Monday, November 13, 2006 - 9:35 AM
81-2
Water Uptake and Hydraulics of the Root Hair Rhizosphere.
The importance of root function in water and nutrient transport is becoming increasingly clear, as constraints on resources are imposed due to water limitations and environmental concerns. However, the basic understanding of transport processes in the rhizosphere has been slow due to historical neglect of below-ground research and the fact that soil is non-transparent to many research tools. The conventional understanding of root hair function is that root hairs increase root surface area; thereby enhancing water and nutrient uptake. Yet, modeling soil water status in between root hairs shows that the soil water potential there reaches a value close to that of the root in a very short time. The corresponding low water content values within the inter root hair domain indicates limited mass water flow and ion diffusion rate towards the root. Consequently, we conclude that when the plant transpires (day time) root hairs do not increase water and nutrient uptake by increasing root surface area. Instead we will demonstrate by employing both MRI technology for measurements and analysis of spatial and dynamic changes in water content in the rhizosphere, analytical and numerical modeling that: i) Root hairs function mostly by water uptake through the root hair tip domain; ii) The growth of root hairs, perpendicular to the root surface, expands the effective absorbing diameter of the root, thereby increasing water uptake; iii) Dynamic root hair growth increases hydraulic head and thus water content, hydraulic conductivity and diffusivity at the soil root interface; iv) Growth of needle-shaped root hairs requires minimal investment in biomass with less mechanical resistance, as compared with alternative strategies that require larger root diameter or root length.
Recorded presentation