1 Department of Biology, Concordia University, Montréal, QC, Canada.
2 Department of Biology, Dawson College, Montréal, QC, Canada.
3 Département de Biologie, Université de Sherbrooke, Sherbrooke, QC, Canada.
4 Centre Sève, Université de Sherbrooke, Sherbrooke, QC, Canada.
5 National Council for Air and Stream Improvement, Inc. (NCASI), Montréal, QC, Canada.
6 Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, QC, Canada.

Climate change is prompting plants to migrate and establish novel interactions in new habitats. Because of the pivotal roles microbes have on plant health and function, it is important to understand the ecological consequences of these shifts in host-microbe interactions with range expansion. Here we examine how the diversity of plant associated microbes varies along the host's current range and extended range according with climate change predictions, and assess the relative influence of host genotype (seed provenance) and environment in structuring the host microbiome. We collected sugar maple seeds from across the species current range, then planted them in temperate and mixedwood/transitional forests (current range) and in the boreal region (beyond range but predicted future range in response to climate change). We used amplicon sequencing to quantify bacterial, fungal, and mycorrhizal communities from seedling leaves and roots. Variation among sites and regions were the main drivers of the differences in host microbial communities whereas seed provenance did not play a large role. No unifying pattern was observed for microbial community richness, diversity, or specialization, demonstrating the complexity of responses of different taxa on above- and belowground plant compartments. Along the latitudinal gradient, we (1) observed reductions in mycorrhizal diversity which can negatively impact maple establishment; (2) and revealed reductions in fungal leaf pathogens which can have opposite effects. Our results highlight the need for an integrated approach including the examination of various microbial taxa on different plant compartments to improve our understanding of plant range shifts and plant-microbe interactions.