Advances in Agronomy

1. Auflage 2014
ISBN: 978-0-12-800322-0
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, Band Volume 127, 276 Seiten

Reihe: Advances in Agronomy

Advances in Agronomy continues to be recognized as a leading reference and a first-rate source for the latest research in agronomy. As always, the subjects covered are varied and exemplary of the myriad of subject matter dealt with by this long-running serial. - Timely and state-of-the-art reviews - Distinguished, well recognized authors - A venerable and iconic review series - Timely publication of submitted reviews

Autoren/Hrsg.

Inhaltsverzeichnis

1;Front Cover;1
2;ADVANCES IN AGRONOMY;3
3;Advances in
AGRONOMY;4
4;Copyright;5
5;CONTENTS;6
6;CONTRIBUTORS;8
7;PREFACE;10
8;CHAPTER ONE - The Global Dispersion of
Pathogenic Microorganisms by
Dust Storms and Its Relevance to
Agriculture;12
8.1;1. INTRODUCTION;13
8.2;2. METHODOLOGY;20
8.3;3. GLOBAL SCALE DUST STORMS, MICROBIAL PATHOGENS AND AGRONOMY;26
8.4;ACKNOWLEDGMENTS;41
8.5;REFERENCES;41
9;CHAPTER TWO - Nature of the Belowground
Ecosystem and Its Development
during Pedogenesis;54
9.1;1. INTRODUCTION;55
9.2;2. ECOLOGICAL SUCCESSION;57
9.3;3. PEDOGENESIS;60
9.4;4. NATURE OF BIOTIC COMMUNITIES;63
9.5;5. LINKAGE BETWEEN BELOW- AND ABOVEGROUND COMPONENTS OF THE ECOSYSTEM;71
9.6;6. DEVELOPMENT OF THE SOIL MICROBIAL COMMUNITY;77
9.7;7. DEVELOPMENT OF THE SOIL FAUNAL COMMUNITY;92
9.8;8. CONCEPTUAL MODEL;101
9.9;9. IMPLICATIONS FOR REVEGETATION STRATEGIES;103
9.10;REFERENCES;105
10;CHAPTER THREE - Agronomic and Physiological
Responses to High Temperature,
Drought, and Elevated CO2
Interactions in Cereals;122
10.1;1. INTRODUCTION;123
10.2;2. OVERVIEW OF RESPONSES TO HIGH TEMPERATURE, DROUGHT, OR [ECO2];130
10.3;3. HIGH TEMPERATURE AND DROUGHT INTERACTION;133
10.4;4. HIGH TEMPERATURE AND [ECO2] INTERACTION;141
10.5;5. DROUGHT AND [ECO2] INTERACTION;146
10.6;6. BREEDING FOR MULTIPLE ABIOTIC STRESS RESILIENCE;151
10.7;7. FUTURE OUTLOOK AND RESEARCH DIRECTIONS;155
10.8;ACKNOWLEDGMENTS;157
10.9;REFERENCES;157
11;CHAPTER FOUR -
Improving Water Productivity of
Wheat-Based Cropping Systems
in South Asia for Sustained
Productivity;168
11.1;1. INTRODUCTION;170
11.2;2. WHEAT-BASED CROPPING SYSTEMS;171
11.3;3. WATER RESOURCES OF SOUTH ASIA;174
11.4;4. WP: CONCEPTS AND DEFINITIONS;176
11.5;5. SCOPE FOR IMPROVING WP;181
11.6;6. EFFICIENT MANAGEMENT OF IW;185
11.7;7. WATER-SAVING TECHNOLOGIES FOR ENHANCING WP IN IRRIGATED AGRICULTURE;200
11.8;8. STRATEGIES FOR ENHANCING WP IN RAINFED AGRICULTURE;223
11.9;9. BREEDING CROP VARIETIES FOR HIGHER WP;233
11.10;10. CONCLUSIONS AND FUTURE STRATEGIES FOR INCREASING WP;238
11.11;ACKNOWLEDGMENTS;241
11.12;REFERENCES;241

Leseproben

Methodology

Sample Collection

Air sampling may be performed using a multitude of different devices, each of which presents benefits and drawbacks that have to be considered according to the research objectives. The methods are summarized in Table 1.1.

Gravity deposition is the simplest and cheapest of methods. It requires exposing a petri dish containing nutrient agar to the environment for a period of time. Although CFUs per volume of air might be estimated considering the recipient surface area and time exposed, results may be biased by factors such as wind speed, petri dish size, and orientation of the dish to the wind (Buttner et al., 2002). Furthermore, larger particles are deposited more readily than smaller ones, which may contribute to misinterpretation of data (Grinshpun et al., 2007; Reponen et al., 2011).

Impaction devices entail the use of an air pump that drives the air toward a surface (adhesive tape, petri dish, cassettes, strips) with typical flow rates ranging from 10 to 700lmin?1 (Fang et al., 2007). Only particles with enough inertia will be captured onto nutrient agar or adhesive surfaces. Although this type of sampler is generally used for fungal spore counts or to determine the number of viable bacteria and fungi CFUs, slit samplers have been adapted to use a liquid medium that allows recovery of viruses and have been successfully used in the study of an SARS outbreak (Booth et al., 2005; Verreault et al., 2008).

Table 1.1

Advantages and Disadvantages of the Most Common Air Sampling Methods

Advantages

Disadvantages

Gravity deposition

Inexpensive Insignificant cell death from impaction

Capture influenced by external factors Large particles are preferably deposited

Impaction

Easy use Portable Low cost Allows determination of culturable microorganisms per volume of air, in some devices, associated to size ranges

Loss of viability due to impact stress Low recovery of smaller particles (viruses) Low sample volumes due to low flow rates

Centrifugation

High flow rates Efficient capture

Loss of viability due to impact stress

Membrane filtration

Portable Inexpensive High efficiency

Loss of viability due to desiccation Predominance of spore-forming microorganisms

Impingement

Sample may used be for different types of analyses Portable

High cost Loss of collection fluid due to evaporation Loss of viability

Electrostatic precipitation

Consumes less power Collection efficiency up to 90% for particles of 0.3–0.5?m Five to nine times higher recovery of culturable microorganisms compared to liquid impingement

Collection efficiency depends on the electrostatic field strength, sampling flow rate, and the electric charges of the microorganisms Low collection efficiency at high sampling flow rate

Centrifugation coupled with different containers (petri dish, wet or dry slides, etc.) has been used to collect airborne microorganisms, reaching flow rates of over 1000lmin?1 (Williams et al., 2001; Wust et al., 2003). Despite their capacity to sample large volumes, viability of the microorganisms may be compromised due to the physical stress associated with the process (Griffin, 2007).

Membrane filtration is one of the most utilized methods to collect microorganisms from air and can be used for both culture- and nonculture-based studies (Griffin, 2007; Peccia and Hernandez, 2006; Smith et al., 2013, 2012). The collection- and extraction-efficiency rates depend on the material of the filter (cellulose, glass fiber, polycarbonate, etc.) and on their pore size, which typically has a lower range limit of 0.02?m (Bowers et al., 2012; Griffin et al., 2011). Filters may be put onto an agar plate to culture viable microorganisms, used for electron microscopy and standard microscopy (light and epifluorescence), and/or they can be used for nucleic acid extraction for assessments using molecular approaches (Smith et al., 2012).

Impingement consists of the collection of air into a liquid matrix using various flow rates, which allows the detection of low concentrations of microorganisms (Agranovski et al., 2005; Bergman et al., 2005). One of the main advantages with this technique is that the sample may be split for different analyses, including both culture- and nonculture-based. This methodology has been utilized in aerobiology studies using both low- and high-flow rates and was recently reviewed by Reponen et al. (2011).

Most recently, high-velocity devices called “aerosol-to-hydrosol samplers” have been developed (Gandolfi et al., 2013). In this case, air is forced through a porous filter membrane where the aerosols are collected, and flow rates may range from 1 to 1250lmin?1 (Xu et al., 2011). Similar to the benefits and problems experienced with impingers, the filters may be partitioned for different types of analyses, but high-flow rates compromise the integrity and health of cells and thus the ability to culture them.

A new type of aerosol sampler has been recently developed and is based on electrostatic precipitation (Han and Mainelis, 2008). This system converts aerosols directly into hydrosols and has demonstrated better recovery results than some liquid impingers under certain conditions (Yao and Mainelis, 2006). A recent adaptation has allowed concentrating the sample down to a volume of 5?l. Moreover, an automated electrostatic sampler version has been demonstrated (Tan et al., 2011). This system collects the air continuously into a vesicle from which it is then routed to an onboard biosensor. This coupling of a sampler with a biosensor offers a promising option in automated bioaerosol monitoring. Future approaches may employ automation to collect, analyze, and report data in real time (Xu et al., 2011).

Microbial Identification

Microscopy

The study and identification of microorganisms by microscopy is one of the oldest microbiology tools still in use today (Griffin et al., 2007; Prospero et al., 2005). Standard light microscopy only allows a minimal level of identification since most species are not discernable based on morphology, and this type of analysis requires expertise and is time consuming. However, detection and enumeration of culturable and nonculturable microorganisms can be made, and results can be obtained within hours after sample collection (Angenent et al., 2005; Buttner et al., 2002). It has been regularly used for identification of airborne fungi spores, usually to genus level (Ho et al., 2005; Wu et al., 2004). Staining may help differentiate unique features: Gram staining for bacteria and the use of lactophenol blue for fungi (Griffin, 2004; Tringe et al., 2008; Yamaguchi et al., 2012). Fluorescence microscopy enables the acquisition of additional data (metabolic state of the cell, direct counts of bacteria and fungi, etc.) through the use of different stains such as acridine orange, SYBR green, LIVE/DEAD staining, or DAPI (Albrecht et al., 2007; Fallschissel et al., 2010; Terzieva et al., 1996). The combined use of microscopy along with immunology or genetic methods allows identification to the species level. Fluorescence in situ hybridization may allow phylogenetic identification of bacteria (Amann et al., 1996; Korzeniewska and Harnisz, 2012). Electron microscopy has been used to enumerate smaller particles such as viruses and allows their classification based on their morphology (Hanssen et al., 2010; Kim et al., 2013; Whon et al., 2012; Yamaguchi et al., 2012).

Culture-Based Analysis

Cultivation is the primary method for the study of viable microorganisms. However, most bacteria in any given sample type are nonculturable (Burrows et al., 2009). Because of this, total concentrations and diversity are typically not attainable (Cho and Hwang, 2011; Ravva et al., 2012), although there are some studies that have demonstrated similar results when comparing molecular methods and culture-based approaches (Fahlgren et al., 2010; Urbano et al., 2011). Choosing the right cultivation assay may result in a better recovery rate of airborne microorganisms. In published studies, incubation temperatures and culture media type used have varied, although ambient temperature and use of a low-nutrient-agar medium seem to produce the best recoveries (Kellogg and Griffin, 2006). Results from culture-based studies are limited in determining the identification and number of CFUs of bacteria or fungi. The cultivation of airborne microorganisms is generally supplemented with other methodologies, such as microscopy and/or polymerase chain reaction (PCR)/high-throughput...