Monday, August 3, 2009 - 2:10 PM

OOS 3-3: Hydraulic redistribution and the fate of root-derived carbon in soil

Zoe G. Cardon, Marine Biological Laboratory, John M. Stark, Utah State University, and Patrick M. Herron, Rowland Institute at Harvard.


Hydraulic redistribution of water in the soil column occurs via roots of deep-rooted plants in a variety of ecosystems, most often at night.  This passive redistribution of water in the soil column from regions of wetter soil, through roots, to regions of drier soil can be facilitated by a number of plant species. Its importance has been explored in the contexts of enhanced transpiration rates that can be sustained next day, transport of rainwater from surface to deep soil layers, and calculation of surface energy budgets and runoff estimates at landscape scales.  Hydraulic redistribution likely also strongly affects localized nutrient cycling rates in the rhizosphere, decomposition of root-derived residues, and thus, potentially, soil organic matter dynamics.  We will discuss soil water potential data gathered during 2007 using thermocouple psychrometers at multiple soil depths  in a sagebrush-dominated, semi-arid landscape on BLM land near Laketown, Utah.  We have combined these empirical data with a mathematical model (built on a foundation described by Ryel et al. 2002, Oecologia) in order to explore sources and sinks of water in soil columns hosting the deep root systems of sagebrush.


We show that in the Laketown, Utah system, the rainstorm-associated, rapid excursions in water potentials observed at mid-depth in soils are likely the result both of redistribution of rainfall and redistribution of deep soil water facilitated by reduced sagebrush transpiration during the rain event. Since hydraulic redistribution is via plant roots, seasonal and shorter-term dynamic soil water availability is concentrated around living root systems that are contributing exudates, secretions, sloughed cells, and even entire fine roots to rhizosphere soil.  We will consider the implications of that dynamic soil water availability for the fate of root-derived carbon and rhizosphere soil organic matter.