Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. I Are low-producing plants sequestering carbon at a greater rate than high-producing plants? A test within the genus Chionochloa A thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Ecology Massey University, Palmerston North, New Zealand Matthew Phillip Sijbe Dickson 2016 II III Abstract Plant life and primary production play an important role in the global carbon (C) cycle through the fixing of atmospheric C into the terrestrial biosphere. However, the sequestration of C into the soil not only depends on the rate of plant productivity, but also on the rate of litter decomposition. The triangular relationship between climate, litter quality, and litter decomposition suggests that whilst low-producing plants fix C at a slower rate than high- producing plants, they may release C at an even slower rate, due to the production of a recalcitrant litter. Here, the relationships between environment, productivity, litter quality and decomposition are investigated to determine their relative influences on C sequestration for taxa in the genus Chionochloa. Annual productivity was measured in situ for 23 taxa located across New Zealand, whilst litter and soil were collected for analyses and two ex-situ decomposition experiments; litter incubation on a common alpine soil, and litter incubation on each taxon's home-site soil. Plant growth rate was found to be positively correlated with both litter nitrogen and litter fibre content. Litter decomposition on the common soil was instead negatively correlated with lignin content, which showed a strong correlation with phylogeny, as opposed to environment or growth rate. When incubated on home-site soils, litter quality had no influence on decomposition, which was instead positively correlated with the rate of soil C decomposition, and negatively correlated with both soil organic matter and soil water content. On the common soil there were weak correlations between productivity and decomposition; however the proportional increase in productivity was greater than the corresponding increase in decomposition, resulting in high-producing plants sequestering C at a greater rate than low-producing plants. However, there was no correlation between productivity and decomposition on the home-site soil, with soil water content being a better predictor of C sequestration rate than productivity. Despite the range of variation in morphology, ecophysiology, productivity and habitat displayed within the Chionochloa genus, taxa all produced litter of a very similar quality. Breakdown of that litter is then most strongly influenced by the environment in which decomposition occurs, as opposed to the quality of the litter. Any subsequent differences in rates of C sequestration are therefore most influenced by the environment decomposition occurs in, with wet and cool environments likely to result in increased rates of C sequestration, independent of the rate of productivity. IV V Acknowledgements Firstly, thank you to my supervisor Dr Jill Rapson. Your knowledge, guidance, and critique have been of great assistance. I have greatly enjoyed our ecological and non- ecological discussions and debates. My appreciation goes also to those who gave insight and comment into topics integral to this research: Dr Kevin Tate, Dr Matthew Krna, and PhD candidate Helen Walker. Thank you for sharing your knowledge. Thank you to Matthew Krna, Hamish Baird, Zuni Steer, Mark Dickson, Jennifer Dickson, Thurza Andrew, James Voss, and Josh Olsen for assistance with field work, and similarly to Stacey Gunn for laboratory assistance. Thanks also to Ian Furkert, Helen Walker, Paul Barrett, and Cleland Wallace of Massey University for providing expertise in the laboratory, and technical experience. All your help was much appreciated. Thank goes to the National Institute for Water and Atmospheric Research (NIWA) for providing annual climate data, Rachel Summers of Massey University for GIS assistance, and PhD candidate Gregory Nelson of Otago University for provision of and assistance with Chionochloa genetic distance matrices. My appreciation goes also to Iris and Kate Scott for kindly providing land access to Chionochloa vireta in the Rees Valley, Kevin Henderson for kindly providing accommodation and land access to Poplars Range, and to the Department of Conservation (DoC), with particular thanks to the Stewart Island DoC boat Hananui and Skipper Stephen Meads, for kindly providing water transport. This research was made possible through funding by the Miss E.L. Hellaby Indigenous Grasslands Research Trust, Project Tongariro, the Heseltine Trust, and the Ecology Group of the Institute for Agriculture and Environment, Massey University. Thank you for supporting environmental research. Lastly, much love and thanks to my family for supporting me in my studies, and to God, who has been generous and faithful in all things. VI VII Contents Abstract III Acknowledgements V Contents VII Chapter 1: Introduction 1 Carbon Cycling and Carbon Sequestration 3 CO2 and Global Warming 3 Litter Quality, Productivity, and Decomposition 4 Theory and Hypotheses 5 Chionochloa as a Suitable Study System 7 Research Sites 11 Objectives 11 References 13 Chapter 2: Variation in Litter quality within a congeneric group: Is litter quality more related to environment or phylogeny? 17 Introduction 19 Litter Quality 19 Factors Influencing Litter Quality 19 Measures of Litter Quality 20 Plant Reponses to Stress 22 Genetic Distance and Plant Functional Group 22 Hypotheses and Aims 23 Methods 23 Experimental Design 23 Environmental Data 24 Soil Collection and Preparation 24 Litter Collection and Preparation 25 Litter Chemical Analyses 25 Analysis 26 Results 27 Litter Chemistry 27 General linear models 31 Genetic relatedness 32 Discussion 34 Leaf Nitrogen Content 34 Leaf Structural Components 35 Phenolics, C:N, and Soluble Compounds 36 Environmental Control of Litter Quality 37 Genotypic Control of Litter Quality 38 Conclusions and Implications 39 VIII References 40 Chapter 3: Investigating relationships between environment, plant growth rate, and litter quality: Can litter quality be determined from plant growth rate? 49 Introduction 51 Plant Productivity 51 Influence of Growth Rate on Litter Quality 53 Environmental and Resource Stresses 53 Aims and Hypothesis 54 Methods 54 Species Sampled and Locations 54 Experimental Design 54 Plant Growth Measurements 55 Annual Productivity 55 Litter Production 58 Productivity Measures 59 Analysis 60 Results 61 Measures of Productivity 61 General Linear Models 66 Productivity and Litter Quality 66 Productivity and Genotype 68 Discussion 68 Productivity Measures 68 Productivity and Environmental Stress 69 Influence of Genotype on Productivity 71 Links between Productivity and Litter Quality 71 Conclusions and Implications 73 References 74 Chapter 4: Is litter quality the determining factor in litter decomposition within the genus Chionochloa? A test under controlled conditions 79 Introduction 81 Decomposition and C sequestration 81 Factors Determining Decomposition 82 Litter Quality Parameters and Decomposition 82 Hypotheses and Aims 84 Methods 85 Location, Species Sampled, Litter Collection and Preparation 85 Experimental Design 85 Soil Collection 85 Soil Preparation and Analysis 86 Incubation Chambers 86 Titration 87 Common Soil Incubation 88 Site Soil Incubation 88 Analysis 89 b) IX Results 89 Decomposition Substrate 89 Temporal Trends in Decomposition 91 Rates of Litter Decomposition 91 Cumulative litter carbon loss 93 General Linear Models of Litter Decomposition 96 General Linear Models for Soil C Decomposition 97 Discussion 99 Common Soil Litter Decomposition 100 Litter Quality as a Predictor of Litter Decomposition 101 Home-Site Soil Litter Decomposition 102 Soil Characteristics as Predictors of Litter Decomposition 102 Conclusions, Implications, and Limitations 104 References 106 Appendix 111 Chapter 5: Synthesis and Discussion: Are low-producing plants sequestering C at a greater rate than high-producing plants? 113 Introduction 115 Synthesis of Findings in Chionochloa 115 P:D Ratios and C Sequestration 116 Relationships between Productivity and Decomposition 117 Relationships between Productivity and C sequestration 119 Rate of Productivity, Litter Quality, and C Sequestration 123 Soil Characteristics and C Sequestration 124 C Sequestration in Chionochloa Grassland 126 Climate Change and C Sequestration 127 Limitations and Future Research 128 Conclusions and Implications 128 References 130 X