Beyond Mutualism: Complex Mycorrhizal Interactions

Abstract

The soil-plant-fungal matrix is inherently complex. There are thousands of species, highly variable environments in time and space, multiple interactions within a range of resources, and exchanges between multiple trophic levels. Here, we look at the structure of that complexity to see if there are emergent properties that allow us to understand that complexity. We emphasize our work from Mediterranean-type ecosystems in California and Oregon, but the perspective is valid across biomes. We examine a diversity of mycorrhizal types, with an emphasis on interactions of arbuscular mycorrhizae (AM) and ectomycorrhizae (EM) with host plants. These taxonomically different fungi differ in structural and biochemical properties including hyphal growth patterns and enzymatic capabilities. Because the symbionts are fungi, their hyphae connect multiple plants, forming networks. Materials (C, N, P, and water) are exchanged between plants through mycorrhizal networks. Importantly, networks themselves have structural properties that confer stability or instability and control the directions of flows. Thus, network theory has the ability to resolve patterns of elemental transfers and exchanges, and thus the outcomes for plant community dynamics. Also importantly, hyphae and fine roots have limited life spans, making interactions highly dynamic. Together, these dynamic interactions will help us unravel the complex relationships and the evolutionary histories that result in community and ecosystem dynamics.