Soil pH and Endomycorrhizal Association

2010 Fairfax County Regional Science and Engineering Fair

The abstract below was written by the student. The Northern Virginia Soil and Water Conservation District made no editorial changes.

Soil pH and Endomycorrhizal Association

by Carrie Bevis, Thanh Nguyen and Nadia Thura, Seniors, Stuart High School


The purpose of this experiment was to determine the relationship between increasing soil pH and ability of endomycorrhizal fungi to colonize the roots of the host plant. Endomycorrhizal fungi forms a mutualistic relationship with host plants, by increasing nutrient (primarily phosphorous) and water uptake in the plant in return for carbohydrates, and conferring resistance to pathogens and other environmental stresses.

It was hypothesized that with increasing soil alkalinity, root infection by endomycorrhizae would increase due to fixation of phosphorous particles to calcium ions, rendering them less available for plant uptake, which would lead to greater need for mycorrhizal association for transfer of phosphorous to plant roots. Pea plants were inoculated with a granular inoculum containing 3 species of endomycorrhizae, and grown until the end of the vegetative growth stage. Calcium carbonate, the main ingredient in agricultural lime, was applied in varying concentrations to the experimental pots to achieve pH levels of 7-8 and 8-9, with pH 6-7 being the control. Roots were cleared and stained, and root colonization by endomycorrhizae was quantified for each level pH using the grid-intersect technique using a dissecting microscope.

The results were in accordance with the hypothesis, with the highest percent colonization observed in soil pH 8-9, next highest in soil pH 7-8, and lowest in the control soil. These results may have agricultural implications by providing insight on the soil conditions favorable to this beneficial fungi in forming relationships with host plants.

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