Abstract
Abstract. By extracting bound water from the soil and lifting it to the canopy, root systems of vegetation perform work. Here we describe how root water uptake can be evaluated thermodynamically and demonstrate that this evaluation provides additional insights into the factors that impede root water uptake. We derive an expression that relates the energy export at the base of the root system to a sum of terms that reflect all fluxes and storage changes along the flow path in thermodynamic terms. We illustrate this thermodynamic formulation using an idealized setup of scenarios with a simple model. In these scenarios, we demonstrate why heterogeneity in soil water distribution and rooting properties affect the impediment of water flow even though the mean soil water content and rooting properties are the same across the scenarios. The effects of heterogeneity can clearly be identified in the thermodynamics of the system in terms of differences in dissipative losses and hydraulic energy, resulting in an earlier start of water limitation in the drying cycle. We conclude that this thermodynamic evaluation of root water uptake conveniently provides insights into the impediments of different processes along the entire flow path, which goes beyond resistances and also accounts for the role of heterogeneity in soil water distribution.
Highlights
Root water uptake is an important process, determining the transport of water between soil and atmosphere and influencing plant productivity and crop yield
In order to evaluate the efficiency of root water uptake and learning how plants may regulate it, we require some understanding of the impediment for water flow and how it is distributed along the soil–plant–atmosphere continuum, especially whether it lies within the plant or the soil compartment (Draye et al, 2010; Vadez et al, 2014)
We model a split-root experiment, where no water flow between compartments is possible and all changes in soil water content are due to root water uptake
Summary
Root water uptake is an important process, determining the transport of water between soil and atmosphere and influencing plant productivity and crop yield. Root water uptake depletes the soil reservoir, leading to more negative soil hydraulic potentials which need to be overcome in order to maintain the necessary gradient between soil and atmosphere to allow for flow Both processes (flow over a resistance network and increasing soil water retention) impede transpiration, but comparing their mutual contribution in form of resistances is not suitable, since the change of soil water retention per water removed has no proper resistance analogue. In this paper we show that additional information about the system can be obtained from a thermodynamic perspective, by combining the hydraulic potentials with mass fluxes, yielding fluxes of energy This approach has the advantage that different processes, such as the change of soil water potential with decreasing soil water content as well as the transport of water over a resistance, can be expressed in the same currency of energy fluxes and dissipation, with units of joules per second (J s−1). In order to illustrate how these fluxes can be interpreted to evaluate impediments to root water uptake and the role of soil water heterogeneity, we illustrate them in a simplified process model, which is a conceptual four-box model for root water uptake
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
