Mycorrhizal Fungi: a Soil Ecology Perspective.

Mycorrhizal fungi play critical roles in wildland ecosystems. However, their application to agriculture and horticulture has rarely equaled their promise. In large part, I propose that this is due to complexities inherent in the interactions between fungal taxa, plant taxonomy and physiology, and soil/environmental conditions. The limits in successful application may also result from our inability to use and interprete observations resulting from application trials and field observations. In recent trials, we found a wide variation in the effectiveness of different arbuscular mycorrhizal “products”, all from reputable sources. One interpretation is that some are useful and others less useful products. But another is that, to be successful, mycorrhizal inocula should be geared to the conditions and the goals of the user. I will present relevant datasets from the literature and our own research demonstrating a need to tease apart these complexities before large-scale applications are likely to be successful. These include measurements showing that a similar initial inoculum can result in very different taxon dominance after only a few repeated growth sessions. In other cases, different taxa show differential survival and growth impacts under changing conditions. In the field, there is always invasion of an inoculum by native residuals, but the inoculum source often survives several years. Field observations show that mycorrhizal fungi exhibit long periods of stasis punctuated by rapid growth and turnover. Management practices should incorporate these dynamics to optimize use of mycorrhizae in the real world. The final conclusion is that widespread field trials are essential if the use of mycorrhizae for sustaining agriculture under reduced fuel, fertilizer and irrigation regimes are to be successful.