Chiquoine, Abella and Bowker, 2016) are challenging the traditional use of single-strains of laboratory reared species (Rossiet al. , 2017).
The implementation of both invertebrate and microbial rewilding projects is impeded by knowledge gaps. Addressing these gaps would include greater monitoring both post-restoration to identify which groups are failing to recolonise revegetated areas and post-rewilding to determine which groups have established (Table 1). Further, for ecological restoration, it might make more sense to consider whole communities: the ultimate success for restoration would be to reinstate biodiversity and ecosystem function in its entirety. To do this, microbial rewilding will need to venture from the plant focused singular AMF inoculation studies, while invertebrate rewilding should broaden from earthworms to communities that include a greater diversity of functional groups, such as those found in litter (Figure 1).