Paper No. 23
Presentation Time: 9:00 AM-6:00 PM


GREENBERG, Kyle A.1, BALOGH-BRUNSTAD, Zsuzsanna1, SHI, Z.2, AREY, B.3, DOHNALKOVA, A.3, NIEDZIELA, S.M.1 and KELLER, C.K.2, (1)Department of Geology and Environmental Sciences, Hartwick College, Oneonta, NY 13820, (2)School of the Environment, Washington State University, Pullman, WA 99164, (3)Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352,

Fungi and bacteria are reported agents of chemical weathering and nutrient uptake. However, the role of rhizospheric biofilm in these processes is unknown. Our study investigates the mineral-fungus-bacteria interface and water chemical changes in the rhizosphere of pine. We hypothesized that under Ca and K limitation, thick biofilm cover would develop to facilitate direct cation uptake from minerals.

Red pine was grown in columns in quartz sand amended with biotite and anorthite. Half of the trees were inoculated with an ectomycorrhizal fungus and forest soil bacteria, and the other half were left without inoculation. Columns without biology served as controls. Nutrient solutions contained Ca and K at 0, 10, 30, and 100% of requirements for healthy growth. At 3, 6 and 9 months subsets of the columns were destructively sampled. Biotite and anorthite were analyzed from each column using scanning election microscopy and energy dispersive x-ray spectroscopy. Drainage water samples were collected periodically for chemical analysis.

Microscopy shows bacterial and fungal attachment to mineral surfaces, but particle and step edges are preferred. Biofilm cover is limited to isolated patches. Over time, the inoculated columns are dominated by bacteria colonies and fungal infection decreases to isolated spots. As Ca and K concentrations increased in solution, biofilm cover decreased and bacteria colonies became less diverse. Weathered crust formation was observed on anorthite and its coverage increased over time in all treatments with trees. Drainage pH decreased to about 4 after 6 weeks and remained low for rest of the experiment in all treatments with trees. The release of dissolved iron was strongly correlated to the water pH, with significantly higher iron concentrations at lower pHs. Lack of an inoculation treatment effect is consistent with limited rhizospheric fungal infection and limited biofilm development in this experiment.