OOS 2-1 - Arbuscular mycorrhizal fungi communities of sugar maple seedlings along two altitudinal gradients

Background/Question/Methods
Global warming in the upcoming years (IPCC, 2021) will affect deeply the spatial distribution of arbuscular mycorrhizal associations and, therefore, forest biodiversity and ecosystem functioning (Barcelo, van Bodegom & Soudzilovskaia, 2019). Based on climate projections, AM tree species such as sugar maple (Acer saccharum) could migrate beyond the northern edge of their distributions (Solarik et al., 2018). Nevertheless, factors such as unfavorable soil properties (Carteron et al., 2019), ectomycorrhizal plant dominance (Carteron, Vellend & Laliberté, 2022), and light availability (Kwit, Rigg & Goldblum, 2010) could limit AM tree migration in novel environments. Here, we investigated how AMF richness, diversity, community composition, and colonization rate change along two elevational gradients. Precisely, we aimed to identify (1) the impacts of soil abiotic properties and understory plant community structure on AM communities; and (2) how it affects sugar maple saplings’ growth and fitness. We randomly selected 100 sugar maple saplings located along two elevational gradients (Mont-Écho and Mont-Mégantic, Québec) and we evaluated spring plant understory diversity around each targeted sapling. Saplings and surrounding soil samples were then collected to evaluate endophytic and environmental AMF community using Illumina MiSEQ amplicon sequencing as well as foliar and soil nutrient status.

Results/Conclusions
We found no significant differences in AMF richness along both gradients. For Megantic and Sutton, PERMANOVA analysis revealed that major drivers of community composition were plant communities (r2 9-28% p = 0,001), altitude (r2 19-31% p = 0,001) and soil pH (r2 7-71% p ≤ 0,04). Procrustean analysis identified a correlation between plant communities and AMF community structure along the gradients (m2­ 31 % p = 0,001). Soil abiotic properties were highly variable between sites and no clear nutrient gradients were found. Opposite to our expectations, saplings growth and foliar nutrients weren’t correlated with AMF root colonization nor soil parameters. Our findings from early-stage analysis suggest that short-distance elevational gradients arbor a mosaic of plant and fungal communities that tend to covary together. These results highlight the importance of small-scale plant diversity on mycorrhizal fungal community structure (Chagnon, Bradley and Klironomos, 2018) that could lead to favorable microsites for sugar maple establishment and growth at the northern edge of its distribution (Solarik et al., 2018). More work is required to disentangle the implication of plant and microbial communities on soil properties by focusing on ecological processes (e.g. priority effect and plant-soil feedback) to better understand plant migration under climate change