Microbiome-Inspired Green Infrastructure (MIGI): A Bioscience Roadmap for Urban Ecosystem Health

Background: Microbiome-Inspired Green Infrastructure (MIGI) was recently proposed as an integrative system to promote healthy urban ecosystems, through multidisciplinary design. Specifically, MIGI is defined as nature-centric infrastructure restored and/or designed and managed to enhance health-promoting interactions between humans and environmental microbiomes, whilst sustaining microbially-mediated ecosystem functionality and resilience. MIGI also aims to stimulate a research agenda that focuses on considerations for the importance of urban environmental microbiomes. Objectives: In this paper we provide details of what MIGI entails from a bioscience and biodesign perspective, highlighting the potential dual benefits for human and ecosystem health. We present ‘what is known’ about the relationship between urban microbiomes, green infrastructure and environmental factors that may affect urban ecosystem health (ecosystem functionality and resilience as well as human health). We discuss how to start operationalising the MIGI concept based on current available knowledge, and present a horizon scan of emerging and future considerations in research and practice. We conclude by highlighting challenges to the implementation of MIGI and propose a series of workshops to discuss multi-stakeholder needs and opportunities. Discussion: This article will enable urban landscape managers to incorporate initial considerations for the microbiome in their development projects to promote human and ecosystem health. However, overcoming the challenges to operationalising MIGI will be essential to furthering its practical development. Although the research is in its infancy, there is considerable potential for MIGI to help deliver sustainable urban development driven by considerations for reciprocal relations between humans and the foundations of our ecosystems –– the microorganisms.


Introduction
Microbial communities play vital roles in ecosystem processes and provisions including carbon and nutrient cycling, climate regulation, animal and plant health, and global food security (Cavicchioli et al. 2019;Guerra et al. 2020). The ongoing degradation of, and climate-associated changes in microbial communities (structure, complexity and composition) pose a considerable threat to global macro-level biodiversity across the planet (Bach et al. 2020;Greenspan et al. 2020;Tibbett et al. 2020). In parallel with these environmental concerns, noncommunicable diseases (chronic non-infectious diseases) are on the rise (Smith et al. 2014;Jairath et al. 2020). For example, in recent decades the prevalence of asthma (El-Gamal et al. 2017;Borna et al. 2019), diabetes (Holman et al. 2010), allergic rhinoconjunctivitis (Kainu et al. 2013), and autoimmune disorders (Dinse et al. 2020;Paramasivan et al. 2020) has increased worldwide. Growing evidence suggests that the global trends of ecosystem degradation, urbanisation, and noncommunicable diseases are deeply interconnected (Haahtela, 2019).
Exposure to diverse environmental microbiomes--the complex network of microorganisms in a given environment--is thought to play an important role in human health (Rook, 2013;Roslund et al. 2020). Environmental microorganisms support the development and regulation of the human immune system (Renz and Skevani, 2020;Roslund et al. 2020). Evidence has shown that degraded habitats may harbour a greater relative abundance and diversity of opportunistic human pathogens, and ecological restoration may restore health-regulating assemblages (Liddicoat et al. 2019;Robinson et al. 2020a). Moreover, microbial exposure in urban green/blue spaces could improve our health but may depend heavily upon environmental and design factors including vertical stratification (layering of microbes in the near-surface atmosphere), vegetation presence, complexity and management (Robinson et al. 2020b;Roslund et al. 2020), airflow, and soil management. However, with appropriate restoration, design and management strategies, these factors could be optimised to create healthy urban ecosystems, to benefit both human and environmental health.
Ensuring long-term urban ecosystem resilience to environmental challenges will depend on our ability to restore and manage the landscape with considerations for the unseen foundations of our ecosystems -the microorganisms. Complex microbial interactions are involved in maintaining the health of urban plant and animal populations (Berg et al. 2017). Considering these microbial interactions as part of any long-term urban development vision will be essential to ensure urban ecosystems can flourish and maintain resilience. However, there are currently few considerations for the role of microbial communities in urban development and landscape design, and multispecies frameworks are rarely used to inform the management of urban ecosystems. Indeed, recognising its importance in sustainability, the recently proposed 'multispecies urbanism' concept puts forward a framework for urban development, driven by considerations for reciprocal relationships between humans and non-humans (including microbes) (Rupprecht et al. 2020;Sharma et al. 2021).
Sharing similar principles to multispecies urbanism, Microbiome-Inspired Green Infrastructure, also known as 'MIGI', was recently proposed as an integrative system to promote healthy urban ecosystems (Robinson et al. 2018;Watkins et al. 2020).
MIGI can be defined as nature-centric infrastructure that is restored and/or designed and managed to promote interactions between humans and environmental microbiomes, with explicit considerations for sustaining microbially-mediated ecosystem functionality and resilience. A considerable challenge to operationalising MIGI is a lack of awareness of the imperative for urban microbiome research, and the translation of existing research into intelligible and practicable outputs. Another challenge is addressing the complex needs and constraints of multiple stakeholders involved in urban landscape management (Marzano et al. 2021).
In this paper, our primary objectives are to: (a) present what is known about the relationship between urban microbiomes, green infrastructure and environmental processes that affect urban ecosystem health (ecosystem functionality and resilience, and human health); (b) discuss how we can operationalise the MIGI concept i.e. actionable insights; (c) present a horizon scan of developmental interdisciplinary considerations for MIGI; and, (d) highlight challenges to the implementation of MIGI, whilst proposing a series of multi-stakeholder engagement workshops.
This article will help to encourage urban landscape managers to incorporate initial considerations for MIGI in their development projects to promote healthy urban ecosystems for humans and the wider biotic community. Although the research is in its infancy, there is considerable potential for MIGI to help deliver complex ecological and modern urban societal needs.

Ecosystem functionality and resilience context
Microbial communities can be considered the foundations of our ecosystems (Cavicchioli et al. 2019) (Fig. 1). Soil-microbe-plant interaction studies have demonstrated that plants rely on microbial communities for favourable health (Nazli et al. 2020). Microbial communities are integral to nutrient and water absorption , and phytohormone production and regulation activities (ur Rehman et al. 2020). These microbial communities include arbuscular mycorrhizal fungi and algae, along with symbiotic, associative symbiotic and free-living plant growth promoting bacteria (Nazli et al. 2020). Endophytes (microbes living in plant tissues) also benefit plants by enhancing competitive abilities and increasing resistance to pathogens and other abiotic stressors (Pavithra et al. 2020). Soil microbiomes are essential to long-term ecosystem resilience in the face of global challenges such as climate change and degradation (Dubey et al. 2019). In addition to plant health, microorganisms play roles in carbon sequestration and biogeochemical cycling (Dubey et al. 2019). It can be further argued that the health of all organisms is interrelated through the cycling of environmental microorganisms from soils, to plants, animals, and back into the environment (van Bruggen et al. 2019) (Fig. 1).
It has been demonstrated that microbiome diversity and network complexity drive multiple ecosystem functions related to nutrient cycling (Wagg et al. 2019). For instance, grasslands with poorly-developed microbial networks and reduced microbial richness have low multifunctionality due to fewer taxa that support functional redundancy and uniqueness (Wagg et al. 2019). With minimal considerations for microbiomes in urban landscape design and management projects, it is likely that poor ecosystem multifunctionality and stability will continue.
To promote long-term urban ecosystem health, it is imperative that this trajectory changes. MIGI provides a framework to operationalise this change.

Human health context
Growing evidence suggests that exposure to naturally-diverse environmental microbiomes can improve human health. For example, studies highlight the importance of green space microbiomes to immunoregulation (Fig. 1). Lehtimäki et al. (2021) showed that risks of asthma and aeroallergen sensitisation are reduced in rural infants due to exposure to more biodiverse microbiomes (compared to urban), and Riskumäki et al. (2021) identified several environmental taxa that are important in augmenting and/or suppressing systemic inflammatory immune responses. A loss of biodiversity in urban areas reduces exposure to diverse environmental microbiomes, whilst increasing exposure to pathogenic microbes (Parajuli et al. 2018). This is corroborated by a review investigating rural vs. urban environmental aerobiomes (microbiome of a given airspace) that showed rural-mediated beneficial immune responses (Flies et al. 2020). Recently, a 28-day biodiversity intervention demonstrated that inoculating a schoolyard environment with biodiverse features (e.g., soil and plants from local forest habitats) significantly altered the microbiome of the children and enhanced important immunoregulatory pathways (Roslund et al. 2020).
Other studies indicate the importance of butyrate-producing bacteria which may be promoted in biodiverse plant-soil systems (Liddicoat et al. 2020;Brame et al. 2021), for example where organic-rich soils experience low redox conditions consistent with fermentative decomposition of organic matter. Butyrate is a short chain fatty acid associated with gut health, immunoregulation, and mental health, and exposure to trace level dust containing the putative spore-forming butyrate-producing bacteria Kineothrix alysoides is linked to reduced anxiety-like behaviour in mice (Liddicoat et al. 2020). Another recent study showed that spending a short period of time in green spaces can significantly change the human nasal and respiratory microbiome (Selway et al. 2020). Indeed, microbiota-mediated environmental health can be thought of as two layers of protective biodiversity (Ruokolainen et al 2017). The first layer, our personal microbiome, is key to health. The second layer, the environmental microbiome, represents an important source for replenishing the first; therefore safeguarding it represents a critical health insurance policy. It is also important to note that a plethora of other potential health benefits are associated with engaging with urban nature, including reduced blood pressure (Ideno et al. 2017), lower levels of stress, anxiety (Birch et al. 2020;Robinson et al. 2021) and increasing positive affect (Cameron et al. 2020).

Vegetation, microbiomes, and the built environment
To operationalise the MIGI framework, we can draw upon several relevant studies.
For example, one important factor is to ensure humans (and other species) are exposed to high microbial alpha diversity associated with naturally-biodiverse environments from a young age, which is important for immunoregulation (Mulder et al. 2011;Zhang et al. 2020). It has been demonstrated that air samples downwind from biodiverse sources (e.g., species-rich plant communities) contain more diverse microbial communities compared to upwind, with ~50% of airborne bacteria in downwind samples deriving from local plant sources (Lymperopoulou et al. 2016).
Therefore, a relatively simple intervention for urban designers could be to develop public spaces and buildings downwind from (macro)biodiverse sources, and to integrate local biodiverse sources within building structures and spaces ( Fig. 2, a).
Recently, it was shown that urban green space aerobiomes are vertically stratified, with an altitudinal decay in bacterial alpha diversity, and possibly a higher relative abundance of pathogenic taxa at higher altitudes (Robinson et al. 2020a). This reflects a transition from local plant and soil-related microbiomes at low heights into a broader urban (typically non-green space) airshed (Robinson et al. 2020b). A potential mitigation measure for this could be to augment vertical planting in urban areas, allowing exposure to higher natural microbial alpha diversity in the vertical dimension ( Fig. 2, b). It would also be prudent to design urban areas with greater consideration for inclusive and direct 'hands-on' human engagement with natural features to promote interactions between humans and diverse environmental microbiomes, and to foster long-term pro-ecological behaviours (Fig 2. c). Mills et al. (2020) provided evidence that revegetation, particularly with native species, can improve urban soil microbiome functional diversity. Other studies show that diverse vegetation communities promote below-ground functional richness, diversity and resilience (Eisenhauer et al. 2018;Canals et al. 2019). Promoting diversity of local vegetation communities is considered a robust strategy to maintain multifunctional processes under current and future environmental conditions (Eisenhauer et al. 2018). As such, MIGI strategies could include the planting of diverse, and where possible, native, vegetation communities to sustain urban ecosystem functionality and resilience (Fig. 2, e). However, it is not yet clear to what extent locally native plant populations will be able to tolerate future climate conditions. Studies on woody plants offer conflicting views, with some research suggesting that intra-population genetic variation may provide sufficient resilience (Borrell et al., 2018), whilst others argue that given the range in possible climate futures, including species beyond those that are locally native will be essential in urban environments (Sjöman et al., 2016;Cameron & Blanusa, 2016). As such, further research is required to understand the relationships between locally-native microbial populations and non-local/non-native plant species, including outcomes for stress tolerance, nutrient acquisition, and reproduction.
MIGI strategies should also include the promotion of urban-rural habitat connectivity via contiguous vertical and horizontal natural corridors (Fig. 3, f). Many urban environments are 'patchy' in terms of quality and connected nature-centric features.
To ensure long-term healthy urban ecosystems, we should aim to connect all natural habitats within towns/cities and provide essential biophysical corridors to the wider landscape. This action has high biodiversity conservation value by providing multispecies resources and improving species interactions and long-term resilience across the landscape, irrespective of species dispersal abilities or population sizes (Christie and Knowles, 2015). Enhancing networks of biologically and functionally diverse urban habitats with high vegetation complexity, also has the potential to improve the distribution of quality aerobiomes, and augment diverse macroscopic species (animals and plants) that contribute to the collective urban environmental microbiome, and broader ecosystem complexity and resilience.

Soil microbiomes
Soil properties will have a key influence on environmental microbiomes associated with MIGI developments. Soil organic matter and clay-content (proportion of claysized particles) are associated with structure, aggregation, nutrient and waterholding properties, and therefore the habitat and diversity of microbes (Jastrow and Miller, 1998;Young and Crawford, 2004;Torsvik and Øvreås, 2002). A key decision during the establishment phase of MIGI will be whether to use in-situ or imported soils. Where feasible, using soils with a moderate amount of clay-content, e.g. sandy loams (10-20% clay content) to loams (around 25% clay content) would be expected to promote microbial diversity. By comparison, sandy soils provide suboptimal microbial habitat, while heavier texture clay soils (often capable of forming suitable aggregation and structure) may be more prone to poorer drainage in wet climates, or greater plant stress in dry climates or during dry periods due to higher wilting-point moisture content (where water is unavailable to plants). Whether using existing insitu soils, or importing new bulk soil, it may be necessary to examine constraints to plant growth. Sometimes these constraints will be naturally occurring (e.g. shallow depth, impermeable layers, presence of toxic or nutrient-limiting subsoil conditions), while other times they can result from management history (e.g. compaction, acidification).
Where appropriate, addressing soil constraints will help optimise the biological activity and microbial diversity of the plant-soil system. If organic matter is being applied, ideally this should be in a nutrient-balanced, or pre-composted form, so that microbial activity and available nutrients can be harnessed to support the growing vegetation. Ongoing management and human interaction should also be considered.
For example, high levels of foot/vehicle traffic can lead to compaction and degradation, and may create zones of poor soil microbiome conditions with suboptimal health influence (e.g. along paths) within a natural space that is offering health-promoting microbial exposures. Exposure pathways to permit beneficial human-soil microbiome contact also remains an area for research. Based on available knowledge, low-level exposure to soil (e.g. dust) with biodiverse content to help contain potential pathogenic activity, would represent a reasonable starting point to supporting immune fitness. It is also expected that soils will gain maximum health-promoting potential by spending the majority of time covered with biodiverse vegetation, which is another consideration for designing MIGI exposure pathways.
There is also growing evidence to show that plant communities require complex mycorrhizal networks, acting as conduits of inter-plant communication, and facilitating pathogen defence, adaptation, growth, and memory (Filotas et al. 2014;Birch et al. 2020). Indeed, healthy vegetation community phenotypes at higher levels emerge from a multitude of localised and often subterranean entities interacting at lower levels (Ibarra et al. 2020). For example, Birch et al. (2020) recently demonstrated that plant growth was significantly associated with the number of ectomycorrhizal connections to other plants, and the number of genetically distinct fungi that were present. Therefore, we must at least consider the condition and ecology of the substrate and its role in sustaining ecosystem functionality and resilience. This will involve viewing habitat conservation and restoration through the lens of complex systems science. However, many experts in this field could provide appropriate consultation at each stage of a development project (Watkins et al. 2020).
Interestingly, a recent study showed that landscaping materials (e.g. compost and mulch) have a 'microbial shelf life', and long-term storage can significantly reduce the availability of bacterial taxa linked to human health and degradation of pollution (Soininen et al. 2021). This suggests that as part of a holistic MIGI strategy, shortterm storage times should be considered when planning the utilisation of landscaping materials (Fig. 2, d).

Bioreceptive materials and bio-integrated design
Bio-Integrated Design refers to interdisciplinary methodologies that merge applied biotechnology, architecture and design, in order to create sustainable systems for the built environment. It encompasses a range of biologically-mediated processes, such as biosilification, biomineralization and bioremediation, as well as the development of material substrates for living systems. Guillitte defined the term 'bioreceptivity' to describe the ability of a building material to be colonised by living organisms (Guillitte, 1995). In the context of bio-integrated design to enable MIGI, bioreceptivity has been explored through the design of architectural scaffolds with the goal of creating self-regulating systems which are host to cryptogrammic species as well as microbial biodiversity (Cruz & Beckett, 2016).
Whilst horizontal surfaces including roofs, terraces or pavements offer scope for plant growth, vertical surfaces (e.g. building facades and infrastructural walls) offer far harsher environments due to excessive water run-off, strong exposure to winds and lack of nutrient rich substrates. But cities have vast areas of xeric surfaces that offer opportunities to be photosynthetically active. For an accelerated creation of primary bioreceptivity on vertical surfaces, a number of design steps can accelerate this process. Porosity and surface roughness are two vital functions. Firstly, the calibration of pore size can enable water absorption and retention, reaching colonising organisms through capillary or surface-binding effects, and secondly as a means to exploit extrinsic factors for bioreceptivity through the collection of organic material and fixation of cryptogamic surface cover. Different compositions of bioreceptive cementitious materials have been explored based on Magnesium Phosphate Concrete (Manso et al., 2015) and other Ordinary Portland Concrete (OPC) mixes with the aim to create long-term carbon offset. Studies of OPC have shown that apart from altering the physico-chemical properties of materials, morphological variations explored via computational design strategies are a powerful means to reduce water run-off and increase moisture retention, extending the residence time to create zones for accelerated growth (Cruz, 2021). In future, quaternary bioreceptive strategies may be used (Sanmartín et al., 2021) whereby surface additives to a material scaffold such as hydrogels or humic material are applied to enhance colonisation. Further studies are needed to test the role of pH on material substrates in biofilm formation and the establishment of microbial communities which are vital to establish cryptogamic growth.
Lichens and, primarily bryophytes play key roles in design of bioreceptive structures within architecture, provoking a biophilic response (Wilson, 1984) through their aesthetic appearance and tactility. However, they are also important components due to their capacity to regulate their photosynthetic activity depending on moisture availability while surviving for long periods without water -poikilohydry. In relation to MIGI, bryophytes harbour ecologies with prokaryotic and eukaryotic algae, bacteria and fungi. Cyanobacteria are keystone species in other nutrient limited environments such as desert crusts (Yeager et al., 2007), where their ability to fix nitrogen and carbon enables succession by other organisms through exchange of metabolites.
However, our understanding of the exact ecological roles of microorganisms associated with bryophyte hosts is nascent. For example, while the presence of certain bacteria varies according to the bryophyte species, in one study
Analogous to the urban environment, during early stages of habitat restoration it has been shown that bryophyte communities enrich populations of microbial life on calcareous rocks (Cao et al., 2020). It may be speculated that colonisation by bryophytes and their associated microbiota could have advantageous effects for growth promotion in other plants due to the presence of bacteria containing genes for production of indole acetic acid, siderophores or solubilisation of phosphate (Insuk et al., 2020). Through this application of bio-integrated design to produce poikilohydric living walls, it is possible to employ more of the surface area that is underutilised within our urban environments to deliver MIGI.

Microbial inoculants
Microbial inoculants have recently been used to shift microbiota in landscaping materials towards an immuno-protective assemblage (Hui et al. 2019). The authors developed a microbial inoculant from biodiverse sources (e.g., forest materials), resembling the microbiome of organic soils. After the study subjects made contact with these inoculated materials, the relative abundance of opportunist pathogens on the skin significantly decreased. Furthermore, Roslund et al. (2020) demonstrated that a biodiversity intervention using microbial inoculants from forest floor materials changed the skin microbiome of children and enhanced immunoregulatory pathways.
Several other studies show that microbial inoculants can be beneficial for plant health, for example, via Plant Growth Promoting Rhizobacteria (PGPR) (Sacristán-Pérez-Minayo et al. 2020). PGPRs have the potential to protect plants from drought and metal stresses and play important roles in plant growth, which itself could minimise the use of harmful synthetically produced chemical fertilisers (Kumar et al. 2019). Therefore, MIGI strategies could incorporate microbial inoculants to enhance ecosystem health (Fig. 3, b).

Supportive tools
Useful tools are being developed that could help with MIGI interventions in the near immunoregulation and homeostasis, such as alpha and functional diversity and beneficial taxa that produce health-regulating compounds (Fig. 3, c).

Bioremediation
Emerging bioremediation research could also be considered in MIGI strategies. Insitu bioremediation enables ongoing decontamination or degradation of pollutants  (Priyadarshanee and Das, 2020). In terms of MIGI, this kind of strategy could be developed with Sustainable Drainage Systems in mind, e.g., a biofilter-embedded rain garden (Fig. 3, d). There are numerous organic compounds that pose a threat to human health, found in elevated concentrations. Microbial mechanisms that may be employed in MIGI are hydrolysis and oxidation, with the goal of producing benign compounds through metabolic activity. For instance, endocrine disruptors such as phthalates and alkylphenols are ubiquitous in water systems as a result of human activity (Bergé et al., 2014) but there are microbial mechanisms to break these down under certain conditions (Boll et al., 2020). Indeed, many bacterial taxa have been identified that have significant pollutant degradation properties (Ojuederie and Babalola, 2017). As an alternative to contained bioreactor systems, creating stable synthetic ecologies and applying eco-evolutionary principles to enhance bioremediation is compatible with MIGI principles (Borchert et al., 2021).

Plant nutrition, soil issues, and anti-microbial resistance
It is suspected that high-dosage artificial agricultural fertilisers are detrimental to mycorrhizal networks, for example, by promoting taxa with pathogenic traits Antimicrobial resistance has important implications for human health by making infections harder to treat and increasing risks of disease spread (WHO, 2020). MIGI researchers aiming to reduce the abundance and diversity of antimicrobial resistant genes in urban environments could explore the strategy of increasing soil microbial diversity. 2014)) and regional levels (Public Health Agency of Canada, 2018), complemented by industry-specific guidance in many countries (Watkins & Arkell, 2019).

Emerging biosecurity considerations
Nevertheless, further work is required to address the open questions and operationalise policy, and MIGI offers an opportunity to address these in a holistic manner. One of the core challenges presented by biosecurity threats is that the technical understanding of biosecurity in the construction and development industries is currently at an early stage, with many practitioners confusing biosecurity with concepts such as biodiversity, and seeing threats posed by biosecurity risks as someone else's responsibility. Integrating existing schemes such as Plant Healthy (https://planthealthy.org.uk) within MIGI will be essential, not only to ensure that best practice is developed but also so that practitioners can clearly understand how their actions reinforce the biosecurity continuum (Sequeira and Griffin 2014).
Biosecurity is one of many layers that prove challenging to translate between research and practice, and to this end, delivering the plant selection database proposed in the MIGI toolkit (Watkins et al., 2020) will provide not only a common understanding of the tools required to deliver MIGI but also a shared vocabulary for different sectors to draw upon when discussing projects.

Social innovation: promoting stronger human-nature relationships
Other important factors within the MIGI framework include social innovation, education and stimulating awe for nature, with emphasis on the foundations of our Studies in this area show increases in wellbeing and pro-ecological behaviour as a result of enhanced nature connectedness (Capaldi et al. 2014;Capaldi et al. 2015).
For the technologically-minded, virtual reality systems could be developed to facilitate urban habitat tours. These could include interactive macroscopic displays of microbial communities, whilst providing information on the composition and functional roles that microbes play in the local ecosystems (Fig. 3, f).   Watkins et al. (2020) identify barriers to operationalising MIGI, relating to the complexity of urban development projects, and communicating the benefits of MIGI interventions to stakeholders involved in urban planning. To ensure the implementation of green infrastructure strategies, stakeholder buy-in is required throughout green infrastructure planning, design, operation and management (Smith, 2020;UK-BCG, 2020

MIGI: Workshop series proposal
To determine clear action points for future research and address the challenges related to divergence of interests among stakeholders, it is vital to ascertain diverse priorities and concerns through early consultation (Khoshkar et al. 2017). This could also aid the development of a "common language" (Ugolini et al. 2018) that translates researchers' findings into verbal and graphic outputs relevant to nonexpert audiences. We are currently developing a series of workshops to discuss what is known about the microbiome in a health and ecosystem functionality context, and reveal tangible opportunities to include MIGI in urban planning. These workshops provide an opportunity to engage with reflective stakeholders in identifying not only challenges but also specific factors (e.g. MIGI toolkits, portfolio of illustrative examples) and alignments between current requirements/protocols, and how MIGI could be integrated. During the workshops we will discuss 'what researchers should be working on', and opportunities and constraints by drawing together the perspectives and needs of different stakeholders. These workshops will form part of a process of long-term engagement and partnership to enhance urban ecosystem health via MIGI strategies.
Developing the MIGI concept has the potential to enhance urban ecosystem functionality and resilience as well as human health. In this paper, we have provided several examples of MIGI actionable insights in addition to a horizon scan of emerging MIGI-related research and practice. A greater emphasis on the roles of microbial communities (from below-ground and up) in our urban ecosystems is needed. Understanding microbial dynamics will likely have an important role to play in the efficacy of our adaptability and long-term resilience to ongoing global environmental change. MIGI research agendas aim to promote this realm of thinking with considerations for multispecies health. However, overcoming the challenges to operationalising MIGI will be essential to furthering its practical development.