Trees generally develop either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) associations with fungi, thereby creating a patchwork of AM and ECM stands in temperate deciduous forests. Our goal was to test if dominant mycorrhizal type of a forest stand is associated with a specific limitation on root growth, resulting in a positive root growth response when the limitation is alleviated. AM soils are usually nutrient-rich and may be plagued by pathogens. Therefore, we predict that root growth in AM stands is limited by plant pathogen activity that will be alleviated by fungicide. ECM soils tend to be nutrient poor but also harbor fewer pathogens, so we predict that root growth in ECM stands is limited by a lack of nutrients, which should be alleviated with fertilizer. To test this hypothesis, root in-growth cores were installed in the ground and filled with soil, with one third receiving a fertilizer treatment, one third receiving a fungicide treatment, and one third receiving no treatment. This was repeated in 48 forest plots with strong AM or ECM dominance across three different states (OH, IN, NY). After approximately one year, the cores were harvested, and root biomass measured as an indicator of root proliferation.
Results/Conclusions
We found that responses to different treatments were site specific. Ohio yielded data most consistent with our hypotheses; fertilizer treatments increased root growth in ECM plots compared to the controls while fungicide treatments elicited a stronger response from AM roots compared to ECM roots. In New York, the fertilizer treatment had minimal impact on root growth and the fungicide treatment decreased growth in both AM and ECM plots compared to the control cores. In Indiana, root growth was generally the same across all treatments with the exception of fungicide significantly decreasing root growth in AM plots, contrary to what we had expected. Alleviation of these two common limitations failed to consistently stimulate root growth, suggesting that interactions of mycorrhizal dominance and mechanisms of limitation are more complex than anticipated but, at the same time, informs future stages of the project. Allowing the cores more time in the soil and identifying fungal species and abundance are the next steps towards revealing the mechanisms of limitation that shape community composition in these temperate deciduous forests.