Although mostly hidden from us, mycorrhizal fungi are nearly ubiquitous. They are responsible for important ecosystem functions like holding carbon in the soil and transferring nutrients from soil to plants. Mycorrhizal fungi accomplish these feats as part of an intimate symbiosis with plant roots in which the fungus both colonizes roots and extends through the soil. The symbiosis is termed mycorrhiza (singular) or mycorrhizae (plural), a word with Greek origins that translates literally as ‘fungus-root’.

Mycorrhizal fungi receive carbon from their host plant and connect individual plants to the fungal mycelium in the soil. This interaction can benefit individual plants by facilitating nutrient uptake, improving drought resistance and providing protection from pathogens. Mycorrhizae are generally considered mutually beneficial. The fungi are obligately symbiotic and therefore always benefit; in contrast studies have found a continuum of plant responses when examining different symbiont assemblages and environmental conditions. On a community level, multiple plants are typically colonized by the same fungus and in this way mycorrhizal fungi connect plant communities in what has been termed both the ‘wood wide web’ or ‘common mycorrhizal networks’. These networks provide pathways for transfer of nutrients and plant signals, but we are just beginning to how these transfers are controlled and what role they may play in plant-plant interactions.

Unraveling how multiple factors interact to affect mycorrhizal function will lead to a predictive understanding of this symbiosis, one that can be applied to improving outcomes in areas such as ecological restoration and sustainable agriculture.

Research Projects

A brief introduction to some of the projects we have been working on:

How can we promote beneficial soil biota in agricultural systems?

Arbuscular mycorrhizal fungi form intimate symbioses with plants which can ‘jump-start’ the plant’s immune system, allowing plants to respond more quickly to pathogen attacks. Our recent work suggests that mycorrhizal fungi can increase the resilience of ‘Meeker’ raspberry plants to the pathogen Phytophthora rubi, which causes root rot, by increasing survivorship of young plants exposed to P. rubi by more than 300% and, on average, doubling the growth of survivors (Whitney, 2020). We also found mature ‘WakeHaven’ raspberry fields can support robust mycorrhizal fungal communities; however, we do not know if these fungi are present in young fields where raspberry plants are most vulnerable. Furthermore, we don’t know if raspberry cultivars differ in their response to soil biota. Producers need data on beneficial soil biota communities in young fields and variability of cultivar responsiveness to soil biota to determine if soil biota community management should be considered after field turnover and/or during cultivar selection.    

Do soil biota influence invasions?

Non-native plant invasions can reduce plant diversity and alter ecosystem processes.  Despite substantial research efforts in the past 20 years, we still lack a predictive understanding of how some exotic plants establish, spread and outcompete native plants. The mutualism hypothesis, postulates that invasions fail due to an absence of specific mutualists or occur because new – and better – mutualists are encountered in the exotic range (the enhanced mutualism hypothesis). There are several ways arbuscular mycorrhizal (AM) fungi could affect – and be affected by – plant invasions. First, some invaders are non-mycorrhizal or have a low mycorrhizal dependency. Their invasions have been shown to reduce the overall abundance of AM fungi and root colonization of mycotrophic, native plants. On the other hand, AM fungi increase growth and competitiveness of some invaders like Euphorbia esula (leafy spurge) and Centaurea stoebe (spotted knapweed).

We have been collaborating with researchers at MPG Ranch in Montana’s Bitterroot Valley to better understand how the invasive plants affect, and are affected by, native fungal communities. We have primarily focused on the invaders spotted knapweed and Potentilla recta (sulfur cinquefoil) across the wet-dry ecotone from the Washington coast to the grasslands of Montana.

Do we need to consider soil biota in restoration projects?

Revegetation following dam removal projects may depend on recovery of arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungal communities, which perform valuable ecosystem functions. We assessed the availability and function of AM and EM fungi for plants colonizing dewatered reservoirs following a dam removal project on the Elwha River, Olympic Peninsula, Washington, United States in combined field and greenhouse studies. Research on long-term mycorrhizal function and fungal community dynamics in the recovering Elwha basin is continuing. However, the work is primarily being done in Jenise Bauman’s lab at the Poulsbo campus and in Erica Cline’s lab at University of Washington-Tacoma.

What is the role of mycorrhizal fungi in decomposition?

Arbuscular mycorrhizal (AM) fungi are not decomposers and they lack genes that code for cell wall degrading enzymes.  Yet, AM fungi have been observed colonizing leaf litter in the tropical montane regions of Colombia (Posada et al 2012, Aristizábal et al 2004), potentially accessing nutrients newly released from the leaves by the actions of saprophytic fungi or other decomposers. If AM fungi are broadly capable of accessing mineral nutrients even before they enter the soil, this has implications for tightening the nutrient cycle and providing a pathway for some portion of nutrients to be recycled from one year’s leaves to the next. We are studying AM fungal colonization patterns of leaf litter in Pacific Northwest temperate forests.

Aristizábal, C., E.-L. Rivera, and D. P. Janos. 2004. Arbuscular mycorrhizal fungi colonize decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. Mycorrhiza 14:221–228

Posada, H., S. Madrinan, and E.L. Rivera (2012). Relationships between the litter colonization by saprotrophic and arbuscular mycorrhizal fungi with depth in a tropical forest. Fungal Biology 116:747-755

Friends & Collaborators

Pedro Antunes (Algoma University)

Tanya Cheeke (Washington State University)

Erica Cline (University of Washington, Tacoma)

Ylva Lekberg (MPG Ranch, University of Montana)