Tunnell John W (14)
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Introduction

Tunnell, John W. Texas A&M University Press ePub

JOHN W. TUNNELL JR.

Coral reefs are among the most biologically diverse, productive, and complex ecosystems on earth. They are economically important as sources of food and medicinal products and they protect fragile shorelines from storm damage and erosion. Coral reefs are a source of cultural value and great natural beauty, and they provide vast revenues in tourism dollars. However, since the late 1970s and early 1980s, people around the world have become increasingly concerned about the degradation and loss of this ecologically and economically valuable marine habitat. Coral reefs are being destroyed at an alarming rate in the Gulf of Mexico and throughout the world. The latest report on the status of coral reefs of the world indicates that “coral reefs are probably the most endangered marine ecosystem on Earth” (Wilkinson 2004). According to the Global Coral Reef Monitoring Network (Wilkinson 2004), the world has lost an estimated 20% of coral reefs. It predicts that 24% of the world’s reefs are under imminent risk of collapse from human pressures, and another 26% are under a longer-term threat of collapse.

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Chapter 10 Reef Fisheries

Tunnell, John W. Texas A&M University Press ePub

CARL R. BEAVER AND ERNESTO A. CHÁVEZ

From the Laguna Madre de Tamaulipas, south through the Bay of Campeche to the reefs and on the outer continental shelf of the Yucatán Peninsula, reef fishes are an economically and ecologically important resource. More than 100 species of reef fish are closely associated with coral reefs and other types of hard bottom habitats in the Gulf of Mexico. Maintenance of healthy reef-fish populations is important to the economic and ecological health of the region. Reef fish are important to different interest groups for a multitude of reasons. Reef-fish user groups have commercial, artisanal, recreational, and scientific interests. Important nonconsumptive uses for reef fishes, such as tourism, sport diving, education, and scientific study, can conflict with traditional consumptive uses such as commercial and subsistence fisheries.

Fishes provide significant ecological benefits to the reef system as well. Reef fishes have evolved numerous symbiotic relationships with other reef denizens, creating highly complex trophic structures that contribute to the ecological balance and diversity of reefs. Unfortunately, overfishing is a major concern for many reef-fish populations. Consequently, fishing may be one of the most important activities contributing to degradation of coral reefs in the southern Gulf of Mexico.

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Chapter 8 Reef Corals

Tunnell, John W. Texas A&M University Press ePub

GUILLERMO HORTA-PUGA, JUAN MANUEL VARGASHERNÁNDEZ, AND JUAN PABLO CARRICART-GANIVET

Editors’ note—Coral reef zonation is discussed in chapter 5 and soft and hard coral biodiversity is discussed in chapter 6.

Recent distribution of the shallow-water zooxanthellate Scleractinia extends to the greater Indo-Pacific (Pacific and Indian Oceans, Red Sea, and Persian Gulf) and the Atlantic, including the Gulf of Mexico. The greater Indo-Pacific is the most prominent and diverse biogeographic province; the Atlantic is far inferior to the greater Pacific in all aspects of species richness (Wells 1956, 1957; Stehli and Wells 1971; Veron 1995, 2000). During the Cenozoic, the Atlantic Province was physically and genetically connected with the eastern Pacific, sharing numerous coral species. However, by the Pliocene, the Central American Isthmus formed a barrier and separated the two ocean provinces, accelerating local extinction processes that have promoted substantial taxonomic differences between them. The Indo-Pacific is now by far the most diverse in terms of species, genera, and families of reef-building corals, with >700 species. This level of scleractinian diversity arose in a complex, geographically large, and highly heterogeneous environment, isolated from continental land masses that protected the region from the effects of multiple glacial periods. This produced, along with the reticulated evolution, a suite of suitable conditions for the appearance of numerous species since the end of the Mesozoic. The reef fauna that survived in the Atlantic, which is mainly composed of long-lived genera derived from the Tethys fauna, is less diverse today (Veron 1995).

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Chapter 7 Reef Algae

Tunnell, John W. Texas A&M University Press ePub

ROY L. LEHMAN

Coral reef algal communities include the zooxanthellae, symbiotic algae in the gastrodermis of the hermatypic (reef-building) corals, free-living, encrusting coralline algae, phytoplankton, mat-forming and boring micro-filamentous algae, and calcified, fleshy, and turf macroalgae. Coral reefs should probably be called tropical reefs, biotic reefs, or even algal reefs. Corals cannot build a reef single-handedly; algae contribute greatly to reef productivity and growth. Nutrients supplied to hermatypic corals by zooxanthellae allow them to grow and reproduce quickly enough to form reefs. Coralline algae contribute greatly to reef biomass, may deposit more calcium carbonate than the corals themselves (Littler and Littler 1984) and are the cement that holds the reef together. Reefs are formed as much by the accumulation of calcareous sediment as by the growth of corals. The spaces formed by coral fragments and large rubble fill with fine and coarse carbonate sediment. Encrusting calcareous algae grow over the sediment, cementing it into place. These algal reef builders also prevent erosion of the reef by waves by consolidating and cementing the substrate together. The stony substrate that is formed is tough enough to withstand waves that can destroy even the hardiest of corals.

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Chapter 11 Island Biota

Tunnell, John W. Texas A&M University Press ePub

JOHN W. TUNNELL JR.

There are 25 islands associated with the 38 emergent reef platforms in the southern Gulf of Mexico (Table 11.1; see Figs. 2.2–2.9 for maps). The most conspicuous biota are island vegetation and birds, both seasonal migrants and nesting seabirds. Less conspicuous are the terrestrial or land crabs, insects, lizards, and nesting sea turtles. Most islands are low sandy cays, or they are mostly sand with some coral rubble and coral ramparts (rocks). A few small islands are composed of coral rubble only (mainly staghorn coral, Acropora cervicornis). Eight islands have “manned” lighthouses (Plates 7, 20b, 20c, 22d, 24, 25a, 49) that were first established in the late 1800s to early 1900s. Although there are no comprehensive geological papers collectively on the southern Gulf of Mexico coral reef islands, several detailed papers by Robert L. Folk and colleagues provide extensive information on sediment origin and composition, as well as morphology of the sand cays of Alacrán Reef (Folk 1962, 1967; Folk and Robles 1964; Folk and Cotera 1971).

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Timothy E Fulbright (12)
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Appendix 2. Metric–English System Unit Equivalents

Timothy E. Fulbright Texas A&M University Press ePub
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5. The Cow: Livestock and White-Tailed Deer Habitat

Timothy E. Fulbright Texas A&M University Press ePub

5

The Cow: Livestock and White-Tailed Deer Habitat

KEY CONCEPTS

▼ Cattle grazing can reduce grass cover and increase forbs in productive plant communities dominated by mid- to tall grasses, but whether or not the increase in forbs may result in improved deer nutritional status or productivity is unclear.

▼ Cattle grazing during winter may reduce forage available to deer, even at moderate stocking rates.

▼ As a general rule, rangelands dominated by native vegetation and grazed by domestic livestock should be managed so that livestock consume 25 percent or less of annual production of herbaceous vegetation to avoid degradation of white-tailed deer habitat and to minimize diet overlap between livestock and deer.

▼ Introduction of exotic deer species is a threat to white-tailed deer populations because exotics are highly competitive with white-tailed deer and can potentially displace them.

Livestock Grazing and Deer

Most rangelands are grazed by domestic animals, although in recent years livestock have been removed on some private ranches in Texas. About 20 percent of respondents in a recent survey of landowners and hunting lessees in South Texas said livestock have not grazed their lease or ranch in the past three years (Bryant, Ortega-S., and Synatzske, n.d.). Contrasting viewpoints exist among natural resources managers in regard to cattle grazing and white-tailed deer. Aldo Leopold (1933) espoused the view that cattle can be used as a tool to improve deer habitat, although he cautioned that livestock grazing can also destroy habitat. Another, similar view is that cattle grazing and deer are complementary and grazing the two together is more efficient use of rangeland. A third view is that livestock grazing is simply destructive to wildlife habitat. An overall goal of this chapter is to present what is known from the scientific literature regarding livestock grazing and white-tailed deer and allow readers to follow the chain of evidence to develop, change, or reinforce their own view on the topic. Our interpretation of the relevant literature is that production of livestock and of white-tailed deer are compatible land uses only when numbers of each are properly adjusted based on available forage. We focus on seven aspects of livestock grazing in this chapter: (1) diet overlap between deer and livestock; (2) effects of livestock grazing on plant communities; (3) social interactions between deer and livestock; (4) grazing systems and deer; (5) calculation of correct cattle stocking rates to benefit deer habitat; (6) livestock water developments, such as earthen stock ponds, and fencing; and (7) effects of grazing on predation on deer. The effect of exotic ungulates on white-tailed deer is a topic related to livestock grazing. Continued introduction and increase of exotic deer and other ungulates may negatively impact white-tailed deer populations.

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4. Estimating Carrying Capacity

Timothy E. Fulbright Texas A&M University Press ePub

4

Estimating Carrying Capacity

KEY CONCEPTS

▼ Carrying capacity is the number of animals per unit area that a habitat can support without degrading forage and other resources.

▼ The number of animals the habitat can support changes continually in time and space depending on availability of food, water, cover, and usable space.

▼ Nutritional-based estimates of carrying capacity should incorporate nutrient needs of free-ranging animals and production needs such as lactation, account for effects of antinutrition factors such as tannins, and include adjustments for habitat preferences.

▼ Forage- or nutritional-based models to estimate carrying capacity may provide values useful as a guideline for management, but values should be regarded as ballpark estimates and may be inaccurate. Management decisions regarding whether deer numbers exceed carrying capacity of the habitat are best made by monitoring level of utilization of important, or key, deer forages.

Carrying Capacity Defined

White-tailed deer population densities vary geographically. The Edwards Plateau region of Texas supports higher densities of white-tailed deer than any other rangeland area in the United States, with greater than 45 deer/km2 (see fig. 1.2; Quality Deer Management Association 2008). In contrast, much of the Great Plains region from Canada south to the Texas Rolling Plains supports fewer than 15 deer/km2. Deer densities in the Great Plains may be locally greater along riparian corridors and other wooded areas such as shelterbelts. Much of the Cross Timbers and Prairies and South Texas Plains supports 15 to 30 deer/km2. Although white-tailed deer were almost extinct by the 1970s because of poaching, habitat destruction, and screwworm infestation, an estimated white-tailed deer population density of 10 to 20 deer/km2 exists in northeastern Mexico (Villarreal G. 1999). These regional differences in deer densities result in part from regional differences in hunting pressure, geographic variation in human population densities, and numerous other factors, many of which may be beyond the control of wildlife managers. Carrying capacity can be enhanced and maintained by habitat management. Proper wildlife habitat management is based on the concept of carrying capacity and an understanding of the limitations of the concept. One of the limitations is that carrying capacity is conceptual rather than an absolute value.

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Appendix 3. Determining Adequate Sample Sizes

Timothy E. Fulbright Texas A&M University Press ePub

Appendix 3

Determining Adequate Sample Sizes

Sample size can be determined by iteration using the following equation (Zar 1996, 107):

n = (t2 × S2) ÷ d2 = (t × S ÷ d)2

In this equation, n is the estimated sample size; t is Student’s t with n – 1 degrees of freedom for a particular alpha; S is an estimated standard deviation (may be the sample standard deviation of an initial sample); and d is the half width of the desired (1 – alpha) 100 percent confidence interval.

If you are estimating biomass of vegetation and desire to estimate the true population mean with a 95 percent confidence interval no wider than 200 kg/ha, then d in the equation would be 100 kg/ha, and the t-value for α = 0.05 would be used for t. If the objective is to obtain an adequate sample that will detect a 10 percent change in vegetation parameters, such as biomass or cover, from one sampling period to the next, ()2 can be used for d, where x k = 0.10 and is the mean of the presample values (Bonham 1989).

Example: A researcher wants to determine carrying capacity of a ranch for white-tailed deer. The researcher obtains an initial sample consisting of twenty 1 m2 sampling frames in which the standing crop of forbs and browse are clipped, oven dried, and weighed. The mean weight is 1,000 kg/ha, and the sample standard deviation is 800 kg/ha. The researcher desires a 90 percent confidence interval with width of 200 kg/ha to estimate the population mean. The following is the initial equation to obtain an estimate of the adequate sample size:

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8. The Gun: Harvest and Management Planning

Timothy E. Fulbright Texas A&M University Press ePub

8

The Gun: Harvest and Management Planning

KEY CONCEPTS

▼ Maintaining deer populations within the carrying capacity of the habitat should be the primary goal of harvest management.

▼ Management decisions regarding whether deer numbers exceed or are below carrying capacity of the habitat are best made by monitoring utilization of key deer forages and monitoring trends in deer body mass, antler development, and fawn survival.

▼ Establishment of a management goal is important, whether managing for trophy males or for maximum-sustainable-yield harvest.

▼ Developing a sound management plan and keeping records of the number, age, sex, body mass, and antler dimensions of harvested deer are important aids in meeting management objectives.

Harvest as a Habitat Management Tool

Aldo Leopold (1933) asserted that game can be “restored” by hunting. Our primary emphasis in this chapter is use of hunting as a tool to maintain deer densities within carrying capacity of the habitat. Maintaining deer populations within carrying capacity allows the most preferred plant species in the habitat to reproduce, affords maximum protection to other resources, and benefits all organisms in an ecosystem. We recommend managing populations based on our forage-based definition of carrying capacity, which results in densities lower than K-carrying capacity, commonly used as the basis for modeling deer population growth and harvest management. Much of the theory underlying harvest management, including the concepts of density dependence, density independence, and compensatory mortality, is based on K-carrying capacity.

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Szaky Tom (10)
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Contents

Szaky, Tom Berrett-Koehler Publishers ePub
Medium 9781626560246

Chapter 9 The Economics of Outsmarting Waste

Szaky, Tom Berrett-Koehler Publishers ePub

Chapter 9

© TerraCycle

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The main reason why waste is sent to landfills and incinerators and why few of our outputs are recycled (like they technically can be) is all tied up in the economics of waste. It is simply more expensive to collect and recycle most things than the results are worth, and it’s cheap—because we allow it to be cheap—to send waste to a landfill or an incinerator.

Because our world is so economically motivated, perhaps we can make outsmarting waste more attractive by speaking the language of economics. There are hidden economic benefits of investing in the process of outsmarting waste on several different levels. Like the whole of outsmarting waste, these benefits can begin with you at home.

Although outsmarting waste may require an investment of your time, every aspect should save you money. If you don’t buy unnecessary items, you can save money for something more important. Packaged processed food tends to be more expensive then unpackaged fresh foods. Durable products, even though they may cost more initially, will last longer than disposables and should save you money over the long term. Buying used instead of new will also leave a few extra bucks in your pocket.

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Chapter 4 The Energy Inherent in Our Waste

Szaky, Tom Berrett-Koehler Publishers ePub

Chapter 4

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From newspapers to hot dogs, all objects have an inherent amount of energy—their “caloric value.” Simply put, caloric value is the amount of energy that is released when a particular thing is burned. Some objects burn at a positive caloric value, including candles, cigarettes, or basically anything that will continue to burn after you put a lighter to it to get it going. This can easily be calculated in a laboratory by measuring the amount of heat that the object releases per gram and subtracting the amount of energy that was used to get the burn going. Objects with a negative caloric value, on the other hand, consume more energy than they produce in the process of burning.

Calories from items with a positive caloric value are exactly the same type that we try to avoid when we go on our annual New Year’s diet. In other words, if you took sugary, buttery, oil-drenched, icing- and sprinkle-topped doughnuts (yum), they would burn much better (giving you more calories) than things like asparagus, celery, apples, and other foods with a negative caloric value.

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Chapter 3 Our Primary Global Solution to Waste: Bury It

Szaky, Tom Berrett-Koehler Publishers ePub

Chapter 3

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When I was a child, I had a pet rabbit that lived in a large cage on our apartment balcony. Every day I would feed her the vegetable peelings from our kitchen; she would happily eat them, later pooping out whatever her body didn’t use as spherical, pearl-like droppings in one corner of her cage. She would spend the rest of her time hanging out, dreaming perhaps about nice boy rabbits, in another corner of the cage. I never once saw her venture near the “poop corner” unless she had some specific business to do. Come to think of it, if I were that rabbit, I probably wouldn’t either.

The desire to be as far away from one’s own waste as possible seems to be hardwired in us. Landfills constantly face NIMBY (“not in my backyard”) challenges when getting zoned, and property values are lower near sewage treatment facilities, landfills, and composting sites. People simply don’t like hanging out near waste. Perhaps that is one of the reasons why we invented the toilet. If you deconstruct what a toilet is, beyond being a nice ceramic seat, it’s a device whose purpose is to move our waste far away from us as fast as mechanically possible.

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Chapter 1 Where the Modern Idea of Garbage Originated

Szaky, Tom Berrett-Koehler Publishers ePub

Chapter 1

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Human refuse—“garbage”—is a modern idea that arose out of our desire to chronically consume stuff that is made from ever more complex, man-made materials.

To outsmart waste we need to eliminate the very idea of waste; to do so we need to understand where the concept of waste came from and what factors brought about its existence.

Why is it that garbage exists in the human system but not more broadly in nature? Nature is a beautiful harmony of systems whereby every system’s output is a useful input for other systems. An acorn that falls from a tree is an important input for a squirrel that eats it. The by-product of that delicious meal—the squirrel’s poop—is an important input for the microbes that consume it. The output of the microbes—rich humus and soil—is in turn the very material from which a new oak tree may grow. Even the carbon dioxide that the squirrel exhales is what that tree may inhale. This cycle is the fundamental reason why life has thrived on our planet for millions of years. It’s like the Ouroboros—the ancient symbol depicting a serpent eating its own tail; in a way, nature truly is a constant cycle of consuming itself.

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Steven Higgs (4)
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Part 3 Destinations

Steven Higgs Indiana University Press ePub

1.Wabashiki Fish & Wildlife Area

2.Chinook Fish & Wildlife Area

3.Fairbanks Landing Fish & Wildlife Area

4.Shakamak State Park / Shakamak Prairie Nature Preserve

5.Minnehaha Fish & Wildlife Area

6.Hillenbrand Fish & Wildlife Area

7.Greene-Sullivan State Forest

8.Goose Pond Fish & Wildlife Area

9.Glendale Fish & Wildlife Area

10.Harmonie State Park / Wabash Border and Harmonie Hills Nature Preserves

11.Lincoln State Park / (Sarah) Lincoln Woods Nature Preserve

12.Thousand Acre Woods Nature Preserve

13.Saunders Woods Nature Preserve

14.Patoka River National Wildlife Refuge

15.Columbia Mine Preserve

16.Pike State Forest

17.Wabash Lowlands Nature Preserve

18.Section Six Flatwoods Nature Preserve

19.Twin Swamps Nature Preserve

20.Hovey Lake Fish & Wildlife Area

21.Goose Pond Cypress Slough Nature Preserve

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Part 2 The Southern Indiana Landscape

Steven Higgs Indiana University Press ePub

From the majestic hills of Dearborn County to the surreal swamps of Posey County, Southern Indiana’s physical landscape, formed over billions of years, is a tilted physiographic plane that, while many of its landforms are treacherously precipitous, is in the geologic sense a rather soft, gentle descent.

Like the rest of Indiana, the state’s southern landscape is underlain with layers of sedimentary bedrock, formed through the ages by the compression of various materials into limestone, dolomite, siltstone, sandstone, and shale. Depending on the location, from east to west, the rock at or near the surface is between 505 million and 266 million years old and was formed during one of five geologic periods, identified in Marion T. Jackson’s The Natural Heritage of Indiana as Ordovician (505–438 million years ago), Silurian (438–408 million years ago), Devonian (408–360 million years ago), Mississippian (360–320 million years ago), and Pennsylvanian (320–266 million years ago).

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Part 1 The Land Stewards

Steven Higgs Indiana University Press ePub

Waldrip Ridge, Hoosier National Forest, Monroe County.

The natural area destinations in this book are owned and managed by a variety of public and private entities, including federal and state governments and private, nonprofit conservation organizations. Some are owned jointly, mostly between Indiana Division of Nature Preserves and nonprofits. Others are contiguous to one another with separate owners and are managed under cooperative agreements.

While the six hundred thousand acres of land highlighted here are stewarded by their owners, some are neither protected nor preserved in the sense that they are off limits to human intervention. Timber harvesting, always a controversial subject in public lands management, is practiced on most state and national forest acreage in Indiana. Since 2005 the Division of Forestry has logged portions of Back Country Areas, which, according to a 1981 news release from Republican governor Robert D. Orr, were established “to be enjoyed by the wilderness seeker as a place of solitude and repose.”

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Part 4 Supplementary Materials

Steven Higgs Indiana University Press ePub

The following plant and animal species are mentioned in this book. This is not an exhaustive list of the flora and fauna that live in or pass through Southern Indiana. It represents what the areas’ land stewards and others, most significantly, various units of the National Audubon Society, prioritized when describing the places.

Rankings for species that are endangered, threatened, or otherwise of conservation concern were drawn from Indiana Department of Natural Resources lists with the following designations.

FE (Federally Endangered): Any species that is in danger of extinction throughout all or a significant portion of its range.

FT (Federally Threatened): Any species that is likely to become endangered within the foreseeable future throughout all or a significant portion of its range.

SC (Special Concern): Any animal species requiring monitoring because of known or suspected limited abundance or distribution or because of a recent change in legal status or required habitat. These species do not receive legal protection under the Nongame and Endangered Species Conservation Act.

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Shabala S (13)
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6 Flooding Stress Tolerance in Plants

Shabala, S. CABI PDF

6 

Flooding Stress Tolerance in Plants

chiara pucciariello* and pierdomenico perata

PlantLab, Institute of Life Sciences, Scuola Superiore Sant’Anna, Pisa, Italy

Abstract

Global warming is associated with an increase in submergence and flooding events, which makes many ecosystems worldwide vulnerable to low oxygen stress. Water submersion can severely affect crop production, since it drastically reduces the oxygen needed for plant respiration, and thus survival. Plants tolerant to flooding have evolved morphological, physiological and biochemical adaptations to oxygen deficiency. In the plant biology model species Arabidopsis thaliana, considerable progress has been made in terms of understanding the molecular aspects governing these responses and the sensing mechanism of an oxygen shortage has been identified. Many studies on oxygen deprivation stress have focused on rice (Oryza sativa), since it is one of the crops that adapts best to a flooded environment. Besides being able to germinate under submergence, rice varieties display different mechanisms for successful survival. Agronomically, the study of rice strategies to survive flooding in ecotypes that have adapted to extreme environments shows great potential in the context of climate change and the increasing global need for food.

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7 Adaptations to Aluminium Toxicity

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7 

Adaptations to Aluminium Toxicity

Peter R. Ryan* and Emmanuel Delhaize

CSIRO Agriculture and Food, Canberra, Australia

Abstract

Soil acidity limits agricultural production globally. Acid soils pose many stresses to plants but the major factor affecting plant growth is soluble aluminium, with Al3+ being the most toxic form. Al3+ damages root cells at sites in the apoplast and in the cytosol, and these rapidly inhibit root growth. Plants have evolved mechanisms that either avoid or minimize these damaging interactions by excluding Al3+ from the roots and leaves or by efficiently detoxifying any Al3+ that enters the cytosol. The genes conferring these resistance mechanisms have now been identified in some important crop species such as wheat, barley, sorghum and rice. Rapid progress in this field over the last decade provides exciting opportunities for increasing the Al3+ resistance of food crops through markerassisted selection and genetic engineering.

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9 Desiccation Tolerance

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9 

Desiccation Tolerance

Jill M. Farrant*, Keren Cooper, Halford J.W. Dace,

Joanne Bentley and Amelia Hilgart

Department of Molecular and Cell Biology,

University of Cape Town, Rondebosch, South Africa

Abstract

Desiccation tolerance is the ability to survive loss of 90% of cellular water or dehydration to tissue water concentrations of ≤ 0.1 g H2O.g–1 dry mass. It is relatively common in reproductive structures such as seeds (termed orthodox), but is rare in vegetative tissues, occurring in some 135 angiosperm species (termed resurrection plants). In this chapter we present an overview of the stresses associated with desiccation and review the current mechanisms proposed to explain how orthodox seeds and resurrection plants tolerate such water loss. Physiological, biochemical and molecular processes involved in protection from mechanical stress, oxidative damage and metabolic disruptions are discussed and similarities between seeds and resurrection plants are drawn. Protective mechanisms unique to vegetative tissues are presented and differences among species are discussed. We review the biogeographical distribution and evolution of angiosperm resurrection plants and propose that the developmentally regulated programme of acquisition of desiccation tolerance in seeds is utilized in the acquisition of tolerance in vegetative tissues of resurrection plants, possibly in response to environmentally regulated rather than developmental cues.

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1 Drought Tolerance in Crops: Physiology to Genomics

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1 

Drought Tolerance in Crops:

Physiology to Genomics

Lakshmi Praba Manavalan and Henry T. Nguyen*

Division of Plant Sciences, University of Missouri, Columbia, USA

Abstract

More frequent and severe drought combined with high temperatures have been recognized as a potential impact of global warming on agriculture. Improving crop yield under water stress is the goal of agricultural researchers worldwide. Direct selection for yield under drought has been the major breeding strategy and was successful in some crops. Drought modifies the structure and function of plants. An understanding of the impact, mechanisms and traits underlying drought tolerance is essential to develop drought-tolerant cultivars. Identification and evaluation of key physiological traits would aid and strengthen molecular breeding and genetic engineering

­programmes in targeting and delivering traits that improve water use and/or drought tolerance of crops. There is an overlap between different osmotic stresses and the selection of appropriate drought evaluation methods. The benefits of genetic engineering have been realized in crop improvement for quality traits, and several promising genes have emerged in the last decade as candidates for drought tolerance. Combining the physiological traits that would sustain yield under drought, and incorporating elite quantitative trait loci (QTL) and genes underlying these traits into high-yielding cultivars, would be a successful strategy.

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12 Heavy-metal Toxicity in Plants

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12 

Heavy-metal Toxicity in Plants

Philip J. White* and Paula Pongrac

The James Hutton Institute, Invergowrie, UK

Abstract

Heavy metals include the transition-metal elements essential to plant nutrition: iron (Fe), zinc (Zn), manganese

(Mn), copper (Cu), nickel (Ni) and molybdenum (Mo), cobalt (Co) (which is required for nitrogen fixation in legumes); and the non-essential elements chromium (Cr), cadmium (Cd), mercury (Hg) and lead (Pb). All these elements are toxic to crop plants at high tissue concentrations. In agriculture, deficiencies of essential heavy-metal elements are more common than their toxicities. Nevertheless, Mn toxicity can reduce crop yields on acidic soils, and Mn and Fe toxicities occur on waterlogged or flooded soils. Toxicities can also arise in soils enriched in specific heavy metals by the weathering of the underlying rocks or anthropogenic activities. The molecular biology of heavy-metal uptake and transport within plants is well understood, and the regulatory cascades enabling heavy-metal homeostasis in plant cells and tissues are being elucidated. Cellular responses to excess heavy metals are also known. Many of these responses proceed through the generation of reactive oxygen species and involve the synthesis of antioxidant compounds and enzymes. Tolerance of high concentrations of heavy metals in the environment is brought about by restricting the entry of heavy metals to the root and their movement to the xylem, and by chelating heavy metals entering the cytoplasm and sequestering them in non-vital compartments, such as the apoplast and vacuole. The mechanisms by which certain plant species are able to hyperaccumulate heavy metals are also providing insight into the ability of plants to exclude and tolerate heavy metals in their tissues.

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