Linking microscale processes with the macro world: Microbes & moisture through the soil profile

Dr Joshua Schimel

Professor in the Department of Ecology, Evolution, and Marine Biology at UC Santa Barbara

Microbes control planet Earth. Yet, integrating microbial information into large scale-perspectives and models remains difficult. Classical biogeochemical models assume that microbes are in equilibrium with their environment, an assumption that is increasingly false as climate change increases extremes. Currently, at least 1/3 Earth’s land experiences regular drought, and climate models suggest this will increase. Important dry-soil phenomena remain unexplained, such as the “Birch Effect”—the pulse of respiration on rewetting a dry soil. Important and surprising processes occur during the dry season. For example, during the summer in California grasslands, soils are dry and plants are dead, but microbial biomass increases, even though activity is limited. Additionally, pools of bioavailable C increase, which primes the system to produce a pulse of activity following rewetting. These changes appear to result from a combination of microbial drought survival physiology and disconnections in soil water films that limit substrate diffusion. A focus of the talk will be about how we bridge the scales from the micro- to the ecosystem. Current dominant carbon cycling models do a poor job of capturing drought and rewetting dynamics—how can we incorporate the dry-soil and pulse processes into large-scale models of soil carbon processes?


Dr. Joshua Schimel is a Professor in the Department of Ecology, Evolution, and Marine Biology at UC Santa Barbara. His research has focused on the intersection of microbial ecology and biogeochemistry, with emphases on N-dynamics in Arctic soils, and on the role of drought on soil organic matter dynamics, focusing on Mediterranean-climate ecosystems in California. This work has emphasized the linkages among soil mineralogy, organic matter chemistry, and soil microbial dynamics to understand how the physical, chemical, and biological components of soil interact. He is an Aldo Leopold Leadership Fellow, a Fellow in the Ecological Society of America and is a Chief Editor for Soil Biology & Biochemistry.

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