Harnessing mycorrhizal fungi for a sustainable forest

Forests cover more than 30% of the Earth's land surface, the bulk of which is made up of natural forest massifs – primary and secondary forests –. These wooded areas are home to over 3,100 billion trees and 80% of all recorded plant, animal and microbial biodiversity. Forests are therefore at the heart of a complex network of interactions between plants, animals and microbes. A detailed understanding of the forest ecosystem requires knowledge of biogeochemical cycles, in which micro-organisms have a decisive influence on soil fertility, but also on tree vigour and health. The composition and longevity of the ecosystem are determined by the links forged between plants and microbes. It is now accepted that trees host a complex community of microorganisms – the microbiota – made up of thousands of species of viruses, bacteria and fungi that influence the growth, development and health of their host plant. As a result, forest microbiology and microbial ecology are now part of a multidisciplinary research approach aimed at describing the biodiversity and functioning of forest ecosystems. In order to mitigate the foreseeable impacts of environmental change, it is urgent to describe, characterize and model the multiple interactions between plants and microbes that weave a formidable ecological network throughout forests. Identifying the factors governing interactions between plants and their microbiota should enable us to make better use of beneficial microorganisms to stimulate tree growth, improve resilience in the face of climatic constraints and limit the negative impact of pathogens. The ecosystem services provided by microbial communities are essential for maintaining soil fertility and contributing to the sustainability of forests. In order to assess these services, it is necessary to develop molecular tools to identify communities and populations of beneficial and harmful microorganisms, monitor their dynamics as the forest evolves towards its climatic stage, and evaluate the impact of silvicultural management. A priority objective of current research is therefore to identify keystone species whose activity is essential for the proper functioning of the microbial community and associated plants. These species could serve as indicators of the health of an ecosystem, but they could also be controlled and exploited within the framework of ecological forest engineering.

Two guilds of fungi are predominant in forests: saprotrophic fungi, which decompose soil organic matter, and symbiotic mycorrhizal fungi. In this article, we present a review of current knowledge on the biology and ecology of forest mycorrhizal symbioses. A major part of the research devoted to the ecology of mycorrhizal fungi aims to understand the role played by these mutualistic fungi in the carbon and mineral element cycle,...