FS561 – Physiology of Woody Plants  Fall 2009

OBJECTIVES AND REFERENCES FOR OCTOBER 13:

Reading - Chapters 11 and12 of Pallardy's book, especially pp. 294-313 and 325-329

Useful additional information:

Tyree.  1997.  The cohesion tension theory of sap ascent:  current controversies

Bond, Meinzer and Brooks. 2007.  How trees influence the hydrologic cycle in forest ecosystems

Richter, A brief history of hte study of water movement in xylem. 

Cruiziat, The cohesion-tension theory at work. 

Koch, How water climbs up to the top of a 112-m tall tree

Learning Objectives:

After this lecture and any supplementary reading you find necessary, you should be able to:

1.  Describe the cohesion tension theory (why are cohesion and tension essential elements of this theory?); explain how the physical characteristics of water and anatomical characteristics of a plant are relevant to the theory.  To "demonstrate thorough understanding" you might be asked to predict how tree height or growth rates or water flux would change in different scenarios (for example, supposing the tensile strength of water were not as great). 

2.  Explain the Ohm’s Law Analogue for the relationship between conductance and resistance.  If given one (i.e., resistance or conductance), you should be able to calculate the other.

3.       Describe both qualitatively and quantitatively (using the Hagen-Poiseuille equation) how the anatomy of wood affects the flow of water through that wood.  Be able to predict quantitatively and qualitatively how changes in wood structure might affect the flow of water through the wood, and the consequences this might have for transpiration rates, and ultimately the photosynthetic rates, of leaves that are "downstream". 

4.       Define 'SPAC' and discuss the ‘SPAC’ in terms of water potential gradients and be able to evaluate the direction that water will flow by mass flow, diffusion or osmosis if given the components of water potential in different plant parts.

5.   Define and appropriately use these terms (to the level of detail that is covered in lecture): isohydric, anisohydric, conductance

6.  Explain why the "leaf to air vapor pressure gradient" is the same as the atmospheric "vapor pressure deficit" as long as leaf temperature is equal to air temperature

7.  Predict how transpiration will change over time as VPD and leaf water potential change for isohydric and anisohydric species.

8.  Given a figure that shows relationships between leaf conductance and VPD for various species, determine which species have high or low hydraulic conductance.  Be able to explain the adaptive significance of these differences, and their likely correspondence with growth rates and photosynthetic capacity.