Plants must gain from the environment the raw materials they need to sustain their structure, growth, and development. In Part I, we learned how they use light energy in photosynthesis and chemical energy generated through respiration to manufacture a wide array of organic chemical compounds. The focus in Part I was very much on the role of carbon from carbon dioxide in this endeavor. Part II is devoted to the question of what else plants need to sustain their growth and development.

In contrast to animals, the nutritional requirements of plants are simple. In addition to carbon dioxide, they need only water and certain chemical elements, all of which they most often take up from the soil. In the first two chapters in Part II, we examine how plants take in and distribute the water and mineral elements they require. The third chapter deals separately with the special case of how plants acquire and use nitrogen. A final chapter describes how plants transport substances of all kinds within and between their various organs.

These physiological processes are often grouped under the collective heading of plant nutrition.

Plants are exposed to unusual environmental conditions, daily and seasonally. Away from the equator, perennials such as trees and shrubs can be subjected to extreme cold in winter; plants growing at high altitude may experience, in addition to cold all year round (at least at night), drying winds and high levels of harmful ultraviolet radiation; desert plants must often suffer through long difficult periods of extreme high or low temperatures; in many locations, extended periods of drought or flooding may have to be endured; tolerance to increasingly saline soils may become necessary as we continue to abuse our arable lands; and soil, water, and air pollutants as a result of human activity may be encountered. Stress and how plants cope with it is the subject of the first chapter in Part IV.

Plants, both wild and cultivated, are surrounded by bacteria, fungi, nematodes, mites, insects, mammals, and other living hazards to their wellbeing, all hungry, many potentially harmful. Plants cannot easily avoid these enemies by moving away or hiding. The first part of the second chapter in Part IV focuses on the strategies plants use to combat the enemies in their environment, first and foremost, the ever-evolving chemical warfare that they wage against constantly adapting foes.

However, plants live in communities, as do other organisms, within which they compete with one another for moisture, light, and soil nutrients. Plants have evolved a variety of ways to create Lebensraum in their generally overcrowded world.

INTRODUCTION

Plants growing in those areas of the world where there are definite seasons synchronize their activities to suit regular variations in the weather. It makes little sense for a seed in temperate regions to begin germinating as soon as it is produced if it is late summer. Onset of winter would likely freeze and kill the fragile seedling before it establishes itself. A tree or shrub faced with an approaching cold season begins, in advance, to make provision to protect tender growing points and leaves within buds (see Chapter 9).

In another example, annual herbs develop vegetatively before diverting their energies to forming flowers, fruits, and seeds. Leaves are most often produced first to supply enough food reserves through photosynthesis before energy-consuming tasks like reproduction begin. Such sequences of events are timed to occur in synchrony with the seasons.

For these, and many other reasons, plants have evolved ways to sense the passage of time; to measure the lengths of days and the onset of seasons. Rhythms in plant life are linked to such cycles in their environment through a number of remarkably exact time-measuring mechanisms.

DAILY AND SEASONAL RHYTHMS IN PLANT LIFE

Sleep movements

It has been recognized for a long time that rhythms in plants exist. Androsthenes, historian to Alexander the Great, was one of the first to observe, over 2300 years ago, that the leaves of some plants adopt different positions during the day than at night.

Climate change as a result of global warming is predicted to be most pronounced at high latitudes. It is known from experimental studies that Sphagnum species respond to enhanced UV radiation by decreasing their growth (Huttunen et al. 2005). Some polar bryophytes reproduce sexually and form sporulating sporophytes, e.g., Polytrichum hyperboreum on the Svalbard tundra. Antarctic mosses tend to reproduce sexually more often at higher Antarctic latitudes (Lewis-Smith & Convey 2002). Simultaneously, increased emissions of nitrogenous air pollutants cause increased nitrogen deposition over the northern hemisphere (Bouwman et al. 2002).

Mires, i.e., wetlands actively accumulating organic material, are believed to play an important role in the global biogeochemical carbon cycle, potentially serving as major long-term carbon sinks. Vegetation structure, however, strongly influences the carbon sink capacity of mires (Malmer & Wallén 2005). In general, carbon accumulation is greater in Sphagnum-dominated mires than in sedge-dominated mires (Dorrepaal et al. 2005).

Graminoid dominance, however, leads to increased methane (CH4) emissions, due both to increased root exudation of precursor compounds for CH4 formation and to plant-mediated transport of CH4 to the atmosphere through aerenchyma tissue, bypassing oxidation in the acrotelm. Because of such feedbacks on global carbon budgets, investigations of vegetation dynamics in response to ongoing pollution and warming are crucial for estimates of future scenarios of global change (Wiedermann et al. 2007).

There is great uncertainty in the estimations of the impacts and possible outcome of global climate changes.

INTRODUCTION

For nearly all of its four and a half billion years of existence, the Earth's environment has followed a path and pace of change affected much less by human activities than by other, much larger, natural forces. Humans began having an impact a few thousand years ago through such activities as the slash and burn gardens in the tropics and the burning of grasslands by hunter/gatherer societies prior to forest clearing for agriculture in temperate regions. In the past few hundred years, however, burgeoning human populations and their activities in all parts of the globe have greatly increased the scale of impact.

The goal of this chapter is to examine the period prior to the advent of widespread human effects on the Earth's environment, especially factors important to plants and the roles they play in the biosphere.

For the first half billion years or so after it began forming, the Earth was shaped and reshaped by physical and chemical forces alone. Around 3.8 billion years before the present (BP), the outer crust, which formed as the Earth cooled sufficiently to form a solid, unbroken surface layer, cracked into a number of massive plates floating on a deeper mantle of molten rock. Ever since, these tectonic plates on which the continents are carried have continued to move from place to place at the Earth's surface and, at their edges, to sink beneath one another into the hot mantle below, a process called subduction.

A plant goes through a highly organized series of stages as it progresses through its life cycle. A fertilized egg, the zygote, divides repeatedly, differentiating into a wide array of tissues and organs, giving rise to a mature plant.

In Part III, chapters on how plants respond to cues from their environment (changes in light, temperature, and gravity) as they grow and develop are set beside discussions of how they sense day and night, respond to the changing seasons, attract pollinators with color, fragrances, and flavors, and use dormancy as a survival strategy.

Introduction

Epiphytes are known to respond sensitively to environmental changes. Because of the tight coupling of epiphytes to atmospheric conditions, changes in the chemical and physical conditions of the atmosphere may be expected to have direct effects on epiphytes (Farmer et al. 1992; Benzing 1998; Zotz & Bader 2009). In temperate regions, non-vascular epiphytes (bryophytes, lichens) have frequently been used as bioindicators of air quality (Hawksworth & Rose 1970). Owing to the lack of a protective cuticle in many bryophytes and lichens, solutions and gases may enter freely into the living tissues of these plants causing sensitive reactions to changes in the environment. By mapping and monitoring the distribution and abundance of non-vascular epiphytes, changes in environmental conditions can be assessed (Van Dobben & De Bakker 1996; Szczepaniak & Biziuk 2003).

Tropical moist forests, especially mountain forests, are very rich in epiphytes, both vascular and non-vascular. In the Reserva Biológica San Francisco, a small mountain rain forest reserve of approximately 1000 hectares in the Andes of southern Ecuador, about 1200 species of epiphytes have been recorded, with more than half of these bryophytes and lichens (Liede-Schumann & Breckle 2008). About one of every two species of plant in the forests is an epiphyte. The almost constantly saturated air in these mountain forests, due to orographic clouds, mist, and frequent rainfall, allows the epiphytic plants to thrive year-round high up on the trees, favoring high species diversity.

The rationale for the 1997 edition was that, the more people that know about the lifestyle of plants, the more likely it is that they will appreciate what has to be done to preserve this component of the biosphere upon which our survival depends. A secondary aim was the hope that people would discover that knowing more about how plants work is not just useful but also fun.

This second edition is addressed primarily to an audience of students of plant sciences but also to keen gardeners, naturalists, or anyone with questions about why the Earth is green, how plants defend themselves against diseases and predators, how they combat the stresses of constant exposure to the environment, and how climate change is affecting plants.

The general alarm voiced in the 1997 edition about the deleterious effects humans are having on our environment through global warming, deforestation, overgrazing by domestic animals, overcropping of arable lands, and pollution of land, water, and the atmosphere, is now, more than 10 years on, more clearly focused. Thus, in addition to making the book's original contents consistent with the most recent knowledge, material has been added to educate students of all ages about how human activities are impacting the lives of plants – how plants are affected at the physiological level by changes to our environment, such as through increasing concentrations of greenhouse gases, higher temperatures, longer growing seasons, increasing ocean acidity, changing water economy of the Earth, and pollutants such as ozone.

Introduction

Changes in structural and functional features of Sphagnum cover may be very sensitive indicators of climatic shift in Western Siberia. The spread of raised Sphagnum bogs in the West Siberian Plain is limited by low temperatures and the presence of a permafrost earth layer in the north, and by precipitation in the south. It is expected that global warming and increases in ambient CO2 concentrations may shift bioclimatic zones northward. Comparative ecophysiological analysis of Sphagnum indexes for contrasting bioclimatic zones is very important in order to forecast possible changes in northern peatlands and to estimate the tolerance range of Sphagnum species.

Western Siberia is located in the central part of the Eurasian continent, covering a vast area from the Urals to the Yenisei River. The extent of the territory is more than 2500 km in the meridional direction; therefore the climate in Western Siberia is very diverse. Within the bounds of the plain territory (West Siberian Plain, WSP) the latitudinal bioclimatic zones (tundra, forest tundra, taiga, forest–steppe, and steppe) are very well distinguished. They replace each other to the south in accordance with temperature and moisture gradients (Richter 1963).

Boggy soils are characteristic of the plain territories. Such types of soils can be explained by the surface slope to the north, high relative humidity, and weak drainage. However, the spread of mires to the north is limited by the presence of a permafrost layer.

INTRODUCTION

Plants can be devasted by attacks from adversaries. Recall the near total damage to vegetation caused by plagues of locusts down the centuries or the wiping out of entire crops by disease as in the infamous example of the potato blight in Ireland in the mid-nineteenth century.

Yet, green plants still dominate the landscape in spite of their countless enemies; plants make up a major proportion of the world's biomass, the total weight of all living things. They have evolved an impressive array of strategies, physical and chemical, to defend themselves. Some plants even seem to use their weaponry to ward off competition from their own kind.

PLANT DEFENSES AGAINST PREDATORS

Indeterminate growth

Plants have an amazing ability to renew themselves even as they are being attacked. Grazing animals may spend major amounts of time cropping their preferred food sources, yet these same plants usually maintain healthy and vigorous growth as long as environmental conditions continue to be favorable. Disease may devastate a plant in the wild but rarely is the attack so complete as to wipe out an entire species. Renewal almost inevitably occurs, given enough time, because plants have an indeterminate growth style.

Physical defenses

Another partial answer to the question of why plants dominate the world is that many of them have developed effective physical defenses.

There is increasing alarm around the world about how human activities are forcing the pace of change in the environment. A major concern is the effect we are having on plants.

Plants are major regulators of the environment through their ability to capture energy from the Sun and convert it to a form available to other organisms; through their influence on shaping the composition of our atmosphere by removal of carbon dioxide and addition of oxygen during photosynthesis; by their retention, circulation, and evaporation of water below, at, and above the Earth's surface; and in their ability to mine and redistribute mineral elements in soil via their roots, thus contributing to the weathering and breakdown of the surface layers of the planet. All of these critical functions of plants are under threat because of stresses imposed on them through global warming, deforestation, afforestation, agriculture, industrial and domestic pollution, irrigation, drainage, and flooding.

Before the Industrial Revolution began a few hundred years ago, the pace of changes to the Earth was affected by human activities in only limited, localized ways. Chapter 15 is devoted to an examination of this phase of development of our planet, particularly the cycling and recycling of some key chemical elements on which living organisms depend.

As industrialization took hold and grew, the pace of alterations to the Earth's environment began accelerating to what has now become an alarming rate, leading to changes to our land, water, and atmosphere resources, causing an increasingly wide array of stresses on plants.

DEMANDS ON A PLANT TRANSPORT SYSTEM

Delivery to all tissues …

Growth can take place in any area of a plant throughout its lifetime (see Part III). However, only green parts of the plant can photosynthesize yet non-green parts also require food to provide energy and other needs. For example, buds at the tips of branches contain many young leaves which are too immature to carry out photosynthesis yet are growing rapidly. The trunks and stems of trees and many shrubs are not green yet contain substantial amounts of living tissues which must be provided with nourishment. Energy is needed to form flowers, fruits, and seeds, none of which may be green, at least when mature. Some plants form food storage organs like bulbs, corms, and tubers, to which, as they swell, food must be delivered.

… At different times

These various demands for food arise not only at widely separated locations in a plant but also at different times during a growing season. In temperate climates early in spring the main need may be to move food from mature leaves capable of photosynthesis or from storage organs to young, developing leaves at stem tips, and to rapidly growing roots. Later, as the plant begins reproductive growth, flowers must be nurtured, followed by fruits and seeds. Later still, if overwintering storage organs are formed they, too, must be supplied with significant amounts of food. All of these organs can be at different locations on the plant body.

Introduction

The old adage that an Englishman's favorite topic of conversation is the weather is surely true, but why bother to consider the flora of Great Britain in an international summary of the effects of climate change on bryophytes? We can offer five main justifications. The first two are the relative thoroughness of Britain's bryological exploration and the long period over which the flora has been repeatedly examined. Third is the high quality of the general recording effort and its documentation in written and computerized records, and in refereed herbarium specimens. Fourth is the exceptional species-richness of the British flora in a regional (European) context.

Our fifth justification concerns the long run of systematic climatic measurements for England which, like the bryophyte records, extends back into the seventeenth century. More recent records are available for a wide range of localities across the whole of the UK. Today, the UK Meteorological Office is one of the world's leading weather forecasters and through its Hadley Centre carries out research into climatic change and publishes regular reports, updating recent weather trends and making available the latest predictions for the future climate of Britain.

Despite the advantages listed above, the task of locating unequivocal examples of recent climate change impacting the British bryophyte flora has not proven to be straightforward. Many areas of Britain are densely populated and almost all its vegetation is managed, often intensively, so that human impacts are all-pervasive; there are no wilderness areas.

Introduction

Anthropogenic ozone depletion in the stratosphere causes enhanced ultraviolet-B (UV-B) radiation on the Earth's surface (Taalas et al. 2000; ACIA 2005). Ozone layer thickness and ozone depletion vary with season and latitude. At present, the ozone layer has had measurable reductions at mid-latitudes, and is most vulnerable near the poles. The ozone hole over Antarctica has occurred consistently since the early 1980s; over the years, it has varied in depth and size. Harmful UV-B radiation is partly absorbed by the stratospheric ozone layer, but the ozone layer has no attenuating effect on UV-A radiation.

The intensity of solar UV radiation incident on organisms and ecosystems is influenced by a range of factors, making it a highly dynamic component of the environment. Solar elevation contributes to latitudinal, seasonal, and diurnal variations in UV; these variations are more pronounced for UV-B than for UV-A. The increase in UV-A penetration with altitude might be little more than that for total irradiance, but penetration of UV-B is higher (Paul & Gwynn-Jones 2003). Clouds, albedo, and aerosols also influence the diurnal, seasonal, and interannual variation of UV radiation (Taalas et al. 2000). The largest relative increase in UV-B caused by ozone depletion has occurred at high latitudes. In the Northern Hemisphere, Arctic areas of Scandinavia are expected to be affected by the largest UV changes and steepest ozone depletion (Björn et al. 1998; Taalas et al. 2000). The greatest increase in UV-B radiation at high latitudes occurs in the spring.

INTRODUCTION

The focus of the previous chapter was on factors that shaped and directed changes to the Earth's environment over the four and a half billion years before the start of the Industrial Revolution in the eighteenth century. But what effects have humans had since global industrialization began? How are the changes to the global environment caused by humans since then influencing plants, in particular, today?

Answers to these and other key questions are by no means complete. Even where answers have been provided, the data on which they are based and their interpretation are often contradictory or contentious. This is not surprising but is confusing even for those who have the broadest and deepest knowledge. Not only is human influence growing and changing constantly but the environment itself is composed of a complex array of components which interact with one another often in ways about which there is inadequate knowledge or none at all.

THE IMPACT OF HUMAN ACTIVITIES ON THE ATMOSPHERE

Central to any understanding of human influence on the global environment is our effect on the atmosphere. The composition of the Earth's atmosphere determines inward transmission of the Sun's energy, its distribution across the globe, and its radiation back into space. The difference between the incoming and outgoing energy from the Sun determines the surface temperature of the Earth, important to organisms because all have a temperature range to which they are adapted.

Although it is difficult to draw general conclusions from such a variety of studies as those presented in this book, it is very obvious that there are already valuable data on bryophyte ecology in relation to many aspects of predicted climate change. There are baseline data from ongoing monitoring studies, as well as experimental research comparing bryophyte responses to ambient environmental factors, with responses to projected changes to those factors under various climate change models. In addition there are some reports of changes in bryophyte distribution (in relation to climatic factors) that have already occurred. In a concluding chapter, Gignac (Chapter 23, this volume) reviews much of the evidence of changing climate, indicates the advantage of utilizing bryophytes as indicators of such change, and provides an overview of bryological research relating to climate change. As Proctor notes in Chapter 3 of this volume, “the only certainty [with climate change] is change itself”, and “normal conditions” are an illusion. As he points out, determining the causes of bryophyte distributional changes in terms of concurrent climate data is fraught with cause/effect and correlational problems, leading scientists to be cautious in their evaluation of data in this field.

A great deal of recent research on bryophytes includes not only ecology and physiology but also the molecular aspects of bryophyte biology. The complete sequencing of the genome of the moss Physcomitrella patens is making newly possible the understanding of how special physiological traits of bryophytes are important to their ecology (Cuming 2009).

Introduction

Climate change is affecting biodiversity (Warren et al. 2001; Hickling et al. 2005; Root et al. 2005; Parmesan 2006; Rosenzweig et al. 2008), and research into appropriate mitigation and adaptation strategies is now recognized as being of highest priority (Mitchell et al. 2007; Hoegh-Guldberg et al. 2008). As with other taxa, climate change is likely to affect the physiology, population dynamics, and spatial distributions of bryophytes. Climate-induced range shifts have already been reported for many central European bryophyte species (e.g., Frahm & Klaus 1997). Climate is the ultimate driver of species distributions at large spatial (e.g., country) scales. Although some traits of bryophytes might make them less vulnerable to changes in temperature, many species are likely to be substantially affected by changes in humidity-related parameters (Gignac 2001; Bates et al. 2005).

Protected area networks are often established based on well-studied flagship species, and although this is mainly driven by increased computer power and available ecological data, there has been a recent shift towards multi-taxon reserve design (Early & Thomas 2007; Kremen et al. 2008; Franco et al. 2009). In addition, it is increasingly recognized that current conservation networks might not provide suitable protection for species in light of future climate change (e.g., Dockerty et al. 2003; Araújo et al. 2004; Pyke et al. 2005). An area under protective legislation today might be climatically suitable for an endangered species but the climatic conditions of that area might dramatically change in the future, making it unsuitable for this species.

Introduction

The concentration of CO2 in the atmosphere has been increasing over the past two centuries from about 280 ppm to a present value of 360 ppm, and is expected to reach more than twice the pre-industrial concentration in this century (Houghton et al. 1990). Variations in atmospheric CO2 concentration are nothing new; CO2 concentrations were higher or lower during some earlier geological periods. Bryophytes as ancient C3 land plants experienced these changes of CO2 concentrations in air. What is new is that the present increase is faster than most changes that have taken place in the geologically recent past. Results of research on bryophytes are compared with those on desiccation-sensitive and evolutionarily younger vascular C3 plants, the most widely investigated group in the field of global change.

Desiccation-tolerant (DT) bryophytes are an important component of the photosynthesizing biomass, including arctic and alpine tundras, temperate, mediterranean and sub/tropical grasslands, and non-arborescent communities of arid and semi-arid habitats (Kappen 1973; Smith 1982; Hawksworth & Ritchie 1993). For example, Sphagnum species are globally important owing to their considerable peat-forming ability and their potential impact on global climatic cycles (Gorham 1991; Franzén 1994).

Globally, peatlands are estimated to cover between 3.8 and 4.1 million square kilometers (Charman 2002), equivalent to about 3% of the land surface. Peat accumulation over thousands of years has resulted in a vast store of 450 × 1015 g C (Gorham 1991), which is at least 20% of the global carbon store in terrestrial ecosystems.