Current capabilities and future needs of root water and nutrient uptake modeling

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The importance of root function in water and nutrient transport is becoming increasingly clear, as constraints on agricultural resources are imposed due to water limitations and environmental concerns. Both are driven by the increasing need to expand global food production. However, the historical neglect of consideration of water and nutrient uptake processes below ground has created a knowledge gap concerning the plant responses of nutrient and water limitations to crop production. The review includes sections on (i) notation and definitions of water potential, (ii) the physical coupling of plant transpiration and plant assimilation by way of the principles of diffusion of water vapor and carbon dioxide, (iii) apoplastic and symplastic water and nutrient pathways in plants, (iv) active and passive nutrient uptake, and (v) a discussion of the current state-of-the-art in multidimensional soil water flow and chemical transport modeling. The subsequent review of water uptake, nutrient uptake, and simultaneous water and nutrient uptake addresses shortcomings of current theory and modeling concepts. The review concludes with an example illustrating a possible multidimensional approach for simultaneous water and nutrient uptake modeling. Specific recommendations identify the need for coupling water and nutrient transport and uptake, including salinity effects on root water uptake and the provision of simultaneous passive and active nutrient uptake. It considers the requirement for multidimensional dedicated root water and nutrient uptake experiments to validate and calibrate hypothesized coupled root uptake models.