11: Transpiration and Root Water Uptake
- Page ID
- 38742
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)In the previous chapter we focused on the process of evaporation, which is the first process we have considered in connection with the energy balance at the land surface. We noted that evaporation, as we define it, is distinct from transpiration, which is the vaporization of water from the interior of plants, predominantly exiting through the stomata. In this chapter we will focus on transpiration and the related process of root water uptake. Like evaporation, transpiration is a process that links together the soil water balance and the surface energy balance. First, let's start with an audio overview for the topics in this chapter [website]
- 11.1: Soil-plant-atmosphere continuum
- We need to understand transpiration and root water uptake within the context of the soil-plant-atmosphere continuum, the continuous pathway by which water moves from the soil, through plants, to the atmosphere. Water moves along this pathway in response to the typically large difference in water potential between the soil and the atmosphere. As a result the water potential difference driving transpiration was reduced by ~50%and the cumulative transpiration of the tomato plants being grown in the
- 11.2: Water status of plants
- This exodus of water vapor from the plant through transpiration must be balanced by root water uptake in order for the plant to maintain a healthy water status. When the rate of transpiration exceeds the rate of root water uptake, then the water stored in the plant tissues begins to be depleted, and the plant begins to shrink or wilt. If this depletion is prolonged, the water potential inside the plant also decreases and the plant reduces the size...
- 11.3: Root water uptake
- The rate of root water uptake can be limited by either the hydraulic conductivity of the rhizosphere soil, i.e. the soil immediately adjacent to the roots, or by the water potential gradient between the soil and the roots. The traditional conceptual model of root water uptake held that root water uptake lowered the water content of the rhizosphere soil, which increased the hydraulic gradient between the rhizosphere soil.
- 11.4: Transpiration and soil water
- Since we cannot easily monitor the water status of the rhizosphere soil itself, for practical purposes, we often seek to understand and manage the relationship between transpiration and the bulk soil water. Several of the main features of that relationship are reflected in the data shown in Fig. 11‑4, which is taken from a classic study on transpiration rates of corn [3].
- 11.5: Soil water availability indicators
- The specific soil water content at which the relative transpiration rate begins to decline depends, not only on the evaporative demand (and on the plant species), but also on the soil water retention characteristics. Therefore, when considering transpiration and plant water use, we often adjust or normalize the soil water content values to account for some of the soil specific differences.
- 11.6: Water use efficiency
- the process of transpiration is inextricably linked to the process of carbon assimilation through photosynthesis. Thus, transpiration is a critical link between three of the Earth’s most important cycles or balances, the soil water balance, the surface energy balance, and the atmospheric carbon balance. A great deal of research attention and even public interest has been focused on one aspect of that linkage—the water use efficiency of plants.
- 11.7: Problem set
- Imagine you are responsible for scheduling irrigation for a corn crop. Your management goal it to keep the corn well-watered so that the evapotranspiration from the field is equal to the reference (or potential) evapotranspiration rate. Create a spreadsheet to perform a simple daily soil water balance for the field to determine the number of irrigation events and total irrigation amount required in the 120-d growing season assuming:
- 11.8: References
- Krueger, E.S., et al., Soil Moisture Affects Growing-Season Wildfire Size in the Southern Great Plains. Soil Science Society of America Journal, 2015. 79(6): p. 1567-1576. Sinclair, T.R., C.B. Tanner, and J.M. Bennet, Water-Use Efficiency in Crop Production. BioScience 1984. 34: p. 36-40. Keenan, T.F., et al., Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise. Nature, 2013. 499(7458): p. 324-327.