Honors College Thesis
 

Preliminary Evidence that the Microbial Community may Produce Aliphatic Constituents and Induce Soil Water Repellency as a Response to Desiccation

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https://ir.library.oregonstate.edu/concern/honors_college_theses/w3763c950

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  • Soil water repellency is one cause of rill soil erosion and overland flow that results in the loss of fertile topsoil. Previous research suggests that since microbial growth depends on temperature/moisture and follows diurnal and seasonal cycles, a biological mechanism would be able to explain the observed seasonality and climate dependence of soil wettability. Here we test whether soil water repellency is induced by the microbial community through the production of aliphatic constituents in their extracellular polymeric substances (EPS) as a response to desiccation stress. In a laboratory setting Quincy soil was subjected to wetting/drying cycles in order to induce desiccation stress. Analyses conducted were water drop penetration time (WDPT), contact angle, chloroform fumigation extraction for microbial biomass, and a hexane extraction to quantify aliphatic constituents using gas chromatography mass spectroscopy (GCMS). Results suggest there may be a threshold moisture content around 1.8% moisture content for repellency. There is also evidence to suggest that the critical surface tension of water penetration of a repellent sand is around a contact angle of 50°- 60°. There was a trend of an increasing aliphatic content as repellency increased. Differences were observed to suggest that the presence of aliphatic constituents induces soil water repellency, however there was no conclusive evidence that this is the mechanism microbes use to induce water repellency.
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