Solute Movement in the Rhizosphere

Abstract

This is a completely revised edition of the previously titled Solute Movement in the Soil-Root System. It describes in detail how plant nutrients and other solutes move in the soil in response to plant uptake, and it provides a basis for understanding processes in the root zone so that they can be modeled realistically in order to predict the effects of variations in natural conditions or our own practices.

Nitrogen regulation of transpiration controls mass-flow acquisition of nutrients

“…8 ). The decline in total biomass with increasing distance from the N source also implies decreasing mass-flow delivery of N. This is consistent with the fact that water flux density at distance ( d ) from the root axis must be proportional to 1/ d 2 ( Tinker and Nye, 2000 ). Despite the gradual N limitation of biomass accumulation with distance from the N source, shoot:root ratios did not vary significantly, suggesting that these plants adjusted their transpiration more than allocation to root biomass for N uptake.…”

“…water use efficiency (WUE); Hack et al , 2006 ] as well as evidence for substantial night-time transpiration in photosynthetically inactive C 3 and C 4 plants ( Caird et al , 2007 ; Kupper et al , 2012 ) suggest that transpiration plays an important functional role in plants. Apart from facilitating leaf cooling ( Parkhurst and Loucks, 1972 ; Nobel, 1999 ) and root to shoot solute transport ( Tanner and Beevers, 1990 , 2001 ), transpiration also powers the movement of water and dissolved nutrients to root surfaces by mass-flow ( Barber, 1995 ; Tinker and Nye, 2000 ; Cramer et al , 2008 ; Cramer and Hawkins, 2009 ), reducing rhizosphere nutrient depletion resulting from active nutrient uptake ( Scholz et al , 2007 ; Kupper et al , 2012 ).…”

Modeling Root Exudate Accumulation Gradients to Estimate Net Exudation Rates by Peatland Soil Depth

“…Aside from the concentration difference, the rate of flux depends upon the solute specific diffusion coefficient, whose values are available in the literature based on empirically measured diffusion in pure water. Solute transport along the inner boundary between two soil cylinders is given by Fick’s Law [ 52 ] as: where is the concentration gradient for solute between soil cylinders and the solute concentration at radius in the adjacent soil cylinder, and is the effective diffusion coefficient for solute in soil layer . Diffusion coefficients for the movement of individual solutes in pure water are modified due to the introduction of a solid phase which reduces the liquid phase space to conducts water [ 53 ] and slows the rate of diffusion since the diffusion pathway elongates from a straight line based on the morphology of the pore space in three dimensions [ 54 ].…”

Agronomic and physiological aspects of nitrogen use efficiency in conventional and organic cereal-based production systems

“…These metabolic pathways are controlled by complex genomic and consequent physiological steps in association with environmental factors that result in phenotypic characteristics. While N availability is mostly determined by environmental conditions and agronomic practices, the quantity of N intake into the root cytoplasm is regulated by passive and active uptake mechanisms controlled by several plant genes (Schenk, 1996; Tinker and Nye, 2000). Passive absorption usually refers to mass flow and diffusion, occurring along transpiration and energy gradients, respectively (Havlin et al, 2014).…”