Effect of Urbanization on Soil: Structure, Chemistry, and Mycorrhizael Fungi

Two students (Tatiana Taylor and Hayden Cooksy) worked with me over the summer. We measured ambient light, soil moisture, soil electroconductivity (ECP), soil temperature, and soil pH along transects at my permanent research sites in Forest Park and at the control sites in the Mount Hood National Forest. At random sites, we dug soil pits to verify soil type and characteristics of each horizon including texture, nutrients, pH, and color. We used an app called “SoilWeb” to verify the soil characteristics and type. In addition, we measured 24 hours CO2 production in twelve containers at random sites to get an indication of soil respiration rates. We also harvested seedlings in order to quantify the amount of ECM (ectomycorrhizae) and AMF (arbuscular mycorrhizae) in the roots. We found that almost all our sites in Forest Park have “Goble” soil; only two sites had “Wauld.” These two soil types are both Inceptisols found in wooded areas. There were no significant differences among site locations for soil pH, moisture, ECP, texture, or light levels. We did find significantly higher levels of CO2 produced in 24 hours at the control sites in the national forest than at sites in Forest Park. This is in accord with last year’s findings that the national forest sites had deeper O horizons and higher C/N ratios than the sites in Forest Park. The C/N ratio and the depth of the O horizon were both significantly positively correlated with the number of seedlings and saplings, but the level of soil respiration was not correlated with any other measured variables. We are still analyzing the roots of the collected seedlings for mycorrhizae. When we harvested the plants at the control sites, we saw ectomycorrhizae on the roots. Unfortunately we only found two seedlings in Forest Park, which reinforces the lack of recruitment in the urban forest. We are working to quantify the amounts of ECM and AMF in the roots of the control site seedlings; the two seedlings we collected in Forest Park will probably not yield sufficient data for a comparative analysis