Plant Litter: Decomposition, Humus Formation, Carbon Sequestration

290 Pages·2003·8.282 MB·English

by  Dr. Björn Berg, Dr. Charles McClaugherty (auth.)

Bjorn Berg . Charles McClaugherty
Plant Litter
Springer-Verlag Berlin Heidelberg GmbH
Bjorn Berg · Charles McClaugherty
Plant Litter
Decomposition, Humus Formation,
Carbon Sequestration
With 76 Figures and 64 Tables
Springer
Dr. BJORN BERG
Department of Soil Ecology
BITOEK
University of Bayreuth
Dr. Hans-Frisch-StraBe 1-3
95448 Bayreuth
Germany
Dr. CHARLES MCCLAUGHERTY
Department of Biology
Mount Union College
1972 Clark Avenue
Alliance, OH 44601
USA
ISBN 978-3-662-05351-5 ISBN 978-3-662-05349-2 (eBook)
DOI 10.1007/978-3-662-05349-2
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Originally published by Springer-Verlag Berlin Heidelberg New York in 2003
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Preface
When starting our work on this book we intended to summarize and synthesize the
new information that had developed in the last 20-30 years in the field of plant lit
ter decomposition. It turned out, however, that the main part of more recent work
was directed towards boreal and temperate forest systems and therefore, with a fo
cus on these ecosystems we finally concluded a synthesis that has a similarity to a
case study. Still, we hope that a deeper insight into the behavior of a limited num
ber of litter species will be of value for a generalization and also for the identifica
tion of process systems that deviate from those presented here.
We have written the book focusing on the transfer from newly shed litter to re
calcitrant humus, describing and explaining the system of chemical changes taking
place in the process both on a mechanistic basis and on a more general and re
gionallevel, considering different climates and species.
As a synthesis, this book gives some new aspects on decomposition that to
some of us may be controversial. Thus, the fact that we emphasize the dominant
role of microorganisms in the process may be disturbing to many readers, as well
as the strong emphasis we give to the fact that humus layers actually do grow over
millennia and that at a considerable rate, and thus really sequester e.g. C and N.
This book is based primarily on data and conclusions made from field studies.
We have focused on undisturbed forest systems in an attempt to create a basic un
derstanding and basic mechanisms for the decomposition and transformation
processes. Its emphasis is on boreal systems for the obvious reason that there ap
peared to exist more data about these systems that could be synthesized. The in
formation from temperate systems has rather supported and extended the con
clusions, suggesting that the synthesis so far may be applicable to at least both
types of systems.
In the topic of litter decomposition and transformations, we can not yet identify
different schools of thought; it appears that this field of research has not yet de
veloped far enough. We would rather consider different directions of the research
work. Thus, some scientists have attempted to understand mechanisms for the
degradation whereas several groups have searched for indices for prediction of
long-term decomposition rates.
Many persons have helped us in the process of collecting and developing the
information that makes up the backbone for this book. We want to thank all of
them and hope they understand that all cannot be listed here.
The synthesis that we present has clearly taken impression of the work by a
smaller group of scientists and research groups that we want to mention. Thus, the
papers emerging from the group around Dr Marie-Madeleine Couteaux, CNRS,
VI Preface
Montpellier has been important to us, like those from Prof John Aber, University
of New Hampshire, and Dr Jerry Melillo, The Ecosystems Center, MBL, Woods
Hole. For the generalization to different climates the approach taken by Prof
Vernon Meentemeyer, University of Georgia, Athens, has been very valuable.
We have also received extremely valuable help and direct support for the work.
Thus, we want to thank Prof. Egbert Matzner, Director of the BITOEK Institute,
University of Bayreuth for his extensive support for this book. The support of the
Brumbaugh Center for Environmental Science, Mount Union College, Alliance,
Ohio is also gratefully acknowledged. Financial support for part of this work
came from the Commission of the European Union, through the CNTER project
(QLK5-2001-00596) and finally the financial support from the company BBB
Konsult, Uppsala, is acknowledged.
Finally, before handing over the book to the reader we would like to thank each
other for an excellent cooperation.
Bayreuth and Alliance, January 2003
Contents
1 Introduction ........................................................................................................ 1
1.1 Overview of plant litter decomposition ........................................................ 1
1.2 A short retrospective .................................................................................... 2
1.3 The ecological significance of litter decomposition and the formation of
humus ................................................................................................................. 3
1.4 Factors influencing decay and humus formation ........................................ .4
1.5 Accumulation of humus and nutrients ......................................................... 5
1.6 The contents and organization of the book .................................................. 6
1.7 Motives for the present synthesis ................................................................. 9
2 Decomposition as a process .•.•.......••................••.......••........••...•....•••....•••••....••.• 11
2.1 Litter decomposition -a set of different processes ..................................... 11
2.2 Definition of litter decomposition .............................................................. 13
2.3 Degradation of the main groups of compounds in litter ............................. 15
2.3.1 Degradation and leaching of soluble organic substances ................... 15
2.3.2 Patterns of degradation of the main organic compounds in litter ....... 15
2.4 A model for decomposition from newly-shed litter to humus-near stages. 18
2.4.1 The early decomposition stage: degradation of solubles and non-
lignified carbohydrates ................................................................................ 20
2.4.2 The late stage: lignin-regulated decomposition phase ........................ 20
Effect of N on lignin degradation ............................................................ 22
2.4.4 Humus-near stage in litter decomposition -limit values .................... 26
What may cause the decomposition to cease? ........................................ 29
3 Decomposer organisms .•................•.......••........•......••........•.........•.••••••••.••..•.•.••• 31
3.1 Introduction ................................................................................................ 31
3.2 General properties of a given microbial population ................................... 32
3.3 The degradation of the main polymers in litter .......................................... 34
3.3.1 Degradation of cellulose ..................................................................... 34
3.3.2 Degradation of hemicelluloses ........................................................... 37
3.3.3 Degradation of lignin .......................................................................... 37
Lignin degradation by white-rot fungi .................................................... 38
Lignin degradation by brown-rot fungi.. ................................................. 39
Lignin degradation by soft-rot fungi ...................................................... .41
Enzymes directly affected by Mn concentration in the substrate ........... .42
VIII Contents
Effect of N starvation on lignin metabolism .......................................... .42
Effect of the C source on lignin degradation .......................................... 43
3.4 Degradation of fibers ................................................................................. 43
3.4.1 Bacteria. .............................................................................................. 43
3.4.2 Soft-rot ............................................................................................... 44
3.4.3 Brown-rot ........................................................................................... 44
3.4.4 White-rot ............................................................................................ 45
3.5 Mycorrhizae ............................................................................................... 45
3.6 Ecological aspects ...................................................................................... 46
4 Initial litter chemical composition .......•.......•.........................•......................... 49
4.1 Introduction ................................................................................................ 49
4.2 Organic-chemical components of plant litter and fiber structure ............... 50
4.2.1 Organic-chemical components ........................................................... 50
4.2.2 Fiber structure .................................................................................... 52
4.3 Nutrient concentrations in newly shed litter .............................................. 54
4.3.1 General features .................................................................................. 54
4.3.2 Nutrient resorption .. , .......................................................................... 54
4.3.3 Nutrients in Scots pine needle litter -a case study ............................. 57
Annual variation at one site .................................................................... 57
Variation among Scots pine sites and in a transect.. ............................... 59
4.3.4 Several deciduous and coniferous leaf litters ..................................... 61
Influence of soils ..................................................................................... 64
Variation over a climatic transect ........................................................... 66
4.3.5 A comparison of some common species ............................................ 66
4.3.6 How much do N and lignin concentrations vary locally and
regionally? ................................................................................................... 68
4.4 Wood and fine root litter.. .......................................................................... 70
4.5 Anthropogenic influences on initial litter composition .............................. 70
4.5.1 N-fertilized Scots pine and Norway spruce monocultures ................. 71
4.5.2 Heavy metal pollution and initial litter chemical composition ........... 76
5 Changes in substrate composition during decomposition ............................. 79
5.1 Introductory comments .............................................................................. 79
5.2 Organic-chemical changes during litter decomposition ............................. 80
5.2.1 A case study on Scots pine needle litter ............................................. 80
Water soluble fraction ............................................................................. 80
Ethanol soluble fraction .......................................................................... 81
Cellulose ................................................................................................. 82
Hemicelluloses ........................................................................................ 83
Lignin ...................................................................................................... 83
5.2.2 Other species ...................................................................................... 84
5.2.3 Relationships between holocellulose and lignin ................................. 84
5.3 Nutrient and heavy metal concentrations during decay ............................. 85
5.3.1 Changes in concentrations of elements in decomposing litter. ........... 85
Scots pine ................................................................................................ 86
Contents IX
5 A Special studies on K, N and lignin dynamics ............................................. 90
504.1 K concentration dynamics .................................................................. 90
504.2. N concentration dynamics over a climatic transect ........................... 93
504.3. Lignin dynamics in a climatic transect ............................................ 100
6 Influence of chemical variation in litter on decomposition ......................... 107
6.1 Introduction .............................................................................................. 107
6.2 A three-phase model applied to litters of different chemical
composition .................................................................................................... 108
6.2.1 Overview of the model ..................................................................... 108
6.2.2 Initial decomposition rates for newly shed litter -early decomposition
stage in plant litter ..................................................................................... 109
Background ........................................................................................... 109
How can initial rates be described? ...................................................... 110
Initial chemical composition and different indices related to initial
decomposition rates .............................................................................. 113
Comments on a deviating foliar litter type: spruce ............................... 116
6.2.3 Decomposition in the late stage -lignin-regulated phase ................. 118
The late decomposition stage ................................................................ 118
Effect of lignin and N on litter decomposition rates ............................. 118
Mass-loss rates of lignin as compared to initial litter N levels .............. 119
The lignin fraction ................................................................................. 120
The biological regulation and the chemical mechanisms ...................... 122
How should we regard the retardation of litter decomposition caused by
lignin? ................................................................................................... 122
Some different lignin-related decomposition patterns among
litter types ............................................................................................. 124
6.204 Litter at a humus-near or limit-value stage ....................................... 128
General comments ................................................................................ 128
General relationships ............................................................................ 129
Groups of litter have different empirical relationships ......................... 133
6.3 Does chemical composition influence leaching of compounds
from humus? .................................................................................................. 134
7 Climatic environment ..................................................................................... 137
7.1 Introduction .............................................................................................. 137
7.2 Microbial response to temperature and moisture ..................................... 138
7.3 Early-stage decomposition of Scots pine needle litter ............................. 138
7.3.1 Decomposition at one site ................................................................. 138
7.3.2 Decomposition over transects ........................................................... 141
Scots pine monocultures ....................................................................... 142
Monocultural pine stands of different species ....................................... 144
7.3.3 Soil warming experiments ................................................................ 147
704 Effect of substrate quality on mass-loss rates in Scots pine transects ...... 149
704.1 Early stage ........................................................................................ 149
704.2 Late stage ......................................................................................... 151
X Contents
7.5 Climate and decomposition of Norway spruce needle litter .................... 154
7.5.1 Climate versus first-year mass loss ................................................. 154
7.5.2 Late stage ......................................................................................... 157
7.6 Climate and decomposition of root litter ................................................. 159
7.7 A series of limiting factors ....................................................................... 160
7.8 Climate and the decomposition of humus and litter in
humus-near stages .......................................................................................... 161
8 Influence of site factors other than climate .................................................. 163
8.1 Introduction .............................................................................................. 163
8.2 Soil factors ............................................................................................... 163
8.2.1 Soil texture ....................................................................................... 163
8.2.2 Forest floor type ............................................................................... 165
8.2.3 Local topography .............................................................................. 165
8.3 Nutrient availability ................................................................................. 167
8.4 Plant community composition and structure ............................................ 16 9
8.4.1 Effect of litter species composition .................................................. 170
8.4.2 Community structure and development... ......................................... 170
8.6 Carbon dioxide levels ............................................................................. 171
9 Decomposition of fine root and woody litter ................................................ 173
9.1 Introduction .............................................................................................. 173
9.2 Woody litter decomposition ..................................................................... 174
9.2.1 Methods ............................................................................................ 174
Decay classes for coarse wood (logs) ................................................... 174
Mass loss rates: percent loss and decay constants (k) ........................... 176
Estimating mass loss in coarse woody litter ......................................... 177
9.2.2 Decomposition rates versus climate ................................................. 177
9.2.3 Carbon dioxide release ..................................................................... 179
9.2.4 Organic chemical changes ................................................................ 179
9.2.5 Changes in nutrient concentrations ................................................... 181
9.3 Fine root decomposition .......................................................................... 184
9.3.1 Fine root litter ................................................................................... 184
Amounts of litter ................................................................................... 184
Chemical composition of fine roots ...................................................... 185
9.3.2 Mass loss rates .................................................................................. 185
9.3.3 Changes in chemical composition .................................................... 187
10 Models that describe litter decomposition .................................................. 191
10 .1 Introduction ............................................................................................ 191
10.2 Two main kinds of empirical models ..................................................... 193
10.3 Models used to describe decomposition of whole litter as a single or
"unified" substrate .......................................................................................... 194
10.3.1 Single exponential .......................................................................... 194
10.3.2 Asymptotic model .......................................................................... 194
10.4 Dominant factors that influence the unified-substrate models .............. 195