Dr Christina Birnbaum, School of Agriculture & Environmental Science, University of Southern Queensland, Toowoomba 4350, Queensland, Australia & Centre for Crop Health, University of Southern Queensland, Toowoomba, Queensland 4370, Australia

Restoration in progress

The United Nations Decade of Ecosystem Restoration was announced in 2021 to highlight the need for collective efforts to revive degraded ecosystems. From 2021 to 2031 nations, governments, non-governmental organisations and scientists are called to act in preventing, halting, and reversing the widespread degradation of ecosystems worldwide.

Coastal or “blue carbon” ecosystems, including mangroves and saltmarshes, are of a significant value to humans as they provide key ecosystem services such as protection from storm surge and erosion, storage and sequestration of carbon as well as recreation (Macreadie et al 2021). However, these coastal ecosystems are experiencing extensive degradation due to sea level rise, flooding, pollution, and pressure from coastal development (Jankowski et al 2017). For example, it has been estimated that Australia has lost half of its coastal ecosystems since the European colonisation, i.e., approximately 25,000 km² of saltmarsh and mangroves and 32,000 km² of seagrasses have been destroyed (Australian Marine Conservation Society, 2022).

Restoration of coastal ecosystems frequently relies exclusively on re-vegetation of aboveground plant communities using active restoration techniques, i.e., direct planting of seeds or seedlings. However, this approach often overlooks the assessment of the belowground soil health and soil biota compatibility with plants, which could increase the overall restoration success.

A seedling in mangrove mud

Plant belowground soil biota is fundamental to plant health, and indeed the planet’s health, and functioning (Averill et al 2022). In the coastal ecosystem restoration context, plant belowground microbiome has rarely been assessed and integrated into coastal restoration management plans, especially in Australia (Farrer et al 2022, Birnbaum and Trevathan-Tackett in review). Thus, there is a fundamental gap in our understanding of the role belowground microbiomes play in restoration success in saltmarsh and mangrove ecosystems and how we can harness that knowledge to facilitate better coastal restoration outcomes.

Coastal ecosystems from a plants’ perspective are very stressful environments for growth as they experience frequent flooding, variable salinity levels and nutrient concentrations and pressure from invasive plants. Soil microbes form diverse mutualistic, symbiotic and antagonistic associations with plants. For example, beneficial arbuscular mycorrhizal fungi can help withstand stressful conditions by helping plants acquire nutrients like phosphorus and moisture they need for growth. Beneficial bacteria, collectively termed rhizobia, that form associations with legumes help plants fix atmospheric nitrogen. Coastal ecosystems experience additional environmental stressors, i.e., prolonged anoxia, and our understanding of soil microbial communities that could withstand and thrive in long-term anoxic conditions is still elusive.

Better understanding and harnessing the role of beneficial soil microbial communities and supressing the role of soil pathogenic microbial communities has the potential to considerably increase coastal restoration success. So, why has the progress been slow in better utilizing soil microbial communities in coastal restoration efforts? We are still facing many challenges that we need to overcome before the full potential of soil biota in restoration can be harnessed. The main challenges are related to the knowledge gaps highlighted above as well as the relatively high cost of microbial analysis.

The United Nations Decade of Ecosystem Restoration is raising awareness about the dire state of many ecosystems globally. It also offers a great framework to work in and hopefully facilitate more collaborative research to significantly advance both fundamental and applied plant-microbial knowledge through better understanding of the importance of coastal microbiomes to restoration success by stakeholders and funding bodies.

References:

Macreadie PI, Costa MDP, Atwood TB, Friess DA, Kelleway JJ, Kennedy H, Lovelock CE, Serrano O, Duarte CM (2021) Blue carbon as a natural climate solution. Nature Reviews Earth & Environment 2:826–839

Jankowski KL, Törnqvist TE, Fernandes AM (2017) Vulnerability of Louisiana’s coastal wetlands to present-day rates of relative sea-level rise. Nature Communications 8:14792

Australian Marine Conservation Society, 2022. Online access 6/10/2022 https://www.marineconservation.org.au/blue-carbon/

Averill, C., Anthony, M.A., Baldrian, P. et al. (2022) Defending Earth’s terrestrial microbiome. Nature Microbiology.

Farrer EC, van Bael SA, Clay K, Smith MKH (2022) Plant-Microbial Symbioses in Coastal Systems: Their Ecological Importance and Role in Coastal Restoration. Estuaries and Coasts 1–18

Birnbaum, C., & Trevathan-Tackett, S. M. Can we aid coastal wetland restoration via the belowground soil microbiome? (in review)