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University of Oxford (2022)

Vegetation response to climate change : a functional traits-based approach (with a specific focus on root traits in Southern Africa)

Kühn, Nicola

Titre : Vegetation response to climate change : a functional traits-based approach (with a specific focus on root traits in Southern Africa)

Auteur : Kühn, Nicola

Université de soutenance : University of Oxford

Grade : Doctor of Philosophy (PhD) 2022

Résumé partiel
Climate change influences all aspects of plant biology. The responses of vegetation to climate changes (particularly water availability in the world’s drylands) constitute a critical and timely research agenda, with potentially significant ecological consequences. This doctoral thesis aimed to investigate vegetation response to climate change using a plant functional traits-based approach, with a specific focus on root traits in Southern Africa by undertaking three interlinked research objectives :

i) Determination of globally important plant functional traits for coping with climate change (Chapter 4 ; Research Paper 1). Here the aim was to synthesize the knowledge to date from the published literature on which traits are important in determining a positive response in plant performance and fitness to climate and associated environmental changes. A systematic review of 148 studies published between 2000-2017 was carried out. Results from this work present a suite of eight key traits that best predict positive plant responses : greater water-use efficiency (WUE), greater resprouting ability, lower relative growth rate, greater clonality/bud banks/below-ground storage, higher wood density, greater rooting depth, lower or higher specific leaf area (SLA) and lower or higher plant height (the latter two varying across biomes). These findings illustrate important and general trait-climate responses within and between biomes that enhance understanding of which plant phenotypes may cope with or thrive under current and future climate change. They also highlight the importance of generally understudied belowground traits in conferring plants the ability to cope with climate change.

ii) Determination of how root traits vary within a dry biome (Chapter 5 ; Research Paper 2). Here the aim was to quantify the contribution of belowground traits to overall trait variation in the semi-arid Fynbos biome of South Africa and analyse how this changed along regional and local water availability gradients. Fieldwork was conducted to collect root and aboveground traits of 124 individuals of dominant woody shrub species. Results from this work show that drier regions have greater root investment (rooting depth, length, dry matter content and root:shoot ratio) which was consistent intra-specifically and in post-fire environments. Additionally, roots accounted for significant whole-plant trait variation and, importantly, in drier conditions increased root allocation (at the expense of shoot allocation) deviated from expected global allometric relationships. These findings suggest that root investment will be especially crucial for plant performance and survival in a drier and warmer future predicted for dryland biomes. Chapter 5 (Research Paper 2) thus contributes to the still deficient field data on belowground traits in drylands.

iii) Determination of the role that roots play in reducing sensitivity to climate variability in drylands (Chapter 6 ; Research Paper 3).

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