Promoting soil microbial community development in early primary succession on waste rock by mulching with ramial chipped wood, in a boreal context

The ecological restoration of mine waste rock corresponds to a context of primary succession, characterized by mineral substrates poor in organic matter and nutrients. The addition of organic matter, specifically in the form of ramial chipped wood (RCW) mulch, could facilitate the development of soil microbial communities crucial to ecosystem recovery on mineral substrates. This study examined the interaction between pioneer boreal tree species and soil microorganisms, exploring how a RCW mulch influences the development of microbial and plant communities in primary succession on different mineral substrates: waste rock and sand. The methodology of this research used an experimental design of four complete randomized blocks on an area composed of waste rock at the Lapa Mine, Quebec. Treatments ( n = 4) included two mineral substrates (scarified waste rock or sand) with or without the addition of RCW. The study focused on seedlings of two tree species: Pinus banksiana and Betula papyrifera . Microbial community development was analyzed by metabarcoding, focusing on the rhizosphere of tree seedlings and bulk soil, five years after tree seedling establishment. After five years, RCW mulch boosted bacterial species richness and diversity, particularly around Pinus banksiana and on waste rock, although its effect on fungal diversity was less marked. RCW also favored the development of bacterial and fungal functional groups useful for plant growth. Microbial diversity was more influenced by the physicochemical properties of mineral substrates than by tree species, indicating a preponderant influence of the mineral substrate physicochemical properties during the very early microbial succession. By promoting beneficial bacterial diversity in pioneer trees, RCW appears to be a promising strategy for supporting ecological restoration in disturbed boreal environments.