FS561 – Physiology of Woody Plants  Fall 2009

OBJECTIVES AND REFERENCES FOR October 20:

Water limitations; xylem dysfunction; stomatal regulation; a quick look at some other drought responses

Reading:  Chapters 11 and 12 of Pallardy's book - especially the sections in chap 11 on cavitation and vulnerability, and the sections in chapter 12 on regulation of transpiration and drought responses

Useful additional information:

Vogt, U.K. 2001. Hydraulic vulnerability, vessel refilling, and seasonal courses of stem water potential of Sorbus aucuparia L. and Sambucus nigra L. J. Exp. Bot. 52: 1527-1536.

Hubbard RM, V Stiller, MG Ryan and JS Sperry. 2001 Stomatal conductance and photosynthesis vary linearly with plant hydraulic conductance in ponderosa pine. Plant, Cell and Environment 24: 113-121.

Zwieniecki et al. 2001.  Hydrogel control of xylem hydraulic resistance in plants. 

Learning Objectives:

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

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

2. given information about water potential conditions in the soil and roots, stems and leaves of plants, determine whether hydraulic redistribution would be possible and explain your reasoning

3.  Describe the mechanisms by which drought and freezing conditions can produce xylem cavitation

4.  Describe what is meant by "runaway cavitation" and the role of stomata in limiting the risk of runaway cavitation

5.  For an isohydric species, describe the controls over transpiration over the course of a warm sunny day.  Explain how the course of daily transpiration would be different for an isohydric or a non-isohydric species.  Explain how isohydric behavior can a way to limit the risk of runaway cavitation. 

6.  Given a set of xylem vulnerability curves for isohydric species, be able to a) evaluate which are more likely to be representative of plants from mesic vs. xeric habitats, b) estimate (at least within a reasonable range) what the typical mid-day minimum water potential is likely to be from the characteristics of the vulnerability curve, c) describe ways that the xylem anatomy might vary (at least relatively) among the species represented by different vulnerability curves

7. Provide examples, with detailed explanations, of "tradeoffs" between drought tolerance characteristics and the potential for rapid growth.