Faced with the increasing frequency and intensity of droughts that threaten young trees, BIAM is taking part in the RESTORE project, which offers a nature-inspired, eco-friendly approach to making forests more resilient. Their solution? Custom‑designed bacterial communities, isolated from forest soils that have been partially deprived of rainfall, to support the growth and survival of newly transplanted seedlings. A promising natural lever for tomorrow’s forest management.
We hear it everywhere: climate change is intensifying the frequency, duration and severity of drought events, particularly in the Mediterranean region. This increased pressure directly endangers young seedlings, whose shallow root system struggle to access the water needed for grow. RESTORE is an international project (France-Germany-Brazil) that brings together BIAM (CEA/CNRS/AMU), the ECCOREV Research Federation, the Federal University of Londrina, the Helmholtz Centre and the Technical University of Munich, and the ONF-PNRGF in Cadarache. Its ambitious aim: to develop nature-based-solutions acting directly on the root microbiome.
Forest bacteria selected drought-stressed soils
Over the course of the project, the team isolated more than a thousand bacterial strains from different compartments and depths of Mediterranean forest soil at the Oak Observatory at the OHP (O3HP)1. Samples were taken from a plot of forest that has been subjected to partial rainfall exclusion for over a decade, simulating the climate expected by 2100. This strategy maximised the ecological and functional diversity of the isolates. From this collection, bacteria naturally adapted to water stress were selected for their ability to produce exopolysaccharides2, synthesize plant hormones or tolerate hostile environments. They were then assembled into complementary synthetic communities—SynComs—designed to diversify functions and mechanisms of action and, above all, to reproduce the natural root environment by combining strains isolated from the root itself and from the various surrounding zones.
However, the approach is not limited to simply adding beneficial bacteria, “it’s based on a bio-inspired concept that allows each SynCom to be adapted to the root strategy of the targeted tree species”, explains Catherine Santaella, BIAM research scientist and co-leader of the Restore project for France. She continues: “each plant species adopts a particular way of structuring its roots to better resist drought. Species with a conservative strategy, such as downy oak, produce thick, long-lasting roots that benefit from microorganisms that help retain water. Conversely, species with an acquisitive strategy, such as the sorb tree, produce thin, fast-growing roots that are stimulated by growth-promoting bacteria. The effectiveness of SynComs is therefore based on a precise adjustment between the microbial functioning and the physiological needs of the plant, establishing a genuine plant-soil-bacteria interaction”, she reveals.
Two Mediterranean species for targeted experimentation
“To validate this approach, we carried out trials under controlled conditions on two species emblematic of Mediterranean environments, the downy oak (Quercus pubescens), which has a
conservative root strategy, and the sorb tree (Sorbus domestica), characterised by an acquisitive strategy,” explains Ivan Aleksieienko, a PhD student at the BIAM who is part of the Restore project. “The SynComs, assembled from bacteria isolated from drought-exposed forest soils, were selected based on key functions such as growth stimulation or enhanced soil water retention. Once the SynCom were adapted to each root strategy, the young plants were subjected to periods of water stress in the greenhouse. We then monitored the development of drought symptoms and the physiological performance of the treated plants compared with non-inoculated controls”.
Promising results to boost plant resilience
The results of these trials are particularly promising, showing that in downy oak, the number of plants showing visible symptoms of drought was reduced by 47% thanks to bacterial inoculation. In the sorb tree, the reduction was even higher with 71%. “These results far exceed those obtained with isolated bacterial strains, demonstrating that microbial cooperation and root compatibility are powerful levers for improving the resilience of young trees,” emphasizes Catherine Santaella. The functional diversity of the SynComs—i.e., the complementary roles played by different bacterial strains within the consortium—underpins their enhanced effectiveness. Each bacterial strain fulfils a specific role – water retention, hormonal stimulation, stress tolerance, etc. – and their coordinated interactions generate synergy, i.e. an effect greater than the sum of the individual effects. These results were supported by statistical analyses integrating multiple microbial traits which demonstrated the robustness of plant-bacteria associations and validated the links between microbial traits, root strategies and drought tolerance.
A tool that can be adapted anywhere in the world
Beyond its local applications, this method offers a new and adaptable way of supporting forest restoration in drought-prone areas, by selecting microbial consortia adapted to each species and their environment. It serves as a management tool for soil biodiversity that can be adapted and implemented worldwide.
Social prospects: nature strengthened by its own allies
The implications of the RESTORE project go far beyond fundamental research, and are aimed at solving practical problems by proposing applicable solutions. Increasing the survival of planted young trees, can make reforestation campaigns more sustainable. This approach is fully in line with climate change mitigation strategies, as healthy forests store more atmospheric carbon and contribute to ecosystem stability. “It also supports the ecosystem services essential to our societies, such as regulating water flows, preserving soil and maintaining biodiversity,” points out the doctoral student.
Spin-offs from Food security
These principles, transposed to the forestry sector to address drought-related challenges, were initially developed for agriculture. Selected microbial consortia can enhance the tolerance of certain sensitive food crops to water stress, thereby contributing to more sustainable agriculture. Finally, this approach is based on tools that can be applied in other drought-prone regions by adapting SynComs to local plant species and soil characteristics. In this way, it demonstrates that nature, reinforced by its own microbial allies, can be a powerful lever in meeting the climatic and ecological challenges of tomorrow.
- O3HP : CNRS INEE, research infrastructure AnaEE
- Exopolysaccharides are complex polymers of sugars that act like a natural glue to help the soil adhere to the roots. These substances enable bacteria to form protective biofilms around the roots, creating a advantageous and moist microenvironment, persisting in periods of drought. By retaining water and strengthening the adhesion of the soil to the roots, these biofilms limit water loss and protect root tissue against abiotic stresses.
Photos © Cyril FRESILLON BIAM CNRS Images
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