Format: ORAL

Christopher B. Blackwood1,2, Andrew C. Eagar1, Princess H. Abu1, Megan A. Brown1, Sara M. Moledor1, Kurt A. Smemo3, Richard P. Phillips4, Andrea L. Case1

1 Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824, USA 2 Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, USA 3 Environmental Studies and Science Program, Skidmore College, Saratoga Springs, New York 12866, USA 4 Department of Biology, Indiana University, Bloomington, Indiana 47405, USA

Arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) tree species tend to differ across a multitude of traits beyond the structure of the root symbiosis, including leaf and root chemistry, litter decomposability, carbon allocation to mutualistic fungi, and protection from root pathogens. Here we explore how, as foundation species, the mycorrhizal type of dominant trees also has a profound mycorrhizal spillover effect on soil biogeochemistry and the soil microbiome, resulting in different stresses experienced by all members of the plant community. We present evidence that, compared to soil in forests dominated by ECM tree species, soils in forests dominated by AM tree species have increased soil mineral nutrient availability, greater abundance and diversity of plant pathogens and AM fungi, and lower abundance and diversity of ECM fungi. Although we will discuss some context-dependency of these patterns, they seem to be consistent even across a continuous gradient of mycorrhizal dominance (i.e., 0 to 100% AM basal area), and for individual species (e.g., for AM plants surrounded by increasing dominance of ECM trees, and vice versa). Based on these patterns, we will describe a new hypothesized framework of additive and interactive effects of mycorrhizal spillover. These mycorrhizal spillover effects shift the strength and direction of plant-soil feedbacks and conspecific density dependence in predictable ways, which has implications for our understanding of future plant community and evolutionary dynamics.