Environmental Plant Physiology

Neil Willey

• Publisher: Garland Science
• Year: 2018
• ISBN:
  9781317206224
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Ciencias en general

Environmental Plant Physiology focuses on the physiology of plant-environment interactions, revealing plants as the key terrestrial intersection of the biosphere, atmosphere, hydrosphere and geosphere. It provides a contemporary understanding of the topic by focusing on some of humankind's fundamental biological, agricultural and environmental challenges. Its chapters identify thirteen key environmental variables, grouping them into resources, stressors and pollutants, and leading the reader through how they challenge plants and how plants respond at molecular, physiological, whole plant and ecological levels. The importance of taking account of spatial and temporal dimensions of environmental change in order to understand plant function is emphasised. The book uses a mixture of ecological, environmental and agricultural examples throughout in order to provide a holistic view of the topic suitable for a contemporary student audience. Each chapter uses a novel stress response hierarchy to integrate plant responses across spatial and temporal scales in an easily digestible framework.

Chapter 1

Contexts, Perspectives, and Principles

Plant growth is affected by variation in independent, interacting environmental variables.

Key concepts

•Plant-environment interactions are the foundation of terrestrial ecosystems.

•Environmental change and food security are significant challenges for humankind.

•Physiology is the study of how and why organisms function as they do.

•Biomass production and quality are dependent on resources, stressors, and xenobiotics.

•The environmental factors that affect plants are independent variables with overlapping effects.

•Major soil types embody the effects of many interacting variables that influence plant growth.

•Spatial and temporal variation provides key perspectives on plant-environment interactions.

•Plants detect environmental variation via signal transduction networks.

•There is a hierarchy of adaptations that underpin plant responses to environmental variation.

•Environmental plant physiology can elucidate key ecological processes.

•Agricultural systems can benefit from insights into plant-environment interactions.

•Models can be used to predict plant behavior in a changing environment.

Plant interactions with the atmosphere, hydrosphere, and geosphere underpin terrestrial ecosystems

The colonization of the land surface by multicellular plants was a momentous phase in the history of life on Earth, in significant part because multicellular plants in effect colonized the atmosphere, providing an unprecedented link between the subsurface, surface, and above-surface environments. It initiated perhaps the most significant ever increase in the number of niches and ecosystems. The evolution of organisms into these new niches transformed not only the domains of life but also the biogeochemistry of Earth. Terrestrial plants are therefore at a crucial nexus of the biogeochemical cycles of the Earth, and help to provide the life-support system for terrestrial species, including humans. Understanding plant function at this nexus provides major insights into many of the environmental challenges that face humankind. This book aims to provide an understanding of plant physiology that is informed by the development of terrestrial ecosystems and relevant to current environmental challenges.

The earliest evidence of multicellular plants that were adapted to the challenges of living on land is provided by spore tetrad microfossils from the Ordovician period. These suggest that, in some terrestrial locations at least, there were quite extensive stands of plants on land by 450 million years ago. Due to the lack of macrofossils, it is uncertain what these plants looked like, but they were probably liverwort-like and inhabited wet environments, perhaps living in shallow standing water. Macrofossils from the subsequent Silurian period suggest that, by 425 million years ago, plants on land were up to 10 cm tall and had rhizoids—they were beginning to function partly in the atmosphere and partly in the regolith. Between 425 and 300 million years ago there was a profound increase in the diversity of terrestrial plants (Figure 1.1). Complex terrestrial ecosystems began to develop in which a diverse range of plants, many of which have descendants in current ecosystems, adapted to the challenges of life on land. Fossils from the Devonian and Carboniferous periods show that some of these plants were many tens of meters tall, and although many of them were clearly swamp dwellers, some probably inhabited drier habitats.

Detailed understanding of the environmental physiology of early plants is difficult, but numerous features of extant terrestrial plants that are interpreted as adaptations to the challenges of life on land were evident in some of the early terrestrial plants. These include adaptations for gas exchange with the atmosphere, for water transport, and for nutrient uptake. It was the profound environmental changes which these adaptations eventually wrought that affected the biogeochemistry of Earth—for example, the composition of the atmosphere from this time on was affected by the activity of terrestrial plants and the decomposition of their dead biomass. The cycling of fresh water was transformed so that a significant proportion of all the water moving from the land to the atmosphere did so through plants. Following the injection of organic matter into the regolith, true soils became extensive for the first time, transforming the geochemistry of the land surface. Terrestrial plants are therefore integral to terrestrial ecosystems at perhaps the most important interface between the biosphere and the atmosphere, hydrosphere, and geosphere (Figure 1.2).

Figure 1.1.The evolution of major terrestrial plant phyla. Extant major groups are shown, but not the first 3.7 billion years of Earth’s history (pre-Cambrian), nor many fossil and minor extant groups. Characteristics in green letters are major adaptations that affected plant-environment relationships. Mycorrhizae = root symbioses with fungi; microphylls = small simple leaves without extensive vascular systems; megaphylls = large true leaves with extensive vascular systems; ovules = structures that contain the female gametophyte. (Redrawn from Ridge I [2002] Plants. With permission from Oxford University Press.)

An ecosystem can be defined as a community of organisms and the physical environment with which it interacts, via flows of energy and nutrients, to develop trophic relationships. This book focuses on the interaction of multicellular terrestrial plants with their abiotic environment—that is, one facet of terrestrial ecosystems. It does so in a way that is useful not only to those whose particular interest in terrestrial ecosystems relates to the plant and biological sciences, but also to those whose primary interests are in the environmental and agricultural sciences. To achieve this, a range of ecosystems are discussed in terms of “unmanaged” and “managed” ecosystems, to reflect some of the systematic differences between “natural” and “agricultural” terrestrial ecosystems. It is indisputable that, in addition to the topics covered here, understanding of both plant interactions with the biotic components of the environment and of ecosystem functioning will be vital to meeting the environmental challenges that face humankind.

Minimizing human impact on ecosystems and achieving global food security are significant challenges

If, as many geologists posit, humans are now a primary agent of environmental change, the current geological epoch can be defined as the Anthropocene. There is much evidence that hunting by early humans had significant adverse impacts on the megafauna of numerous regions on Earth—for example, large mammals were often hunted to extinction after the arrival of humans. However, it was with the initiation of agriculture that humans began to have effects on the environment that were detectable on a wide scale. The invention of agriculture between 10,000 and 8000 years ago is perhaps the most significant event in the human story, and it has been suggested that it defines the start of the Anthropocene. However, despite the environmental impact of early humans, it is generally accepted that in the twentieth century the human impact on terrestrial ecosystems was unprecedented and initiated “something new under the sun”—that is, a truly global scale of environmental impact on Earth by a single species. The Millennium Ecosystem Assessments, the United Nations Environment Program Global Environmental Outlook (“GEO”) reports, and numerous other assessments have described the global scale of human impact on terrestrial ecosystems, which now constitutes one of the greatest challenges facing humankind. The social and natural sciences will both clearly have vital roles in meeting this challenge. A striking number of aspects of the latter and many of the potential solutions do, however, occur at the nexus of plant-environment interactions. Some of the most important impacts of changing concentrations are, directly or indirectly, on plant growth, but plants also help to control atmospheric concentrations. Threats to unmanaged ecosystems include uncontrolled exploitation by humans for food, fuel, and plant products, and contamination with nutrients and xenobiotics, but manipulation of plant growth might also help to solve some of these problems. Such current challenges and potential solutions mean that in order to minimize human impacts on the environment, an understanding of the interactions of plants with their abiotic environment is probably more important now than it has ever been.

Figure 1.2.Plants at a primary interface. The soil is a primary interface between the atmosphere, hydrosphere, and geosphere. Plants function at this interface, affecting many of the most important biogeochemical cycles on Earth, and providing the foundation of terrestrial ecosystems.

In the 1970s it was difficult to predict when global population growth might stop, but now most credible predictions suggest that the global population will peak at 10–12 billion in the second half of the twenty-first century. This is a very significant increase in population when the strain on terrestrial ecosystems from the current population of about 7 billion is already so significant. The intensification of agriculture during the latter part of the twentieth century was one of the most profound and successful of the many applications of science that were developed in that century. In 1900 it was inconceivable that it would...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Preface
• Acknowledgments
• Table of Contents
• Chapter 1 Contexts, Perspectives, and Principles
• Chapter 2 Light
• Chapter 3 Carbon Dioxide
• Chapter 4 Water
• Chapter 5 Nitrogen
• Chapter 6 Phosphorus
• Chapter 7 Essential and Beneficial Elements
• Chapter 8 Temperature
• Chapter 9 Salinity
• Chapter 10 Soil pH
• Chapter 11 Flooding
• Chapter 12 Inorganic Toxins
• Chapter 13 Organic Toxins
• Chapter 14 Air Pollutants
• Chapter 15 Synopsis and Outlook
• Abbreviations list
• Glossary
• Index