Dani Or
Professor, Chair in Environmental Physics of Terrestrial Systems 
Swiss Federal Institute of Technology, Zurich

This special talk will be held noon - 1:00pm in Geo Corner - Bldg. 320, Room 105.

Dr. Dani Or is the 2013 Birdsall Dreiss Lecturer of the Geological Society of America.  Dr. Or's forum talk titled Biophysical Processes Shaping Bacterial Life in Soils - An Unexplored Universe Under Our Feet was presented as the 2013 Birdsall-Dreiss Lecture.

His research focuses on mass and energy transport in porous media, on mechanics of abrupt landslides and avalanches, and on linking physical processes and biological activity in soils. Dr. Or has authored over 170 refereed publications, co-authored a book, and over 270 proceeding papers and abstracts. Dr. Or is Editor in Chief of the Vadose Zone Journal, recipient of the Kirkham Soil Physics Award (2001), 2004 Fellow of the Soil Science Society of America, chair of the 2008 Gordon Research Conference on Flow and Transport (Oxford, UK), and 2010 Fellow of the American Geophysical Union.


By some accounts exploring the microbial diversity found in soils represents an uncharted scientific frontier at a scope similar to that of space exploration. The immense diversity of soil microbial life is attributed to the complex and heterogeneous pore surfaces and spaces with highly dynamic aqueous and chemical microenvironments. In most unsaturated soils a flickering aqueous network defines nutrient diffusional pathways and shapes microbial dispersion patterns. We quantitatively explored effects of microscale hydration on biophysical interactions affecting microbial dispersion and controlling coexistence of competing bacterial species inhabiting unsaturated surfaces. The rapid fragmentation of the aqueous phase yields a surprisingly narrow range of hydration-enabled motility, and marks the onset of flux limiting and heterogeneous diffusion fields that promote coexistence. Conditions promoting coexistence occur under mild unsaturated conditions within matric potential values of a few kPa nearly independent of soil or rock type. The spontaneous spatial organization of interacting microbial populations and formation of consortia shaped by dynamic diffusion fields and trophic interactions offer a fascinating and robust level of self-organization that support high diversity found in soil. The resulting length scales for interactions offer new insights into biogechemical function of soil microbes and could guide bioremediation activities of the subsurface.

Sponsored in conjunction with Civi & Environmental Engineering and Environmental Earth Systems Science.