Regeneration Mechanisms in Swamp Paperbark (Melaleuca Ericifolia Sm.) and Their Implications for Wetland Rehabilitation
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Regeneration mechanisms in Swamp Paperbark (Melaleuca ericifolia Sm.) and their implications for wetland rehabilitation Randall Robinson School of Biomedical Sciences Institute of Sustainability and Innovation Victoria University St Albans Victoria Australia June 2007 Declaration I, Randall William Robinson, declare that the PhD thesis entitled Regeneration mechanisms in Swamp Paperbark (Melaleuca ericifolia Sm.) and their implications for wetland rehabilitation is no more than 100,000 words in length including quotes and exclusive of tables, figures, appendices, bibliography, references and footnotes. This thesis contains no material that has been submitted previously, in whole or in part, for the award of any other academic degree or diploma. Except where otherwise indicated, this thesis is my own work Randall William Robinson 28 August 2007 II Table of Contents Summary 1 1.0 Introduction 4 1.1 General ecological background to the project 7 1.1.1 Melaleuca 7 1.1.2 Adaptations to soils and climate 9 1.1.3 Vegetative growth 10 1.1.4 Genetic diversity 12 1.1.5 Sexual reproduction 15 1.1.6 Rehabilitation approaches 17 1.2 Aims of this project 18 2.0 The study site 21 2.1 Introduction 21 2.2 History of Dowd Morass 23 2.2.1 Water levels over past ∼ three decades 26 2.2.2 Salinity regimes over past ∼ three decades 29 2.3 Water quality in Dowd Morass 30 2.3.1 31 2.4 Sediment quality in Dowd Morass 34 III 2.4.1 Carbon, nitrogen and phosphorus contents 34 2.4.2 Soil salinity 35 2.4.3 Soil pH and the presence of acid-sulfate soils 36 2.4.4 Heavy metals 39 2.5 Vegetation of Dowd Morass 40 3.0 Clonality in Melaleuca: a study of population structure and dynamics using molecular analyses and historical aerial photographs 44 Abstract 44 3.1 Introduction 45 3.2 Methods 50 3.2.1 Sample collection and molecular analysis 52 DNA isolation 57 Primer screening 57 DNA amplification 57 Data analysis 58 3.2.2 Analysis of aerial photographs 60 Determination of growth rates and longevity based on Aerial photography interpretation 61 3.3 Results 64 3.3.1 Vegetative reproduction 64 3.3.2 ISSR analysis 66 3.3.3 Growth rates and longevity, determined from aerial photographs. 70 IV 3.4 Discussion 75 3.4.1 Clone size and growth type. 75 3.4.2 Implications for revegetation. 77 4.0 Comparison of two contrasting life forms of Melaleuca in south-eastern Australia. 80 Abstract 80 4.1 Introduction 81 4.2 Methods 84 4.2.1 Seed collection 84 4.2.2 Seed viability 86 4.3 Results 88 4.3.1 M. ericifolia 88 4.3.2 Melaleuca parvistaminea 91 4.3.3 Comparison of M. ericifolia and M. parvistaminea. 91 4.4 Discussion 93 4.4.1 Trade-offs between sexual and nonsexual reproduction 93 4.4.2 Other factors influencing sexual reproduction in M. ericifolia. 94 4.5 Conclusions 98 V 5 .0 Germination characteristics of Melaleuca ericifolia Sm. (Swamp Paperbark) 99 Abstract 99 5.1 Introduction 100 5.2 Materials and Methods 103 5.2.1 Seed collection 103 5.2.2 Seed viability 103 5.2.3 Interactive effects of salinity, light and temperature on germination 104 5.2.4 Effects of preliminary exposure to salt on germination 106 5.2.5 Effects of seed burial and substrate type on germination 106 5.2.6 Statistical analysis 107 5.3 Results 108 5.3.1 Viability 108 5.3.2 Interactive effects of salinity, light and temperature on germination 108 5.3.3 Effects of preliminary exposure to salt on germination 112 5.3.4 Effects of seed burial and substrate type 115 5.4 Discussion 116 5.4.1 Poor seed viability and its causes 116 5.4.2 Effects of chronic and acute exposure to salt 118 5.4.3 Effects of environmental variables on germination 120 5.4.4 Effects of seed burial and substrate type 121 VI 5.4.5 Implications for rehabilitation of coastal wetlands 122 6.0 Hypocotyl hairs and their importance for recruitment success in seedlings of Melaleuca ericifolia Sm. (Swamp Paperbark). 124 Abstract 124 6.1 Introduction 125 6.2 Methods 129 6.2.1 Field site 129 6.2.2 Life history of M. ericifolia 131 6.2.3 Seed collection 132 6.2.4 Effect of surface sterilisation on hypocotyl hair development 132 6.2.5 Hypocotyl hair structure 132 6.2.5 Effect of water availability on hypocotyl hair development 133 6.2.7 Effect of salinity, light and temperature on hypocotyl hairs 134 6.2.8 Data analysis 136 6.3 Results 137 6.3.1 Effect of surface sterilisation 137 6.3.2 Origin and characteristics of hypocotyl hairs 138 6.3.3 Hypocotyl hairs and seedling development 141 6.3.4 Effect of water availability on hypocotyl hair development 141 6.3.4 Effect of salinity, light and temperature on hypocotyl hair, root hair and secondary root development 143 VII 6.4 Discussion 149 6.4.1 Functions of hypocotyl hairs in M. ericifolia 149 6.4.2 Effects of environmental variables on hypocotyl hair Development 150 6.4.3 Implications for seedling establishment and plant Recruitment in the field 152 7.0 Historical recruitment events of Melaleuca ericifolia at Dowd Morass 155 Abstract 155 7.1 Introduction 156 7.2 Methods 159 7.2.1 Historical aerial photographs 159 7.2.2 Climatic and salinity data 159 7.3 Results 161 7.3.1 Recruitment events determined using aerial photographs 161 7.3.2 Climate data 163 Rainfall 163 Temperature 169 7.3.3 Salinity data 170 7.4 Discussion 172 7.4.1 Aerial photographs 172 7.4.2 Climate 173 VIII 8.0 Safe sites for recruitment of M. ericifolia in Dowd Morass 175 Abstract 175 8.1 Introduction 176 8.2 Methods 180 8.2.1 Recruitment sites in Dowd Morass 180 8.2.2 Statistical analysis 183 8.3 Results 184 8.3.1 Recruitment sites determined in field inspections 184 8.4 Discussion 190 8.4.1 Recruitment sites 190 9 General Discussion 194 9.1 Clonality in M. ericifolia 196 9.2 Trade-off between sexual and asexual recruitment and impacts on germinability 199 9.3 Environmental requirements for seedling establishment 201 9.3.1 Germination 201 9.3.2 Hypocotyl hairs 202 9.4 Safe sites for germination in M. ericifolia 204 9.4.1 Temporal requirements: climatic conditions 204 9.4.2 Spatial requirements: the importance of hummocks 205 9.5 Implications of plant and germination characteristics for management of brackish wetlands 207 References 211 IX Figures 1.1 Distribution of Melaleuca forests and woodlands in Australia. 7 2.1 Map of the Gippsland Lakes, Victoria. 22 2.2 Dowd Morass, showing the location of internal levees. 26 2.3 Recent (since 1991) patterns in water levels in various sections of Dowd Morass. 28 2.4 Recent (since 1991) salinity patterns in various sections of Dowd Morass. 30 2.5 Rookery in Area B of Dowd Morass in mid 2006. 33 2.6 Algal bloom in Area B (the rookery) at Dowd Morass. 34 2.7 Location of the four sites used for a complete sulfidic analysis of Dowd Morass sediments. 39 2.8 Stands of Swamp Paperbark, M. ericifolia. 42 2.9 Dense swards of Common Reed, Phragmites australis. 42 2.10 Aerial photograph of a section of Dowd Morass, showing areas of Common Reed (DR) and Swamp Paperbark (SP). 44 3.1 Exposed root system of a mature patch of M. ericifolia. 50 3.2 Individual patch of M. ericifolia at Wilson’s Promontory National Park, Victoria. 51 3.3 Location of sampled patches of M. ericifolia at Dowd Morass. 53 3.3a M. ericifolia patch A1 showing sample points. 54 3.3b M. ericifolia patch A2 showing sample points. 55 3.3c Doughnut-shaped M. ericifolia patches showing sample points. 56 3.4 Exposed edge of a patch of M. ericifolia showing the depth of the X extensive network of roots, Narawntapu National Park, Tasmania. 65 3.5 Two large patches of M. ericifolia showing individual genets (1-5) determined by ISSR. 67 3.6 ISSR DNA profiles for all samples using primer 814. 68 3.7 Visual differentiation of phenotypes. 70 3.8 Historical aerial photographs of a section of Dowd Morass. 72 3.9 Mean expansion rates of individual M. ericifolia clones at Dowd Morass. 73 3.10 Mean expansion rates of all clones of M. ericifolia. 74 4.1 Distribution of M. ericifolia in Australia. 82 4.2 Distribution of M. parvistaminea in Australia. 82 4.3 Linear regression of seed weight versus germination rate for M. ericifolia. 90 4.4 Germination rate for various population sized of M. ericifolia in Victoria and Tasmania. 90 4.5 Comparison of germination rates and seed weights of various populations of M. parvistaminea and M. ericifolia. 92 5.1 Effects of temperature, salinity and light regime on the germination of M. ericifolia seeds. 111 5.2 Effects of prior exposure to saline conditions for up to 16 days, followed by exposure to freshwater conditions, on the germination of M. ericifolia seeds. 114 6.1 Percentage germination and presence of hypocotyl hairs 22 days after soaking with sodium hypochlorite (30 sec to 30 min soaking) and de-ionized water (5 to 30 min soaking). 138 6.2 Microscopy images of seedling without and with hypocotyl hairs. 140 XI 6.3 Development of hypocotyl hairs on seedlings grown on substrates made up with various concentrations of agar.