Modeling of Experimental Soil-Plant Root Interactions.

Generally, there is a lack of information on soil-plant root water processes as controlled by environmental conditions near the plant-root interface. Specifically, both natural and agricultural ecosystems often suffer from spatially-distributed environmental stresses (water, nutrient, salinity, temperature), and the plant/crop responses to such limiting factors are highly relevant for understanding their functioning and survival strategies. For example, adaptations of plants to climate warming affect biodiversity and invasive species distribution, and irrigated agriculture will be key in feeding the rising world population within the context of diminishing fresh water resources.   The presented root water and nutrient uptake model links soil physical principles with plant physiological concepts, crossing disciplinary boundaries as required for advancing the science for the broad and complex study of soil ecology.  The modeling approach will greatly improve scenario testing for soil-plant systems, by including plant uptake mechanisms such as compensated root water and active root nutrient uptake.

We present field and laboratory experimental data that are coupled with a multi-dimensional unsaturated water flow model to better integrate scientific principles. Laboratory experiments include presentation of selected innovative measurement techniques, providing highly spatial resolution data that characterize the response of spatially-distributed soil environmental stresses on plant growth.  Field experimental results include 3-dimensional soil water content and water potential data that are coupled with a multi-dimensional soil water flow model, to infer the functional form of a 3-dimensional root water uptake model, using inverse modeling. In addition,  an intensive field monitoring experiment in the Sierra Nevada Mountains is presented, illustrating experimental needs  for monitoring tree response to changing environmental conditions in natural ecosystems. To improve the mechanistic description of environmental stress on root water and nutrient uptake, we present a new modeling approach that allows for inclusion of compensated root water and nutrient uptake, and provides for differentiation between passive and active nutrient uptake.