Anatomical variation in twig wood across Australian angiosperms

244 Pages·2014·25.59 MB·English

ANATOMICAL VARIATION IN TWIG WOOD
ACROSS AUSTRALIAN ANGIOSPERMS

Kasia Ziemińska

Thesis submitted for the degree of doctor of philosophy
Department of Biological Sciences, Macquarie University, Sydney
May 2014
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Contents
Contents ..................................................................................................................................... 3
Figure list .................................................................................................................................... 6
Table list ..................................................................................................................................... 8
Thesis abstract .......................................................................................................................... 9
Statement of candidate .......................................................................................................... 11
Acknowledgements ................................................................................................................ 13
Chapter 1 INTRODUCTION ................................................................................................... 15
1.1 Background .......................................................................................................... 17
1.2 General approach ............................................................................................... 20
1.3 Thesis plan ........................................................................................................... 21
1.4 Methodological note ........................................................................................... 22
1.5 References ............................................................................................................ 26
Chapter 2 DISSECTING STEMS: WHAT CAN WOOD ANATOMY DISCLOSE ABOUT
PLANT STRATEGIES? ............................................................................................ 31
2.1 Abstract ................................................................................................................. 33
2.2 Introduction ......................................................................................................... 33
2.2 Overview of functional processes and traits ................................................... 38
2.3 Fibres ..................................................................................................................... 42
2.3.1 Fibre structure ..................................................................................................... 42
2.3.2 Fibres and climate ............................................................................................... 44
2.3.3 Fibres and functional traits ................................................................................ 45
2.3.4 Fibres in experimental studies .......................................................................... 46
2.4 Parenchyma ......................................................................................................... 47
2.4.1 Parenchyma structure ........................................................................................ 47
2.4.2 Parenchyma and climate.................................................................................... 49
2.4.3 Parenchyma and functional traits .................................................................... 50
2.4.4 Parenchyma in experimental studies .............................................................. 51
2.5 Vessels .................................................................................................................. 52
2.5.1 Vessel structure ................................................................................................... 52
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2.5.2 Vessels and climate ............................................................................................ 54
2.5.3 Vessels and functional traits ............................................................................. 56
2.5.4 Vessels in experimental studies ....................................................................... 57
2.6 Synthesis: wood functional systems ................................................................ 58
2.6.1 Mechanical system ............................................................................................. 58
2.6.2 Metabolite transport and storage system ...................................................... 59
2.6.3 Hydraulic system ................................................................................................. 60
2.7 Conclusions .......................................................................................................... 62
2.8 Acknowledgements ............................................................................................ 63
2.9 Figures .................................................................................................................. 65
2.10 Tables .................................................................................................................... 73
2.11 References ........................................................................................................... 84
Chapter 3 FIBRE WALL AND LUMEN FRACTIONS DRIVE WOOD DENSITY VARIATION IN
TWIGS ACROSS 24 AUSTRALIAN ANGIOSPERMS ............................................ 97
3.1 Abstract ................................................................................................................ 99
3.2 Introduction ......................................................................................................... 99
3.3 Materials and Methods .................................................................................... 102
3.4 Results ................................................................................................................ 106
3.5 Discussion .......................................................................................................... 109
3.6 Acknowledgements .......................................................................................... 113
3.7 Figures ................................................................................................................ 115
3.8 Tables .................................................................................................................. 129
3.9 References ......................................................................................................... 130
3.10 Appendix 1 ......................................................................................................... 137
3.11 Appendix 2 ......................................................................................................... 142
Chapter 4 WOOD ANATOMICAL VARIATION LARGELY INDEPENDENT OF WOOD
DENSITY IN TWIGS OF 69 AUSTRALIAN ANGIOSPERMS .............................. 151
4.1 Abstract .............................................................................................................. 153
4.2 Introduction ....................................................................................................... 154
4.3 Materials and Methods .................................................................................... 158
4.4 Results ................................................................................................................ 166
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4.5 Discussion .......................................................................................................... 175
4.6 Acknowledgements ........................................................................................... 183
4.7 Figures................................................................................................................. 185
4.8 Tables .................................................................................................................. 207
4.9 References .......................................................................................................... 209
4.10 Appendix ............................................................................................................. 217
Chapter 5 DISCUSSION ....................................................................................................... 229
5.1 Axes of variation ................................................................................................ 231
5.1.1 Wood density dimension ................................................................................. 231
5.1.2 Anatomical variation independent of density ............................................... 233
5.2 Limitations of this study and possible paths forward ................................. 236
5.3 Thesis context and significance ...................................................................... 238
5.4 References .......................................................................................................... 240

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Figure list
Figure 1-1 A map of Australia and study sites. .................................................................. 23
Figure 1-2 Photographs of six study sites. ......................................................................... 25
Figure 2-1 Fibres. ................................................................................................................... 65
Figure 2-2 Parenchyma. ........................................................................................................ 67
Figure 2-3 Vessels. ................................................................................................................. 69
Figure 2-4 Vessels and tracheids. ........................................................................................ 71
Figure 3-1 A twig cross-section of Grevillea parallela, Proteaceae. ............................... 115
Figure 3-2 Tissue fractions for 24 species arranged in order of decreasing wood
density. ................................................................................................................ 117
Figure 3-3 Relationship between fraction of wood outside vessel lumens (fraction )
NV
and the density of that non-vessel fraction (wood density ). ................... 119
NV
Figure 3-4 Relationship between non-vessel density (wood density ) and fibre
NV
fraction in non-vessel area (fibre fraction ). ............................................... 121
NV
Figure 3-5 Relationships between non-vessel density (wood density ) and (a) fibre
NV
wall fraction in non-vessel area (fibre wall fraction ), and (b) fibre lumen
NV
fraction in non-vessel area (fibre lumen fraction ). ................................... 123
NV
Figure 3-6 Relationship between the fraction of the non-vessel area that is fibre wall
or is fibre lumen (a) and its schematic illustration (b). ................................ 125
Figure 3-7 Cross-sections through twigs of four species. .............................................. 127
Figure A3-1 Box plots showing comparisons in non-vessel wood density (wood
density ), non-vessel fibre wall fraction (fibre wall fraction ) and non-
NV NV
vessel fibre lumen fraction (fibre lumen fraction ) between the four sites.
NV
............................................................................................................................. 147
Figure A3-2 Overall tissue fractions for Leucopogon ericoides from cool-wet site and L.
ericoides from cool-dry site. ............................................................................. 149
Figure 4-1 Illustration of wood tissues (a) and image analysis method used (b). ...... 185
Figure 4-2 Stack bar graph of tissue fractions across 69 species. ................................ 187
Figure 4-3 Relationship between total fibre fraction and total parenchyma fraction.
............................................................................................................................. 189
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Figure 4-4 Relationship between fibre wall fraction and fibre lumen fraction across 93
species (a) and a diagram illustrating this relationship (b). ........................ 191
Figure 4-5 Cross-sections through twigs of three low-density species. ....................... 193
Figure 4-6 Box plots showing differences in anatomical traits and wood density
between sites (and vegetation types). ............................................................ 195
Figure 4-7 Relationships between parenchyma traits and vessel area. ...................... 197
Figure 4-8 Relationships between parenchyma traits, fibre wall fraction plus vessel
wall fraction and modulus of elasticity. ......................................................... 199
Figure 4-9 Relationship between ray parenchyma fraction and pith area. ................. 201
Figure 4-10 Site and family comparisons for the 21 species from Myrtaceae and
Proteaceae. ........................................................................................................ 203
Figure 4-11 Bar graph representing estimated density of swollen cell wall material
across 69 studied species. ............................................................................... 205

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Table list
Table 2-1 Summary of variation in quantitative anatomical traits reported in the
literature. .............................................................................................................. 73
Table 2-2 Relationships between fibre traits and climate. ............................................. 74
Table 2-3 Correlations between fibre and functional traits. .......................................... 75
Table 2-4 Relationships between parenchyma traits and climate. ............................... 76
Table 2-5 Correlations between parenchyma and functional traits. ............................ 78
Table 2-6 Relationships between vessel traits and climate. .......................................... 79
Table 2-7 Correlations between vessel and functional traits. ....................................... 82
Table 3-1 Species list and sites of collection. ................................................................. 129
Table A3-1 Details of the four sites sampled in this study. ............................................ 137
Table A3-2 Wood density and tissue fractions of 24 species averaged across three
replicates. ........................................................................................................... 138
Table A3-3 Wood density and tissue fractions of non-vessel proportion of 24 species
averaged across three replicates. .................................................................. 140
Table A3-4 Site mean and standard deviation of wood density and tissue fractions.
Values calculated on six species per site. ...................................................... 145
Table A3-5 Site mean and standard deviation of wood density and tissue fractions of
non-vessel proportion. Values calculated on six species per site. ............ 145
Table 4-1 Site details. ......................................................................................................... 207
Table 4-2 Traits overview. ................................................................................................. 208
Table A4-1 Species and families. ........................................................................................ 217
Table A4-2 Tissue fractions: total parenchyma, axial parenchyma, ray parenchyma,
total fibre, fibre wall, fibre lumen. .................................................................. 218
Table A4-3 Tissue fractions: total vessel, vessel lumen, vessel wall, conduits ,
15µm
mucilage canals. ................................................................................................ 220
Table A4-4 Anatomical traits: axial parenchyma relative to total parenchyma, fibre
wall relative to total fibre, pith area. .............................................................. 222
Table A4-5 Vessel traits. ....................................................................................................... 224
Table A4-6 Non-anatomical traits. ..................................................................................... 226
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Thesis abstract
This thesis explores variation in wood anatomical structure and its potential
ecological implications. Woody stems are major plant organs performing vital functions
such as mechanical support, water transport, and metabolites storage. The various ways
plants perform those functions are determined by wood anatomical structure. Despite
this fundamental role of anatomy, surprisingly few studies have rigorously quantified
anatomical traits, especially across a broad number of species. Moreover, twig wood has
been especially overlooked in favour of main trunks. This thesis quantified anatomical
variation across a relatively broad number of species in twig wood and explored the
correlations of anatomy with other plant functional traits. The overarching aim was to
contribute a quantitative anatomical understanding to our knowledge of plant functions,
as they relate to plant ecological strategies.
Wood density has been considered a key plant functional trait, yet its anatomical
nature is not entirely understood. First, anatomical underpinnings of density variation
were quantified across 24 species with densities ranging from 0.37-0.83 g cm-3. Density
proved mainly to be driven by the fraction of wood occupied by fibre walls. There was
also substantial anatomical variation that was independent from density, representing
mainly a trade-off between fibre and parenchyma fractions. The ecological significance
of this dimension of variation is not understood. Since fibre-parenchyma variation was
wider among lower-density species, anatomical variation in 69 low-medium density
species (0.38-0.62 g cm-3) was quantified in order to capture this fibre-parenchyma
trade-off more thoroughly. Potential correlates such as plant height, leaf area to
sapwood area ratio, and modulus of elasticity were also measured. These other traits
proved not to be well correlated with wood anatomy. For example, parenchyma fraction
(an index of storage capacity) was expected to correlate with plant height (indexing
canopy access to light), but it did not. The fraction of parenchyma (being soft, thin-walled
tissue) was expected to covary with mechanical properties, but this expectation was only
weakly supported. In addition to these two bodies of new empirical work, literature on
anatomical knowledge from across diverse disciplines was synthesized. Other gaps in
our current comprehension of wood anatomy and function in angiosperms were
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highlighted. For example, the function of parenchyma has commonly been described as
metabolite transport and storage. However, the available evidence suggests that, next to
metabolite storage, parenchyma may play a major role in water storage or vessel
refilling.

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