ABSTRACT Intensively managed fast-growing plantations can provide a significant portion of the world's wood biomass and preserve natural or extensively managed forest ecosystems by limiting harvesting pressure and associated disturbances. However, the establishment of plantations should not be at the expense of soil organic carbon stocks, and their potential as a carbon source or sink may depend on their initial stocks prior to planting. The choice of plantation sites is therefore crucial in minimizing losses or allowing the accumulation of carbon from a hybrid poplar plantation. The aim of our study was to determine the impact of afforestation with fast-growing hybrid poplars on soil carbon stocks of sites of different origins: Abandoned agricultural land (AAL) with a herbaceous vegetation cover; shrubby AAL; and logged (previously forested) sites. Our results showed that 15?years post-afforestation, previously forested sites where fast-growing hybrid poplar plantations were established had lower soil organic carbon stocks than their non-afforested equivalents and than other plantations established on AALs, while plantations on AALs had similar soil organic carbon stocks to their non-afforested counterparts. AALs would therefore appear to be the preferred establishment site for taking advantage of the high yield of hybrid poplars while preserving soil carbon stocks.

In recent years, plant–microorganism interactions and their impact on plant growth and health, and in turn on plant-driven ecosystem services (e.g., carbon storage, phytoremediation) have gained a lot of interest in the scientific community. This interest has been stimulated by the development of high-throughput sequencing technologies that greatly improved the capacity of scientists to efficiently characterize microbiomes, which are defined as the pool of genomes of the microorganisms (e.g., bacteria, fungi) present in a particular habitat. Among trees, the poplar microbiome is one of the most extensively studied. The goal of this chapter is to summarize the current literature on the poplar microbiome, first by describing the microbiomes of belowground and aboveground parts of poplars, and second by highlighting links between poplar genetic and the microbiome. This second part includes a review of studies specifically addressing the impact of transgenesis on the poplar microbiome. Overall, this chapter highlights the diversity of the poplar microbiome and the importance of further assessing links between tree genetic and the microbiome.