DESERT WISDOM/AGAVES and CACTI:
CO2, Water, Climate Change
by
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Chapter 1. Current Uses of Agaves and Cacti
To hint at the multiple possibilities for the future uses of agaves and cacti that take into account climate change, we begin with their current uses. These range from food (for humans) to fiber to forage (where the animals search in the field) to fodder (where the material is brought to the animals) to fruits to fructose (for diabetics) to funny stuff (e.g., dyes, hormones, and hallucinogens) to fancy plants (ornamentals) to friendly beverages (from aguamiel to tequila). We start with the genus Agave, containing about 140 species. Agave is the largest genus in family Agavaceae, whose name is based on the Greek for “noble” (agauos) to recognize the group’s many ancient uses by humans. We then tackle the much larger family Cactaceae, containing about 1600 species. Cactus (family Cactaceae) comes from the Greek kaktos, referring to a spiny, thistle-like plant. These two taxa contain many remarkable plants.
Much of the optimism for the future of agaves and cacti rests with platyopuntias, a group of cacti in the genus Opuntia that has flattened stem segments referred to as cladodes (see Fig. 1-1). Beginning long ago, cladodes were detached from plants in the wild and placed in the ground near houses. Admirably, such planted hunks grew into tall plants in a few years. Anyone could have noticed their potential for fodder and food, as rodents, rabbits, wild pigs, and deer ate them voraciously despite the spines. As an added benefit, platyopuntias (or “opuntias,” for short) produce edible fruit.
Chapter 2. Advantages of Crassulacean Acid Metabolism.
The uniqueness of the “When” for CAM plants continues. The bound CO2 is released the next day within the plants when the sun comes up (or the lights go on in a house or in an environmental chamber for growing plants). This CO2 is then available to Rubisco (Fig. 2-1), which now performs photosynthesis in the light, as usual. The stomata of CAM plants are mostly closed during the daytime, which prevents the escape of the internally released CO2. Thus the spatial (cellular) separation between cells for the initial CO2 fixation and for the Rubisco in C4 plants is replaced by the temporal separation within the same cell in CAM plants (Fig. 2-1). The timing of this biochemistry has major consequences for the efficient use of water considered later in this chapter.
So far we have not explained the term CAM, other than to say it is an abbreviation for Crassulacean Acid Metabolism. The name comes from the fact that this pathway was observed and carefully studied in the family Crassulaceae, which contains the leaf succulent jade plants and sedums. What is the most famous CAM plant? The prize goes to Ananas comosus, pineapple! This bromeliad is enjoyed as a fruit worldwide and is cultivated on approximately 900,000 hectares (about 2,200,000 acres). Initial hints about the uniqueness of CAM were based upon the nocturnal stomatal opening, which, as we will see, is the most curious aspect of CAM and also the most important aspect for water conservation. Also, the tissue acidity of CAM plants increases at night, which accounts for “Acid Metabolism.” Now we know the reason for the acronym “CAM.”
Chapter 4. Issues of Global Climate Change
What if you were to offer a banker more money? Or to offer an athlete more food? Or a plant more CO2? All would say, “Yes, I’d like that!” In this regard, Equation 2.1 indicates that atmospheric CO2 is fixed in plants by the process of photosynthesis. The higher the atmospheric CO2 level, the higher is the rate of photosynthesis, at least up to a point. Plants have coped with various atmospheric CO2 levels over geologic time. But the advent of increased release of CO2 into the atmosphere since the beginning of the Industrial Revolution has been good news for them as far as photosynthesis and productivity are concerned. Actually, the news varies with the photosynthetic pathway utilized, as we consider next.
Yet the plausible increase in photosynthetic rates by providing more CO2 is only part of the good news for plants. If a higher concentration of CO2 is present in the atmosphere, then the stomata do not have to open as much to let sufficient CO2 to diffuse into the leaves and the stems to support the ongoing rates of photosynthesis. If the stomata do not open as much, less water is lost by transpiration, which raises the Water-Use Efficiency (WUE, Equation 2-3). Thus increased atmospheric CO2 levels are a win-win situation for the WUE of plants, as the amount of CO2 fixed by photosynthesis increases and the amount of water lost by transpiration decreases.
Chapter 7. Future Utilization of Agaves and Cacti.
Many of the future uses of agaves and cacti in new areas involve expansions of their utilization for fodder (Chapter 1). Fodder production already involves the most land area for all commercial CAM plants and is crucial for raising cattle, sheep, and goats in many regions worldwide. These animals can thrive on the cladodes of Opunia ficus-indica and other platyopuntias. … As we consider various areas for future cultivation of agaves and cacti, another question is how global climate change will increase the minimum temperatures, thereby opening up new opportunities for cultivation. For convenience, we will often refer to frost-free regions, but O. ficus-indica can withstand temperatures of −10°C (14°F), as discussed in Chapter 3. In any case, freezing temperatures are a real limitation to extending the cultivation of CAM plants, but breeding and biotechnology hold great promise for improving their low-temperature tolerance in the future (Chapman et al., 2002; Nobel et al., 2002; Felker et al., 2009)..
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About the Book
Agaves and cacti thrive under the higher temperatures, variable rainfall, and increased CO2 characteristic of global climate change. Moreover, their remarkable biomass productivity promises multitudinous new uses in addition to current uses ranging from tequila to delicious fruits to fodder consumed by animals worldwide. The book also discusses the water conserving ability of agaves and cacti based on nocturnal opening of stomata and hence nocturnal uptake of carbon dioxide, a photosynthetic pathway referred to as Crassulacean Acid Metabolism.
About the Topics
Although widely differing taxonomically, agaves and cacti are remarkably similar physiologically. Both conserve water and produce well in arid and semi-arid regions. Both can cope with climate change, including increasing atmospheric CO2 levels, increasing temperatures, and changing rainfall patterns. Indeed, they are ideal plants for the future—the best is yet to come!
About the Book
DESERT WISDOM/AGAVES and CACTI: CO2, Water, Climate Change delivers crucial scientific information on Crassulacean Acid Metabolism (Chapter 2), plant tolerances (Chapter 3), and crop improvements using an Environmental Productivity Index (Chapters 5 and 6). A reader can also focus on the uses of agaves and cacti (Chapter 1), climate change implications (Chapter 4), and bright ideas for coping with future climates (Chapter 7). Cross-referencing, a Glossary, and References for further reading enhance its utility for everyone.
About the Author
The world’s leading authority on the environmental biology of agaves and cacti, Park S. Nobel has published more than 300 scientific articles and four other books on these plants: The Cactus Primer (with A.C. Gibson), Harvard University Press, 1986; Environmental Biology of Agaves and Cacti, Cambridge University Press, 1988; Remarkable Agaves and Cacti, Oxford University Press, 1994; and Cacti: Biology and Uses (as editor), University of California Press, 2002..
About the Author
My scientific career began with a Bachelor’s of Engineering Physics from Cornell University in 1961. Entering graduate school at the California Institute of Technology, my interests ranged from solid state physics to astrophysics to biophysics. After a Masters Degree, I transferred to the University of California, Berkeley, to pursue a Ph.D. in Biophysics, which I received in 1965. My research at that time focused on chloroplasts, the subcellular organelle responsible for photosynthesis. After a National Science Foundation Postdoctoral year at the University of Tokyo followed by another year at King’s College of the University of London, I settled into the University of California, Los Angeles. I have been there ever since (currently as a Distinguished Professor of Biology Emeritus in the Department of Ecology and Evolutionary Biology). Website:
A pivotal switch in career occurred during a Guggenheim Fellowship at the Research School of Biological Sciences, Australian National University, Canberra in 1973/74. Stimulated by questions from students in a plant ecophysiology course, I moved toward environmental research on air boundary layers for rigid structures that did not flap in the wind. What better specimens than agaves and cacti of deserts! What began as a study of heat transfer across their air boundary layers progressed to everything entering or leaving such plants. Indeed, modeling and computer studies soon involved questions dealing with how desert plants cope with their extreme environment. Using agaves and cacti as taxa of interest, I thus shifted toward ecology, including responses of the roots. Also, I transferred approaches based on physics and engineering to plants with agronomic importance, such as Agave tequilana of tequila fame and various cacti cultivated for fruits and fodder in many regions of the world.
Besides nearly 400 research articles, I have written or edited 15 books. Beginning in 1970, I published a book entitled Plant Cell Physiology: A Physicochemical Approach (W.H. Freeman). As I became more interested in environmental biology, the scope broadened to include whole plants and plant communities. The seventh book in this series is Physicochemical and Environmental Plant Physiology, 4th ed., published in 2009 by Academic Press/Elsevier. I am also engaged in a series of books on agaves and cacti. The first was The Cactus Primer with Arthur Gibson as senior author (Harvard University Press, 1986, reissued in 2009), followed soon by Environmental Biology of Agaves and Cacti (Cambridge University Press, 1988, reissued in 2003). Next came Remarkable Agaves and Cacti (Oxford University Press, 1994) and then the edited book Cacti: Biology and Uses (University of California Press, 2002). Recently I completed a book entitled “DESERT WISDOM/Agaves and Cacti: CO2, Water, Climate Change” as indicated here.