Principles and Measurements in Environmental Biology

264 Pages·1983·10.856 MB·English

by  F I Woodward and J E Sheehy (Auth.)

Principles and Measurements in
Environmental Biology
F I Woodward J E Sheehy
Department of Botany, University of Cambridge Grassland Research Institute, Hurley, Maidenhead
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First published 1983
© Butterworth & Co (Publishers) Ltd 1983
British Library Cataloguing in Publication Data
Woodward, F.I.
Principles and measurements in environmental
biology.
1. Biometry
I. Title II. Sheehy, J.E.
574 QH323.5
ISBN 0-408-10637-9
Filmset by Northumberland Press Ltd, Gateshead, Tyne/Wear
Printed and bound in Great Britain by Mackays of Chatham
Foreword
This book was written to provide students with an The gap between theory and practice often appears
understanding of some important physical principles and wide. Chapter 10 gives selected examples of studies in
of how to apply them in environmental biology. In par­ order to demonstrate an obvious framework linking theory
ticular, a major aim was to describe how instruments and practice.
utilizing those principles can be used to measure environ­ Some of the examples in this book are concerned with
mental and biological processes and their interactions. rate processes affecting plants, such as photosynthesis.
We have tried to provide a conceptual link between theory The interpretation and success of such studies often
and experimental practice in a single text. require parallel observations on plant growth. The general
Often when attempting to test a hypothesis concerning techniques of growth analysis have therefore been covered
a biological process, the difficulty of deciding precisely in the final chapter. This may direct readers to consider
which measurements to make is matched by that of the wide gulf in knowledge between observations of
deciding how to make them. Usually, biological processes growth, the environment and the actual biological
are strongly dependent on environmental conditions and mechanisms of interaction.
both may be modified by the measuring instruments. Numerous important environmental processes occur in
We hope that we have been able to integrate the the soil; although many of the principles and instruments
physical, biological and instrumental concepts, to pro­ described in this book may be used in that environment
vide guidance for deciding how, when and where no direct reference is made to it. This in part reflects
measurements may be taken. the authors' field of experience and the fact that there
Chapter 1 provides a brief review of the influences on are many excellent texts specifically dealing with prob­
plants and animals of climatic variables: solar and lems in that area.
terrestrial radiation, temperature, water, wind speed, The policy of modern scientific writing has been to use
carbon dioxide and pressure. The simple physics of these units of measurement which conform to the Systeme
variables is described in Chapters 2 to 4, which also con­ International d'Unites (SI), and the fundamental
tain examples of environmental and biological inter­ approach adopted in this book has been no different.
actions. The whole of Chapter 5 is devoted to the However, we felt it important to demonstrate, in examples,
micrometeorology of plant communities. the techniques of converting various units of measure­
The chapters dealing with sampling and errors ment to their SI equivalents. Often no precise conversions
(Chapters 6 and 7) introduce a logical and constructive from one set of units to another can be made. Neverthe­
framework for experimental design and the treatment of less, approximations can be extremely useful in making
variability. calculations and so where possible, such approximations
Instruments and suitable recording devices are always have been given.
necessary, and Chapters 8 and 9 review the mechanism
of operation and typical errors associated with recent
instrumentation, as well as referring to earlier techniques F. I. Woodward
and instruments. J. E. Sheehy
Acknowledgements
We should like to acknowledge the scientific advice of
Dr J. Cobby, Professor J.P. Cooper, Dr J.R. Etherington,
Dr O.G. Heathcote, Professor J.M. de Jager, Dr E.L. Leafe,
Professor R. Loomis, Professor J.L. Monteith, Professor
CD. Pigott, Professor W. Raines, Professor W. Stern,
Mr W. Stiles, Dr J.H.M. Thornley and Mr A. Windram
during our scientific careers and in the writing of this book.
Any errors in the text are due entirely to the authors.
We are grateful to Mrs P.M. Woodward for typing the
text, to Diane Mole for preparing the illustrations and
to Julia Prickett for much help with the proof-reading.
We should like to thank our families for their
encouragement and their tolerance of both absent minds
and bodies.
J.E.S. would like to thank the Marlow Stragglers' XV
for ascribing dismal playing performances to absent-
mindedness rather than cowardice.
F.I.W.
J.E.S.
VI
To Pearl and Gaynor
Chapter 1
Introduction to the effects of the environment
on biological organisms
'But pleasures are like poppies spread—
You seize the flow'r, its bloom is shed;
Or like the snow falls in the river—
A moment white—then melts for ever;
Or like the Borealis race,
That flit ere you can point their place;
Or like the rainbow's lovely form
Evanishing amid the storm.'
Tarn o' Shanter, Robert Burns, 1759-1796.
Solar radiation
The sun emits radiation over the whole of the electro­ explained in terms of a wave-like character but can be
magnetic spectrum from gamma rays to radio waves. The understood if radiation is considered as discrete particles,
greater part (98%) of this radiation is emitted in the each with a specific energy content that is inversely
waveband 0.25-3.0 μπι. This waveband is used generally proportional to the wavelength of the radiation. (This
to define the limits of solar radiation that are of importance dual nature of radiation is considered more fully in
in biology. The extraterrestrial radiant flux from the sun Chapter 2.) Discrete particles of radiation are termed
(Figure 1.1) has an energy spectrum characteristic of a quanta and a quantum of light is called a photon.
radiator or emitter with a temperature of 6000 K (5727 °C), A photon of radiation with a wavelength of 0.46 μπι
with a peak emission at 0.48 μπι. The physical properties has an energy content of 4.3 x 10"19 J, while a photon
of solar radiation can be fully explained only if radiation with a wavelength of 0.69 μπι has a quantum energy
is considered in two quite distinct manners. Direct of 2.9 x 10"19 J.
radiation (5b in Figure 1.1) is scattered and absorbed by Solar radiation controls life by heating the earth and
the atmosphere on its path to the earth's surface. The atmosphere and by providing the energy required in
scattering varies with wavelength, as described by photosynthesis, for the conversion of carbon dioxide and
Rayleigh's law (see Chapter 2), and radiation at 0.4 μτη water into the primary source of food: carbohydrates.
(blue light) is scattered nine times as much as is radiation The food chains of the world are all based on these
at 0.7 μπι (red light). The diffuse radiation flux (Sd in photosynthetic products, which have been estimated to
Figure 1.1) derived in this way has a different spectral provide 3 x 1021 J of energy annually or 2 x 1011 tonnes
composition from the direct flux and causes the blue of carbon (Hall and Rao, 1977).
coloration of clear skies. This property of scattering can The waveband and energy content of solar radiation
be explained only if solar radiation is considered to have have been effective constraints in the evolution of photo-
a wave-like character.
biological processes. The majority of these processes
The human eye can detect solar radiation in the have action spectra limited to the 0.3-0.95 μπι waveband
waveband 0.4-0.7 μπι. This process is called vision and (Figure 1.1) and the effectiveness of solar radiation in
solar radiation in this waveband, when concerned with these processes is determined by the quantum energy
vision, is called light. The process of vision depends on content and the flux density of radiation in the wave­
the excitation of the pigment rhodopsin by light. The band.
process of excitation depends on the capture of light by Photosynthesis is an important example of a biochemical
the pigment, followed by the transfer of this energy to process which can only be driven by the high energy
an electron that may change its orbit or orbital velocity, content of solar radiation. It is powered by radiation in
within certain limits. Only light within the 0.4-0.7 μηι the 0.35-0.95 μπι waveband (including bacterial). The
waveband has the correct energy content for this process. production of carbohydrates from carbon dioxide and
The electron will subsequently return to its original water requires an energy input of 477 kJ for every mole
level, releasing energy that can be used to drive a bio­ of carbon dioxide fixed. This is supplied by photo-
chemical reaction. This property of radiation cannot be synthetically active radiation (PAR) at an average
1
2
2000 h
E
CM 1500 h
Έ
1000 h
v_^--
öi 500 h
ω
Q.
' f
0.2 0.5 1.0 1.5
2.0
Wavelength (μΐη)
Action spectra for photobiological responses (μνη)
Photosynthesis (1) ι
Photomorphogenesis and phototaxis in plants (2) |
Human vision (3)
Insect vision (4)
Insect photoperiodism (5) |
Insect phototaxis (6)
Haemolysis (7)
Erythema (3) h
Vitamin D production (7) l·-
Skin cancer (8) r-
DNA absorption r
Melanin oxidation (3)
Photosensitization of skin by phototoxic substances (10)
Hyperaemia (3)
Pit-organ sensitivity (4) I
Figure 1.1 Spectral distribution of solar radiation (1966); 8, Epstein (1970); 9, Caldwell (1971); 10. Giese
and action spectra of photobiological responses. Data for (1971).
spectral distribution from Koller (1965) and Szeicz (1974).
S = direct irradiance on horizontal surface
Data for photobiological responses from: 1, Hall and Rao b
S = diffuse irradiance
(1 977); 2, Mohr (1 972); 3, Koller (1 965); 4. Ricklefs (1 973); d
Set = extraterrestrial irradiance
5. Goldsmith (1973); 6, Dethier (1963); 7, Robinson
Solar radiation 3
Figure 1.2 Apparent photo-
synthetic rate of a leaf of Lolium
perenne (perennial ryegrass), at
different irradiances
100 200 300
-0.2 Irradiance (0.4-0.7 μΐτι waveband) (Wr2)
I I I
0.28 x 1020 4.25 x 1020 8.5 x 1020
ω
CO Quantum irradiance (quanta nrr2 s~1)
efficiency of 5% for an individual leaf. At a temperature version, is achieved in the initial slope of the curve.
of 25 °C the proportion of molecules with sufficient Here about 14 photons of radiation are required to fix
energy for this reaction is a very small fraction, of the 1 molecule of carbon dioxide. On the plateau of the curve
order of 1.4 x 10 "21, indicating that the reaction would 14 photons are still required to fix 1 molecule of
be very unlikely to occur without the high energy of carbon dioxide; however, a further 100 photons are
solar radiation. absorbed by the leaf, causing its temperature to rise.
The photons of radiation required to drive photo­ At very low irradiances there is a net loss of carbon
synthesis are absorbed by pigment molecules such as dioxide by respiration.
chlorophylls, carotenes and phycobilins, each with specific The wide range of photobiological processes in the
wavelengths of peak absorptivity. Chlorophyll a, plant and animal kingdoms is shown in Figure 1.1 with
for example, has two characteristic absorption bands at specific action spectra. The diagram illustrates the effective
0.42 and 0.66 μτη. These bands are defined by the specific spectral range of particular processes; however, it is
quantum energy contents of the photons of these wave­ important to note that the responses are not generally
lengths. This precise packet of energy is required to equal across the whole active range. For example, the
elevate the energy potential of an electron, which in turn sensitivity of the human eye is optimal at 0.55 μτη and
can be raised within a certain energy range only if it is is reduced to approximately 90% of this value at 0.65 μπι,
to be coupled to the biochemical reactions of photo­ although vision is still possible.
synthesis. Photosynthesis is also controlled by the flux Some photobiological processes are based on photo­
density or rate of photon delivery of solar radiation chemical reactions that transform biologically inactive
within the required waveband. The general term applied compounds into active compounds, or vice versa. In
to the radiant flux density incident on a unit surface is plants the chromoprotein phytochrome occurs as either a
irradiance. Figure 1.2 shows the relationship between biochemically active form, phytochrome Pf, or an
r
the photosynthetic rate, measured by carbon dioxide inactive form, phytochrome P. These two forms can be
r
uptake, irradiance and photon flux density. The greatest interconverted by solar radiation at two specific wave­
photosynthetic efficiency, in terms of radiation con­ lengths as shown in equation 1.1 (from Mohr, 1972).
4 Introduction to the effects of the environment on biological organisms
radiation into the skin. The formation of pigment
icu ugm ^υ.υυ μιιΐ)
Phytochrome P * Phytochrome Pf (1.1)
r r involves two distinct photochemical processes. The first
far-red light (0.73 μνα)
stage, melanin formation, can be induced by wavelengths of
Experiments in controlled-environment conditions have radiation from 0.25 to 0.65 μηι, although the optimal
demonstrated that phytochrome Pf is the physio­ waveband is in the uv region. The second process of
r
logically active form which may, for example, stimulate melanin oxidation (pigment darkening) is induced by
germination, leaf growth and flower induction, after the wavelengths in the 0.3-0.66 μιη waveband, with a peak
plant has been exposed to red light at the wavelength at approximately 0.45 μπι.
0.66 μιη. Exposure of plants to far-red light (0.73 μπι) Many of the effects of uv radiation are harmful to
converts phytochrome Pfr to the generally inactive form organisms, for example skin cancer, haemolysis, nucleic
phytochrome Pr. In the natural situation it is the ratio acid damage and bactericidal effects. The processes of
between the flux densities of radiation of 0.66 μτη and damage are complex but in some cases it has been
0.73 μτη that can determine the plant response, an example suggested that uv radiation may induce DNA damage.
being the growth responses of plants under shade The nucleic acids carry the codes for life and it is
conditions (Morgan and Smith, 1978). fortunate for the evolution of life that the flux of ultra­
Ecologically, responses such as photomorphogenesis, violet radiation is reduced by more than 60% in its
phototaxis and vision are important in providing informa­ passage through the atmosphere to the earth's surface.
tion for the sensing organisms. The detection of time, All materials on earth absorb and emit radiation at
the direction of movement and the transfer of visual longer wavelengths than solar radiation, between approxi­
information to the brain are used to control and co­ mately 3 and 100 μηι. The flux of the emitted long-wave
ordinate the basic processes of development, movement (infra-red) radiation is proportional to the temperature
and reproduction. of the body and to its emissivity (see Chapter 2). In the
The spectral responses of these processes are confined waveband from 3 to 100 μιη most natural objects absorb
to the 0.35-Ό.73 μτη waveband where irradiances are nearly all the incident radiation and are called black
high and the quantum energy content is sufficient to carry bodies in the waveband. All good absorbers are good
out the high-energy-requiring photochemical reactions. emitters of radiation and so will efficiently emit radiation
The response curves of hyperaemia (the accumulation in this waveband.
of blood in a tissue), the reddening of human skin The sun may be considered as a black body which
(erythema), and the pit-organ of pit vipers, such as the absorbs and emits radiation efficiently. The peak wave­
rattlesnake, extend into the infra-red region of the solar length of emitted radiation (0.48 μιιι) is related to its
spectrum. These processes are essentially temperature- absolute temperature (6000 K) as described by Wien's law
controlled processes dependent only on the total energy (see Chapter 2). The same law applies to terrestrial
absorbed and independent of wavelength. This is not objects and so an object at 293 K (20 °C) will have a
entirely true for the pit-organ, which is apparently peak emission at 9.89 μπι.
insensitive to wavelengths less than 0.55 μπι. Hyperaemia A terrestrial body will always be absorbing and
is caused by the temperature excess of the blood in the emitting long-wave radiation, even when solar radiation
blood vessels of the skin. The pit-organs of the pit is absent. Long-wave radiation transfer is important in
vipers are sensitive radiation thermometers (with a determining the thermal or temperature relationships of
sensitivity of 0.002 °C) and are used to detect radiation organisms in their environment. As an example, the walls
emitted and reflected by prey. of the room in which you may be reading this book will
Ultra-violet radiation (0.27-0.4 μπι) has a higher be exchanging long-wave radiation with your body. In
quantum energy content than any other waveband of solar the absence of a large influx of solar radiation, heat
radiation and is capable of driving a range of photo­ from heating supplies and wind movements (and ignoring
chemical reactions requiring very high energy. the effect of evaporation), long-wave radiation will be
Particularly important for human health is the con­ exchanging between your body and the walls and will
version of certain sterols in the skin to vitamin D. Better determine your level of comfort.
known is the induction of erythema or sunburn, which The atmosphere is differentially transparent to long­
may be seen to occur after periods of exposure of pale wave and to solar radiation, being highly transparent to
skin to the summer sun. This painful process is generally solar radiation and partly opaque to long-wave radiation.
followed in light-skinned humans by increased pigmen­ The opacity of the atmosphere to long-wave radiation is
tation of the skin—tanning (at present a socially desirable due to the absorptivity of water vapour, liquid water
response). Tanning is caused by the formation and and carbon dioxide for long-wave radiation. However,
migration of the dark pigment melanin to the superficial at wavelengths between 10 and 12 μηι the absorptivity
layers of the skin. This is a protective response that of water and carbon dioxide is very low and so the
effectively reduces the transmission of harmful uv atmosphere is effectively a 'window' to long-wave
5
Solar radiation
800ΓΙ
600Μ
100
Ί
Ε
180
I 400 h
Ε
>
■ο Q.
CCCO 140 Ο
200 ω
<
Η20
8 10 12 14 16 18 20 22
λ(μηη)
Figure 1.3 Wavebands of solar and long-wave radiation
and radiation characteristics of a typical plant leaf. ( )
Solar radiation at sea-level; ( ) atmospheric long-wave
emission (263 K); (—·—■—) leaf long-wave emission
(288 K); ( ) leaf absorptivity. (From Gates, 1962)
radiation in this waveband. The temperature of the clear The table indicates that the net loss of radiation (hence
atmosphere is very low, temperatures as low as — 80 °C the negative signs) is diminished with decreasing cloud
being possible, and the atmosphere will represent a sink base, indicating the importance of the downward flux of
for long-wave radiation emitted by warmer terrestrial radiation from the clouds. The cloud temperature is also
organisms. The waveband of the window also coincides inversely related to the height of the cloud base.
with the peak emission of many terrestrial organisms and The importance of both solar and long-wave radiation
so there will be a long-wave flux from the organisms to biological organisms is demonstrated by Figure 1.3.
through this window. It may be seen that the leaf strongly absorbs solar radiation
The influence of the window can be felt by humans to approximately 0.75 /mi, the longest effective wave­
on clear nights, which feel cold, in contrast to cloudy length for higher-plant photosynthesis. Between 0.75 μπι
nights which, even at the same air temperature, feel and 2.1 μιη the leaf absorbs solar radiation weakly,
warmer. On cloudy nights the clouds are at a higher thereby escaping the radiation load from solar radiation,
temperature than the cloudless atmosphere and emit a which in this waveband is not effective in photosynthesis.
greater downward radiant flux. This effect is quantified At wavelengths greater than 2.1 μιη the leaf strongly
in Table 1.1 for a range of different cloud types. absorbs radiation; however, the solar radiation flux
density and the flux from the atmosphere are both low
Table 1.1 Net radiation loss from the earth's surface in this region. These two sources of radiation will not
with different cloud cover
cause much radiative heating of the leaf, which would
Cloud type Net long-wave Mean height be the case in the 0.25-1.5 μπι waveband. The importance
radiation flux of cloud base of the high absorptivity of the leaf in the long-wave
(Wm~2) {km) region is due to the correlation between emissivity and
Nimbostratus -3 to -14 1.5 absorptivity, as described by Kirchhoff's law (Chapter 2).
Altocumulus -7 to -28 3 Thus bodies with high absorptivity have high emissivity
Cirrus -70 to -91 6
and vice versa. At a temperature of 293 K (20 °C) the leaf
Cloudless atmosphere -84 to -126
will have a peak emissivity at 9.89 μηι, which is in the
Transparent atmosphere -350
long-wave window of the atmosphere.
From Van Wijk and Schölte Ubing (1963)