Nonpathogenic Fungi: Natural Regulators in Forest Ecosystems?

Jack D. Rogers, Ned B. Klopfenstein, Lori M. Carris, Mee-Sook Kim, Paul J. Zambino, Raini C. Rippy, John R. Goetz III, and Paul F. Hessburg

Washington State University Department of Plant Pathology (1,3,7), USDA Forest Service Rocky Mountain Research Station (2,4,5,6) and Pacific Northwest Research Station (8)

Forest biologists have long investigated the ecological roles of pathogenic, mycorrhizal, and wood-decay fungi, but key contributions of other fungi and fungus-like organisms (e.g., non-pathogenic ascomycetes, basidiomycetes, zygomycetes, fungi imperfecti, and straminipiles) to forest ecosystems have been largely overlooked. Previously, such fungal species have been inadvertently overlooked because of difficulties in surveying/identification and preoccupation with obvious pathogens, mycorrhizal species, and wood decay fungi. Currently, coupled molecular and morphological characterizations of fungal cultures are allowing the survey of two groups of nonpathogenic, fungal communities that were previously poorly characterized: wood decomposers and root endophytes. These inconspicuous fungal groups may play critical roles in regulating forest response to disturbances.

Fungal decomposers are essential for nutrient recycling, bioremediation, and soil structure formation. They play key roles in balancing fuel deposits and woody residue decomposition, so knowledge of their activity is critical to understanding fire risk due to fuels buildup. In addition, some fungal decomposers strongly compete with root pathogens for woody substrates. Their presence and long-term viability can reduce root disease incidence and severity by direct antagonism or by competition for specific niches. Current studies are identifying fungi associated with decomposition in forest stands in various habitat types, soil types, and under different fertilization regimes. In ongoing surveys of fungi associated with wood decomposition in forest soil, over 1,100 isolates of nonpathogenic fungi from 16 families have been identified; many are in genera having species active in natural biological control of forest diseases. Our results suggest that inconspicuous and generally overlooked fungi are prevalent among the initial colonizers of fresh woody substrates in forest soil. These fungi could be playing important roles in moderating fire and disease threat to forests and facilitating recovery after disturbances.

The ecological roles of endophytic fungi in woody roots are not well understood. Our continuing studies have recovered over 500 unique isolates of endophytic fungi representing approximately 30 genera from living woody roots of ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii) in the Inland Northwest, USA; many belong to genera with species that exhibit relatively high tolerance to soil heating and/or provide known biological control of fungal pathogens or insects. Current studies are underway to determine the ecological roles of these endophytic fungi in various environments, by monitoring their presence in interactions with fire and fuels treatments.

Knowledge of the occurrence and ecological roles of nonpathogenic and nonmycorrhizal fungi could aid prediction and management of forest disturbance regimes, especially under shifting climatic and management scenarios. We synthesize new scientific information to help forest managers understand the role of these inconspicuous fungi in relation to threats to western forests. As far as we are aware, no other programs are underway to inventory or determine the ecological roles of nonpathogenic and nonmycorrhizal fungi in forest ecosystems of the USA.

Native Pests Session - Wednesday Afternoon

corresponding author:

Ned Klopfenstein
USDA Forest Service
Rocky Mountain Research Station
1221 South Main Street
Moscow, ID 83843
208-883-2310
nklopfenstein@fs.fed.us