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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). Here the aim was to use empirical belowground trait data and remote sensing imagery to explore belowground processes with space-borne, spatially continuous data that allow for regional assessments. A statistical analysis was conducted on the relationship between root depth data and remotely derived vegetation sensitivity to climate variability (VSI, after Seddon et al. (2016)) in Southern Africa. Results from this work show that a significant negative relationship between root depth and vegetation sensitivity exists in Southern Africa, as well as a significant positive relationship between root depth and temporal autocorrelation in vegetation productivity. These relationships were influenced by both biome and growth form, but generally imply that deeper roots reduce vegetation responses to concurrent climate variability and dampen temporal variability in aboveground productivity. These findings suggest that accessing deeper water resources during times of water stress through deeper roots is a potential resilience mechanism for drylands under future climate change. In this thesis I conclude that traits play a key role in determining vegetation response to climate change. Specifically, I conclude that in dry biomes often-neglected root traits contribute significantly to overall plant trait variation and are thus key in reducing sensitivity to climate variability and determining positive plant responses to climate change. The novelty of this body of work includes but is not limited to the following findings: i) there is a global set of traits important across biomes to cope with multiple climate changes, ii) both local and regional drivers of water availability are significant drivers of belowground trait variation in the semi-arid Fynbos biome of South Africa and, iii) aboveground plant-climate interactions are reflected by belowground trait.

Rare-earth (RE) 4f elements play a key role for technological applications. The strong magneto-crystalline anisotropy (MCA) and large magnetic moment of the 4f electron shell makes these materials important ingredients for magnetic devices. Being able to control magnetism in 4f materials on ultrafast timescale is one of the major challenges in ultrafast spin physics. Required for an ultrafast, non-thermal control of magnetic alignment are pathways to directly act on the magnetic moment. With the spin angular momentum being a conserved quantity, it is the orbital degrees of freedom that provides an ultrafast handle on the atomic magnetic moment, but mechanisms for light-induced changes of 4f orbital angular momenta have not been discussed, yet. Here we show for Tb metal that after near-infrared laser excitation, 5d-4f electron-electron scattering leads to selective excitations in the 4f shell, which modify the orbital state and locally flip the MCA within femtoseconds. Our study provides a new level of understanding of optically controlled magnetism in 4f metals and shows a path towards ultrafast, non-thermal modification of the 4f-atomic magnetic moments., Comment: Manuscript (20 pages, 2 figures) and Supplementary Information (26 pages, 9 figures)

Electronic structure modifications due to strain are an effective method for tailoring nano scale functional materials. Demonstrated on nickel oxide NiO thin films, Resonant Inelastic X ray Scattering RIXS at the transition metal M2,3 edge is shown to be a powerful tool for measuring the electronic structure modification due to strain in the near surface region. Analyses from the M2,3 edge RIXS in comparison with dedicated crystal field multiplet calculations show distortions in 40 nm NiO grown on a magnesium oxide MgO substrate NiO MgO similar to those caused by surface relaxation of bulk NiO. The films of 20 and 10 nm NiO MgO show slightly larger differences from bulk NiO. Quantitatively, the NiO MgO samples all are distorted from perfect octahedral Oh symmetry with a tetragonal parameter Ds of about amp; 8722;0.1 eV, very close to the Ds distortion from octahedral Oh symmetry parameter of amp; 8722;0.11 eV obtained for the surface near region from a bulk NiO crystal. Comparing the spectra of a 20 nm film of NiO grown on a 20 nm magnetite Fe3O4 film on a MgO substrate NiO Fe3O4 MgO with the calculated multiplet analyses, the distortion parameter Ds appears to be closer to zero, showing that the surface near region of this templated film is less distorted from Oh symmetry than the surface near region in bulk NiO. Finally, the potential of M2,3 edge RIXS for other investigations of strain on electronic structure is discussed

Information technology demands continuous increase of data-storage density. In high-density magnetic recording media, the large magneto-crystalline anisotropy (MCA) stabilizes the stored information against decay through thermal fluctuations. In the latest generation storage media, MCA is so large that magnetic order needs to be transiently destroyed by heat to enable bit writing. Here we show an alternative approach to control high-anisotropy magnets: With ultrashort laser pulses the anisotropy itself can be manipulated via electronic state excitations. In rare-earth materials like terbium metal, magnetic moment and high MCA both originate from the 4f electronic state. Following infrared laser excitation 5d-4f electron-electron scattering processes lead to selective orbital excitations that change the 4f orbital occupation and significantly alter the MCA. Besides these excitations within the 4f multiplet, 5d-4f electron transfer causes a transient change of the 4f occupation number, which, too, strongly alters the MCA. Such MCA change cannot be achieved by heating: The material would rather be damaged than the 4f configuration modified. Our results show a way to overcome this limitation for a new type of efficient magnetic storage medium. Besides potential technological relevance, the observation of MCA-changing excitations also has implications for a general understanding of magnetic dynamics processes on ultrashort time scales, where the 4f electronic state affects the angular momentum transfer between spin system and lattice.

Membrane trafficking is a complex, essential process in eukaryotic cells responsible for protein transport and processing. Deficiencies in vacuolar protein sorting (VPS) proteins, key regulators of trafficking, cause abnormal intracellular segregation of macromolecules and organelles and are linked to human disease. VPS proteins function as part of complexes such as the homotypic fusion and vacuole protein sorting (HOPS) tethering complex, composed of VPS11, VPS16, VPS18, VPS33A, VPS39 and VPS41. The HOPS-specific subunit VPS41 has been reported to promote viability of dopaminergic neurons in Parkinson’s disease but to date has not been linked to human disease. Here, we describe five unrelated families with nine affected individuals, all carrying homozygous variants in VPS41 that we show impact protein function. All affected individuals presented with a progressive neurodevelopmental disorder consisting of cognitive impairment, cerebellar atrophy/hypoplasia, motor dysfunction with ataxia and dystonia, and nystagmus. Zebrafish disease modelling supports the involvement of VPS41 dysfunction in the disorder, indicating lysosomal dysregulation throughout the brain and providing support for cerebellar and microglial abnormalities when vps41 was mutated. This provides the first example of human disease linked to the HOPS-specific subunit VPS41 and suggests the importance of HOPS complex activity for cerebellar function., Sanderson et al. describe ten individuals with biallelic variants in the gene encoding the vacuolar protein sorting protein VPS41, presenting with cerebellar dysfunction and abnormal membrane-bound vesicles. Mutant zebrafish recapitulate the cerebellar dysfunction phenotype, further implicating VPS41 as a human disease gene.