Table Of ContentSOIL -PLANT
RELA TIONSHIPS
An Ecological Approach
DAVID W. JEFFREY
CROOM HELM
London & Sydney
TIMBER PRESS
Portland, Oregon
© 1987 David W. Jeffrey
Croom Helm Ltd, Provident House, Burrell Row,
Beckenham, Kent BR3 lAT
Croom Helm Australia, 44-50 Waterloo Road,
North Ryde, 2113, New South Wales
British Library Cataloguing in Publication Data
Jeffrey, David W.
Soil-plant relationships: an ecological approach.
1. Botany - Ecology
I. Title
581.5'26404 QK901
ISBN-13: 978-0-7099-1464-8 e-ISBN-13: 978-94-011-6076-6
DOl: 10.1007/978-94-011-6076-6 Pbk
First published in the USA 1987 by
Timber Press,
9999 S.W. Wilshire,
Portland, OR 97225,
USA
All rights reserved
ISBN -13: 978-0-7099-1464-8
Contents
Preface vii
Part I: A plant-centred biological complex 1
1 Plants, roots and ion absorption 3
2 Mineral composition of plant tissues and the
function of ions 18 -
3 Plants and water 50
4 Symbiotic and other associations for nutrient
capture 63 -
5 Herbivores, decomposers and other soil organisms 82
6 Vegetation and fire 91
Part ll: Environmental complexes 95
7 Soil formation 97
8 Soil matrix and soil water 109
9 Soil atmosphere and soil temperature 129-
10 Some examples of mineral nutrient supply 136-
11 Measuring availability of nutrients and toxic ions 150
12 Experimental approaches to the study of soil
variables 161
Part ill: Interactions in the real world. Some
case histories 173
13 The autecology of two contrasting species 175
14 Restoration of derelict land 185
15 Two aspects of forest mineral-nutrient economy 202
16 Australian heathlands and other nutrient-poor
terrestrial ecosystems 211
17 Three aspects of the Alaskan Arctic tundra
complex 224
18 Saltrnarshes and the coastal zone 235
v
CONTENTS
19 Calcareous and serpentine soils and their
vegetation 257
Further reading 277
Bibliography 280
Index 291
vi
Preface
Soil-plant relationships once had a limited meaning. To the student
of agriculture it meant creating optimum conditions for plant growth.
To the ecologist it meant explaining some plant community distribu
tion patterns by correlation with soil type or conditions. This dual
view has been greatly expanded at an academic level by the discovery
of the ecosystem as a practical working unit. A flood of concepts and
information subsequently emerged from the International Biological
Programme. At a totally different level of resolution, it is appreciated
that certain soil-based ecological problems have a molecular basis,
and must be addressed by physiological or biochemical approaches.
From ecosystem to molecule we have powerful new tools to increase
the flow of ecological data and process it for interpretation.
Society is now experiencing a series of adverse global phenomena
which demand an appreciation of soil-plant relationships. These
include desertification leading to famine, soil degradation accom
panying forest destruction, acidification of watersheds and the
spasmodic dispersal of radionuclides and other pollutants. It is public
policy, not merely to identify problems, but to seek strategies for
minimising their ill effects.
This book is written as a guide to soil-plant relationships, cen
trally oriented towards ecology, but of interest to students of geo
graphy and agriculture. For ecology students it will bring together
subfields such as microbiology, plant physiology, systematics and pro
vide interfaces with animal biology, meteorology and soil science.
Ideas contributing to the formulation of hypotheses are emphasised,
rather than overloading readers with information better obtained first
hand from the primary literature or encyclopaedic reviews.
The selection of case histories in ecological investigation indicates
the range of possible approaches to demonstrate that ecology is a
positive and applicable science, capable of earning its keep in the eyes
of the world.
I must gratefully acknowledge the contributions made to my ideas
by past and present colleagues in Ireland, Britain, Australia and North
America. They are too numerous to name individually and their
generosity has been unbounded. However, lowe most in terms of
concept development and stimulation to my students and my family.
David W Jeffrey
Dublin 1986
vii
Part One
A plant-centred biological complex
The theme of this section is the response of plants in relation to ions
and water in the soil environment. It draws special attention to the
close biological relationships between plants, microorganisms and
other organisms in the food web. The role of plants as primary
producers is taken for granted, even though limits to plant growth
imposed by soil conditions will be encountered many times. This
account should be read in conjunction with the prolific literature on
production ecology.
1
1
Plants, roots and ion absorption
INTRODUCTION
The view of ecology adopted here is that it comprises the study of
ecosystems and their surroundings. Plants are thus seen in relation
to the cluster of organisms most closely associated with them and to
their environment. Plants are located in an environmental complex
of energy, atmosphere and soil. Within an ecosystem context, plants
have three principal functions:
(a) Absorption of photosynthetically active radiation which is
applied to the synthesis of carbon-to-carbon bonds. Compounds
synthesised in this way serve as the only energy currency for the
ecosystem.
(b) Absorption and assimilation of ions as a source of essential
elements for the ecosystem. Photosynthesis is necessary for ion
absorption and assimilation, and ions are an essential part of the
photosynthetic system and all other metabolism.
(c) Plants process water on a sufficiently large scale to make a large
contribution to the hydrological cycle of the Earth. Some of this
water use is ancillary to photosynthesis, general metabolism and
the fabric of plant structure. Much is involved with the special
place of plants in unavoidably intercepting solar heat while
simultaneously optimising gas exchange. Leaves are cooled by
evaporative water loss.
These activities are represented in a simple way by Figure 1.1,
which symbolises leaves and roots configured for their respective
functions. Storage of energy and ions is also regarded as a universal
feature.
3
PLANTS, ROOTS AND ION ABSORPTION
Figure 1.1: Plants are organisms that are rooted in soil and
receive and process energy, water and ions. They are the
foundation of ecosystems and contribute to hydrologic and
geochemical processes
ENERGY
Atmosphere
Soil
WATER
The ecologist should observe the vegetation being studied with
the eye of the designer, the systems analyst, the civil engineer and
even the artist. This appraisal will prove valuable in hypothesis
building. The simple realisation formalised by Raunkier, that plants'
life forms can be readily classified and that whole communities have
common morphologies and growth behaviours, is still important. It
makes us realise for a start that sheer maximisation of biomass pro
duction is not a characteristic of predominant ecological importance.
Long-term persistence of a species is much more subtle, entailing
the optimisation of: assimilating the materials for primary produc
tion; producing and disseminating propagules; accommodating to
the short-term variations in environment; accepting predation; and
adapting to long-term environmental fluctuation and even cataclysm.
The means for long-term persistence under particular soil
environment regimes entails a range of features including
4
PLANTS, ROOTS AND ION ABSORPTION
morphological and physiological plasticity, ecotype formation,
species characteristics and indeed the collective properties of larger
taxa. Ecologists will broadly recognise the association between the
vetches and peas (Papilionoideae) and nitrogen fixation; between the
heathers (Ericaceae) and survival on infertile, acid substrates;
between the glassworts and seablites (Chenopodiaceae) and suc
culence and salt tolerance; and between the Cactaceae and survival
in arid zones. It seems overwhelmingly obvious that the vascular
plants have, at least in part, had their evolution moulded by soil
characteristics.
ROOTS
The three functions of all roots which are outwardly directed'to the
environment, and which are worth discussing in an ecok>gical
context, are absorption, anchorage and storage. Storage may,
according to some opinions, fall into the category of internal
metabolic functions for roots, which include, for example, the pro
duction of growth regulators such as kinetin and abscisi~ acid
(Russell 1977). However, it is not possible to discuss the absqrption
and fate of mineral metabolites without reference to storage~
Root growth and root structure
Unlike the complex apex of the shoot, the root apex is small and
compact. It cuts off files of cells which differentiate to produce
epidermis, cortex and vascular bundles behind the apex and cells of
the root cap before it. The first stage of cell differentiation is elonga
tion. The energy for this process is generated from the translocation
of osmotically active metabolites, sugars or ions, to the vacuoles of
the expanding cells. Entry of water and development of a substantial
pressure potential elongates the cells. Orientation of cellulose fibrils
in cell walls, which resembles that of the hoops of a barrel, co
ordinates the direction of growth. This uniaxial extension growth
can be thought of as a jacking action, with a force of up to 10 bars
(1.0 MPa) , which drives the root cap through the soil, reacting
against the frictional and other forces gripping the older parts of the
root.
The dimensions of a typical root apex, in the order of 0.2 mm
diameter, are sufficiently small to penetrate most inter-aggregate
5
