Studies on the ecological restoration or rehabilitation of deeply disturbed and degraded ecosystems, and reintegration of fragmented, dysfunctional landscapes around the world report failures or unsatisfactory outcomes. These failures are increasingly attributed to inadequate consideration of substrate and its implications for plant and microbial establishment and survival (Mendes et al., 2019). Much greater knowledge of soil processes and interactions is needed if we are to develop techniques and technology that will help us come reasonably close to achieving global restoration aspirations (Cross et al., 2019; Aronson et al., 2020).

Better consideration of soil biota, and other critical edaphic factors, is clearly needed to ameliorate and revitalize substrate conditions and plant-soil interactions so as to sustainably restore and support indigenous microbial, invertebrate and vertebrate fauna, and vegetation communities, ecosystems and landscapes (Cross and Lambers, 2017; Cross et al., 2021a; Cross et al., 2021b). It has been proposed that, at least in some regions, soil characteristics and their changes through time likely represent among the strongest drivers, filters and leverages for species establishment, ecological succession and recovery, and overall effectiveness in ecological restoration and rehabilitation (ERR) projects (Bauer et al., 2015; Cross, 2021; Cross and Lambers, 2021).

The processes influencing pedogenesis and nutrient cycles in soils also impact the establishment and succession plant species and assemblages through time (Eger et al., 2011; Lambers et al., 2011; Laliberté et al., 2013). They are also dynamic and influenced in their turn by complex plant-soil, plant-microbe, and microbe-soil interactions (Lambers et al., 2008; van Schöll et al., 2008; Shanmugam and Kingery, 2018). Recent studies have identified substrate conditions limiting, or totally blocking ERR efforts. These include, but are not limited to, highly altered materials presenting ecologically hostile chemical environments (such as extreme pH), challenging hydrological and osmotic conditions, unsuitable macronutrient stoichiometry for ecologically specialized native vegetation, shortfalls of organic biomass, insufficient or disproportionate abundance of key functional soil microbial groups, or high concentrations of biologically toxic contaminants (Huang et al., 2012; Cross and Lambers, 2017; Cross et al., 2017; Busso and Pérez, 2018).

Recognition of these multiple, complex, and interwoven obstacles has led to significantly greater consideration of the role of substrate and edaphic factors in ERR (Nolan et al., 2021); this has reached the point of calls for projects to consider ‘engineering’ substrates that are suitable for desired biota following significant disturbance to substrates from activities such as mining (Huang et al., 2012; Kumaresan et al., 2017), or to artificially inoculate soils with commercial microbial blends (Farrell et al., 2020; Valliere et al., 2020; Contos et al., 2021), despite limited and inconsistent experimental evidence for the efficacy and risks associated with these techniques (Lance et al., 2019; Wong et al., 2022; Zhong et al., 2023).

Current understanding of the natural processes and mechanisms driving soil development and determining patterns of vegetation and microbial diversity and composition continues to hinder progress in ERR, as well as in related undertakings such as regenerative agriculture and urban regreening projects. But we must also support and learn from the pioneering sites, programs, networks, and breakthroughs taking place in the worldwide movement of ecological restoration and improved ecosystem management. In this collection of papers, we bring together articles on one of the critical focal and leverage points where we can intervene to improve ecosystem trajectories at terrestrial sites undergoing ERR: the intricate and complex ecosystems that are soils.

Our Research Topic solicited studies presenting empirical data pertaining to the interactive relationships connecting soil, soil microbes, invertebrates, and plants, aiming to enhance our understanding of soil and vegetation developmental processes in the context of ERR. As Tedesco et al. (2023) have recently summarized, and many other authors have provided evidence for, from long-term experimental restoration sites at landscape and smaller spatial scales (Jellinek et al., 2014; Budiharta et al., 2016; Hein et al., 2019; Hong et al., 2022): ecological restoration in today’s world must go “beyond ecology” and become “a process for social-ecological transformation” (Tedesco et al., 2023). There is a risk otherwise that ERR activities will not achieve their full potential as an investment in human, social, cultural, and natural capital (Aronson et al., 2020). The global literature continues to add new and powerful evidence that soils and soil microbiota should be considered a very high priority for research and development, as key places to intervene along ecosystem recovery trajectories to advance and accelerate restoration processes (Nolan et al., 2021).

While none of the four articles in this Research Topic explicitly undertake or assess ecological restoration, each examines different mechanisms and processes relating to plant-soil-microbial interactions that have deep relevance to the theory and practice of ERR.

The first article by Beñares-de-Dios et al. provides a detailed examination of the literature pertaining to the role of soil and climate as determinants of floristic composition, focusing on tropical forests. The authors examine the relative importance of different environmental factors as drivers of plant species occurrence across different spatial scales and in different forest ecosystems. Beñares-de-Dios et al. contribute to growing understanding of the importance of soil and climatic factors as drivers of vegetation and microbial community patterns over large spatial scales. This builds upon the seminal work of Nottingham et al. (2018), and supports previous hypotheses around a strong importance of edaphic factors as determinants of species establishment and development at smaller scales in ERR (Cross, 2021; Cross et al., 2021a; Cross et al., 2021b).

Second, Fu et al. use high-throughput sequencing to evaluate the degree to which soil microbial diversity varies among different urban forest ecosystems as a function of soil and other environmental characteristics. The degree to which ecological degradation and, conversely, ERR, act as drivers of the diversity and composition of soil microbial communities has attracted significant international research interest in recent years (Hu et al., 2016; Li et al., 2016; Hamonts et al., 2017; Kumaresan et al., 2017; Deng et al., 2020). This interest has intensified with increasing accessibility and decreasing cost of sequencing technologies (Hart et al., 2020). Fu et al. report strong association between vegetation composition and microbial community, with considerable distinction in microbial diversity among different vegetation types, in line with previous studies highlighting soil microbes as powerful drivers of plant diversity (Van Der Heijden et al., 2008).

Thirdly, Jiang et al. examine the resource limitations influencing microbial communities in unique Karst tiankeng (limestone sinkhole) habitats, in the context of ecological degradation in these ecosystems, using soil ecoenzymatic stoichiometry. The contribution of microbial communities to biogeochemical cycling in ecological recovery activities, and the degree to which their natural contribution to ecological functioning is impaired by disturbance or degradation, is a topic of considerable interest in ERR (Hamman and Hawkes, 2013; Gagen et al., 2019; Moreira-Grez et al., 2019; Sun and Badgley, 2019). Jiang et al. notably report that level of degradation considerably impacts resource availability for microbial communities and contextualize their results around regional biodiversity conservation and restoration prioritization. The development of approaches prioritizing ERR activities to achieve maximum outcome is another hot topic in the international literature.

Lastly, He et al. present the results of an experimental pot study examining the potential utility of three perennial grasses in ameliorating soil contaminated with cadmium or petroleum hydrocarbons. Phytoremediation of contaminated soils in this manner (whether through the activity of plants, microbes, or both) is a growing international focus point (Pilon-Smits, 2005; Ali et al., 2013; Grison, 2015; Losfeld et al., 2015), particularly as a component of post-mining ERR where substrates, especially tailings, frequently contain high concentrations of heavy metals (Hur et al., 2011; Stojanović et al., 2012; Cross et al., 2017; Xie and van Zyl, 2020). He et al. assess the action of root exudates from the studied grasses in assisting the translocation of cadmium and petroleum hydrocarbons into above-ground biomass in different soils, and conclude that such root exudates likely represent a tool of significant utility in phytoremediation. Outcomes from their study contribute to a large and growing body of work improving our understanding of the complex mechanistic processes required to effectively ameliorate, and subsequently rehabilitate or restore, contaminated sites.

There is a clear and growing urgency for ecological restoration and rehabilitation, advanced phytoremediation, and other allied activities to be undertaken around the world. Ecological degradation is widespread and profound, eroding biodiversity and ecosystem functionality, not to mention landscape connectedness, and human health and wellbeing, at scales ranging from local all the way to the biospheric. Increasingly, scientists and practitioners are recognizing the crucial importance of soil and soil microbiota in ecosystem recovery in all ecological, and social-ecological systems. Stronger emphasis is being placed on these organisms when promoting and testing methods to support and maintain spontaneous recovery following degradation, and when undertaking active interventions for ERR in all contexts. As the four articles presented here illustrate, there are significant opportunities for examination of plant-soil-microbial interactions to improve the approaches, efficiencies, and outcomes of efforts to halt and reverse ecological damage to our global ecosystems.