Functional Diversity of Mycorrhiza and Sustainable Agriculture: Management to Overcome Biotic and Abiotic Stresses

By Michael J. Goss, Mário Carvalho and Isabel Brito

Functional Diversity of Mycorrhiza and Sustainable Agriculture is the first book to present the core concepts of working with Arbuscular mycorrhizal fungi to improve agricultural crop productivity.

Highlighting the use of indigenous AM fungi for agriculture, the book includes details on how to maintain and promote AM fungal diversity to improve sustainability and cost-effectiveness. As the need to improve production while restricting scarce inputs and preventing environmental impacts increases, the use of AMF offers an important option for exploiting the soil microbial population. It can enhance nutrient cycling and minimize the impacts of biotic and abiotic stresses, such as soil-borne disease, drought, and metal toxicity.

The book offers land managers, policymakers, soil scientists, and agronomists a novel approach to utilizing soil microbiology in improving agricultural practices.

• Provides a new approach to exploiting the benefits of mycorrhizas for sustainable arable agricultural production using indigenous AMF populations and adopting appropriate crop production techniques
• Bridges the gap between soil microbiology, including increasing knowledge of mycorrhiza and agronomy
• Presents real-world practical insights and application-based results, including a chapter focused primarily on case studies
• Includes extensive illustrative diagrams and photographs

• Language: English
• Publisher: Academic Press
• Release date: May 19, 2017
• ISBN: 9780128042861

Michael J. Goss

Michael Goss is a soil scientist and worked for over 20 years in the UK (Letcombe Laboratory, Rothamsted Research and the James Hutton Research Institute), collaborating with colleagues in France, Germany, Portugal and Australia. In 1990 he joined University of Guelph, Canada, as Research Chair in Land Stewardship and is Professor Emeritus in the School of Environmental Sciences. Michael is an Honorary Member and Fellow of the British Society of Soil Science. He was Editor-in-Chief of ‘Soil Use and Management’ and part of the editorial team for 10 years until 2019. He has written over 175 academic papers, edited two books and co-written a University-level textbook (2 editions) on water in plant production and a book on the management of arbuscular mycorrhizas.

Book preview

Functional Diversity of Mycorrhiza and Sustainable Agriculture

Management to Overcome Biotic and Abiotic Stresses

Michael J. Goss

School of Environmental Sciences, University of Guelph, Guelph, Ontario, Canada

Mário Carvalho

Institute of Mediterranean Agriculture and Environmental Sciences, University of Évora, Évora, Portugal

Isabel Brito

Institute of Mediterranean Agriculture and Environmental Sciences, University of Évora, Évora, Portugal

Table of Contents

Cover image

Title page

Copyright

List of Figures

List of Plates

List of Tables

Preface

Taxonomy of Arbuscular Mycorrhizal Fungi Referred to in this Book

Chapter 1. Challenges to Agriculture Systems

Abstract

1.1 Current and Future Challenges to Agriculture Systems

1.2 The Approach to Meeting the Challenges to World Agriculture

1.3 Conclusions

Chapter 2. Agronomic Opportunities to Modify Cropping Systems and Soil Conditions Considered Supportive of an Abundant, Diverse AMF Population

Abstract

2.1 Components of Cropping Systems

2.2 Key Aspects of Agricultural Systems on Diversity of Mycorrhiza

2.3 Conclusions

Chapter 3. The Roles of Arbuscular Mycorrhiza and Current Constraints to Their Intentional Use in Agriculture

Abstract

3.1 Benefits of Arbuscular Mycorrhiza

3.2 Constraints to Intentional Use of AMF in Agriculture

3.3 Conclusions

Chapter 4. Diversity in Arbuscular Mycorrhizal Fungi

Abstract

4.1 Ecological Roles of Arbuscular Mycorrhizal Fungi

4.2 Basis of Functional Diversity in Arbuscular Mycorrhizal Fungi

4.3 Functional Diversity Associated With Host-Plant Benefits

4.4 AMF Diversity Associated With the Management of Different Ecosystems

4.5 Conclusions

Chapter 5. Impacts on Host Plants of Interactions Between AMF and Other Soil Organisms in the Rhizosphere

Abstract

5.1 Interactions Between AMF and Other Soil Microbes

5.2 Interactions Between AMF and Other Fungi

5.3 Interactions Between AMF and Soil Fauna

5.4 Conclusions

Chapter 6. The Significance of an Intact Extraradical Mycelium and Early Root Colonization in Managing Arbuscular Mycorrhizal Fungi

Abstract

6.1 Importance of Early Arbuscular Mycorrhizal Fungi Colonization

6.2 Arbuscular Mycorrhizal Fungi Inoculum Sources

6.3 ERM as an Effective Arbuscular Mycorrhiza Inoculum Source for Field Crops

6.4 Multiple Roles of ERM and Common Mycorrhizal Networks

6.5 Conclusions

Chapter 7. New Tools to Investigate Biological Diversity and Functional Consequences

Abstract

7.1 Genetic Markers

7.2 Functional Diversity

7.3 Conclusions

Chapter 8. Management of Biological and Functional Diversity in Arbuscular Mycorrhizal Fungi Within Cropping Systems

Abstract

8.1 Managing Indigenous AMF in Agroecosystems

8.2 Opportunities to Develop ERM From Indigenous AMF Within the Cropping System

8.3 Some Final Comments

References

Index

Copyright

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List of Figures

List of Plates

List of Tables

Preface

Michael J. Goss, Mário Carvalho and Isabel Brito

The current world population of 7.5 billion is expected to be 20% greater by 2050 and so we have little over 33 years to ensure the means of producing sufficient food to meet the expected demand. One of the options that previously were available to us for expanding world production of cereals, vegetables, fruits, and meat, namely bringing more land into production, is no longer possible and consequently we must everywhere increase the productivity of the land. But this time we must not attempt it without making every effort to safeguard the environment. Put in a slightly different way, we have to grow more but conserve the soil and its biodiversity, be more efficient in terms of water use, improve nutrient-use efficiency so that fewer applied nutrients end up contaminating our freshwater and eutrophying our lakes and shallow seas or adversely affecting the quality of our air and contributing to the atmospheric loading of greenhouse gases. If we add in a desire to reduce the application of pesticides, especially those targeting root pathogens, it would seem to represent an extremely challenging task. Perhaps it will be a surprise to some that the answer to many of these challenges might well be one result of the development of techniques that allow us to determine the make-up of microorganisms, which has had huge impacts on soil science and its application in agronomy.

Beginning with the ability to differentiate the fatty acid and phospholipid profiles of microbial communities in soil and reaching the current status, where the whole genetic code of an organism can be determined, the previously rather opaque world of soil microbiology is being clarified at an unprecedented rate. From around the time that the word mycorrhiza was coined by Frank in 1885, mycorrhizal fungi have been of interest because of their special relationship with the vast majority of land plants. For agronomists the most important are the endomycorrhizal fungi that produce tree-shaped branched structures called arbuscules inside the cortex of most crop plants. Evidence steadily accrued that established their importance in supplying the essential element phosphorus to plants but the availability of mineral fertilizers, such as superphosphate, caused many to assume that the contribution from mycorrhiza was unnecessary and even in fertile soils the organisms were more like parasites than partners of their hosts. But eventually there came the realization that arbuscular mycorrhiza provided far more services than supplying phosphorus. The recent appreciation of the biological diversity of mycorrhizal fungi and the functional consequences for mycorrhiza with different abilities to protect their host from the impacts of toxic metals, to counter the invasion of root diseases and to enhance the formation and stabilization of soil aggregates, renewed interest in the ecological significance of mycorrhiza.

The challenge for agronomists and those interested in availing their crops of the potential benefits from arbuscular mycorrhiza is how to manage them. One obvious approach is to develop a source of inoculum that can be applied to a field prior to or as part of seeding a crop that could benefit from the formation of a mycorrhizal symbiosis. However, not only is that a relatively expensive activity it is also fraught with uncertainty over its efficacy. Another approach is to encourage the adoption of farming practices that support a wide variety of indigenous arbuscular mycorrhizal fungi (AMF) that will provide specific benefits sought for the crop. But in many respects this is not enough. It is a long way from providing the supportive environment for a specific fungus or consortium of fungi to dominate the mycorrhiza that form on most crop plants in a field. That goal requires the development of new farming strategies.

The approach we take in this book is to expand on the current challenges to meeting the requirements for feeding a much larger world population and suggest how arbuscular mycorrhiza can contribute to the solution under many agricultural climatic zones. We consider the farming practices that can be deleterious to maintaining a diverse population of mycorrhizal fungi and the systems and practices that can encourage their survival and effectiveness. We discuss the interactions between the fungi and other soil organisms, some of which are now known to improve the functioning of arbuscular mycorrhiza, and how the symbiosis influences many of the basic plant processes. The possibilities for obtaining specific information on individual fungi offered by the new generation of molecular methods are also presented. Finally we present a view as to how indigenous AMF might be managed in a practical setting.

The opportunity to put our combined thoughts and ideas into a book owes a lot to the discussions we had with Marisa LaFleur, commissioning editor with Elsevier, and subsequently with commissioning editor Nancy Maragioglio. Both have been wonderfully supportive and we can’t thank them enough. We are equally indebted to Billie Jean Fernandez, who has been of enormous help in pulling us over the finish line. Lisa Jones, the Production Editor, has been superb in converting our ideas on presentation into reality; she has worked tirelessly to ensure we would be proud of the finished product. We sought the help of two experts to ensure that the chapters on new generation molecular methods and diversity among the AMF would be as up-to-date as possible. It is difficult to express just how grateful we are to Diederik van Tuinen, a very good friend and colleague, for his contribution on modern molecular methods in relation to the elaboration of functional diversity. The contribution of Clarisse Brígido in developing the chapter discussing the complexity of functional diversity in AMF was also critical and she too has been of incalculable help and support. We are extremely grateful to Sabaruddin Kadir and Luis Alho, who generously provided material used in Chapter 5, as well as provided important feedback on the contents.

March 2017

Taxonomy of Arbuscular Mycorrhizal Fungi Referred to in this Book

There have been some major changes in the taxonomy associated with arbuscular mycorrhizal fungi (AMF). In consequence, some have undergone more than one name change in the last 30 years. To avoid as much confusion as possible, the names used in the text are those reported by the authors of the papers referenced. We have used Schüßler and Walker (2010) and Redecker et al. (2013) to provide a list of the current names of these species.

aIdentifying the current name for Glomus intraradices is problematic. The isolate DAOM197198 was renamed from Glomus intraradices to Glomus irregularis and then to Rhizophagus irregularis. As not all isolates have been reanalyzed, we now have some which are Rhizophagus sp., some R. irregularis, and some still R. intraradices.

Chapter 1

Challenges to Agriculture Systems

Abstract

Food production has to be greatly increased simply to feed a population growing from 7 billion to in excess of 9 billion over the next 35 years and we still have more than a billion undernourished people. To increase global food production is an unprecedented challenge in the history of agriculture, particularly if we consider that the solutions adopted in the past are much less of an option. Previous solutions have been to increase the area made available for agriculture and to enhance land productivity by an increase in crop yields, with the latter being particularly important. Only limited areas of new land are available for adoption by agriculture but soil degradation and urbanization are removing considerable areas from the existing productive land bank. In consequence, intensification of production is going to be essential. At the same time there is an urgent need to reduce the environmental impacts of food production. It will be crucial to close the gap in yield between the climatic potential and what farmers achieve across the different regions of the world, particularly those areas where the difference is greatest due to environmental, economic, and social conditions. The world is not in a position to ignore the possible contribution from any technological solution on ideological grounds and the concept of sustainable intensification of agriculture has to be on the agenda. Among the possible solutions the intentional use of beneficial soil microbes in agricultural systems is only in its early days. There is a much greater need than ever to find ways of exploiting the benefits from the microbes in our soils and to develop tools that will help farmers implement strategies related to sustainable soil use and management. Our focus is on arbuscular mycorrhizal fungi (AMF) that can impact several soil processes, including the cycling of phosphorus and nitrogen, their acquisition by plants and reducing losses of nitrogen by leaching or volatilization, as well as play other crucial roles within the agricultural ecosystem. AMF can protect their host plants from both biotic and abiotic stresses, including root pathogens, toxic metals, and water shortage. Managing the soil microbiota, particularly AMF, has the potential not only to increase production, while decreasing the incorporation of inputs, with the potential to be applied to productive and marginal soils and used in regions of the world where the resources required by farmers are scarce.

Keywords

Population growth; agricultural production; environmental impacts; sustainable intensification; agricultural land bank; yield gap; technological solutions; soil biota

Chapter Outline

1.1 Current and Future Challenges to Agriculture Systems 1

1.2 The Approach to Meeting the Challenges to World Agriculture 5

1.3 Conclusions 14

1.1 Current and Future Challenges to Agriculture Systems

Food production is probably one of the greatest challenges facing the world. Despite the increase in agricultural production since the 1960s, when the green revolution started to be implemented in the developing world, we still have more than 1 billion undernourished people (FAO, 2009, 2015a). There has to be a greatly increased production simply to feed a population growing from 7 billion to in excess of 9 billion over the next 35 years (Fig. 1.1).

Figure 1.1 The rapid increase in world population since 1960 and the associated reduction in the average area of arable land per person. Note that the average area of arable land area per person is less than half that in 1960 and is now smaller than 0.2 ha (FAOSTAT, 2015; US Census Bureau, 2014).

This growth in population, the improvement of world gross product (WGP) and consequent greater consumption of food, together with changes to the human diet, particularly the switch to grain-fed animal protein, all combine to exert further pressure on agricultural production. Even allowing for the uncertainties related to each of these factors, it is estimated that by the year 2050 world food production will have to increase by 50%–70% (FAO, 2009; The Royal Society, 2009).

A key concern is how this additional production is going to be achieved. In the past, the response in both developed and developing countries to a greater demand for food has been to increase the area made available for agriculture and enhancing land productivity by an increase in crop yields. For example, over the period 1961–2005, expansion of harvested land contributed between 14% and 25% to improved crop production compared with the 78%–86% resulting from improved productivity, with about 10% of the latter resulting from increased cropping intensity, that is the ratio of harvested land to the total arable land (Table 1.1) (Bruinsma, 2011). Nevertheless, the aggregate land area in developed countries showed a decline over the same period, so improvement in yield was even more important as a factor (Bruinsma, 2003).

Table 1.1

Estimation of relative contributions to improved crop production of increases in harvested land area, crop yieldsa and cropping intensity of agriculture over the period from 1961 to 2005 (Bruinsma, 2011).

aWeighted yields (international price weights) based on 34 crops.

The available evidence strongly points to the conclusion that increasing the land area under cultivation will be inadequate as an option to meet the current challenge. In 30 years after 1950, more land was converted to cropland than in the 150 years between 1700 and 1850 (Millennium Ecosystem Assessment, 2005). Worldwide agriculture has already been responsible for the conversion of 70% of grassland, 50% of savanna, 45% of temperate deciduous forest, and 27% of tropical forest biome (Foley et al., 2011). This represents 38% of Earth’s terrestrial surface with the soils most suitable for agriculture already under cultivation. In addition to the reduced opportunity for further land use change, good agricultural land is lost every year to build houses and necessary infrastructures to accommodate the growth of the world population and the migration to cities (Fig. 1.2). By 2030 there are expected to be 1.75 billion more urban residents, requiring about 42.4 million ha of new urban land cover (Dumanski, 2015).

Figure 1.2 The urbanization of the world population since 1961 (FAOSTAT, 2015).

Degradation of land due to desertification, soil erosion from water or wind, acidification, nutrient deficiency or being affected by salt, compaction, or contamination by toxic materials is also a threat to the available land dedicated to food production (Box 1.1). In addition to these aspects, climate change will impact land productivity in large area of the planet and will likely compound the negative impacts of agriculture on land degradation. The net combination of anthropogenic impacts has meant that the average area of arable land per person has more than halved since 1960 and is currently a little less than 0.2 ha (Fig. 1.1).

If a significant increase in the land area dedicated to agriculture is not an option then, greater soil productivity is an essential strategy to face the challenge of feeding the world population in the near future.

Box 1.1

Soil Degradation

Soil degradation is defined as a change in the soil quality status resulting in a diminished capacity of the ecosystem to provide goods and services for its beneficiaries (http://www.fao.org/soils-portal/soil-degradation-restoration/en/). It is estimated that 5 billion hectares are degraded worldwide, with 64% of this area in dry regions (Eswaran et al., 2001). There are several causes for land degradation. Erosion by water and wind is the main cause and contributes to about 85% of land degradation (Oldeman et al., 1992). On a global scale the costs to the world of an annual loss of 75 billion tonnes of soil is about US$ 400 billion year−1, or approximately US$ 70 person−1 year−1 (Pimentel et al., 1995; Lal, 1998). Soil compaction is mainly important in the regions of the world where mechanization has been intensively used. On-farm losses through land compaction in the United States have been estimated at US$ 1.2 billion year−1 (Gill, 1971), and it has caused yield reductions of 25%–50% in some regions of Europe (Eriksson et al., 1974) and North America, and between 40% and 90% in West African countries (Charreu, 1972; Kayombo and Lal, 1994). Soil acidity also threatens crop yields, either by reducing the availability of important nutrients for crop nutrition or through the associated toxicities of Al and Mn. Around 50% of the world’s potentially arable soils are acidic and the use of fertilizers and biological nitrogen fixation are promoting soil acidity. Salinization is also an important aspect of soil degradation. Salt-affected soils occur in more than 100 countries and their worldwide extent is estimated at about 1 billion ha (FAO and ITPS, 2015). Some 10%–20% of dry lands are already degraded due to desertification while a much larger number is under threat (Millennium Ecosystem Assessment, 2005). The United Nations Environment Programme (UNEP) estimates that 16% of the world’s productive land